Battery Controllers

Hi Everyone,

Over the years there have been numerous postings/comments/veiws on dual battery set-ups in vehicles. It is amazing that there are so many variations on a theme.

From that introduction .............. my question.

How do people control the power to remote battery set ups??

IE there at two under bonnet batteries being controlled by a Redarc controller.

All good at the moment ..................

How do you look after ........... for instance, the camper trailer mounted 2x100 amp hr deep cycle batteries? Long wire run to heavily used batteries.

Two batteries under bonnet, similar controller and two deep cycle batteries mounted in the forward part of the tray in a daul cab Hilux?

I would like comments back on this, please.

This information is going towards the battery set ups in two very different vehicles and their respective battery set ups.

T.I.A.

Regards,
Wayne & Sally.





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Reply By: Member - John and Val - Sunday, Mar 25, 2012 at 08:48

Sunday, Mar 25, 2012 at 08:48
Hi Wayne and Sally,

Why so much diversity in answers to what seems a pretty simple question? Because of different physical layouts with different wiring and wiring losses, coupled with different usage patterns, different batteries........

In the two cases you mention, there is an existing auxiliary battery mounted in the engine bay with a controller to connect it in parallel with the cranking battery once that has come up to a "charged" voltage. Since this aux battery is mounted close to the cranking battery, this should work well and both should be properly charged (subject to being similar types).

Case 1. 200 Ah storage in a camper trailer. Because of the length of wiring and the unavoidable resistive losses, I would opt for a 20A or 30A dc-dc charger mounted close to the batteries in the camper, and would use heavy wiring (say 6 B&S twin) to couple to a SECOND controller in the engine bay to connect to the cranking battery. (Without that 2nd controller the trailer batteries will be charged from the under-bonnet aux battery while the engine isn't running. Here I'm assuming that most charging will be by the alternator - if though you are likely to camp for more than a few days without running the engine, we have to consider solar, opening up a whole new (expensive) scenario.

Case 2. 200A storage in the back of the ute. Similar constraints, though using heavy cabling, it should be possible to parallel these batteries with the under-bonnet aux battery and use the existing controller, without the dc-dc charger. Again there are constraints - all these should be batteries of similar chemistry, and characteristics. This arrangement is not ideal as the temperature of the alternator and cranking battery will influence charging of all these batteries. Nothing is simple!!

You may find Electricity for Camping a useful read.

Cheers

John
J and V
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Follow Up By: Allan B (Member, SunCoast) - Sunday, Mar 25, 2012 at 09:10

Sunday, Mar 25, 2012 at 09:10
Hi John, I was expecting you to respond but eventually was typing while you were posting! Not aiming to cut across!

There are many variations so as you say, nothing is simple!

Cheers
Allan

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Follow Up By: Member - John and Val - Sunday, Mar 25, 2012 at 13:45

Sunday, Mar 25, 2012 at 13:45
Hi Allan,

No problem! It seems to happen pretty often - a well considered response takes time and so there's plenty of opportunity for almost simultaneous responses. This time the responses are all in agreement (unusual!). Thanks to daylight saving, we southerners have had a 1 hour advantage, but that goes away in one more week!


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John
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Follow Up By: Allan B (Member, SunCoast) - Sunday, Mar 25, 2012 at 16:25

Sunday, Mar 25, 2012 at 16:25
Hi John,
Oh I think we are usually in agreement.
This delayed respons is because we just got back from lunch at the Kin Kin Hotel where the band singer introduced the other members with one being nominated as the "only one with a driver's licence"! She was 16, the drummer 13, and the guitarists 16 and 17. Marvellous, and it was a good sound too. Great kids.

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Reply By: Allan B (Member, SunCoast) - Sunday, Mar 25, 2012 at 08:51

Sunday, Mar 25, 2012 at 08:51
Where there is an auxiliary battery mounted some distance from the alternator it is best to use a dc-dc charger such as the Redarc BCDC-1220 located close to the remote battery. This device will accept input voltage as low as 9 volts yet still charge the battery at up to 20amps. It also acts as an isolator to prevent back feed from the auxiliary battery and is controlled by the ignition to only charge when the engine is running. As well as that, it is also a 3-stage charger to optimise the battery charging. A versatile device.

Although the BCDC-1220 will operate with as little as 9 volt input, it is still desirable to use cabling heavy enough to minimise volt-drop losses as much as possible.

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Allan

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Follow Up By: LeighW - Sunday, Mar 25, 2012 at 19:23

Sunday, Mar 25, 2012 at 19:23
"This device will accept input voltage as low as 9 volts yet still charge the battery at up to 20amps."

It may run on 9V but certainly wouldn't be a good idea, if we assume the aux is initially being charged at 20A and 14.5V this would equate to 290W. Now if the input is 9V then the current drain from the input source would be 37A allowing for losses.

If we assume the source is running at 14.2V we would be dropping a whopping
192 Watts in the vehicles wiring, yes it would work but very inefficient.

Would have been better to run suitable cable in the first place to handle the current
and keep the voltage drops to a minimum in which case you wouldn't need the charger to start with.

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Follow Up By: Allan B (Member, SunCoast) - Sunday, Mar 25, 2012 at 23:27

Sunday, Mar 25, 2012 at 23:27
Yes Leigh, I quoted the 9v specification to demonstrate the flexible function of the BCDC charger, but also pointed out the desireability of using adequately heavy cabling. I wouldn't really expect to operate such a system with only 9v supply.

In order to preserve the necessary charge voltage at the remote battery even 0.1 volt drop in a 10m cable loop will require a 35mm2 cable, so the employment of a dc-dc charger can be an advantage with the bonus of obtaining a more sophisticated charging regime.

To expect to properly charge multiple batteries from a single voltage controlled source (alternator) and with differing cable volt drops is not really a good idea.

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Allan

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Reply By: Mick O - Sunday, Mar 25, 2012 at 08:54

Sunday, Mar 25, 2012 at 08:54
A second larger DC-DC controller like the Redarc Redarc 12/40. This should be mounted close to the batteries. I am using the Redarc BMS 12/15 to manage 2 x 140 A/H Powersonic AGM's in the rear pod of the ute. A 12/40 sits over the front auxillary. (Both the BMS and the 12/40 have inbuilt MPPT solar controllers so you can plug your solar panels directly into them whilst stationary).

Have a read of the power management section of my ute build blog.


Cheers Mick
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trip would doubtless be attended with much hardship.''
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Reply By: Wayne's 60 - Monday, Mar 26, 2012 at 03:45

Monday, Mar 26, 2012 at 03:45
Hi everyone,

Thank you for some very informative answers to my original question and all the answers are food for thought

I understand that there are a large number of variations to a theme ...... all good.

Maybe at this point I should re-qualify the question ..........

.............. and ask

What do you use to control the power output to remote location batteries, "from under the bonnet"??

Regards,
Wayne & Sally.
AnswerID: 481407

Follow Up By: Allan B (Member, SunCoast) - Monday, Mar 26, 2012 at 07:56

Monday, Mar 26, 2012 at 07:56
A Redarc BCDC-1220 or similar.

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Allan

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Follow Up By: Member - John and Val - Monday, Mar 26, 2012 at 08:19

Monday, Mar 26, 2012 at 08:19
Hi Wayne and Sally,

To actually switch power under the bonnet to the line leading to the remote batteries (and their charger , if any) something like this one, which senses when the voltage is high enough to indicate that the alternator is charging and connects the cranking battery to the line. This is a Voltage Sensitive Relay or VSR.

The Redarc BCDC-1220 referred to by Allan is a reputable dc-dc charger that includes a VSR. Using this in your trailer, you would not use under-bonnet switching, simply run through a big fuse (or circuit breaker) from your cranking battery to the trailer via heavy twin cable. (Twin, so as to carry both +12V and a continuous ground connection too.) The switching will take place in the trailer.

Cheers

John
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