Equalizing battery charges

Submitted: Sunday, May 08, 2005 at 18:51
ThreadID: 22777 Views:4511 Replies:3 FollowUps:4
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Hello I have a 24v Safari which I have had for 18 months.
To date I have had no battery issues and have 24v auxilaries for my fridge.

I now want to run more lighting, UHF, air compressors and the like and it is become too painful trying to find 24v gear. So I am trying to find the best way to get a solid 12v supply.

It is easy enough just to pull 12v off one of the batteries but the issue seems to be with the batteries getting to different potentials. Redarc have a charge equalizer that will do the job at a price or a 24-12 transformer at a greater price :(

Is there a cheaper way? I was thinking I could connect a portable battery charger to the low battery every now and then to equalize the charge. Maybe even monitor them individually via an in cab meter. Hey, what about a switch in the cab, so when the in cab meters show one is low, I can then switch to the other!. UHF won't draw much and the compressor is normally only used once at the end of a trip. Wadda ya reckon?
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Reply By: Tim HJ61 (WA) - Sunday, May 08, 2005 at 19:30

Sunday, May 08, 2005 at 19:30
Hi Batboy,

My favourite topic!! Not so with too many other forumites who lead electrically simple lives. :-)

I have a 24v HJ61 Landcruiser, and tried both a 24v to 12v reducer and the Redarc charge equaliser.

If you have had no problems with the 24V system and battery charging to date, I'd suggest you bought a reducer, or run the Redarc as a reducer. This is on the proviso you want to run low current items, such as your UHF. I bought a 20A unit second hand and it stopped working after I overloaded it. New ones have better internal protection so would be okay I'd imagine.

IF on the other hand you want to be able to pull whatever current you like from the low battery, centre tap, positive pole of the low battery, or negative pole of high battery, whatever you want to call it, then I'd suggest using the Redarc as it's designed, as a charge equaliser.

They work well in balancing the voltage across the two batteries, but your drain is taken from the 12v supply, not via the Redarc - that just looks after the charge equalising. Hook it up with a relay on the 24v feed to your Acc switch and it'll be fine. This is my set up now.

You could set up some switches for your UHF I guess, but I'd be concerned at getting the batteries out of sync and then how do you equalise them again? This would happen with the compressor, unless you pumped up two tyres from each battery, ie equal draw from both batteries.

Try this link for an extensive story on what you are asking.

>To date I have had no battery issues and have 24v auxilaries for my fridge.
Do you have 24v aux batteries set up?

Have fun with the set up!! Running basically a second electrical system has it's moments. :-)

Tim

AnswerID: 110339

Follow Up By: Batboy - Sunday, May 08, 2005 at 20:33

Sunday, May 08, 2005 at 20:33
Wow that thread is huge!
Just kidding about the switchs etc, far too much work anyway
The equalizer struck me as the best fix but at $250 bucks it ain't cheap but nor are batteries! The compressors maximum draw is 30amps so I would not be able to use the redarc as a reducer.

I have twin 90amp/hr AGM batteries running a 80l Waeco which works fine and the lower amperage of running 24v is a bonus here. If i go the redarc i will probably install it on these.
I decided to go with 24v for the Aux as I can use these to crank the engine if needed plus smaller cables etc

Thanks for your advise and it is nice to meet a fellow 24volter
Its actually a big advantage once you get set up properly!

Cheers Jim

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FollowupID: 366881

Follow Up By: Tim HJ61 (WA) - Sunday, May 08, 2005 at 21:53

Sunday, May 08, 2005 at 21:53
Batboy,

For clarification, and me trying to be helpful, you said:
>The compressors maximum draw is 30amps so I would not be able to use the redarc as a reducer.

That is correct. But you never plug a 30amp compressor into a power outlet, you attach the compressor directly to the batteries, so you wouldn't be drawing through the Redarc anyway. The problem comes then with unequal discharge, which you understand, and is what the Redarc is for.

>If i go the redarc i will probably install it on these. (24v Aux batteries)
Yes, this would seem to be okay. Depends on how you have set things up. If you draw ALL your accessories draw through the Aux battery bank, then it would make sense to draw the 12v from it too. That would leave your 24v starting batteries alone completely.

I draw down on my main start batteries to 12.2v each via a Redarc Smart Start solenoid before that switches off and I draw totally from my 12v aux battery if I have it installed. I figure I have a heap of capacity in my cranking batteries that I might as well use.

>Thanks for your advise and it is nice to meet a fellow 24volter
There are a few on the forum, not many. The Canadian sites can be helpful as they import the 24v Cruisers too.

>Its actually a big advantage once you get set up properly!
AGREEEE. Just wish more accessories came in 24v so I didn't have to spend so much time and money recreating a second power network - but now it is in place and working, it's all cool. Hate to be the person following up from me though! :-)
My Engel was an investment from my EH Holden days many years ago, so I was pretty much locked into a dual voltage system from the start.

Regards
Tim
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FollowupID: 366896

Reply By: F4Phantom - Sunday, May 08, 2005 at 19:46

Sunday, May 08, 2005 at 19:46
You may never need to charge them individually. Are the batteries the same A/H capacity?? if they are not you cannot use them together in series or parrallel. If they are identical batteries, hook em up in parrallel, but give them both an initial charge before hooking them up to get them both full. Then hook them up and use them both in charging and discharging them and they will start to get a "feel" for each other and act as one battery. In fact if you want to use several batteries together you should hook them together when new and never charge or discharge individually, this way they act as one large battery. Forget the meters etc, just make sure they are both full when you first put them together. I work with rechargeable batts for my job, it's all quite interesting.
AnswerID: 110341

Follow Up By: Batboy - Sunday, May 08, 2005 at 20:09

Sunday, May 08, 2005 at 20:09
Sorry Phantom These fellas are hooked up in series to give me 24v
As I understand it you are correct in what you say but not quite what I was looking for
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FollowupID: 366877

Follow Up By: Tim HJ61 (WA) - Sunday, May 08, 2005 at 22:00

Sunday, May 08, 2005 at 22:00
F4Phantom,

Good points. I wish battery sellers understood this. See my thread 22300 for tale in how things don't go right.

As an update, I've been charging my N70 Exide Extremes up with a manual 10A charger and at last have got them balanced on the hydrometer and both showing green on the hydrometer. If only they had been balanced and properly charged when I bought them, as you indicate they need to be, I would have been saved a bunch of hassle.

Batboy's issue was one of taking 12v from his batteries and being concerned, rightfully, of how he was going to return the batteries to their normal balance.

Tim
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FollowupID: 366898

Reply By: Peter 2 - Monday, May 09, 2005 at 22:02

Monday, May 09, 2005 at 22:02
I've been running a Redarc charge equaliser in my Humvee (its 24v too) for 3 years now with absolutely zero problems. You can suck as much 12v from either battery as you want .
I've got mine activated by the accessory postion on the ignition so it only equalises when either in acc or the engine is running.
I much prefer 24v, less current flow etc, the engine starts really easily, the Autofridge runs on 24v direct which brings current drain down to around an amp.
Peter
1996 Oka Motorhome

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AnswerID: 110544

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