DIY Lifepo4 charge cycle
I thought some of you who are considering Lifepo4 might be interested in seeing an actual charge cycle. This is a 560ah 2p4s [2 cells in parallel / 4 cells in series] config. I installed them June 2020. They were represented to be 280ah EVE cells, 1st quality and matched. I don't know if these are EVE but the capacity is over 560ah. They are not 1st quality or matched - and I didn't expect them to be for the price I paid.
The graphics below are from the REC BMS dashboard and show today's charge cycle and a 150a load. When I left the boat Monday the Lifepo4 battery was at 95% SOC. Returning today SOC was 51%. I leave the frig and security system on.
I've been off the boat since Monday - so 6 days. I wanted a some heat and hot water so fired up the generator.
This is the BMS dashboard when I got onboard today:
51.5% SOC
13.05V
-6.90A
The BMS also monitors each cell voltage. The variance among cells here
is 0.003 volts.
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Here are some of the settings for the system. They are the most critical. All settings can also be configured via command line.
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The charger is a Freedom 25 130amps set for cool wet cell @ 14.4v. The battery is accepting 120a. Voltage jumps a bit and there is a 0.030v variance among cells [more in this later].
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Around 92% SOC the first cell passes 3.45v. This is my setpoint to initiate cell balancing. This BMS employs active balancing @ 2amps. This can be seen by the high cell #4 resistance as the charge is shunted by 2amps and lower voltage cells receive more charge. This was 3hr 4min after starting the charge cycle. The battery is at 13.72v accepting 102a. There is a 0.036v variance among cells.
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The charger transitions to constant voltage - absorption, and amps start dropping around 14.25v and tail to about 5a at 14.30v and 97% SOC. This was 3 hr 17min after charge started. Note the rapid voltage increase that occurred within 15 minutes. Cell voltage variance gap closes as amps drop.
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The cell voltage variance under 150a load was 0.047v.
-------------------
The cells are really out of balance when under high charge / loads. These cells didn't pass the 1st QC and landed in the secondary market. There are fewer paths for a consumer to purchase top quality cells and much more expensive. The EVE cells need to be top balanced every year.
I will be disconnecting the system next week so will wait until spring commission to top balance the cells. The voltage variances are not an issue for my current use. But if my use were to change where I need to discharge 100a+ for prolonged period of time - like the convection oven for 3 hours for a roast - I would be replacing these cells with Winston 700ah or 1000ah cells [for well over 3x the cost].
The graphics below are from the REC BMS dashboard and show today's charge cycle and a 150a load. When I left the boat Monday the Lifepo4 battery was at 95% SOC. Returning today SOC was 51%. I leave the frig and security system on.
I've been off the boat since Monday - so 6 days. I wanted a some heat and hot water so fired up the generator.
This is the BMS dashboard when I got onboard today:
51.5% SOC
13.05V
-6.90A
The BMS also monitors each cell voltage. The variance among cells here
is 0.003 volts.
-------------
Here are some of the settings for the system. They are the most critical. All settings can also be configured via command line.
--------------
The charger is a Freedom 25 130amps set for cool wet cell @ 14.4v. The battery is accepting 120a. Voltage jumps a bit and there is a 0.030v variance among cells [more in this later].
---------------
Around 92% SOC the first cell passes 3.45v. This is my setpoint to initiate cell balancing. This BMS employs active balancing @ 2amps. This can be seen by the high cell #4 resistance as the charge is shunted by 2amps and lower voltage cells receive more charge. This was 3hr 4min after starting the charge cycle. The battery is at 13.72v accepting 102a. There is a 0.036v variance among cells.
------------------
The charger transitions to constant voltage - absorption, and amps start dropping around 14.25v and tail to about 5a at 14.30v and 97% SOC. This was 3 hr 17min after charge started. Note the rapid voltage increase that occurred within 15 minutes. Cell voltage variance gap closes as amps drop.
------------------
The cell voltage variance under 150a load was 0.047v.
-------------------
The cells are really out of balance when under high charge / loads. These cells didn't pass the 1st QC and landed in the secondary market. There are fewer paths for a consumer to purchase top quality cells and much more expensive. The EVE cells need to be top balanced every year.
I will be disconnecting the system next week so will wait until spring commission to top balance the cells. The voltage variances are not an issue for my current use. But if my use were to change where I need to discharge 100a+ for prolonged period of time - like the convection oven for 3 hours for a roast - I would be replacing these cells with Winston 700ah or 1000ah cells [for well over 3x the cost].
I considered installing these also - they take less room than 2 golf cart batteries - but the system gets more complicated. These tested better than the EVE so I may swap them over to see how they work in operation. Anyone interested in a set of 8 280AH cells?
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