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Old 04-26-2022, 02:48 PM
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edwardc edwardc is offline
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Thanks for the nudge.

To refresh, I have eight EVE 280AH LiFePO4 prismatic cells.

I ended up ordering the Rec Active BMS. The manufacturer was very quick to reply to my questions, and I now understand how to configure the BMS to operate as part of a distributed system.

In addition to the BMS, I ordered a pair of 500A contactors, one for the charge bus and one for the load bus, and the WiFi adapter so I could configure and monitor the BMS without needing the Windows-only software package (I'm a Mac guy).


Initially, I strapped all the LiFePO4 cells in parallel, and hooked them to a regulated supply. I brought them up to full charge in steps. For instance, I initially set the supply to 3.0V and limit it to 4.5 amps (Its only a 5A supply), and let this sit until the current dropped off to ~100 mA. (this took a LONG time (days) due to the MASSIVE AH capacity of eight paralleled cells, 2240AH!). Then I would bump it up a few tenths of a volt and repeat. Each cycle took less time. By the time I was pushing all the cells up into their fully-charged state, the last cycle took just over an hour. This process "top balances" all the cells.

I next rewired all the cells in a 2P4S (2 parallel 4 series) configuration to create a 12V 560AH battery pack. I wired up the bms sense leads to each of the 4 series cell-groups, connected the charge and load contactors to the appropriate drive leads from the BMS. The charge bus was connected to my supply (now setup for the correct charge voltage) and the load bus was connected to a 1000W inverter. The inverter was connected to a small heater and a collection of incandescent light bulbs to bring the total up to around 900W. This would produce a DC load current of around 75A.

I since setting all this up had brought the battery pack down below full charge, I first tested the high limit charge cutoff. Turned on the supply and let it charge. As soon as the pack reached the charge max voltage that I had set, the Charge contactor shut down as designed. Keep in mind that this is NOT the normal charge voltage, but the "Never Exceed" voltage for the pack. In normal operation, this should never happen. Its just a protection to keep a failure elsewhere from overcharging and destroying your batteries. Meanwhile, the load contactor remained connected, which would allow you to drain the pack down to a safer level.

Next test was a crude capacity test. With the supply turned off, I activated the inverter. The idea was to see where the pack capacity was (according to the BMS monitor) when the load contactor cut off. This test was a reasonable success. It ran about 7 1/2 hrs. The problem was that the inverter shut down due to low voltage before the pack was down to what the BMS considered the 0% State-of-Charge for the pack. This inverter cutout happened within a few Amp-Hours of of the spec value of 560AH, so I considered the capacity test to be a success. The BMS monitor showed all the cells individual voltages stayed within the proper amount, so it looks like the cells I received are reasonably matched.

After a few minutes of sitting, the pack voltage "rebounds" some. This allowed me to temporarily reconfigure the low voltage cutout to a higher voltage than the point where the inverter cuts out. Turned the inverter back on, and this worked perfectly, shutting down the Load contactor, but leaving the Charge contactor on.

So far, I'm satisfied with my purchases. Still need to configure a relay to cutoff the Balmar alternator controller in case of a BMS shutdown of the charge contactor and test that for all cases.

After that, the next step is to start creating a new battery box area in the boat. The old battery location is effectively in the engine compartment, and gets too hot for the LiFePO4's max operating temp of 140 deg F.
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