Power from White Plug to Anderson Plug

[QUOTE="drivesafe;1920590"]Hi Brett and sorry mate but your math just doesn’t add up.

For a start, over long cable runs, you will NOT damage your batteries if charged direct from your alternator as the high current draw caused by the batteries being in a low state will make the cable act as a quasi voltage/current regulator, but your batteries, IF IN A LOW STATE, will charge much faster from your alternator, and with out any risk of damage. (I understand this logic)

Next, if you had low batteries when you set off on that return trip from Warren River, there is no way on gods earth you could have had batteries at 98% SoC after such a short drive, and I’m guessing 5 hours at most. (Not low, but not full. Batteries had 180 watts of solar connected so this would help keep them topped up)

If your batteries were at 50% SoC and this is not low but average use levels, and you DID NOT have the fridge connected, using your 25 amp charger would at very best, got your batteries somewhere between 85% to a bit over 90% “IF” the drive was 5 hours long. (Have never seen my batteries get that low)

With your fridge running off your batteries and drawing 15 amps, your batteries would be lucky to be at 75% SoC after a 5 hour drive. (You are making too many assumptions. Fridge does not draw 15 amps all the time, only while compressor is running. 25 max amps going in, with less than 15 amps (max 7.5 amps per hour based on running 50% of the time) ... my batteries have never got as low as 50% SoC due to constant charging from solar panels)

As to your cable-only set up, direct from your alternator, only providing 10 amps to your batteries, well the batteries must have been near fully charged to be drawing that low a current level over decent cabling, “OR” you had some serious problems with your cabling. (Agreed, as I always have a battery charger connected....I am paranoid about keeping batteries full...the reason why my batteries last so long. Cabling, as mentioned, was checked by an autosparky and tested with camper connected.)

When I first got my ( my wife’s ) D4, I carried out load/charge testing and with 10m of 6B&S twin cabling, and three low batteries, totalling 260Ah, I monitored currents of up to 63 amps and over a 4 and a bit hours drive I raised the batteries from 20% SoC ( 11.58v ) to just under 80% and averaged 36 amps per hour and note, the cranking battery was also low at the start of the drive but was not monitored.

I suspect your batteries are never in a genuine low state so your DC/DC device is doing nothing more than topping your batteries up, not charging depleted batteries. (Correct....I have solar panels keeping them up while camped. For longer periods (around 5 days more or less depending on weather) I may start my gennie and let the other 40 amp battery charger give them a tickle for a few hours.....but rare and still batteries not as low as 50% SoC)

My xantrex battery monitor provides all the information I need to confirm state of charge and current in and out, current over a 24 hour period, etc....if this is giving me wrong readings, then I have posted wrong readings. But I think the readings are correct, and I am happy with this setup, as it has worked better for me than previous setups (15 years of using bulk chargers and now 5 years of DC to DC charges is a better solution for me...not for all).

Brett....

Hi again discotwinturbo and seriously, with your type of battery usage, you could LITERALLY throw away the DC/DC device, remove one of the batteries and the remaining battery would still die of old age before your power demands had any effect on the battery’s longevity.

The best thing you have for your batteries is your solar set up. That will cover your power requirements will your are using the batteries on a trip, and the solar will give you perfect maintenance of the batteries while they are stored away between trips.

As to using the 12S socket, if you are running a 3 way fridge then yes this socket’s output would be idea because 3 way fridges are not as finicky when it comes to voltage drop.

BUT, contrary to suggestions made, these sockets are not suitable for charging batteries in the way we use batteries here in Australia.

In Blighty land, as someone has already pointed out, they tend to go from one powered site to another and the battery circuit in these sockets is intended to do no more than trickle charge the house battery(s) to keep them in a fully charged state.

Now for a reality check.

Using one of these circuits to power the fridge is fine. You know what the total load of the circuit is going to be at all times. Nothing unusual with that.

The same thing does not apply when setting up a circuit for charging batteries.

For a starter, there is no constant current factor to work from or base the limitations of the circuit on.

While your can guestimate the maximum current a low battery or number of batteries will draw but this is not enough.

In a conventional circuit, with a known maximum current requirement, you can select the cable and circuit protection to allow for safe supply of the needed current for the circuit and still cover for the potential of a short circuit condition occurring.

Just two simple factors to work with.

In a Dual Battery System there is a critical third factor and the one that must be given considered and that is a current overload situation.

Most people have no idea of what sort of problems can be caused by current overload and this is probably the most common cause of damage in DBS set ups.

It’s a long and involved topic and I will not go into detail here other than to state that the 12S socket wiring is not up to the job of charging house batteries in a CT or caravan being towed by a D4.

Works for me....certainly wont consider your advice about throwing it out.

Brett.....

The beauty of forums is that there is plenty of discussion which should be used to make an informed decision. The ugliness of them is when they turn ferrel and folks just tell someone else that their opinion or choice is wrong.:(


There are advantages and disadvantages in the variety of systems out there. I have planned my total system based on my usage and style of camping and being a "system" it all works together well. My battery capacity was selected to never go below 50% charge as AGM's life can be considerably shortened by repeatedly doing so. If you are constantly charging AGM's from 20%Soc then you have the wrong capacity batteries on board should you wish to save replacement costs sooner then later. I chose a DC/DC smart charger because again I calculate that with 25A charging current it should take no more than 2 hours to bring my 100A/Hr battery from 50% to full charge (almost 100%) and will then gently float it there. (again, a well matched charger for the battery) I chose the DC/DC smart charger method because I prefer the more gentle charging profiles for my batteries for longevity reasons. Coupled with the fact that it has an MPPT solar regulator with it My 160W panels used when I'm set up ensure that I can charge at surprisingly fast rates and never have need for power. Call me old fashioned but having looked after big old batteries aboard submarines - nice and slow with low temps is the best way to charge. Particularly with sealed batteries fitted with pressure relief devices:o.

Don't buy from Redarc direct! I got my BCDC1225 on ebay for half the price readarc charges. (around the $320 mark from memory) I too believe that over 600 bucks for a battery charger is a joke!

There are no real right and wrongs just preferences so please lets try to allow each other there own preference.

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Originally Posted by Tombie

G'day Muddy

Option 4 is a Bad idea.

DC/DC chargers will take about 18-20hrs of driving to charge a 20%SOC charge (acceptable) battery.

No good for normal use.

Nothing beats the Aux under bonnet and Anderson cable to trailer setup.

Dc/Dc chargers are over hyped and often sold on BS by salesmen who have no idea or are pushing a sale.

Your alternator is a far better charging solution.

And the wiring on that plug, whilst protected by a 15a fuse is not enough to get the job done...

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Well, as I said Preferences should be allowable Tombie. For my style of camping I would not wish to have my only power source on the vehicle as when the vehicle is away the fridge in the camper is OFF (unless you travel around with the fridge in the back of the car when not hitched up. Also, while away from the camper in the vehicle, the solar panels are charging my camper battery through the chargers Mppt regulator making sure I never run out of juice. As an electrical engineer with sales experience I am immune to salesperson BS and have made the decision using my own knowledge and experience and am just trying to share my set up and decisions why I favour one way over the other with others who might be considering their own set ups.

Sorry Tombie but I also meant to say in my last post that I was at pains to point out that the 25A charger would be connected to the 30Amp circuit not the 15A Ignition Positive. Sorry If I didn't mention this clearly enough earlier.

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Originally Posted by Muddy Diver

There are no real right and wrongs just preferences so please lets try to allow each other there own preference.

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Hi Muddy and this will probably upset you but you are WRONG about your charging times.

Your 25 amp DC/DC device will take about 3 hours to raise you 100Ah battery from 50% SoC to somewhere around 95 to 97% SoC

That’s about the same time an alternator, running at 13.8 to 14.0v will take to do get ordinary AGMs and wet cells to about 90 - 95% SoC.

If the alternator is running at a higher voltage then it will do it in a shorter time.

If you had something like an Optima, or in the case of Tombie, with two 55Ah Optimas, you could safely charge them from 50% SoC to well over 85% SoC in the first hour of driving and have them over 95% in the next 30 minutes.

So it all depends on your knowledge as to what constitute good battery house keeping.

But Tombie’s system goes one major step further in that his system will also result in his cranking battery being in a much higher state of charge then the normal D4 cranking battery will be, whether there is a DC/DC device fitted or not.

Your system works for you but it does not mean you could not have improved on it and for less money.

For instants, because of Tombie’s set up, his cranking battery is likely to last long than the average D4’s cranking battery so more money saved there.

While his two Optimas will have cost a lot more than your single battery, he already made up for the difference because he didn’t waste his money on a DC/DC device in the first place, and as the Optimas will out least most other AGMs, once again, more money saved.

The advantages go on and on so please Muddy, again while you may be happy with your set up, you really need to know how your set up actually works before you compare it to others.

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Originally Posted by drivesafe

Hi Muddy and this will probably upset you but you are WRONG about your charging times.

Your 25 amp DC/DC device will take about 3 hours to raise you 100Ah battery from 50% SoC to somewhere around 95 to 97% SoC

That’s about the same time an alternator, running at 13.8 to 14.0v will take to do get ordinary AGMs and wet cells to about 90 - 95% SoC.

If the alternator is running at a higher voltage then it will do it in a shorter time.

If you had something like an Optima, or in the case of Tombie, with two 55Ah Optimas, you could safely charge them from 50% SoC to well over 85% SoC in the first hour of driving and have them over 95% in the next 30 minutes.

So it all depends on your knowledge as to what constitute good battery house keeping.

But Tombie’s system goes one major step further in that his system will also result in his cranking battery being in a much higher state of charge then the normal D4 cranking battery will be, whether there is a DC/DC device fitted or not.

Your system works for you but it does not mean you could not have improved on it and for less money.

For instants, because of Tombie’s set up, his cranking battery is likely to last long than the average D4’s cranking battery so more money saved there.

While his two Optimas will have cost a lot more than your single battery, he already made up for the difference because he didn’t waste his money on a DC/DC device in the first place, and as the Optimas will out least most other AGMs, once again, more money saved.

The advantages go on and on so please Muddy, again while you may be happy with your set up, you really need to know how your set up actually works before you compare it to others.

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Well done Drivesafe yet another offensive thread entry. Having stated my set up is different to suit my style of camping and that my choice is ALWAYS to charge batteries a little slower, you tell me that my choice is wrong, question my knowledge and claim I don't know how my system works!!! Nice one mate, not a great advertisement for your business is it.

OK, if this the way this forum works I'm unsubscribing till people like you are banned for their aggressive and derogatory posts.

Hi Muddy and I stated from the outset that you would be upset at what I was posting and while I apologies for coming on so strong, I will not apologies for correcting you.

Your DC/DC device will take at least 50% longer to achieve what you have been told it will do in the time you posted.

DC/DC devices and battery chargers charge at their full rate unlit a battery gets to around the 80% SoC and then these devices reduce the charging current. If they didn’t reduce the charging current, the battery would be cooked and destroyed after just a couple of cycles.

This means they will take a lot longer to fully charge a battery than you calculated and by the way, this is exactly how an alternator charges batteries. So you could say DC/DC devices are just mimicking what an alternator does naturally.

As I have posted time after time, people are being DELIBERATELY mislead into thinking these wonder devices will do things they just can’t do and then when the REAL facts are put to them, many like yourself, get riled.

The FACTS are these device should be the last thing to consider, not the first, as they are so often promoted.

For example, and this is not to rub your noise in it but for the benefit of others who maybe considering a set up like yours, for the same reason.

If someone is out to protect their battery and think these devices do the best job, a better set up that would cost the same or even less to install, would be to simply add a second battery, and while it does NOT have to be the same size, I will use the same size to demonstrate the advantages.

But first, this is only an advantage if you have the room.

If you do have the room then consider these operating advantages based on both usage and charging parameters.

If you use 50% of a 100Ah battery when camping and you want to avoid heavy charging, for what ever reason. By adding a second 100Ah battery and using the same power, you will now only discharge the batteries down to 75%. This in itself will extend the operating life of batteries beyond the same type batteries if they are discharged to 50%.

Then when you get on the road, the batteries, because they are only discharged down to 75%, will take 1/3 less driving time to get them to around the 90 - 95% charged state, and both batteries will be charged with a lower current than your device will use, so again, this set up will be kinder on these batteries than the so called “Gentle charging profiles” of a DC/DC device.

Now note, this is based on a dual battery set up using any brand of standard type isolator.

If some one whats to achieve the same usage as above but fits one of my isolators, they can do so for hundreds of dollars less than what a DC/DC set up can do and won't need the second auxiliary/house battery.

On top of all this, with two batteries, if your power requirements increase, your power requirements can literally double before the two battery set up is being discharged as low as a single battery set up.

And one more important fact that is never pointed out when people are being told how wonderful these devices are. If you do indeed find you have a need for more capacity, you have two choices, discharge you existing battery to a much lower state or add a second battery.

In both cases, these wonder devices will now take much longer to charge the battery(s) to a 90 - 95% charge than an alternator will, which means you have to drive longer to achieve what an alternator can do.

Again Muddy, if you and discotwinturbo are upset at the way I replied to your posts then sorry for that, but I am not sorry for once again, having to correct the gross misconceptions people have about these “wonder” devices.

Hey Muddy, I don't think that Tim said your your set up was wrong, He said your calculations were wrong for charging times.

While I agree he he may have come across a bit strong in explaining his point I don't think he was trying to say your choice of system is wrong. He is trying to clear up any possible misconceptions(in his view) around the different capabilities/limitations of the various systems.

I am sure he completely respects your choice and understands that it suits your needs.

He is a long time contributor to the forum who has helped many a person with his extensive knowledge of these cars and battery systems.

Don't take it too personally - the key board is not the best form of communication, too easy to misunderstand and be misunderstood.

Stick around - don't throw the baby out with the bathwater.

PS Brett, I don' think he said to throw out your system, he said, by way of example, that you could remove part of your system:

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you could LITERALLY throw away the DC/DC device, remove one of the batteries and the remaining battery would still die of old age before your power demands had any effect on the battery’s longevity.

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Low stress and casual be thy way ;)