Forgive me if this is a dumb question but why is there a 4% maximum discharge limit on a battery claiming to be 100% Depth of Discharge? I have a 9.5KWh battery so assuming there is in reality a larger battery in there to accommodate for 9.5KWH DoD, so why is there a "cant discharge to 0%" limit?
Sorry if its obvious but its not 100% DoD if you can only use 96% is it?
As far as I know you do get the full 9.5kw, the 4% is extra so it does not fully run out of power. But if you top up to 100% and discharge to empty it should be 9.5kw ish.
But surely that is out of date? Based on the 8.2kw 80% DOD battery?
THALL Not sure what your point is.
AFAIK the 4% is reserved to keep the inverter powered up in case of a grid disconnection. The 4% does trickle out in ECO mode when there is no PV and when the battery SoC hits 0%, it charges up to 4% to keep the inverter powered up in case of a grid disconnection.
The argument is moot as the SOC algorithm is flawed. The battery voltage can drift to very low levels which can result in irreversible damage.
ispookie666 The argument is moot as the SOC algorithm is flawed
Maybe. Or maybe it's the BMS. Maybe it's SoC algorithm. Maybe it's the inverter firmware. Maybe it's the operational use. It doesn't manifest itself in every battery.
I'm not denying there are problems in a number of cases (who knows how many - Givenergy that's who), but the OP was asking a question about capacity and that is what I was trying to help with.
Apologies for hijacking this thread but it was relevant to something I was curious about so thought I'd ask here; I have a new 9.5kWh battery and the minimum charge threshold can't be set to anything below 5%. I've been assuming that the 95% useable capacity that I have available equates to 9.5 kWh, however all the talk here about a 4% reserve has left me somewhat confused.
Edit: Just a correction to the above; while I can see in the settings that there is a reserve set of 4%, when I try to drain my battery completely it never drops below 5%. Hardly the end of the world, and I never see any other sudden drops or jumps in SoC so it doesn't look like the big SoC problem that everyone is talking about, but I'm just curious as to why I can never seem to get that last 1% out of the battery.
THALL Just pointing out an out of date article.
In what way is it out of date? It is relevant to anyone with an 80% DoD battery and explains the concept of DoD and reserve to people whether theirs is 80% or 90% DoD. Our Batt8.2s are 100% DoD but inside there are cells with a total capacity of 10kWh. It was marketed as an 8.2kWh battery but could easily have been marketed as a 10kWh 80% DoD. With these Batt8.2s (100% DoD), there is still a 5% top end-stop and a 15% bottom end-stop.
BrettDavis but I'm just curious as to why I can never seem to get that last 1% out of the battery.
AFAIK the SoC is a calculation from battery voltage, temperature and other fudges related to energy flow. The parameter stopping the discharge will be the battery/cell voltage measured by the BMS (Battery Management System) but the fudged calculation for your battery comes out at 5%. If the fudge was adjusted slightly, it would come out at 4% but it would still be the same cell voltage measured by the BMS that stops discharge. The KB article linked above explains why there is a lower end stop for battery discharge.
BrettDavis the minimum charge threshold can't be set to anything below 5%.
Apologies, I just read your post again. Are you saying that under battery options in the portal, the minimum reserve you are able to set is 5%? Here's a screenshot of one of our batteries with a 4% minimum reserve.
Tim Yesterday one of my two batteries decided to change the reserve to 96% off its own bat and so stopped discharging. I corrected it back to 4% and did a restart after checking the rest of the settings were correct. This morning I discovered that the charge period on that battery had zeroed out so I didnt get an overnight charge. I've reset it to 00.30-07.30 to fit in with my ECO7 supply. But I wondered if this was a common occurrence and known about or is it a one off oddity?
BarryForde It isn't unheard of for a setting to change. Givenergy have been known to credit the user with finger trouble on the app. You could try a reset to defaults, which should set everything at the correct limits. There are registers which end users cannot see or change which I think the reset to defaults does also reset.
BrettDavis Your chart looks like the battery capacity reduces to 5% some nights and then charge very slowly for a short period until the timed charge window opens. Amazing that your capacity and use are so well matched. I take it that the chart is from Home Assistant? I can see why you would want the battery to continue to drop to 4%. Might be worth a call to Givenergy just in case there's something odd that's not obvious.
Thanks for all the info.
If that graph is from HA then I get wildly different numbers in HA than the GE app. So often in HA it shows my battery SOC as 97% and it does not seem be charging more. In GE app its 100%. So I would assume there is some discrepancy in what GivTCP states is Battery SOC. I do not often get as low as 4% but in the few times I have let it get that low it did say 4% in the morning when I checked it in HA. But it may have been tickle discharging for many hours at that point. What does the GE app say when it's 5% in HA? The same or 4%?
