Quote:
Originally Posted by Piotrsko
Hmm so the low cells trigger the bms and you have a wider range of voltage mismatch. Wonder if they are cutting corners on the assemblies. If you turn it off, let it rest, does the SOC recover much?
any given day the maximum difference in my pack is only .2 volt between cells, pretty much the same cell locations charged or discharged. I tried a top balance, and a bottom balance and it didn't make any change worth noticing.
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That isn't my data it is from ChevyBolt Forum member gallen. His post is the only on I've found were someone has actually driven their Bolt until it stops moving. Unfortunately he did not start this test with a full battery so he didn't have data on starting cell voltage or total kWh used by the vehicle on the run.
When his car stopped moving his readings were:
0% SOC from the app
0.4% User SOC (PID 228334)
4.9% Raw SOC (PID 22432f])
As to cell values he said:
Cell volts spread gets larger as %SOC gets low - up to 0.4 volts range. All cells were +/- 0.01 V when charged, but one cell was much lower than all the others as SOC approached 0, starting at a few % user SOC.
For another look at the Bolt battery there is:
(
https://allev.info/2019/02/bolt-battery-buffer/)
He says RAW SOC isn't actually battery SOC and claims there is no buffer in the Bolt battery and GM allows 0% to be used. I don't really follow his logic - it is from a based on a graph from a paper on a different battery - but keys things from the article to me:
He is showing fully charged cell voltage at 4.165 and dead at 2.7 Volts.
When fully charged the Raw SOC is 96.5% when the app shows 100% SOC
Assuming Raw SoC is actual SoC GM is holding back 8.5% of the battery capacity - which what most of the industry was doing 5 years ago.
That is also very close to the 9% I found to be missing on my test. So it looks like the software recall might be holding back another 20% of the battery capacity
in addition to the 8.5% that was originally held in reserve.