New battery Charger with batteries in parallel

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nveater

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Nov 4, 2021
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Vessel Name
Pathfinder
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Mainship Pilot 30
I am getting ready to install a new Xantrex battery charger and I have some questions. I have two battery banks each with 2 batteries that are in parallel. I am running one appropriately sized cable from each bank back to the charger to the separate bank outputs on the charger. Does it matter which positive terminal from the two in the bank that I use to make the run to the charger. Also is there a difference which bank goes on the first bank terminal in the charger ? Older videos of installing chargers seems to suggest that it does.

I am not re- using the setup from the old battery charger because the cables to the charger seem to be thin little wires spliced from larger cable which seem to be coming from the batteries but they are buried under a mass of other cables- it's a bit confusing down there.

Thanks
 
Assuming all batteries are identical(brand, age, capicity)...it probably does not make a difference. But for best battery life I would use 2 separate chargers. Some chargers are more sophisticated than others about how the control for 2 outputs. If you go with 2 chargers you not only have more granular control but you charge faster and have redundancy if on fails (you would have to add cables in that case or just rely on 1 bank).
 
Does it make a difference? Yes. Enough that you care? Maybe.

The better way is run one wire then split it into two and hook to both positive terminals.
 
When you have parallel batteries you want to put the positive cable on one end and the negative cable on the other end. That way the charging current goes through both batteries not just one. The same thing with supply cables for drawing power out of the batteries. If you only cable off one battery then the other battery can “disappear “ due to the resistance in the cables hooking them together. Not much resistance but it does matter.
 
The negatives are already connected to DC ground on the batts. The negative cable from the charger also needs to connect to DC ground. Just the charger positives need to go to the batts and if the parallel cables on the batts are nice and fat and short it won't matter much.
 
This is per Nigel Caldera’s’s Boatowners Association Mechanical and Electrical Manual. He says that you should hook to one batteries positive and the other batteries negative. That is what I was trying to say in my previous post. Maybe I didn’t say it well.


When you have two or more batteries paralleled, make the positive connection to the boat’s circuits at the positive terminal on the battery at one end of the bank, and make the negative connection to the boat’s circuits at the negative terminal on the battery at the other end of the bank (i.e., not off the same battery as the positive connection). This ensures that all batteries get discharged and recharged equally.
 
Thanks for all the input ! So my batteries are already set up so the positive running to ship's main power supply is on one battery and the negative to ship's ground is from the other battery. Interestingly, the negative from the old charger is ground on the engine chassis- thoughts on keeping that set up or look for a different grounding point ?
 
I would move the negative cable to the negative post on the opposite side of the batteries from the positive cable. Less chance of a bad connection.
 
Yeah, I would go to either ship ground or the battery, whichever is closest. Yeah, you don't want engine oil and vibration messing with your ground.
 
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