3 batteries and only have a 2 bank charger

Submitted: Thursday, Feb 19, 2009 at 21:17
ThreadID: 66115 Views:1975 Replies:5 FollowUps:4
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If I have a 12 volt cranking battery and 2 12 volt aux batteries , the aux batteries are connected in series to power a trolling motor and not connected to the cranking battery. I have a 2 bank battery charger. Is there a problem connecting 1 bank of the charger to the cranking battery and connecting the cranking battery to the 1st aux battery in parallel and then connecting the other bank of the charger to the 2nd aux battery without disconnecting the 2 aux batteries to charge all three batteries. And can I leave the cranking battery connected in parallel to the first aux battery as the aux batteries power a 24 volt trolling motor? Any help would be greatly appreciated.
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Reply By: Member - Brenton W (SA) - Thursday, Feb 19, 2009 at 22:26

Thursday, Feb 19, 2009 at 22:26
Would love to help but my head is in a spin after reading your querie think i need stemetil, might have to be careful charging two different types of batteries not sure though, good luck
AnswerID: 349969

Reply By: Member - Roachie (SA) - Thursday, Feb 19, 2009 at 22:56

Thursday, Feb 19, 2009 at 22:56
Yeah, no worries..... I have this exact set-up in my Patrol. Two batteries permanently coupled in parralel for starting and all the other "normal" stuff, plus a Fullriver gel battery for fridge and some other accessories.
I have a Durst 15 amp 3 stage charger which has 2 separate outlets, so I have them connected as you describe.

AnswerID: 349974

Follow Up By: _gmd_pps - Thursday, Feb 19, 2009 at 23:31

Thursday, Feb 19, 2009 at 23:31
he said in series .. which makes 24V
either one of you is wrong
have fun
FollowupID: 618289

Follow Up By: Member - Roachie (SA) - Friday, Feb 20, 2009 at 08:09

Friday, Feb 20, 2009 at 08:09
OOOps.... that'd be me I reckon..... I "didn't see" that he has them wired in series (but would have thought a trolling motor would be 12 volts anyway.....)
FollowupID: 618324

Reply By: Member - Fred B (NT) - Friday, Feb 20, 2009 at 00:16

Friday, Feb 20, 2009 at 00:16
If I have read and understood correctly what you are trying to do; you are definitely going to have problems with circulating currents. If you get "a runnaway" battery, you are going to have a major fire on your hands. Chargers operate by measuring voltages and adjust the current flow accordingly. You just might be creating a nightmare for yourself. You might also be invalidating your insurance if you do not meet Australian Wiring Standards.
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AnswerID: 349985

Reply By: Ray - Friday, Feb 20, 2009 at 08:56

Friday, Feb 20, 2009 at 08:56
Dig deep and buy a second battery charger
AnswerID: 350011

Follow Up By: RV Powerstream P/L - Friday, Feb 20, 2009 at 21:04

Friday, Feb 20, 2009 at 21:04
A Pro Mariner Pro Sport is made for the Bass boats in USA and you can get them in different sizes but the popular one is 20A 3 outlet that allows one connection to the cranker and two in series to the trolling batteries.

The big Pro Tournament units have a 30A 4 outlets that allows 4x12V or 2x12V and 1x24V or 1x12V and 1x36V or just 1x48V

They are not separate fixedchannels they send the most power to the most needy batteries first and then vary the charge accordingly as those batteries rise in charge.

So one charger can do it all and its fit and forget.

One of the top Competition fishermen in Aus uses one in his Skeeter.

FollowupID: 618460

Reply By: GerryP - Friday, Feb 20, 2009 at 21:06

Friday, Feb 20, 2009 at 21:06
Hi Miguel,

Had to think about this one for a while, but if I read you correctly and what you are suggesting is as per the diagram below, then I'm afraid it will NOT work.

By connecting your main battery in parallel to your first auxiliary for charging purposes, you are effectively creating a dead short circuit across the second bank of the charger. Follow the diagram from the second charger and you'll see what I mean.

Most 2 bank chargers will charge either 12 or 24 volt. Check to make sure yours won't. If it does, then leave the main isolated from the auxiliary string and charge the 12 and 24 volt systems separately.

AnswerID: 350145

Follow Up By: GerryP - Friday, Feb 20, 2009 at 21:13

Friday, Feb 20, 2009 at 21:13
Hi again,

Just had another think... it's starting to hurt :)

You could do it provided:

1. You isolate the batteries from any form of common earth and

2. Your charger doesn't mind effectively having the negative from bank 1 connected directly to the positive from bank 2. This may be OK provided the two charging circuits are completely independent from each other.

Personally, I don't think it's worth the risk.

Time for a beer now - my head needs a rest...

Cheers and good luck
FollowupID: 618462

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