[Electric Boats] One strange cell

 

Hello again,

I did parallel the batteries for 5 days (they were pretty much good after 1 day, but I didn't get to them until the following weekend).

This weekend I put them into their final 2P4S 48V 260Ah configuration and charged the pack to 3.4*4*4 54.4V. These are LiFePO4s in car-battery style, so each battery is 4 cells in series (each cell is many paralleled 18650s or similar). The BMS gives me cell voltages, so I have 4*8 = 32 cell voltages.

30 of them tracked very closely. One of them was a little higher. The last one was the strange cell: when the others read 3.3, it read 3.8. But it never went over 3.875V, and when the charge was complete it went back down to 3.4 like the rest.

So is something wrong with that cell? Does that indicate it is going to fail early? The battery cycle counter is about 100 cycles, the other batteries in the pack are 40 cycles.

Is this "keep an eye on it" or "fix immediately"?

In other news, I tested the whole system today and it ran great. Next stop is the boatyard for bottom paint, then the boat is going in the water!

Thanks,

Brian

---In electricboats@yahoogroups.com, <kd5crs@...> wrote :

Hello,

I'm about to install my traction pack into my boat. It is a 2p4s pack made from 8 Valence LiFePo4 U27-12XPs. I've got a BMS (custom) and Thunderstruck 48V charger.

I individually charged all of the batteries to an initial 80% SOC as reported by the BMS.

My question: Should I hook all the batteries together in parallel (so 8p1s, 12V) and wait for them to fully equalize before connecting them in their final configuration (2p4s, 48V) and charging at 48V? My reasoning is that if they are all in parallel until they equalize, each one will be sure to have the same "charge in the tank" to start with.

Are there any hazards this setup would introduce, like would it be stressful on the center or end batteries in the parallel string? Or do I have this concept wrong, and charge will equalize throughout the pack in 2p4s and I don't need to do more than put them in 2p4s and wait prior to charging at 48V?

Thanks,

Brian

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Posted by: kd5crs@gmail.com

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