Not actually a problem but…. We have recently, for the first time, run out of battery power a couple of times (9.5 and 5kw gen 1) with the house switching over to the grid at 4% which I expected. Then half an hour later it switches back to the battery which then shows 5% and cheerfully carries on supplying 2/3/4/500watts depending what is running for at least another half hour. I don’t know how long it would carry on for as both times it happened the Intelligent charge period at 23.30 has started. I haven’t done the recent 3015 update and won’t till after Xmas. Recalibration needed?
#2nophead
I think it is quite normal. I think when the battery is idle its BMS can equalise power amongst the cells and that allows it to discharge a bit more without any cell going under voltage.
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#3rio911
That was my system yesterday. Just before 10pm, the battery is already flat, at or below 5%. The house load is then supplied by the grid.
Then something happens, the BMS then adjusts the SOC to around 10%, without ever charging the battery. The house is back supplying from the battery.
OP can check their battery performance? I expect there will be something like this. Could be recalibration or internal balancing of the cells. I don't know.
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#4SimonClarke
rio911 yes almost exactly the same. Not noticed before this month as we haven’t used the battery up before. Yesterday coincided with the saving session but normally would have been enough but we had used a bit extra so it ran out at 21.30 at 4% then we ran off the grid for half an hour before it showed 5% and started supplying again. Not worrying about it just curious.
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#5killythebid
Our twin 5.2kWh battery system does much the same as the OP. it will go idle at 4-6% and then find a few more Wh down the sofa and start discharging again for a while it can do this several times.
Most often the individual batteries can report quite different and higher SOCs than the total SOC stated by the inverter. I never know which to believe.
We have only run out of battery a couple of times this winter so far when the solar panels have generated less than 0.5kWh all day.
Still, shortest day tomorrow so at least in terms of daylight hours we shall be on the up again from then but no telling how many grey and dark days we will get over the remainder of the winter.
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#6rio911
@SimonClarke I don't know what causes it, just noticed it recently as well. It is strange.
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#7Vestas
The BMS will run its own internal calibration routine when its idle for 30 minutes and below 40% (IIRC) SoC.
That's what you're seeing when it hits the cutout SoC setting - battery goes idle then starts internal calibration 30 minutes later, which takes a further 30 minutes. So an hour in total. Normally you're looking at a couple of hundred Wh at most being recovered due to cell balancing.
If you stop charge/discharge and idle the battery for an hour before the cutout is hit then the SoC usually goes down rather than up.
D
#8DD
Same for me: on the last couple of savings-session days, when my 9.5kWh battery has run very low at the end of the day, it seems to pause itself at 5%, then do it's calibration, find another few % charge, and resume discharging.On the 18th, for example, it paused at 22:15, resumed discharge at 22:50 on 7%, and rose up as high as 14% while continuing to discharge at 300W, finishing at 13%
