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BretS

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Mar 30, 2021
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171
**Edit... made changes marked with **

My system so far consists of a DIY LiFePO4 bank of twelve 310Ah cells in 3P4S for 12V, a REC Active BMS, a Multiplus II 2x 120V, a Cerbo GC, and an Orion 12/12-30A DC-DC Charger. I am setting up with conservative charging settings to maximize cycles (based on Will's sticky post). I would appreciate any feedback on the below settings (in order from highest to lowest):
charge:
-REC max cell 3.55V (14.2V)
-REC end of charging 3.52V (14.08V)
-REC balance end 3.50V (14.00V)
-Multiplus absorption 14.00V (3.50V)
-REC balance start 3.40V (13.60V)
-Orion absorption 13.80V (3.45V) **13.60V (3.40V)
-Orion float 13.50V (3.375V) **13.35V (3.33V)
-Multiplus float 13.50V (3.375V) **13.35V (3.33V)

discharge:
-Multiplus inverter low shutdown 11.00V **12.00V
-Multiplus restart/low pre alarm 12.60V **12.25V
-REC Min cell 2.70V (10.80V) **2.95V (11.80V)

I ran the pack down to 13.10V using the 15K Air Conditioner on battery - it ran for a good half hour, and nothing got even warm anywhere on my MP or busbars.

I then charged a bit using the Orion and my truck running to verify it worked well, and to check the engine not running function. It worked great.

I then started my generator connected to the 50A shore power with a 30A dogbone. The MP charged the bank back up in around 45 minutes. I was watching the BMS and it started and completed the balancing perfectly! It was really interesting to watch it all happen - I learned a lot about how the balancing function works. After the balancing was done, it reset to 100% state of charge and went into float.

Anyone see any issues with anything? I am also attaching some pics of my system and screenshots of the BMS under load and my settings. Thanks in advance for any input...


20210605_164654.jpg20210606_145457.jpgBMS settings.jpgBMS under load.jpgInverter settings.jpgMP charger settings.jpg
 
Last edited:
Why are your multiplus and orion absorption voltages different?
As for the low cutoff I suggest you watch your cell deltas while you discharge the battery at a representative rate and set the cutoff to coincide with your weakest cell dropping off.
That assumes a decent top balance.
Also watch the cell deltas on charge to see how high you can safely charge without triggering a high cell cutoff.
 
Why are your multiplus and orion absorption voltages different?
As for the low cutoff I suggest you watch your cell deltas while you discharge the battery at a representative rate and set the cutoff to coincide with your weakest cell dropping off.
That assumes a decent top balance.
Also watch the cell deltas on charge to see how high you can safely charge without triggering a high cell cutoff.
I set the Orion lower because it is not on the Canbus and the REC can't control it for balancing. So, if I am driving it will cut off before the balancing and top off with balancing when I use shore power or generator (later solar)

I raised my cutoff to 12.00V on the inverter now.
 
I just checked my cutoffs today.
I have it set to 24.8 volts which puts the lowest cell at ~3.05 volts and a 75mv delta.
bms cutoff is 2.9 per cell or 23.2 volts for the pack.
 
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