Day 2, BMS Temperature Faults

• A

  Adam

  12/3/21, 10:20 AM
  Good Afternoon, I turned on my system last night, then turned on the PV this morning. The battery should be very near 100%, though a single cell appears to be lagging. I now see the BMS throwing internal temperature faults: Should I be concerned about this? A.
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• R

  Richard OGM Support Staff

  12/3/21, 10:37 AM
  Sounds like you did not pre-balance your system by paralleling all cells overnight, or you have mismatched cells. The BMS is working overtime to bring them into a balanced state and having to release a lot of heat in doing it.  The aluminum case is your heat sink.  Depending on the size of your pack this could go on for a few days.  I suggest you remove your cells and pre-balance or provide some means for extra airflow until it gets your system into a more balanced state. Alternatively you can use some sort of large resistive device and manually pull down your highest few cells.  I have used a cheap battery load tester in the past.  
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• A

  Adam

  12/3/21, 10:44 AM
  Thanks for the quick response! I did, in fact, top-balance them to 3.65v a week or so ago, before putting them in series. But one of the cells was lower by just about 0.1v when I powered everything on. I hope I don\'t have to replace the cell… Is it actually possible for the BMS to balance this out over time or am I hooped? A.
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• R

  Richard OGM Support Staff

  12/3/21, 10:56 AM
  Give it a few days to try to get itself balanced, or help it along as suggested in previous post. Then do a few deep cycles and recharges and see how it comes back each time.  Do you get a cell falling off fast during discharge, before you get close to the expected capacity?  Does one cell seem to peak very fast when recharging? The BMS also has to ability to extrapolate each cells internal resistance but it takes quite a few cycles to be able to get a reliable calculated value for each cell.  The user manual explains it a bit. Fingers crossed
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• A

  Adam

  12/3/21, 11:21 AM

  Quote from Rick-admin on December 3, 2021, 3:56 pm

  Give it a few days to try to get itself balanced, or help it along as suggested in previous post. Then do a few deep cycles and recharges and see how it comes back each time.  Do you get a cell falling off fast during discharge, before you get close to the expected capacity?  Does one cell seem to peak very fast when recharging?

  Well huzzah: So that went pretty quickly, actually. I guess we\'ll see what happens over a few discharges. These are really inexpensive 280 Ah cells, so I\'m not expecting them to be perfect. I\'ll be quite happy to get 80% of their specified capacity. Thanks for your help, A.
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