Parallel 12V Batts

[READY]

Bachus (and others) Will Prose has some very good videos about best wiring practices. That drawing is not ideal. Not saying it will be catastrophic but better to bring the plus and minus to a bus bar then run 3 equal length cable pairs to each of the 3 batteries.

 

[Bacchus]

I dont have the equipment, time or interest to attempt a computer model or mock up of this but would suggest one way to see if the equal jumper theory holds true is to used a simple 3 batty buss bar set up and vary the jumpers to two battys - keeping the total length equal for all 3 but changing the mix of + side to - side. Keeping total jumper L equal in 3 cases below.

Batty 1 - Pos side long jumper, Neg side short
Batty 2 - Pos side same as Neg side
Batty 3 - Pos side short jumper, Neg side long

Measure amps is each Batty circuit under charging and discharging conditions.

I dont know but will guess that even with new " identical" battys the internal resistance varies and maybe more than the wiring associated with different configurations. Even the balanced diagrams must make some simplifying (but likely unrealistic) assumptions that battys are EQUAL. Not ideal but that's real world.

The reason I'm even interested in this is my plan to switch from 2 8D AGM house bank to 4 GP31 AGM bank when my existing 8Ds need replacing. My plan includes wiring similar to method 4 which mixes lengths of jumpers but all batty circuit see the same # of long and short jumpers.

 

[Iggy]

I'm done.... count the number of jumpers! Why is that so hard? It is VERY DIFFERENT. The diagram may look similar but it is NOT the same situation... If you can count.
I understand your mind is made up and closed to reason.
Your scheme is perfectly balanced so no issues what so ever.

My post is for others info.

I only see 2 jumpers on each side. A total of 4 and the main cables. This looks like method 1 less one battery from the PDF. Am I wrong?

Keep in mind that we are talking about a three battery bank. Or at lest I have been. Not four batteries, is that the confusion. My original question was, how to do this with three batteries.


Below is the PDF that someone uploaded and I have been working from which I think has added to my confusion. Vs the other one.

https://www.iotaengineering.com/-/media/abl/iota/files/balancedcharging.pdf?forceBehavior=open

Enough said, yes my head is starting to hurt too.

 

[Boatcrazy]

FWIW, there is another option.....buy/use a 3-battery charger. We have a Pro-Mariner (West Marine) Pro-Nautic 50-3 to charge our 3-battery house system. The batteries (each "battery" is 2 Trogen T-105) are all connected to a (+) bus bar and a (-) bus bar with equal size & length cables; the house load is then connected to those bus bars. But the Batt chgr has 3 separate charge leads, one for each of the 3 batteries, and (supposedly) charges each "battery" as it needs. We've had this system for 7 years, the batts seem to do well on it, and we've never run out of power. We do run our genset daily (the admiral very much prefers cooking electric, and our refer and watermaker are both AC too-the refer needs to run at least 1/day to keep the boxes at temp. It seems to work well.

 

[ProMaritime]

Confusing responses here. Paralleling 12V batteries, or any number of batteries, is just what it sounds like. It doesn't matter if you have 2 batteries or 50. Gang all the positive terminals together with a suitable size wire and run one wire (very, very large if 50 batteries) to your battery switch and then to your main DC breaker and/or to your switch/breaker panel. Gang all negative terminals together and run one wire of equal size to your grounding bus bar or direct to the engine block.

 

[Iggy]

FWIW, there is another option.....buy/use a 3-battery charger. We have a Pro-Mariner (West Marine) Pro-Nautic 50-3 to charge our 3-battery house system. The batteries (each "battery" is 2 Trogen T-105) are all connected to a (+) bus bar and a (-) bus bar with equal size & length cables; the house load is then connected to those bus bars. But the Batt chgr has 3 separate charge leads, one for each of the 3 batteries, and (supposedly) charges each "battery" as it needs. We've had this system for 7 years, the batts seem to do well on it, and we've never run out of power. We do run our genset daily (the admiral very much prefers cooking electric, and our refer and watermaker are both AC too-the refer needs to run at least 1/day to keep the boxes at temp. It seems to work well.

Nothing wrong with doing it that way. I talked to ProMariner on the same setup on my last boat. But the three bank charger is seeing all three batteries as one bank. A one bank charger can do the same job.