Defender second battery location

[Rexy]

Have a tdi300.

Car isn't with me so can't measure it up but from memory I'd fit a second N70 under the passenger seat.

Just not sure if a ctek dc to dc would fit under there as well. Does anyone have two n70 under passenger seat and a dc to dc as well? Or would there be room?

Other option is under drivers seat, guessing an N70 or even bigger would fit fine.

Thanks

[manic]

Will it fit. Yes!

Are you about to get chastised for opting for a DCDC charger set up - probably!

I have a ctek , two batteries n70ish, a cut off switch, an alarm unit, fuse box, and custom electical box for voltage sensitive switching. All tucked in there

If you go for DCDC, its not a bad idea to have all your load switched to the alternator when driving. That way all the DCDC amps are dedicated to charging your aux.

Or keep it simple, avoid the ctek and just have a voltage sensitive relay.

I went with ctek for solar and to limit load on the alternator when starting up on a depleted aux.

Que drivesafe

[Ancient Mariner]

2- 130 ah and even a roll of shock absorber bushes[smilebigeye]

[Tombie]

I’ll do it Manic...

A DcDc charger is a woftam in these vehicles. [emoji41]

Put the money into an SC90 or equivalent and use the rest for beer tickets.



There, all done.

[manic]

May the OP has a good reason for dcdc. Lithium perhaps?

[Tombie]

May the OP has a good reason for dcdc. Lithium perhaps?

Certainly wouldn’t be fitting a Ctek to control a Lithium [emoji6]

A good single Lifepo4 will have it’s own BMS now.

[Rexy]

Its for an AGM, also want the ability to add solar.

[Tombie]

Its for an AGM, also want the ability to add solar.

Simple system and a Victron Solar Charge controller.
Ctek will cripple your charging system reducing charge capability and increasing time to recharge.

[DiscoMick]

I had this dilemma, but went a different route, because of the limited space in the battery box.
I had Off Road Systems (ORS) build drawers for the rear, but got a short drawer. That left space behind the drawer for a battery on its side. There is a lift off lid, or the rear seats can be folded for access. Wiring and a DBC connect the first and second batteries. A solar panel on the roof rack is permanently connected through a simple PWM regulator next to the starting battery. Anderson plugs connected to both batteries allow extra solar or a generator with portable 25 amp charger to be connected to either battery just by opening a vehicle door. No need for a DC-DC charger in the vehicle.
Having it all hidden works well. We are on the road for three months and it's all good.
I'm very happy with this setup.

BTW lithium need special chargers which can charge at 14.7 volts.

[Tombie]

Would work well Mick. [emoji106]

My reason for staying with the under seat boxes is central and low mass. ‘Lara’ was quite heavy bias to the rear axle and really didn’t want to add more back there if avoidable.

[DiscoMick]

Fair enough. We have rear airbags running at 20 psi so no problem with a droopy bum. And the 2nd battery is at floor level anyway and over the rear axle.

[manic]

Ctek dual might be cheaper option than Traxide and victron mppt

The ctek can only output 20amps. It will be slower to bulk charge for sure, but better towards full charge.

IME with the ctek250, I am always fully charged by next camp spot. And it continues to charge on solar. So it's not a bad bit of kit for ~250 buck.

Also when starting up after a good run down on the batteries , I have bulk amps off the alternator going to the starter battery as priority. And 20 amps dedicated to the aux.

Some batteries have better absorption rates than others. AGM batteries will generally absorb around 50amps in a downwards taper. So by the time the starter is full off the alternator , the aux is only calling for <20amps anyway. That last 10% to full is where the DCDC excells. The ctek temperature awareness and 5 stage charging map helps also to get as much as you can into the top end of the battery.

Its working well for me anyway. So not a complete waste of time and money.

[drivesafe]

Hi Rexy and this is just a suggested setup but will easily give you the best option.


First off, being a Land Rover, there is absolutely no advantage to fitting a DC/DC device, other than being able to use unregulated solar panels, but if you permanently fit the solar to your vehicle, you can only get power from one source at a time, meaning the other is wasted.


You are far better off using a dedicated solar regulator, and then you can be recharging your batteries from the alternator and the solar at the same time while driving.


As Tombie suggested, if you use one of my DT90 isolators but an Optima D34 Yellowtop, a 55Ah battery, you will have a system that will give you around 80Ah of accessories power and a recharge time of up to 6x faster than any DC/DC device can do.


You will also have over discharge protection for both the cranking battery and the auxiliary battery, again, something no DC/DC device can offer.


If you use a DC/DC device, you will need to have that 105Ah battery to get the same amount of usable power, but now you will need to drive for MANY more hours to allow the DC/DC device to recharge a low auxiliary battery.


My suggested setup would be about the same price but would give you a far superior system.

[manic]

How can a 300tdi with a 65amp alternator charge the aux battery 6 times faster than an aux charged from a dedicated 20 amp DC?

And at what point in terms of SOC does a yellow top or common AGM stop taking on more than 20amps? Will the fluctuating 13.x volt alternator output on a typical TDI be quicker to full charge once the battery's amp acceptance drops to <= 20 amps?

Would a battery last longer if charged at a regulated voltage with temperature consideration and proper float? Or constantly force fed by a poorly regulated alternator?

For sure, the Ctek 250 does not provide low voltage protection, so it is not a stand alone dual battery solution. And it will limit the charge rate potential to your aux battery. You still need to add a vsr, and ideally have the relay switch all your aux loads to alternator whilst driving to get all of the dcdc charging capacity. But the charge stages are correct, it adds solar and you might see advantages to charging your aux with a little less urgency. Pros and cons.

I have had the ctek 250 in the TDI Defender for what must be at least 4 years now. It has been submerged up on the Cape and rattled over the gun barrel. It's proved to be reliable, and the battery it is looking after now is the longest lasting deep cycle I have ever owned.

I have no issues with the DCDC charge rate. It takes around 2 hours of driving to bounce back from a long night out camping. Less or no time at all if solar had its time. 100AH AGM.

I will admit it was been a bit of a faff to get the low voltage cut out and aux load switching set up properly to support the ctek. But on the other hand solar was built in and ready to go.

[Rexy]

Fridge will be the only thing drawing power while driving. If I need to I can either plug it into the ciggy socket or an Anderson off the house battery while driving.

Fridge has a low voltage cut out but I do have a vsr here I can run the other equipment through. Ctek does have low voltage cutout on the house battery so wont drain it flat.

Its a ute without racks, isn't really anywhere to add a solar panel while driving.

I just want something simple that will give me extended battery life as it wont be used all the time. Not looking to add 4 specific controllers when the ctek can do all those things already.

Drivesafe, if I pull up at a camp how will a 55ah battery give me the same usable power as a 100ah battery with your system? Once the cars off (which is where a second battery comes in handy) your system plays no part I would have thought?

[drivesafe]

Hi again Rexy and you will have to pardon me as I have just assumed you would have had the 100 amp upgrade done before any dual battery set up was carried out and this depends on intended use.


If you have not done the upgrade, I would suggest going down that road first.


Hi manic, and with the standard 65 amp alternator still fitted, the last think you need is an energy wasting device like a DC/DC charger fitted.


For they need a lot more amps in to a DC/DC unit than comes out, particularly if the voltage runs as low as you make out. I have not done much monitoring of the 65 amp alternators but feedback shows they usually run in the low 14V area.


Rexy, to your question of a 55Ah battery providing up to 80Ah while camping.


Unlike ordinary VSR type isolators and DC/DC devices, where you only have access to your auxiliary battery, my isolators allow up to 50% of the cranking battery to be used to assist in the powering of accessories while camped.


By using an Optima Yellowtop, you will have no problem fitting it alongside your cranking battery and still have plenty of room for the isolator as well.


If you do still have the 65 amp alternator, this setup will still give you much faster recharging especially as the Optima is a rapid charge battery.


For example, if you have been camping for a while and both batteries are down around the 50% SoC mark, the two batteries will draw everything available from your alternator but as the two batteries charge, your cranking battery will draw less as it charges up passed the 75% mark, but the optima will continue to draw as much current as it can until it get to around the 90% to 95% mark, when it too, will start to reduce its charge current draw.


This simply means you have a far more efficient use of the limited charge power available.


The other advantage it that if you do not drive long enough to get both batteries up around the 95% charged mark, when you turn your motor off, the Optima, being in a higher state of charge, will slowly back discharge into the lower charge cranking battery, helping to keep it in a better state of charge.


There is a lot more to it but that’s the basics.


Again, depending on how much use you intend for you Defender and you intend to use it, like if you are planning long trips with lots of free camping, if you have not upgraded to a 100 amp alternator, this might be the first thing to consider.


If you are only planning the occasional weekend away and lots of short trips around town, then the smaller alternators is fine but the Optima will still be a big advantage over more conventional auxiliary batteries in this type of usage.

[DiscoMick]

Reading these posts, I realised I forgot to mention I have a Traxide 160 dual battery controller fitted. This means the fridge in the back can draw half of the 120 amp AGM second battery plus half of the starting battery or about 110 amps total. The 80 watt solar panel on the roof feeds the starting battery, so as it is charged the Traxide keeps the two batteries connected.
Incidentally, an ammeter plugged into the Anderson plug on the rear bumper tells me it is sending about 8 amps to the camper trailer. As the fridge-freezer is drawing about 4 amps it means about twice as much is going in as is being used while driving. When camped we plug in extra solar.

[Rexy]

I dont want to draw any power from starter battery. Problem is with remote locations come back and car wont start. If I was going to do that i'd just get the biggest starter I could fit under the seat.

[drivesafe]

I dont want to draw any power from starter battery. Problem is with remote locations come back and car wont start.
Hi Rexy and sorry mate but there is no grounds for that statement when using one of my isolators.


If you were to come back to your vehicle and could not start it with a battery at 50% then there is every likelihood that your cranking battery is already stuffed and whether it was at 50% or 100%, when you left it, it’s still stuffed.


Most people are unaware that the CCA rating of their battery is based on a battery tested at 40% SoC and at a temperature of 0 degrees. So again, if your battery won’t start your vehicle when at 50% SoC it is already stuffed.


Furthermore, because my isolators keep the batteries together, every time you start your motor, while most of the energy needed to start the motor will still come from the cranking battery, the load is shared over the two batteries and and this has a multitude of advantages over a normal single battery setup.


Because the starting load is shared, you motor will start easier and this in itself helps to reduce ware and tare on the starter motor.


Because the starting load is shared, the cranking battery is not worked as hard while starting the motor, and this will help to extend its operating life.


Because the starting load is shared, the cranking battery will not be discharged as low as with a single battery system, and this means the cranking battery will back to a fully charged state in a shorter drive time. Again this will help to extend its operating life.


All this helps to extend the cranking battery’s life spans and as pointed out earlier, by allowing the auxiliary battery to keep the cranking battery in a better state of charge in the first place, again this will make starting the motor easier and again this will help to extend its operating life.


When using one of my isolators, your cranking battery will eventually die, but it is likely to be in use for years longer than with any other setup or where there is no setup at all.


There is no down side to the way my isolators work but there are many upsides to using them.

[Rexy]

Seems like there a few down sides.
1, draws power from starter to 50%. Who would intentionally want their starter at 50%, may as well save on weight and put a swift battery in there.
2, draws power from second battery for starting -a lot/most deep cycles are not covered under warranty for use as a starter, nor are they intended for this purpose.
3, will not give me the required 14.7v that the agm requires.

Im sure its a great system for people running old tech batteries but its really just a fancy vsr close to dc to dc price with no solar ability.

[Tombie]

It’s the very system used in a large majority of vehicles running AGMs.

None are suffering what you’re claiming.

Also, cycling the main battery to 50% SOC is a good thing, cycling batteries is a good thing.

Don’t listen to us though, Drivesafes only been doing this for decades and I only worked on Military electronics and electrical systems - what would we know [emoji41]

[drivesafe]

Seems like there a few down sides.
1, draws power from starter to 50%. Who would intentionally want their starter at 50%, may as well save on weight and put a swift battery in there.
2, draws power from second battery for starting -a lot/most deep cycles are not covered under warranty for use as a starter, nor are they intended for this purpose.
3, will not give me the required 14.7v that the agm requires.

Im sure its a great system for people running old tech batteries but its really just a fancy vsr close to dc to dc price with no solar ability.
Hi Rexy and it is obvious that no matter what advantages are shown to you, your heart is set on using a DC/DC device, without any regards for having a far better system. So be it, but at least others reading this thread can now make a far better educated choice when trying to decide which system is the best for their needs.

Also, can you please list any AGM batteries that require 14.7v to fully charge them. There are none on the market that I know of?

[W&KO]

I choose not to draw down my starter OMG.....I had a traxide in my last defer but have fitted a basic redarc to my current defer. Yep going against the grain whoopie doooo, but this is a personal choice and I’m with the OP on this one.

Re: DC-DC, I have never run one of these and agree that limited the charging rate and I prefer to get maximum out of the alternator.....although a few people I know that run DC-DC (mostly 40amp units) seem to be fully charged each time they pull up to camp. So all hype about batteries won’t recover I haven’t seen, and with nearly everybody having solar I think most out there seem to get by.

Just because the OP doesn’t have the perfect arrangement of components that one seems to have to have in a Land Rover doesn’t mean we need to write him off.

I’ll have to read back through the posts and see how much assistance there has been to optimize his current set up/investment.

Funny thing is...nah won’t go there

[Rexy]

Traxide, follow this link ctrl f and search for agm.

https://www.centurybatteries.com.au/content/documents/battery-talk/issue-2-battery-talk-battery-charging.pdf

Everything it says about agm your system can't do.

AGM batteries should be charged using a chargerwith a mode switch for AGM type batteries. It is recommended to usea charger, current limited to 20% or 0.2C of the batteries capacity at acharging voltage of between 14.6 – 14.8V following deep cycle use, or13.6V – 13.8V for standby use. Charging should be paused if the batteryor ambient temperature exceeds 50°C.

Everything I can find online says AGM should be charged to over 14 volts.

The ctek does all the things agm require so I should see a lot more battery life and easy recoup the savings over the traxide kit- not to mention the solar ability.


Tombie, Its not me not listening, read the original post. From the outset you've never even answered what Ive asked, just crapped on about a system I do not have nor want. I understand Traxide is trying to sell a product but it does nothing I want and I never asked about it.

If cycling is so good for a traditional start battery why is there the move away from them in stop start. Everyone knows it isn't ideal to run down a starter battery. Run them flat too many times and they wont last at all.

[W&KO]

Er whoops, I thought Rexy already had the DC-DC.

If it was me this is what I’d do on a dirty of tdi

- upgrade alternator to a 100amp/hr disco, I did mine when the OEM one failed, if you have the coin that upgrade sooner
- two batteries will fit but I relocated the AUX that previous owner fitted under the passenger seat to the cargo area. A normal size battery won’t fit under the drivers without serious mods
- fit a redarc battery isolator either the basic or the one that allows back charge from solar to dart battery
- fit Victron regulator
- fit Anderson plug somewhere convenient to plug solar into.
- run cable from fridge to load side of regulator
- fit fuse box if want more circuits.

Oh two batteries under the seat doesn’t leave a lot of room for much else....so to answer your main question, it’d be tight adding a c-Tek in there as well and be a pain when you need to work on the system.

The above set up seems to work well for me, give me the capacity I require, leaves the starter alone, seem to get good life out of batteries...although I do swap them out st three years regardless.

[drivesafe]

Hi W&KO and it is not so much a case of writing the OP off, it is just that there is no logical reason for using a DC/DC device in any Land Rover.

Those using them may or may not achieve fully charged batteries but one of the misconceptions that a DC/DC will treat the batteries better than an alternator can, because they THEORETICALLY go into float mode, is a myth.

If you use even any reasonable SMALL amount of auxiliary/house battery capacity and then drive to recharge the battery with a DC/DC device, it is HIGHLY UNLIKELY that you will ever drive long enough for the DC/DC device to get the battery charged to a state where the DC/DC device can go into float.

Just one of the many myths used to sell a device most people never needed in the first place.

[Tombie]

I didn’t say run down, I wrote cycle. Big difference.

AGMs like any Lead/Acid battery can be charged by voltage differential, that’s all it takes.

I didn’t say buy Traxide at exclusion of all others - that’s your choice - I was only pointing out the unnecessary DcDc device - heck, in a TDi a simple solenoid will do the job.

Add a solar controller and you’ll be golden.

AGMs aren’t magic. Or new tech.

I’m not going to waste time typing any more as your google research has given you what you want to hear.

[drivesafe]

Traxide, follow this link ctrl f and search for agm.

https://www.centurybatteries.com.au/content/documents/battery-talk/issue-2-battery-talk-battery-charging.pdf

Everything it says about agm your system can't do.

AGM batteries should be charged using a chargerwith a mode switch for AGM type batteries. It is recommended to usea charger, current limited to 20% or 0.2C of the batteries capacity at acharging voltage of between 14.6 – 14.8V following deep cycle use, or13.6V – 13.8V for standby use. Charging should be paused if the batteryor ambient temperature exceeds 50°C.

Everything I can find online says AGM should be charged to over 14 volts.
Hi again Rexy and not having a go at you but you either have no real understanding of how batteries are charged or don’t quite get what you are reading about.


The link is to how to charge a battery with 230vac battery charger.


Furthermore, 14.7v is not the REQUIRED charge voltage, it is the MAXIMUM SAFE voltage that most AGM can be charged with and all AGMs can be FULLY charged with much lower voltage.


A perfect example is an Optima Yellowtop. It can be safely charged with voltages up to 15.1v but can be FULLY CHARGED with 13.65v and these are the manufacturers specs.


DC/DC devices are regularly peeled as being JUST LINK A BTTERY CHARGER, and they operate initially in a similar manor.


But there is one major, MAJOR difference. Its the time required to charge a battery.


With a 230vac battery charger, there is no real time restraint and a battery can achieve a fully charge state.


With a DC/DC device, as I have pointed out repeatedly you are highly unlikely to ever drive long enough to fully charge a battery with either a DC/DC device or an alternator, but an alternator will always have your battery in a MUCH higher state of charge at the end of a drive and the higher the state of charge BEFORE its next use, is far healthier for any battery.


This following info is for yours and manics benefit. This shows how a DC/DC device REALLY works and makes a mockery of the mythical claims about DC/DC devices and their multi stage charging mythical “BENEFITS”.






WILDESIDE - OPTIMA D34 TEST CHARGE - 06/07/19.
Optima D34 55Ah Yellowtop charged from 30% SoC after being discharged down to 11.71v using a 2 amp load, drawing a total of 35.7Ah from a fully charged state, reached at 08:27, Voltage settled up to 12.67v by start of charging cycle with a Sterling Wildside - 25 amp Battery to Battery Charger -.


The Wildside was powered via a bench power supply, so that there was a constant 14.5v to see how quick the Wildside could recharge a battery in perfect conditions.


The first column is the TIME, the second column is the TERMINAL VOLTAGE at the battery, the third column is CHARGING CURRENT, the forth column is the amount of used battery capacity replaced at each time reference and the last column is the percentage of replaced used battery capacity.


11:02 11:83v 00.00a 0a
11:04 12.67v 19.35a 0a
11:34 13.06v 19.16a 9.591a 25.5%
12:04 13.55v 19.07a 19.160a 51.0%
12:34 14.94v 14.88a 28.285a 75.2%
13:04 15.00v 06.02a 33.270a 88.5%
13:34 15.04v 02.37a 35.216a 93.7%
14:04 15.09v 01.09a 36.027a 95.8%
15:04 15.12v 00.46a 36.723a 98.0%
16:04 15.14v 00.28a 37.083a 98.6%
17:04 15.15v 00.22a 37.326a 99.3%
18:04 15.15v 00.17a 37.518a 99.7%
18:25 15.15v 00.16a 37.579a 100%


The Wildside went into FLOAT at 18:26

EDIT :- here is the graph for the test above and note the time taken before the DC/DC device went into float!

155360

[drivesafe]

If cycling is so good for a traditional start battery why is there the move away from them in stop start. Everyone knows it isn't ideal to run down a starter battery. Run them flat too many times and they wont last at all.
Rexy I have no idea where you are getting info from but this is the complete opposite to reality.


All cranking batteries can be used in deep cycle application, and before about 2000, the only batteries used for auxiliary batteries in vehicles and house batteries in caravans, motorhome and in marine use, were cranking batteries.


The only disadvantage that cranking batteries have over deep cycle batteries is the the size and weight vs Ah capacity compared to a deep cycle battery.


If you have a deep cycle battery and a cranking battery of the same physical size the cranking battery will have between 10 to 30% less Ah capacity than the deep cycle battery.


But unlike most AGM deep cycle batteries which have charge current limit and the best are just 35% of the total capacity, cranking batteries, regardless of whether they be wet cell or AGM, have no charge current limitation and are self regulating.


This means a cranking battery can be used as a deep cycle battery but can be SAFELY recharge ( faster recharged ) with much, Much higher currents that a standard deep cycle battery can be.


As for the change to STOP/START batteries. This has absolutely nothing to do with older cranking batteries MYTHICALLY not being able to be deep cycled.


STOP/START batteries have an even faster recharge capability and this means they will recharge in an even shorter time than a standard cranking battery.


To further debunk this myth that cranking batteries can not be used as deep cycle batteries. For decades now, European cranking batteries were/are marked with both their CCA rating and their Ah capacity.


This is because the Europeans have and still use cranking batteries as deep cycle batteries, they call them Leisure Batteries.

[Rexy]

Drivesafe,

To keep you happy ill just leave my lights on when Im not in the car. That should replicate your system of drawing 50% of the starter battery. I'll also run jumper leads from starter to deep cycle to get that no nonsense quick charge and less than ideal charge setup (according to the people who make the batteries). That'll let me start off the second battery too.

And if I spend another $160 ill be able to add solar. Still have to sell my ctek to someone, be worth nothing though surely. I guess no need for the temp sense wire, inbuilt solar, agm or isolation functions the ctek has.

Glad someone was able to answer the question of what I can fit under the seat early on in the thread.

[Ancient Mariner]

The 2- 130 AGM batteries in my previous post are start deep cycle and are getting on to 7years old and still going great. Charged by a 120 ah alternator 100w solar panel and Projecta isolator The second battery has fridge, compressor some lights aswell as the winch wich is not recomended .So no fancy charger and no problems[thumbsupbig]



AM

[manic]

EDIT :- here is the graph for the test above and note the time taken before the DC/DC device went into float!

155360

That graph is as expected. The bulk charge to 75% is obviously slower than an alternator that can supply more than 20amps. But still, it's only a couple of hours. And the DCDC only needs to charge one battery.

Where's the comparison graph for a 65amp TDI trying to get two depleted batteries to true 100%?

And why is it that when the yellow top got over 75% of the charge , current demand fell below 20 amps?

Long drives are common for me when I take the Defender out on a trip. The morning camp sees a solar precharge so I would rarely ever need to recover from as low as 11.8v. I'm more often charging up from >=12.2v and on float before next camp. From 75% to float, a wobbly TDI alternator is unlikely to beat a dedicated 20amp DCDC.

But for those who regularly discharge to low voltage cut off , have no solar and take short drives - a 20amp DCDC would obviously be a poor choice.

[drivesafe]

Hi Manic and a bit of fudging the facts there mate.


First off, and the obvious, my specs are for a 55Ah battery and you have a 100”ish”Ah battery but there is no difference in the charge capacity of the two DC/DC devices.


So your battery will take at least 4 hours and because of its larger capacity, will need to be charged to around 85% SoC before it goes into the Absorption stage. Your setup will still require another hour or so, to get that battery up around 90 to 95% charged


With one of my isolators and the 65 amp alternator, even if driving at night, with all the lights draw power as well, both batteries will easily be way over 75% in under two hours.and after less than three hours the two batteries will be around 90 to 95% charged


This puts my setup’s charge capability two hours better than yours in a vehicle with a 65 amp alternator in a worst case drive time.


During the day, with the lights turned off, the drive time needed is even shorter.


Regardless of what charging source is being used, very few people will ever drive long enough to get the batteries to 100% and this means a DC/DC device could not get to the float mode anyway.


Or are you saying you drive for 9 hours straight every time you have been at a camp spot?

[manic]

With one of my isolators and the 65 amp alternator, even if driving at night, with all the lights draw power as well, both batteries will easily be way over 75% in under two hours.and after less than three hours the two batteries will be around 90 to 95% charged

This puts my setup’s charge capability two hours better than yours in a vehicle with a 65 amp alternator in a worst case drive time.


OK so obvs no graph, but what do you base that on? 30 amps to each battery and 5 amps for the lights - or what?

With the dcdc you have 45 amps for the starter battery and accessories, and 20 charging the aux.




Or are you saying you drive for 9 hours straight every time you have been at a camp spot?


Often 6 but very rarely 9. And after a night I dont get close to battery cut out. In the morning there is solar. And so no, it doesn't take me any where near 9 hours to get back up to float!

[manic]

A TDI alternator IME having owned a few, usually fluctuate between 13.5v and 13.9v. And when under heavy load I have seen them drop as low as 13.1v!

Here is a graph that demonstrates what voltage drop can do to charge potential/rate

Worst case 13.5 average
https://www.nationalluna.com/wp-content/uploads/2018/09/National-Luna-Excessive-Discharge-Zone-Charging-curve.jpg


Best case 13.9v average
https://www.nationalluna.com/wp-content/uploads/2018/09/National-Luna-Excessive-Discharge-Zone-Charging-curve-02-1024x664.jpg


And that's on a 100amp alternator, which the TDI does not have.

I think this helps to explain how I have been able to get a better SOC on my aux with the DCDC than I used to get straight off the TDI alternator. With 4-6 hour drives.

[drivesafe]

Hi Manic and first off those graphs are next to useless.


All it states is that they used a 115Ah AGM battery. What brand, what type?


With the Optima 55Ah Yellowtop, discharge to 30% ( same as their test level ), that 100 amp alternator, operating at 13.5v, would have the Optima up around 95% charged in under the first hour.


Now to your TDi300. With the lights on and on high beam, you would have a load of between 15 and 20 amps, leaving around 40 amps available to recharge the two batteries.


This is a worst case scenario.


Because the batteries are in a low state of charge ( cranking battery at 50% and the Optima at 30% ) the total load being applied to the alternator would be greater than it’s total capacity of 65 amps.


This would cause the alternator voltage to drop, but it would still provide all available current to the two batteries.


Regardless of the voltage, the two batteries collectively, will be drawing a little over 40 amps, and this will continue for about 30 to 45 minutes.


The alternator voltage will have now risen to 13.5 ( OR HIGHER ) as the batteries are charging and reducing their current draw on the alternator and this is where the batteries will go into the Absorption stage of the charge.


After about two and a half hours, the two batteries will be up around 90% and over 95% within three hours.


During the day, with no lights on, you could be over 95% in less than two and a half hours

[roverrescue]

RexY
I’ll only weigh in to the controller Debate is that in direct comparison with a Victron solar controller the solar side of your DCDC is disappointingly poor.
Not sure how that plays into your plans
But with a load of a single fridge I would at least consider mounting a 120W panel to the raked roof good charge controller and big AGM and then just having a simple switch to connect to TDI if needed

I run a fridge permanently standalone in the back of my ute with no need for any charge between vehicle wiring and solar system. I do have an off/1/2/both switch so can link into the crank battery if needed but that is more for redundancy to use the solar to charge the Cranker if ever needed.


Now to answer your actual question!!!!

Yes you can fit two N70s in a TDI battery box but it is tight
That is what I use to run
Also won’t be much room at all for much else

But as you have a Ute (if it’s a tray) consider this setup
Using that dead space between outrigger and tray I have a 130ah AGM
It is bigger than N70

At times I’ve run two fridges constantly but in those occasions i doubled my solar panel input from 130W to 250W

Anyways - pics attached

S

[manic]

Have to agree with that. The ctek250 has a solar charge controller but it's not a serious one. It could easily be better, but my unit is quite old now. I don't know if they improved the mppt tracking on the newer models, but the original which I have works well enough to supply a good deal more amps than I draw at camp. So has me covered.

For a more serious solar set up, say on a well kitted out camper/caravan I would certainly run a dedicated solar charge system. I have a 40amp EPEver charging Tesla lithium for a static caravan, and that of course is way beyond the requirements of a small dual battery system that runs a radio some led lights and a 40litre Engel.

Which Victron do you use?

[roverrescue]

For this setup just the baby
100/15 with BT dongle attached
It is stored in waterproof enclosure (bolted to Al tray chassis for heat sink)
Onboard of that battery

Amazes me how efficient it can be with 130W of panel
Fridge running at beer temp in full sun she will hit float by mid morning

With fridge at freeze temps it obviously hammers things a bit harder

S

[W&KO]

For this setup just the baby
100/15 with BT dongle attached
It is stored in waterproof enclosure (bolted to Al tray chassis for heat sink)
Onboard of that battery

Amazes me how efficient it can be with 130W of panel
Fridge running at beer temp in full sun she will hit float by mid morning

With fridge at freeze temps it obviously hammers things a bit harder

S

The later Victrons have BT built in

[DiscoMick]

Every situation is different and I'm no
expert so I can only say what works for me, both on our current Puma Defender and previously on a 300Tdi Discovery.
I don't see any advantage to a DC-DC in a vehicle, but I do believe they have a place in caravans and campers, where the amps coming down the trailer plug could be boosted when the batteries are low and need a big initial charge, before dropping to lower amps after they hit around 80% charged. The last 20% takes much longer to reach. I have seen my 240 volt Projector charger sit on 0.5 for many hours overnight before going on float.
If an alternator is making 60-100 amps, why would you want to limit it to 25-40 amps by using a DC-DC?
My Defender has fat wiring and 60 amp resettable fuses between the starting and second batteries, so any DC-DC would actually limit the amps reaching the second battery.
I believe AGM batteries need about 13.5-14 amps to charge. Lithium need 14.7.
Starting batteries have thinner plates to give a greater initial boost to start the vehicle and faster recharging, while deep cycle batteries have thicker plates for slower discharge, needed by fridges, and take longer to recharge.
As for Traxide vs other DBCs, I have no brief for anyone, but I can only say when you camp for a week without mains power, it is an advantage to be able to draw some power from the starting battery, while knowing there is still plenty left to start the vehicle.
Hope that helps.

[manic]

If an alternator is making 60-100 amps, why would you want to limit it to 25-40 amps by using a DC-DC?

Consider the OP. 65amp alternator, two batteries. Potentially with only 25a per battery to spare with the alternator running flat out right from cold start.

Now consider a DCDC charging one of those batteries at 20amp at up to 14.7v on a 5 step process that can take the battery all the way to float. Whilst the starter still gets its 20-30amps at a wobbly 13.5 to 13.9v from the alternator.

With the above set up, and after a good day the road, the DCDC wil be at a higher SOC than the alternator charged battery, and with less stress all round.

Even if you isolate the starter from discharge and point a 100amp alternator at your depleted AUX, you might find your battery type and its SOC at start rarely call for more than 25-30amps bulk.

I hear the yellow tops can suck it up though. Drive safe wil know - how many amps will they sink at 50%SOC?

Also consider

- the DCDC can continue to charge with the engine off (solar)
- the DCDC is temperature aware and can adjust the charge rate to reduce thermal stress on the battery.
- Many deep cycle AGMs max out at 30amp bulk charge, which can be easily met by 40amp DCDC chargers
- DCDC chargers are getting cheaper,
- Lithium batteries are getting cheaper.
- Faster bulk charges put more thermal stress on the battery
- Higher current demands put more stress on the alternator.

Why limit to 20-40 amps? I'm not saying you should, but some applications don't need to charge any faster than that - and some already can't. So if the DCDC charge rate suits the OP, then it comes down to cost.

What the OP was looking at:

Ctek 250 with built in solar + LVD + 100ah AGM battery

And now the proposed set up for fastest bulk charge:

VSR with built in LVD + solar mppt + 100amp alternator upgrade + two 55ah yellow tops

[drivesafe]

Hi folks and some clarifications.


Rexy, it was not until well into this thread that yo stated you already had a DC/DC unit. As such I and a number of others simply tried to warn you not to buy one because they are so useless, particularly with regards to your small alternator.


While not stating that you already had one, my mistake for not enquiring to this fact, you ( and Manic ) posted up posted up claims of how better DC/DC chargers perform when those claims were based on nothing more that the usual DC/DC advertising misinformation.


So Rexy please don’t shoot the messengers for trying to help you.


Manic, for some strange reason you just do not want to understand how DC/DC devices and alternators FACTUALLY work. You are just blindly your system is the best and everybody should be using similar.


First off, if you do actually drive for 9 hors just about every time you drive while on a trip, then you would fall into a VERY rare range of drivers, with less than 0.1% of people driving those sorts of hours on a regular basis, and I don’t just mean Land Rover drivers, all drivers.


Even when on long trips, most people will very VARY rarely drive for 9 hours while doing a trip around Australia, so you are doing well driving 9 hours all the time.


The vast majority of people will rarely drive more that 5 hours a day and even less when towing a caravan.



Now consider a DCDC charging one of those batteries at 20amp at up to 14.7v on a 5 step process that can take the battery all the way to float. Whilst the starter still gets its 20-30amps at a wobbly 13.5 to 13.9v from the alternator.As has already been demonstrated, if the auxiliary battery is low, you will need to drive for many hours before the battery gets to the absorption stage of the charge, so you can forget all the other stages.

With the above set up, and after a good day the road, the DCDC wil be at a higher SOC than the alternator charged battery, and with less stress all round.Again, nothing but pure fabrication. If the auxiliary battery is low, no one drives ling enough to get a battery to 100% and how the hell can you “stress an alternator”, that is pure pulp fiction. All alternators are self protecting against overloading them, so again how do you “stress an alternator”



Even if you isolate the starter from discharge and point a 100amp alternator at your depleted AUX, you might find your battery type and its SOC at start rarely call for more than 25-30amps bulk.I will cover this irresponsible garbage further down in this reply.





Also consider


- the DCDC can continue to charge with the engine off (solar)As has already been pointed out Ctek units are renowned for their gross inefficiency when used as solar regulators. You are far better off having a decent independent solar regulator.



- the DCDC is temperature aware and can adjust the charge rate to reduce thermal stress on the battery.If you use the correct batteries, temperature will not be a problem.



- Many deep cycle AGMs max out at 30amp bulk charge, which can be easily met by 40amp DCDC chargersThis is nothing but total garbage. If a battery is designated as having a maximum charge current tolerance of 30 amps and if some poor unsuspecting person follows your “EXPERT” advice and they fit a 40 DC/DC devices to charge it, in just a couple of trips, if they get more than one trip in, they will have destroyed their battery. Manic, you have no idea what you are taking about because the DC/DC manufacturers themselves state NOT to use higher current chargers in these types of setups.



- Faster bulk charges put more thermal stress on the batteryBoth cranking batteries and Optima Yellowtop batteries have no charge current limitation and Optima specifically state this on their website. So once again, another ignorance based claim.



- Higher current demands put more stress on the alternator.As covered above, all alternators are self protecting against overloading them, so again how do you “stress an alternator”

[Tombie]

Everyone take a step back.

The OP has decided what he’s doing and now knows an N70 should fit.

Let’s leave him to his own devices (pun intended). And let’s go back to our daily life.

[drivesafe]

Hi Tombie and yep I should let it go but when a self-proclaimed expert "advises" people on how to set up their systems so they can destroy the batteries, I had to warn others about this garbage.

BTW, my claim is not an exaggeration. When the first these 40 amp DC/DC devices came on the market a few years back, within months of their release, the different manufacturers were issuing warnings to suppliers and end uses about not using them on certain types and sizes of batteries because they were already cooking the crap out of heaps of batteries.

[manic]

...


As far as I can see no where on this thread has anyone claimed to be an expert.

All my comments should be taken in context as they pertain only to:

1) My experience with the ctek-250
2) The OPs setup, goal and requirements - which is similar to mine.


.First off, if you do actually drive for 9 hors ....

Please read what I have posted. It does not take me 9 hours to charge my aux. Not even close. Your comparison does not match the use case. You are looking at a user who has solar and rarely starts up with a battery in a state of deep discharge. Yet you still claim 9 hours and have yet to concede that when it comes to the absorption stage of the charge cycle a DCDC can reach a higher SOC that an alternator with low voltage output.


I have stated clearly that I regularly do 5-6 hours of driving per day when out using my dual battery set up. And suggested that my set up would not be suitable for those who have larger battery banks, and/or frequently deep discharge, and/or don't do a lot of driving, and/or don't have solar.

Your calculations are based on full discharge up to an unspecified SOC on the back of a high output alternator that can sustain enough amps+volts to reach your SOC target (unspecified). My comments are in context of low discharge cycles, solar assisted, with 4-6 hours drives that add a sustainable 20amps and 14.5-7 volts. My SOC target is 100% float - and it gets there!



how the hell can you “stress an alternator”, that is pure pulp fiction. All alternators are self protecting against overloading them, so again how do you “stress an alternator”

More load on the alternator must cause more wear and tear. Whether or not that toll is enough to make a significant difference to alternator/belt longevity - I don't know for sure. And again consider the application. For example a 200tdi. The belt set up on these vehicles can barely hold on when its alternator is being asked for all its amps! The 300tdi is better, but still putting max load on the alternator every start up will surely take a toll. I feel happier when my alternator isn't glowing and my belt isn't screaming. If I need to make the alternator work that hard, I will have it work that hard. But with my use case it does not need to, and so there is an additional benefit there with a 20amp limited charger in this case. It spreads the charge across my drive. I am happy with that, and the alternator and battery don't complain either.





As has already been pointed out Ctek units are renowned for their gross inefficiency when used as solar regulators. You are far better off having a decent independent solar regulator.

Yes, but if the Ctek unit provides enough amps to meet my requirements even when overcast - that's all that matters. Context: small dual battery set up, low power demands. 4 years and I have no need to upgrade.



This is nothing but total garbage. If a battery is designated as having a maximum charge current tolerance of 30 amps and if some poor unsuspecting person follows your “EXPERT” advice and they fit a 40 DC/DC devices to charge it, in just a couple of trips, if they get more than one trip in, they will have destroyed their battery. Manic, you have no idea what you are taking about because the DC/DC manufacturers themselves state NOT to use higher current chargers in these types of setups.


I agree with you there on the 40DC, my comment could mislead. To clarify, I am not suggesting people go out and buy a 40amp to charge a 30amp limited battery. The point I was trying to make is that the DCDC's on offer can meet or even exceed max charging requirements. I will admit that I was under the impression that batteries would only take as much current as they need, and that DCDC's adjust output to meet that requirement similar to an alternator. But I trust, as you are the resident expert on charging, that this is not the case.

Also, I think you are being a bit sensationalist there with 'a couple of trips'. The DCDC will have a temperature probe on the battery, and should be able to detect over charge. On the flip side I have left an overcharged battery by the side of the road, bulging at the seams, hissing - for fear of imminent explosion. Whether it was the battery or alternator regulator at fault I suspect an appropriately sized DCDC would have prevented the battery reaching this extreme state.



Both cranking batteries and Optima Yellowtop batteries have no charge current limitation and Optima specifically state this on their website. So once again, another ignorance based claim.


I have asked you, as the resident expert on this thread, a couple of times already - How many amps will a yellow top consume off the alternator when at 50% SOC, if given a source of unlimited amps? Whilst the website states no charge limit - you might be misleading the reader into thinking that the battery can absorb as many amps as your alternator can throw at it. Whilst your VSR has a 50amp fuse, I suspect that for many batteries that limit is not well beyond the capabilities of a 20-40amp DCDC charger.

Optima also state on their website that their batteries will last longer if charged slower.

[drivesafe]

Please read what I have posted. It does not take me 9 hours to charge my aux. Not even close. Your comparison does not match the use case. You are looking at a user who has solar and rarely starts up with a battery in a state of deep discharge. Yet you still claim 9 hours and have yet to concede that when it comes to the absorption stage of the charge cycle a DCDC can reach a higher SOC that an alternator with low voltage output.
So every time you go camping, the suns always shining and you get most of your used charge replaced before you even start driving which is a best case scenario.


Nothing like looking at the world through rose coloured glasses.


In a worst case scenario when the weather is poor and your solar is of no use and with a low battery, then your will need to drive for 9 hours to get your battery charged enough for the DC/DC device to into float mode.


BTW, what advantage is there if your DC/DC device goes into float mode? Going into float mode doesn't protect your battery, it's the actual drive time that protects all batteries.


Now I don’t ware rose coloured glasses and I always give my customers info on a setup based on worst case scenarios, so they have a genuine idea of the limitations of their system.


But there is nothing stopping someone using the same size solar panel you are using and if they used the same amount of battery capacity that you use and then drove to their next stop.


But in this case, because they would be using a separate solar regulator, and it is highly likely to be way more efficient that what you are using, when they started their drive, their batteries are going to be in a higher state of charge.


Then because they have been sharing the load over their two batteries, again, their batteries are going to need less that half the amount of charge your single battery needs.


Once again, their batteries are going to reach a higher state of charge hours before your battery will.


My isolator come with a 50 amp auto resetting circuit breaker but the fundamentals are the same for automotive fuses and circuit breakers and once again, you obviously don’t know how either type of device works.

[DiscoMick]

I'll let those more expert than me argue the finer details and just focus on what I think is the key question for me: do I have anything significant to gain by fitting a DC-DC between the starting and second AGM batteries?
So far I can't see any significant advantages for my vehicle. As I said above, I think there is an argument for a DC-DC in a caravan/camper, although I don't currently have one fitted in our camper.
I think changing from a PWM to a MPPT solar regulator might give more benefits than a DC-DC, but that's another argument.
I haven't noticed any mention of the difference between a traditional alternator and a smart alternator in this discussion. A traditional alternator just pumps out a steady output, in our Defender's case 14 volts. A smart alternator decides when the starting battery is charged and then cuts it's output, which can cause problems for charging a second battery.
Is this a factor affecting if a DC-DC would be beneficial in the OP's case?

[drivesafe]

Hi DiscoMick, can I suggest you start a separate thread as the OP has the info he requested and then your own thread can go in directions of its own as needed.

[manic]

Yeah yeah the old rose tinted glasses again. And another attack on the solar.

There have been numerous firmware if not hardware revisions to the ctek250. The later ones have improved MPPT . I have not compared, but it is likely that the concern you have with it is now out dated.

I have a number of mppts here and can tell you that some of the cheap Chinese 'crap' is just as good at maxi-point tracking as some of the premium gear. In so far as amps recovered in same conditions on same panel are near enough identical.

-------



My isolator come with a 50 amp auto resetting circuit breaker but the fundamentals are the same for automotive fuses and circuit breakers and once again, you obviously don’t know how either type of device works.


Riiiight. I think everyone on this thread knows the difference between a fuse and a CB. This answer adds nothing. The 50amp limit still applies. Just an unnessesary attempt to discredit the conversation. Thanks for that!

--------


Look this isn't rocket science. And we can boil it down to:

The alternator can out out more amps.

The DCDC can put out more volts (context TDI alternator)


And with my alternator:
The DCDC can get to 100% faster than the alternator can. And my alternator can get me to 85% faster than my DCDC can.
But my alternator cannot get me to 100% - even after 9 hours!

The better set up for someone with less than ideal alternator voltage output would be a hybrid set up, where bulk is supplied direct from alternator and absorb to float is done via DCDC.

Ultimately the decision comes down to cost, needs, reliability.

My needs have been met, the unit cost me nothing, and it has been reliable.

If the unit left me wanting I would have ripped it out long ago.

------


On my next trip I will log the charge cycles on both starter charged direct from alternator, and aux by DCDC.

And maybe then you will see how even on a grey day, it is still looking rosey! [emoji41]

---------

If you want a cheap and basic set up on the TDI, there is a VSR behind the instrument cluster that is used to enable the heated rear window function when alternator output has been detected. A connector on the loom can be found on the engine side of the bulkhead (black, silver stripe - from memory).

Run a line from that to a suitably rated relay in your battery box, and use that to link your batteries when alternator is running. Protect it with a fuse or resettable CIRCUIT BREAKER!

Then add an Anderson plug so you can plug your solar panel in with a panel mounted mppt.

Hook up your aux circuit to the aux battery with a fuse/cb and LVD.

If you add a switch between VSR trigger and relay you can manually link and disconnect the batteries. As well as auto switching on alternator output detection.


Job done

[Rexy]

Sold the ctek. Picked up an enerdrive 40amp dc to dc. About same price as a drive safe unit with victron mppt but suits my needs better. Only run a fridge and yes I do long trips or a hours of driving around a paddock. The traxide kit is just not something I’m interested in at all sorry. We all want certain features and don’t want others. Draining any power from starter is one, connecting the two for starting is another.

[drivesafe]

Hi Rexy and sorry mate for raising a ruckus in your thread, but as stated earlier, you originally did not say you already had the Ctek so I was trying to give you a warning to the drawbacks of DC/DC charging.


Just a question for you. Did you get any advice on that size unit before buying it, because you will have to derate it down to 20 amps output as it is way too big for your 100Ah battery you were saying you wanted to get?


If you do not derate it, you will stuff the battery.


Again, if you do not derate it, you will need to upgrade your alternator or you will have some very interesting night driving.


Why did you not just keep the Ctek?

[Rexy]

Gets better, in a previous post you said all alternators are self protecting.
You also banged on about how your kit can provide way more amps than a ctek now the 40amp dc to dc is providing too much. The graph you posted earlier showed the 25amo dc to dc adjusted amps according to charge and battery capacity.

I understand you are selling a product but really if it were so great it would sell itself. To me it’s an overpriced and complex vsr with none of the features I need. Anyway this thread wasn’t for you to advertise it was to find out how I can work around the limited room. You never attempted to answer that just shove your product down the throat of everyone.

[vnx205]

.. .... ...
We all want certain features and don’t want others. Draining any power from starter is one.
.. .... ...


I am not offering advice or criticism of any system, but I wonder if people who are worried about drawing some power from the starter battery before switching to the aux battery are being paranoid.

I realise that no-one wants to be stranded with a battery that won't do the job, but my experience suggests that 50% SoC should be more than enough.

When I had a 7 year old battery that was on its way out, it wasn't going to be a problem at home if it failed to start one morning. So I checked the voltage each morning for a few weeks before I started the engine. During that time, my multimeter read 10.5 volts, yet the engine still started .

My understanding is that 10.5 volts is probably less than 10% SoC and certainly a long, long way below 50%.

I wouldn't head off on a trip with a battery that dropped to 10.5 volts overnight with no load, but I can't believe that a good battery with 50% SoC would have any trouble starting.

When I had the Series III, I had even less concern about low voltages because after two consecutive nights running the fridge in the NT, all I had to do was get the crank handle out. [smilebigeye] Ah! the good old days. [bigsmile1]

[drivesafe]

Gets better, in a previous post you said all alternators are self protecting.
You also banged on about how your kit can provide way more amps than a ctek now the 40amp dc to dc is providing too much. The graph you posted earlier showed the 25amo dc to dc adjusted amps according to charge and battery capacity.

I understand you are selling a product but really if it were so great it would sell itself. To me it’s an overpriced and complex vsr with none of the features I need. Anyway this thread wasn’t for you to advertise it was to find out how I can work around the limited room. You never attempted to answer that just shove your product down the throat of everyone.
Rexy, mate, if you actually understood what I had posted, and this is my fault for not explaining it better, but you hit the nail on the head.

All alternators are self-protecting against overloading.

And as I posted, they do this by dropping their output voltage when ever the load is greater than they can produce.

Has the penny dropped yet????

Even during the day, because that DC/DC unit is way to big for your alternator's size, if your auxiliary battery is low, unless you can keep the revs up high enough so your alternator can produce its maximum current at all times you are going to have problems.

With a low auxiliary battery, that size DC/DC will try to pull more current than your alternator is turning out, so your alternator will protect itself by dropping its output voltage. As are all alternators designed to do.

Unfortunately the lower voltage will cause the DC/DC unit to try compensate for the continually lowering voltage by trying to pull even more current and again this even high current draw will cause the alternator to lower its voltage further again.

All you have done is created a catch 22 situation.

But there is a fix.

When the alternator voltage gets too low, the the current difference will be made up by the device drawing on your cranking battery.

So while you are driving, unless you keep the revs up, you will actually have a situation where you will be DISCHARGING YOUR CRANKING BATTERY WHILE YOU ARE DRIVING.

So my isolators are no good because they allow you to use the surplus energy from your cranking battery, while camped, but your setup now, which actually discharges your cranking battery while driving, is much better.

Thank you for that education.

BTW, what I was on about when I posted that your night time driving was going to be interesting. The first time you drive at night with a low auxiliary battery, even if you keep your revs up, you are going to have a situation where you headlights are going to get duller and duller.

When this occurs, the "ONLY" way for you to be able to continue driving is to turn the DC/DC unit off, and this usually means you have to disconnect it.

BTW Rexy, you were half correct, I was promoting my isolators, but I was also trying to warn you about the drawbacks of using DC/DC devices, particularly in your specific situation, with such a small alternator.

All the best to you.

[drivesafe]

Riiiight. I think everyone on this thread knows the difference between a fuse and a CB. This answer adds nothing. The 50amp limit still applies. Just an unnessesary attempt to discredit the conversation. Thanks for that!
I am really interested to hear how "The 50 amp limit still applies"?

[Rexy]

I’ve got an aftermarket alternator. It’ll be fine. Have another at home from a disco as well

[drivesafe]

Now Rexy, isn’t this something I suggested to you in the first place.


See I haven’t wasted my time and everybody elses. You do take notice of good advice.


Seriously, Rexy my posts were not just about flogging my isolators. I sell DC/DC devices.


The thing is though, no Land Rover needs them and regardless of what make of vehicle it might be, any vehicle with such small capacity alternators should never have a DC/DC device of any form used to charge an auxiliary or house battery.


Anyway, fitting the bigger alternator will give you a safer setup than what you have now.

[drivesafe]

BTW Rexy, just incase you think my warning was a tongue in cheek remark.


It was not an off the cuff remark.


As posted earlier, once you decide what battery you are going to use, READ THE INSTRUCTION MANUAL and then setup the DC/DC device according to what they state.


Do not use the unit until it is set up correctly, otherwise, and regardless of whether you change the alternator, you will cook a battery if the setting is incorrect.

[manic]

I am really interested to hear how "The 50 amp limit still applies"?You constantly dance around the questions put to you when it comes to the max amps your suggested battery will absorb when charging from a sensible low voltage cut off.

I have never owned your kit, so I am not familiar with it. But on the sc80, dt90 suggested on this thread - isn't the link from stater to aux in effect limited by a 50 amp circuit breaker?

[Tombie]

A 5 second google search of the forum would have returned lots of images of dual batteries in Defenders - then there wouldn’t have been any of this discussion. [emoji41]

[Tombie]

You constantly dance around the questions put to you when it comes to the max amps your suggested battery will absorb when charging from a sensible low voltage cut off.

I have never owned your kit, so I am not familiar with it. But on the sc80, dt90 suggested on this thread - isn't the link from stater to aux in effect limited by a 50 amp circuit breaker?

The can of worms on what Amperage a rated breaker will trip at is also a fun discussion. [emoji41]

[DiscoMick]

Rexy , can I just ask if you have checked the specifications of your battery to find its maximum charging rate?
I would be surprised if it was 40 amps.
For example, the maximum charge rate for my Kickass 120 ah AGM is 25 amps.
That is why the 240 volt charger I sometimes put on it is only 25 amps.
If you put a 40 amp charger on a battery that can only accept 25 amps, then I suggest you run away, fast. [emoji15]

KickAss 12V 120AH Portable Deep Cycle AGM Battery | Australian Direct (https://www.australiandirect.com.au/Battery-Systems/AGM-Deep-Cycle-Batteries/KA12120)

[Tombie]

Rexy , can I just ask if you have checked the specifications of your battery to find its maximum charging rate? I would be surprised if it was 40 amps.

Mick,

Based on Fullriver, the 40a inrush is quite possible.

https://uploads.tapatalk-cdn.com/20191106/cec315fcbf756b70620a27e72cee61e1.jpg

See the left Axis, 0.25x C20
The bigger the battery, the more it can take.

Of note (not posted) but known, as temperature increases, charge voltage should lower.

[Ancient Mariner]

For all the paranoid wot watchers among us. Run your battery down to 3 volts (not Recomended)[bighmmm] Great bit of gear[thumbsupbig].





AM

[Bill Wallace]

This is as tight a fit as you will physically get. There is also a Victon 100/15 MPPT charger and a Traxide unit in there.

You need spaghetti fingers to get in. https://uploads.tapatalk-cdn.com/20191109/2c73c4cf17d52959391be233e35446f1.jpg

[DiscoMick]

Geez I thought our battery box looked crowded with a starting battery, Traxide and PWM solar regulator in there, but yours beats ours easily.
I had to fit an Anderson plug outside to make it easier to attach a battery charger or extra solar panel.

[Tombie]

During the install on Ike... a little different.

https://uploads.tapatalk-cdn.com/20191110/3deb25fe105494fe340fe1f1e0da86e9.jpghttps://uploads.tapatalk-cdn.com/20191110/45c27a812e0ac0d2291379bfbee0b7bb.jpghttps://uploads.tapatalk-cdn.com/20191110/a9917289155fed1528198188d499a2f3.plist

[Bill Wallace]

Geez I thought our battery box looked crowded with a starting battery, Traxide and PWM solar regulator in there, but yours beats ours easily.
I had to fit an Anderson plug outside to make it easier to attach a battery charger or extra solar panel.For jump starting. https://uploads.tapatalk-cdn.com/20191110/3a1798e9b5737e42c5fb7e994c0b00b5.jpg

[drivesafe]

You constantly dance around the questions put to you when it comes to the max amps your suggested battery will absorb when charging from a sensible low voltage cut off.

I have never owned your kit, so I am not familiar with it. But on the sc80, dt90 suggested on this thread - isn't the link from stater to aux in effect limited by a 50 amp circuit breaker?
Actually Manic, I have not "danced around the question"

If you ave a look at the link bellow, you will see I covered most of your "enquiries" in that thread, and if you scroll down the page, most of your questions are alder answered.

I will, as soon as time permits, cover Circuit Breaker and fuse operation and usage in my next post on that thread. This will also explain in even more detail about how a Land Rover alternator does a much faster and ultimately, better job of charging batteries that any DC/DC device can.

I am going to post this info up in my thread and leave Rexy to do what ever he wants i his thread.

On-Line auto electrical info (https://www.aulro.com/afvb/the-verandah/246755-line-auto-electrical-info-9.html)

[manic]

Good job on that link, appreciate the effort.

I tried to limit my comments to context on this thread and my own use case.

Your proposed set up on the linked thread is a split yellow top system where the AH is shared across main and starter. Same as you proposed here. Its a well thought out system that fits a lot of use cases. I'm not knocking it.

But like the OP, I chose to have a dedicated starter in reserve and a 100ah aux used in isolation when in camp. But even so, this kind of set up does not need a DCDC. A simple relay could cover it.

To sumise my reasoning and experience with the ctek250:

I went with DCDC because at the time I was not happy with my aux battery SOC on direct alternator. I also had a battery failure from overcharging. So I gave the DCDC a shot.

At time of install I did have concerns about limited charge rate not covering my needs and reliability.

Years have now passed, and if I had to start over on the TDI battery bay today I would go again and get another DCDC with selective lead acid and lithium charge maps. I now know for sure that 20amps of dedicated bulk charge on a 100ah battery is enough to replenish my usage on that vehicle. And I have had zero faults on the unit even though it has been submerged in rivers and vibrated through dusty hell back. I can have mix and match batteries and my aux is very happy with the dcdc charge map.

The new ctek 250 has a charge map for lifepo4 and much improved solar mppt algorithm. So I would give it another look.


Now there are the 100ah lifepo4 batteries that are starting to drop to around the $500 mark - I think DCDC set ups will become more common .