On Oct 1, 2018, at 9:09 PM, 'Myles Twete' matwete@comcast.net [electricboats] <electricboats@yahoogroups..com> wrote:
Mine: 20P*(12S*(2P))
Delivering 700ah @ 31-48v since 2013
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
Sent: Monday, October 1, 2018 6:19 PM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Battery replacement
I would disagree with the recommendation to have more cells in parallel, I agree with the other James, that you should try and limit the the total number of connection. If you can not do 16S because of the battery box size, then use the next lowest "P" you can. So if 400 amp cells are a no go space wise, do a 16s2p. The chance of having thermal/arcing issues with loose terminal connection is many times greater then having internal resistance issues with cells all bought at the same time.
Or think of it this way, a good BMS is designed to over come slight internal resistance issues via balancing, but nothing automated is going to help you with arcing issues from loose terminal connections. Your batteries will be on a rocking moving boat, the less total connection you have the less chance you have of having issues, and the less time you will spend checking for loose connections.
As noted before in this thread once a year I check my battery under load with a thermal imager, loose connect is what I am looking for when I do that. That and a spot check of the voltages it the only maintenance I ever have to do on my batteries.
People that use a lot of dissimilar cylindrical (used laptop) batteries are the one that use lots of parallel strings to compensate for weak used cells, they generally use very accurate test equipment to sort the cells in to matched strings. This is not anything that really applies to building batteries with new prismatic cells. It is really a way to avoid throwing out marginal cells and getting the most bang from there used cells.
James Sizemore
On Oct 1, 2018, at 6:08 PM, clh5_98@yahoo.com [electricboats] <electricboats@yahoogroups.com> wrote:
James,
Thanks for the suggestion. A little more about my battery storage. I built my 2 battery boxes 6 years ago to fit 8 GC2 FLA batteries in each box.. With Lithium I can reduce to one box leaving the other box for storage, or bigger fuel tank for the generator. Without major cutting of the battery boxes, I'm limited to which cells I can use. 32 X CALB 180, or 200 won't fit without cutting the box. 64 X CALB 100 wont fit either. I have found some taller cells that fit my space better. One is the FPT 220 Ah. I can easily fit a 16S2P pack using these cells. Another tall cell is the Frey New Energy 100 Ah. I can easily fit a 16S4P pack using these cells.
Does anyone have experience, or opinions about these cells?
I've read some that more cells in parallel can be beneficial in LiFePO4. Lower internal resistance is one with more in parallel, and that a weak cell can be "propped up" by the others and still be detected by the BMS as an issue. I don't know though.
Chris
Posted by: "james@deny.org" <james@deny.org>
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