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Eg4 lifepower soc drift

underdog5004

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Jun 6, 2023
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I have six life Power Batteries 48 volts all in parallel to a bus bar. Number two wire between the batteries and the bus bar.

I noticed that one of my batteries was only showing three lights when the others were showing four lights state of charge. At first I was worried about the capacity. I hooked up my computer and check the BMS and yes the battery with only three lights was showing a capacity remaining of 78 amp hours while the others were showing full 100. I was very worried that I had lost capacity in this battery. The state of health still showed 99.8. Actually it's not state of health anymore it just shows remaining ampacity.

Before I called Signature solar for a warranty replacement I decided to turn off my other batteries and drain the One battery with the three lights. As I drain the battery I noticed that the voltage was not dropping as I had expected and even after I pulled 78 amps out of the battery the voltage was still around 51 volts. Encouraged, I continued to drain the battery until it was at 48 volts, 3 volts per cell. After recharging this battery it shows 100 amp hours of capacity or really 99.8.

From this experience I decided that the battery was fine but the state of charge had drifted. So this is just a public service announcement that the state of charge measurement can drift, obviously, and the way to reset that that I found was to drain that battery down to 48 volts and then let it recharge.

This battery bank usually never dips beneath 75% state of charge. My loads are simply not great enough compared to the incoming solar power. Just wanted to let everyone know.
 
With the BMS_Test software you can see what the "Bal_Start_Volt" setting in the BMS is. Just select the "ParameterSetting" tab and scroll to the bottom of the left panel. The "Bal_Start_Volt" is set to 3.45. This is the cell voltage at which the BMS will start balancing and will reset the SOC to 100%

Monitor all batteries using the "BatInfo" tab and the "MultiPacks" tab. As the cells in a battery reach 3.45 volts you will see a "(Bal)" indication preceding the cell voltage and the SOC will reset to 100%. At this time you might want to decrease the charge voltage to around 55.5 Volts to prevent a cell going into OVP (Over Voltage Proptection) and stopping the charge on that battery. I do this periodically and let the batteries "soak" for 30 minutes or so. Once I get all batteries balanced I also reset my Victron SmartShunt to 100% SOC.

New batteries should be individually charged as above so each battery when placed into service has an accurate SOC reference and will generally play well with the others.
 
SoC accuracy drifts. Batteries need to regularly reach true 100% SoC to track accurately, and that's as defined by the BMS, not by you. :)
Yeah I understand that the batteries need to come to 100% state of charge. These batteries do they are regularly brought to 55.6 for an hour and a half absorb and then float at 54 Volts for the rest of the day. That's why I was surprised at the drift because I was regularly topping them off. Apparently the BMS needs to see a low voltage as well as a high voltage in order to calibrate the state of charge. I don't know I'm just guessing but I thought it would be a useful anecdote for others
 
Yeah I understand that the batteries need to come to 100% state of charge. These batteries do they are regularly brought to 55.6 for an hour and a half absorb and then float at 54 Volts for the rest of the day. That's why I was surprised at the drift because I was regularly topping them off. Apparently the BMS needs to see a low voltage as well as a high voltage in order to calibrate the state of charge. I don't know I'm just guessing but I thought it would be a useful anecdote for others
Also because I'm only bringing them up to 55.6 maybe I should think about taking them up to 56 or 56.2 for an hour and a half so that the actual voltage at the battery sells exceeds 3.5 volts per cell. 55.6 volts per battery equals 3.475 volts per cell
 

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