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brbrv avatar image
brbrv asked

Added LiFeP04 Batteries But See No Change

We recently added a 4th bank of four 138ah Valence LiFeP04 batteries to bring our total storage to 16 batteries, equally divided into 4 banks. Everything is properly connected diagonally and 4/0 cables lead to busbars, ground cables lead to a Victron 500a SmartShunt. All four 4/0 ground cables meet on the correct side of the shunt. They are connected to a heavy duty BlueSea busbar that connects to the shunt via a 3 inch 4/0 jumper cable. We changed the ah on the BMV from 1520ah to 2064ah. By 10:00am the following morning after the installation, all 16 batteries reached 14.51v, kicked into absorption, and hit float at 13.5v. Nothing unusual. With just our refrigerator, running on AC all day, our BMV reads -140ah by 6:00pm, and we normally hit 13.15v when switching to propane. Since the installation, for the past week, same process, we’re still hitting 13.15v. Shouldn’t the voltage be higher with the extra bank? Is there another setting we’re missing? The solar intake has been consistent before, during, and since the installation.

Our system includes …

  • 2 banks x 4 LiFeP04 120ah Batts
  • 2 banks x 4 LiFeP04 138ah Batts
  • 14x Solar Panels
  • BMV-712
  • 2x MPPT 150/85 Controllers
  • 1x Cotek 3K Inverter/Charger
  • 4/0 cables
battery chargingLithium Battery
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3 Answers
shaneyake avatar image
shaneyake answered ·

LiFeP04 Batteries have a pretty steep curve (14.4V)in the beginning and then you hit a very flat curve(13V) in that range. I wouldn't expect to see much difference in the voltage. Voltage isn't a good measure of SOC with LiFeP04 batteries.

What does the BMV say about the SOC? Are you still at 90% You will need to really discharge the pack to notice the additional batteries.

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brbrv avatar image brbrv commented ·
Thank you Shane. The reading for 13.15v is 93%. Is that strange? We never look at the %. Only voltage. Also, is 14.4v the optimal max charge setting? We’ve always had ours set to 14.5v.
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shaneyake avatar image shaneyake brbrv commented ·

I would start to rely more on the SOC % than voltage. LiFeP04 voltage is really not a good indicator of charge like it was with lead acid.

93% with -140ah makes sense to me.

I would charge to 3.5v per cell which is 14.0V
For Discharge you can go much lower than 12.9V or 3.2V per cell.
I normally go down to 3V per cell or 12V but most packs are not empty till 2.8V per cell or 11.2V

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

14.5V seem a bit much for LiFePO4 batteries, look at the datasheet.
13.15V is pretty much the normal resting voltage with a small load running for a some hours.

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brbrv avatar image brbrv commented ·
Thank you Matthias. What would be a good max voltage setting for charging? 14.4v? I cannot find the data sheet.
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brbrv avatar image brbrv commented ·
I should have mentioned that the sticker on the batteries indicates 14.5v as the optimal max charge. However, we want our batteries to last as long as possible.
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brbrv avatar image
brbrv answered ·

I suppose we will run all the batteries down. We usually never get them lower than 12.9v. Our alarm on the BMV is set to alert at 12.4v.

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