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Parallel battery wiring techniques

jbird526

Solar Enthusiast
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The screenshot below from the Victron Wiring PDF. There are 4 techniques for parallel wiring shown. Are there any reasons to pick one over another when wiring for LiFePO4, other than less wire required for some connections?
  1. Posts has identical length wiring so could see some value in identical resistance.
  2. Diagonally seems to be the most prevalent that I have seen in the forums or videos. If the length of wire coming off Diagonally to the inverter is the same as between individual batts would it basically equal what is being done in Posts?

This is a link to Impact Battery and they are showing that Halfway is the "Perfect" solution, but they are referring to lead acid.
https://www.impactbattery.com/blog/post/how-to-charge-marine-and-rv-batteries-in-parallel

https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf
Screen Shot 2021-04-05 at 1.29.59 PM.png
 
Chemistry doesn't matter. Any of the options are substantially better than doing it wrong. Of all of them, bus bars is typically the best, but it is also the most costly.
 
Chemistry doesn't matter. Any of the options are substantially better than doing it wrong. Of all of them, bus bars is typically the best, but it is also the most costly.
When I mentioned the Impact Battery page I was probably not completing my question.

Since most LiFePO4 batts will be using a BMS, vs a lead acid, is it not as important which of the 4 above is used as the BMS will compensate to a certain degree? If there is any slight difference between one set of wires and another.

I should assume that resistance on the bus bars is the least and provide the most efficient/most expensive option.

Probably just digging too deep in the weeds on this.

BTW @snoobler thanks for having this PDF in your signature. Very helpful reference.
 
When I mentioned the Impact Battery page I was probably not completing my question.

Since most LiFePO4 batts will be using a BMS, vs a lead acid, is it not as important which of the 4 above is used as the BMS will compensate to a certain degree? If there is any slight difference between one set of wires and another.

The BMS doesn't matter when paralleling batteries. The BMS only monitors the cells in its battery. It has no influence on the others in parallel.

I should assume that resistance on the bus bars is the least and provide the most efficient/most expensive option.

Yep.

Probably just digging too deep in the weeds on this.

Yep, but sometimes you have to get through the weeds.
 
I have tried them all and find that they bus bar method best for long term maintenance, as you will have a dead cell or bad bms from time to time. With the bus bar you can just remove 1 battery without disconnecting the entire system.
 
I know this is an older thread, but I am working my way through several options for powering a small electric motor that runs on 3 volts, typically a pair of D-cell batteries, wired in series. Instead of two D-cell batteries, I'm using a single Li-NMC or LiFePO4 cell, at 3.7v nominal, and using only the low power setting on the motor. This has resulted in a very simple and cheap (efficient?) way of powering this little air pump with a rechargeable battery solution.

My question is as follows: When connecting just 2 cells in parallel, do you have to connect the positive ends of each battery to one another, as well as the negative end? If I use pure nickel strip to solder the negative ends together, do I have to do the same on the positive end, or can I just come off of the positive end with a lead that powers the motor? It is my understanding that the case itself, protected by the cell wrapper, is part of the negative conductor, so I'm not sure how to wire the positive ends of the cells without creating a short between the two cells. (Yes, I know how dumb that sounds!)

I have two 21700 (5000mah) cells mounted in a parallel configuration, with a plastic housing on each end. This housing does not include any wiring or contacts to connect one cell to another; they are really just a way to hold the cells. I have attached a picture, below.
 

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What do I need to do on the positive ends to join them in a parallel configuration, without shorting out against the case body?
you use an insulator ring it has a pre-punched area to access the positive post to spot weld to.Screenshot from 2021-06-05 09-30-01.png
 
OK, looks like I need to place another order, for some insulator pads, some pure nickel strip and a spot-welder.

Can anyone recommend a spot-welder for $100 or less? Keep in mind I'm looking at doing a grand total of about 40 welds, unless this thing works out really well.
 
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