Discovery 2 Dual Battery

[Yakuza]

Hi, in My D2 i have an dual battery setup from the previous owner and the battery isolator isnt working correctly, so i want to know what should i look for in an solution? Its all connected well and charges but doesnt isolate it,

Also there seems to be and fuse running from the box out and then its cut off so i dont know whats that for.

Any help would be good

Thanks

[rrturboD]

There are a great number of different "isolators" available, a photo of the installation would help us.....

[Yakuza]

True, but its all good now its worked out

[geordiepride]

the isolator /solenoid may have been bypassed

so both battery's are hooked up full time

if its one of those digital things allow time for it to kick in and out

[d2dave]

If you need a new isolator, get one from Tim at Traxide.
In my opinion, you can't beat them

[Bohica]

If you need a new isolator, get one from Tim at Traxide.
In my opinion, you can't beat them

I've had a Traxide SC80 for about 6 years. A wonderful bit of kit. Why people use a DC - DC chargers is beyond me.

[austastar]

Why people use a DC - DC chargers is beyond me.

Hi,
A Li battery has a different charging profile, so a dc-dc is needed to get a full charge in to it.
Cheers

[d2dave]

Hi,
A Li battery has a different charging profile, so a dc-dc is needed to get a full charge in to it.
Cheers

There is a little more to it. A lead acid battery will only receive the amount of charge that it wants.

When flat it will take a large amount, but as it becomes charged the amount of current that it receives tappers off, reasonably fast.

A Lithium on the other hand, regardless of state of charge, will take what ever you throw at it.

As an example. I have a lithium battery which has 190 AH capacity. Lets say I use 150 amps whilst camping.

It is raining all day so my solar is not working. I decide to pack up and drive home. My D2 alternator is going to supply its full output to the battery, minus what the car needs.

Lets say I leave at night. I don't know what the D2 needs in AH for night driving. I will just pick a number, lets say 30 amps. I think the D2 alternator is 120 amps

This leaves 90 AH available for charging the lithium. The battery will accept this and it will take about an hour and a half to charge it.

So your alternator will be outputting its full capacity for one and a half hours.

Do this regularly and your alternator is not going to last very long.

This is why I have to run a DC to DC charger. I have one that outputs 50 amps max. This protects my alternator.

A DC to DC is also required for lead acid on late model cars that have a smart alternator.

[austastar]

Hi,
Yep, I have dialled the dc-dc to 20Amp for similar reasons. Since going Li with the house battery, I'm not chasing the last rays of sun with a solar panel.
Nice!

Cheers

[austastar]

Edit
The dc-dc charger stops charging the Li when it reaches full charge.
Cheers

[d2dave]

Edit
The dc-dc charger stops charging the Li when it reaches full charge.
Cheers

When a lithium is fully charged the battery's inbuilt BMS will cut off the charge, not the charger stopping.

[Bohica]

A Lithium on the other hand, regardless of state of charge, will take what ever you throw at it.



Not in EVs, the higher the state of the charge, the slower the charge rate, although that could be the EV BMS?

[Tins]

Not in EVs, the higher the state of the charge, the slower the charge rate,

Can't have the things blowing up, now can we?

[drivesafe]

A lot of care must be used when selecting a lithium battery as an auxiliary battery.

SPECIAL NOTE, lithium batteries should NEVER be used as a cranking battery.

The primary difference between charging a lead acid battery and a lithium battery is that a lead acid battery requires three stages of charging, Bulk, Absorption and a Float charge.

Whereas Lithium Batteries require two stages of charge, Bulk and Absorption, and once charged, the charging source must turned off.

ALSO NOTE it is very rare for a Lithium battery’s BMS to act as a current limiter during charging, In other words, the lithium battery’s BMS does not shut down the battery once it is fully charged.

Many Lithium Battery BMS will shut the battery down if there is a high current DISCHARGE, this has nothing to do with charging.

The above info relates to charging with a DC/DC device, Solar Regulator and a 240vac Battery Charger, it has little to do with charging from an alternator.


ALTERNATOR CHARGING OF LITHIUM BATTERIES.
There are a number of specific requirements when charging lithium batteries directly from an alternator.

First and foremost, when selecting a lithium battery for charging directly from an alternator, with a Discovery 2 or 3, the battery MUST HAVE a CONTINUOUS CHARGE CURRENT rate of at least 100 amps.

NOTE this is NOT the MAXIMUM charge current makes on a lithium battery, as this is something a lithium battery can only tolerate for a very short time of a few seconds to a few minutes.

If you have discharged a lithium battery to a low state and you then drive for a few hours, the battery could be receiving a charge current as high as 100 amps for quite some time.

Note, this does not apply to a Discovery 4 or any vehicle with a SMART alternator function.

I have tested charging a Lithium battery with a 140 amp alternator and with a 100Ah lithium battery mounted in the rear of the vehicle and Twin 6B&S ( 13.5x2 ) cabling connecting the lithium battery, via a DT90 isolator, to the cranking battery.

While I monitored the currents in both directions ( Charging and discharging ) I would periodically blow a 50 amp fuse but an 80 amp fuse allowed 70+ amps of continuous charging and up to 140 amp discharging while starting the motor.

How fuses work is for another time.

I could change the operation of the alternator in the vehicle I used, from a SMART alternator function, similar to a D4, to a Variable Voltage alternator function, similar to how a D3 alternator works.

My tests were two fold. They were to see how my SC90 and DT90 isolators worked with a lithium axiality battery and how well a lithium battery could be charged with an alternator.

When charging a lithium battery from an alternator, you do not have to worry about shutting the charging off once the lithium battery is fully charged as this will happen every time you turn your motor off.

Constant charging of a fully charged lithium battery from an alternator would only be a problem if you were to regularly drive for 10 to 15 hours straight. Not likely to happen.

My findings were that my isolators worked fine with a lead acid cranking battery and a lithium auxiliary battery but I got some interesting results relating to using a Lithium Auxiliary battery.

First off, because lithium batteries have a higher and constant rested voltage ( around 13.2v -13.4v ) my isolators would remain on, regardless of whether they were set to Ignition mode or Shared mode.

So when I turned the motor off, with the lithium auxiliary battery sitting at 13.3v, and the lead acid cranking battery sitting anywhere from about 12.3v to 12.7v, the lithium would slowly discharge back into the cranking battery.


I used this setup for a little over two years.

The alternator operating in Variable Voltage mode, would really get much over 14.0v and regularly settled down to 13.5v, while driving.

This still allowed the lithium battery to be fully recharged ( 95% or higher ) even after short drives.

NOTE, the cranking battery was on its last legs and beginning to fail to start the motor, through age, when I first put the lithium battery in.

As I stated, the lithium battery was used in this setup for a little over two years, but with in a few days of installing the lithium auxiliary battery, the cranking battery’s starting performance improved dramatically.

After having the lithium auxiliary battery in for two years, I decided to remove it to carry out a fully monitored bench discharge test.

The lithium battery still had a 100% capacity.

But the surprising thing was that the “STUFFED” cranking battery lasted another 6 months and I only replaced it when my BM2 Bluetooth Battery Monitor warned me that the cranking battery voltage went too low when starting the motor.


Now when camping, with two lead acid batteries, the cranking battery and the auxiliary battery, while camping, your fridge, camp lighting, phone and computer charging, etc, current would be shared and come from both batteries.

With a lead acid cranking battery and a lithium auxiliary battery, all the power would initially be coming from the lithium battery even though the two batteries are still connected.

Only if the lithium battery was discharged down to about 15 to10% SoC, would power start coming from the cranking battery.

In this situation, the DT90 isolator still protected the cranking battery from being over discharged and the DT90 would completely shut down before the Lithium Battery’s BMS shut the Lithium battery down.

When you went for a drive, even with both batteries discharged to their lowest allowed level, both batteries would be back over 95% in about 90 minutes.

If you decide to use a lithium battery as an auxiliary battery, you could use two lithium batteries with a continuous charge current of 50 amps, as long as they are wired in PARALLEL.

I have also posted this info up in the VERANDAH section, in the On-Line Auto Electrical thread.

[admiralranga]

I've had a Traxide SC80 for about 6 years. A wonderful bit of kit. Why people use a DC - DC chargers is beyond me.

Depends where the second battery is, when it's at the opposite end of the car and volt drop starts to affect the maximum it'll charge to it they make more sense.

[Bohica]

Depends where the second battery is, when it's at the opposite end of the car and volt drop starts to affect the maximum it'll charge to it they make more sense.

My aux LiPO4 battery is in the rear luggage bin, driver's side. I have hefty cables. I get 14.6V at the aux battery, when the engine is running. I guess I do not need a DC-DC charger.

[drivesafe]

Depends where the second battery is, when it's at the opposite end of the car and volt drop starts to affect the maximum it'll charge to it they make more sense.

As I posted, I was getting as much as 70+ amps at the Lithium auxiliary battery, and this was mounted in the boot. So it actually depends on cable size and as posted, I use 6B&S ( 13.5mm2 x 2 ).

I have set up caravans and again seen 73 amps at the house batteries in the van while charging with an alternator.

There are very few DC/DC devices that can deliver that sort of charging and they would not work at that current rate in a D2 because the DC/DC devices are so inefficient.

[Bohica]

Can't have the things blowing up, now can we?

True, I mean with 321 cars a day in the USA catching fire, we want to reduce the number that burn. Oh that is the number for petrol and diesel vehicles.
Data from Sweden had ICE vehicles have a 1 in 38,000 chance of catching fire, those numbers include hybrid cars. Ice vehicles have a 1 in 1300 chance of catching fire. Access Denied (https://www.motortrend.com/features/you-are-wrong-about-ev-fires/)

[reid25]

As I posted, I was getting as much as 70+ amps at the Lithium auxiliary battery, and this was mounted in the boot. So it actually depends on cable size and as posted, I use 6B&S ( 13.5mm2 x 2 ).

I have set up caravans and again seen 73 amps at the house batteries in the van while charging with an alternator.

There are very few DC/DC devices that can deliver that sort of charging and they would not work at that current rate in a D2 because the DC/DC devices are so inefficient.

I'm curious to know why a lot of people here are not so fond of DC-DC's? for years I've seen them to be the ideal choice for aux systems. Is it a price thing? e.g. isolators are much more cost effective?

[drivesafe]

I'm curious to know why a lot of people here are not so fond of DC-DC's? for years I've seen them to be the ideal choice for aux systems. Is it a price thing? e.g. isolators are much more cost effective?
Hi mate and this is a touchy subject for anyone who thinks DC/DC devices are the end all.

First off, and I will use a D4 as the example, DC/DC devices are only about 80% efficient and thats as long as the auxiliary battery is not too low and the alternator voltage is high enough.

Whereas, my Traxide isolators are at least 99% efficient regardless of alternator voltage.

The current charge limit of a DC/DC device means it can take as much as 6x as long to replace the same amount of used energy that a Traxide system will replace in a much shorter time.

And this something moist people are unaware of, modern DC/DC devices are, for safety reasons, INPUT current limited. This means as the voltage from the alternator drops, a DC/DC device needs to draw more current from the alternator to maintain the OUTPUT charging current.

But again, as stated, for safety reasons, this INPUT current is now limited and as the alternator voltage drops, the OUTPUT charge current reduces, regardless of whether the auxiliary battery is in a low state of charge or not

So while the DC/DC device may be rated as a 40 amp charger, it is not uncommon for them to be charging at less that 20 amps when used in a vehicle with a SMART alternator, like D4s.


Lot more to it but this is a start.

[Tins]

True, I mean with 321 cars a day in the USA catching fire, we want to reduce the number that burn. Oh that is the number for petrol and diesel vehicles.
Data from Sweden had ICE vehicles have a 1 in 38,000 chance of catching fire, those numbers include hybrid cars. Ice vehicles have a 1 in 1300 chance of catching fire. Access Denied (https://www.motortrend.com/features/you-are-wrong-about-ev-fires/)

You can make statistics say anything you want. ICE cars of course have fuel that burns. That's what combustion means, after all. EVs are not supposed to burn, but they do, and you can't put the bloody fires out.

MotorTrend has skin in the game. You may want to broaden your reading.

[Bohica]

You can make statistics say anything you want. ICE cars of course have fuel that burns. That's what combustion means, after all. EVs are not supposed to burn, but they do, and you can't put the bloody fires out.

MotorTrend has skin in the game. You may want to broaden your reading.

I'd suggest that ICE vehicles are not meant to burn either.

Data is data. No matter what the source.
There was a Tesla Semi fire a few weeks ago. made the news. First one. How many diesel semis catch fire each day in the US?

[Tins]

I'd suggest that ICE vehicles are not meant to burn either.

Data is data. No matter what the source.
There was a Tesla Semi fire a few weeks ago. made the news. First one. How many diesel semis catch fire each day in the US?

Data can be manipulated, Julian. That's obvious, happens every day. That's the purpose of the MSM, of which MotorTrend is a part. What is the ratio between diesel and electric prime movers? What caused the fire? Do diesel PMs catch fire when simply parked? Do they catch fire if the operator is stupid enough to refuel them? When they burn, can the fire service extinguish them? Does the fire service then have to monitor them, and follow them to their grave, do they need to be isolated from everything else for months afterwards? No. Do they have to have special sections set aside for parking, or on ferries? No. Can you say the same about EVs? No.

Have a look at who owns MotorTrend. Check out just where their income is sourced. Nothing to see here?

[reid25]

Hi mate and this is a touchy subject for anyone who thinks DC/DC devices are the end all.

First off, and I will use a D4 as the example, DC/DC devices are only about 80% efficient and thats as long as the auxiliary battery is not too low and the alternator voltage is high enough.

Whereas, my Traxide isolators are at least 99% efficient regardless of alternator voltage.

The current charge limit of a DC/DC device means it can take as much as 6x as long to replace the same amount of used energy that a Traxide system will replace in a much shorter time.

And this something moist people are unaware of, modern DC/DC devices are, for safety reasons, INPUT current limited. This means as the voltage from the alternator drops, a DC/DC device needs to draw more current from the alternator to maintain the OUTPUT charging current.

But again, as stated, for safety reasons, this INPUT current is now limited and as the alternator voltage drops, the OUTPUT charge current reduces, regardless of whether the auxiliary battery is in a low state of charge or not

So while the DC/DC device may be rated as a 40 amp charger, it is not uncommon for them to be charging at less that 20 amps when used in a vehicle with a SMART alternator, like D4s.


Lot more to it but this is a start.

Yeah that makes sense, thanks mate. I guess I have learnt all my dual battery knowledge from mainstream sources so they're always going to spruke large brands and dc-dc products etc. - I've probably never had an issue with my dc-dc / aux battery charging since I mostly have had solar input backing it up

[drivesafe]

Yeah that makes sense, thanks mate. I guess I have learnt all my dual battery knowledge from mainstream sources so they're always going to spruke large brands and dc-dc products etc. - I've probably never had an issue with my dc-dc / aux battery charging since I mostly have had solar input backing it up
Con't get me wrong, I have never claimed DC/DC setups can't charge batteries, they are just not the only or best way to do it.

Most people get what they pay for when installing a DC/DC setup, but they can usually get a better setup for less money.

[Tins]

Thought this might be of interest. I don't know one way or the other, but I would like to hear Tim's opinion.

<br>
https://youtu.be/TdvyTOFmGSk'si=p--GJXK3p8IAnkLf

[drivesafe]

Hi Jay Tee, and I will use how my isolators work to demonstrate how you can get around the charging problem he has.

First and foremost, from the data he supplied in his video, my guess is that his auxiliary battery is badly sulphated.

My reason for this is that the battery went down to as low as 11.80v in a short period of time, when under load. The current load of two fridges would not have been that large. This indicates that the battery was down to around 30 to 40% State of Charge of its “AVAILABLE” capacity.

Then when he went for a drive, the 25 amp DC/DC charger only charged in the Bulk/Absorption cycle for about an hour and then went into Float mode.

This means that it only supplied about 20 amperes of capacity, at best, in that short time before the DC/DC deice determined that the battery was near fully charged.

The auxiliary battery looks like an 80Ah to 100Ah capacity.

I’ll use the 80Ah capacity to demonstrate the problem.

Again based on the data supplied, the battery is so severely sulphated that it has about only 20 to 30% of its original capacity available for use.

He needs to Desulphate the battery before he does anything else, otherwise, it early demise is imminent.

The other solenoid type isolator will not solve his problem but it allow the auxiliary battery to get a bit more of a charge.

This is on a Toyota, which does NOT have a SMART alternator, but if this was in a vehicle with a SMART alternator, the problem would be worse and the solenoid type isolator would not help.

With my Traxide isolators, while you will still get Sulphation happening if you don’t maintain your batteries properly, it does take much linger to occur.

There are a number of reasons for this, but basically you get better performance with a Traxide isolator because it shares the load of two batteries, which means the two batteries will never be as low as a single battery setup, and this means you will recharge the two batteries in a shorter drive time, and because the two batteries are always in a higher state of charge, Shulphation takes much longer to buildup..

Unlike DC/DC devices ad their limited charge current, the Traxide isolators all everything an alternator can turn out too again, recharge the two batteries in a shorter time.

Also note, the guy is using a Deep Cycle battery as the auxiliary battery, but I ALWAYS recommend you use a CRANKING type battery as the auxiliary battery because they are specifically designed to take high currents ( fast charge ) while charging. Because of the design, Deep Cycle batteries actually take much longer to fully charge.

[Slunnie]

Ahhh, thats the advantage of a Traxide unit over a traditional voltage sensitive relay that isolates when the alternator stops charging.

[TonyC]

Also note, the guy is using a Deep Cycle battery as the auxiliary battery, but I ALWAYS recommend you use a CRANKING type battery as the auxiliary battery because they are specifically designed to take high currents ( fast charge ) while charging. Because of the design, Deep Cycle batteries actually take much longer to fully charge.

Hi Tim,

If you discharge a battery to a low state of charge regularly, what is the difference in life between a deep cycle and cranking battery?

As always, thanks for your input to AULRO.

Tony

[drivesafe]

Hi Tony and sorry for the delay in replying but I am flat-out.

The principal difference between Deep Cycle batteries and cranking batteries “WAS” the number of deep cycles each battery could provide before needing to be replaced.

I emphasised WAS because this really only applies to older type deep cycle batteries verses older type cranking batteries.

With the older type batteries, while you could always deep cycle both types, dedicated Deep Cycle batteries could deliver far more cycles that a cranking battery.

Prior to about 25 or so years ago, the RV industry used cranking batteries for all its needs, like Auxiliary batteries in vehicles and House batteries in caravans and Motorhomes, and while camper trailers were only just beginning to be produced in numbers, they too were supplied with cranking batteries.

The original Deep Cycle batteries were glass and some came with as much as an 18 year warranty, but being glass were totally useless for RV use.

These Glass batteries were designed to be used in Remote Area Power Supplies and Uninterruptible Power Supplies, where they were used in large banks of batteries, where large currents could be drawn from the bank, while only drawing very small currents from each battery in the bank.

Again these banks were also charged with high currents but each battery would only be drawing a small charge current.

The first Deep Cycle batteries we recognise today were still specifically intended for the original use. as such, they had a number of limitations that made them unsuitable for RV use, but people tried to use them anyway.

Wet cell Deep Cycle batteries could be used as long as they were not placed in the engine bay.

When the first AGM type Deep Cycle batteries started being used in RV situations, it was quickly realised that they had a very short lifespan. This is because, like the old Glass type Deep cycle batteries, they did not tolerate high temperatures, or high charging currents and especially had no tolerance for high voltages.

As the manufacturers came to realise that there was a huge potential market for their batteries in the RV industry, battery techknowledgy improved, first with the maximum voltage rising from 14.1v to 14.4v then finally 14.7 to 15.0v.

At the same time, maximum charging currents rose from 20% to 35 to 40% and higher with some Deep Cycle batteries.

BUT, not sure heat tolerance has risen enough for safe under bonnet use. ( personal opinion )

Then about 15 years ago, the first AGM cranking batteries came on the market and these offered high operational advantages over AGM type of Deep Cycle batteries.

All AGM cranking batteries tolerate at least 14.7v and many are safe at 15v. They literally have no charge current limitation but best of all, they are completely safe to use under the bonnet.

All cranking batteries have been safe to discharge down to 20% SoC and many of the newer ones, as stated by the manufacturers of these batteries, can be safely cycled down to 0%.

Particularly with their rapid recharging capability, this makes AGM cranking batteries ideal to use as auxiliary batteries.

[Tins]

All cranking batteries have been safe to discharge down to 20% SoC and many of the newer ones, as stated by the manufacturers of these batteries, can be safely cycled down to 0%.

Particularly with their rapid recharging capability, this makes AGM cranking batteries ideal to use as auxiliary batteries.

So, can you recommend a budget battery for this? I need a "house" battery for my OKA. It will have the SC-80 I got from you for my D1 fitted to it. I won't have much power draw, fridge/freezer, device charging and probably StarLink with a laptop or Mac Studio. No TV. It has a 180 watt or thereabouts solar panel, with a MPPT40 solar controller. I am mindful of what you say about a cranking batt. Would an AGM that is capable of starting amps for a few seconds do? The OKA starts almost instantly, usually. It has and old school alternator, albeit with a high output ( have to check how high ). I will also carry a generator for emergencies, like keeping the campsite awake.

I ask because Kings and a few others have affordable AGMs. I know where they sit on the quality ladder, but even if I get a couple of years out of one.... the 115 ah one apparently can deliver 920 amps for 5 seconds.

Seems i have forgotten all I used to know about batteries. And battery tech has forgotten about me.

[ozscott]

Very happy with the Red Arc 50amp DC2DC with my lithium battery in my tub. The Lithium is an great quality battery built by Mr Wei in Slacks Creek. A man who knows quality cells and battery builds. I have another of his in my boat. Blue tooth BMS so I can see what amps are going in. If the battery is down the Red Arc puts in over 50 amps. I have accidentally let the battery drop to shut off twice and each time the Red Arc triggered charging when the vehicle was started. The Red Arc's built in MPPT solar charger works very well. It will prioritise solar when the alternator is spinning but I only use solar when stationary camping. Spent a few weeks up at Cape York and the 65 litre Evakool, camp lights, 12v camp cooker etc worked great with this set up. Cheers

[drivesafe]

So, can you recommend a budget battery for this? I need a "house" battery for my OKA. It will have the SC-80 I got from you for my D1 fitted to it. I won't have much power draw, fridge/freezer, device charging and probably StarLink with a laptop or Mac Studio. No TV. It has a 180 watt or thereabouts solar panel, with a MPPT40 solar controller. I am mindful of what you say about a cranking batt. Would an AGM that is capable of starting amps for a few seconds do? The OKA starts almost instantly, usually. It has and old school alternator, albeit with a high output ( have to check how high ). I will also carry a generator for emergencies, like keeping the campsite awake.

I ask because Kings and a few others have affordable AGMs. I know where they sit on the quality ladder, but even if I get a couple of years out of one.... the 115 ah one apparently can deliver 920 amps for 5 seconds.

Seems i have forgotten all I used to know about batteries. And battery tech has forgotten about me.

Hi Jay Tee, I personally like the SSB HVT range of batteries but they are nearly twice the price of the Kings batteries, so go with them and see how it lasts.

[Tins]

Hi Jay Tee, I personally like the SSB HVT range of batteries but they are nearly twice the price of the Kings batteries, so go with them and see how it lasts.

Thanks Tim. Those have been recommended before, probably by you and I think Mike ( tombie ). In an ideal world I would go with them I think, but circs are that I need to do something soon and cheap. If circs are better than they appear atm I'll upgrade.