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47V but 45% capacity?

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PapaK

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Oct 23, 2020
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Can anyone tell me what’s going on here? My 6 batteries are showing a capacity between 45% and 25% right now but for example this battery shows 45% and a total voltage of 47v. Something isn’t adding up. Also, I have been net positive for solar for the past 5 days. Usually a couple more kWh than I’m using but the batteries are slowly going down any way. Any insight?


IMG_0696.jpeg
 
Perhaps the system is on standby and the inverter consumption cannot be detected by the bus?

My 20kWh stack is on standby for now and it runs for a week before the voltage starts to tank... the SOC does drop because the Bms in the Ruixu can't detect anything below 0.5A.. So the larger the bank theore power you have to draw for it to register in the SOC reading.
 
PapaK said:
My 6 batteries are showing a capacity between 45% and 25% right now but for example this battery shows 45% and a total voltage of 47v.
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I'm assuming these batteries are 16s LiFePO4 batteries. If not, just totally ignore everything that follows...
At 47.3V, they are not at 45% or 25%, they're <10%. And with that lowest cell at 2.718, it's at maybe 1% or 2%.
PapaK said:
Something isn’t adding up.
Click to expand...
We need a little more info on your system to be able to help figure out what's going on. What component is reporting the 45% SoC? The BMS? They tend to not be very good at that task, and even worse if they aren't set up properly, though that's not always something you can change.
PapaK said:
Also, I have been net positive for solar for the past 5 days.
Click to expand...
What are you basing this on? How are you measuring what's going in and what's going out? At low voltage like that, if you're charging you should certainly see voltage increasing, at least until it reaches about 51.5V, then voltage will change slowly while it takes on more charge, until rising rapidly again above about 54V when the batteries are approaching 100%.
 
Most bms are terrible at estimating the SOC , especially after days without discharging and charging fully. Either use voltage to control charge and discharge, get an external shunt (which usually seems to do a better job of tracking current) or find a way to fully charge them to reset the bms counter.
 
PapaK said:
Can anyone tell me what’s going on here? My 6 batteries are showing a capacity between 45% and 25% right now but for example this battery shows 45% and a total voltage of 47v. Something isn’t adding up. Also, I have been net positive for solar for the past 5 days. Usually a couple more kWh than I’m using but the batteries are slowly going down any way. Any insight?


View attachment 195572
Click to expand...
Welcome to winter.

Either fully charge them or discharge them.

Personally I'd go for fully charging to 56.6v so the SOC is calibrated.
 
Aww forgot to mention...update your BMS firmware.

The Low Cell Voltage should trigger a 0% calibration once you trigger it.
 
I have had issues before with it being very inaccurate below 50%. Last night I had 2 SOC lights on. I should jaut tape over them if they are that usefulness

I ordered a Victron smart shunt and I will use that from now on.

I was using the 6500ex display to show me energy in and energy out. I’m not shocked at all that it probably isn’t accurate.

I will have more panels installed soon. I’m only running 2000w but I have 14,000 more to install.

One of my 6500ex is in for warranty work and my PV2 in stopped working on the other one. I still yet to have a call back from their support team after they opened a ticket. Anybody reading this, skip signature solar inverters and shell out the money for victron.
 
Zapper77 said:
Welcome to winter.

Either fully charge them or discharge them.

Personally I'd go for fully charging to 56.6v so the SOC is calibrated.
Click to expand...
Also jsut for information purposes I had it fully charged about 10 days ago. I’m surprised it loses calibration that fast
 
Hard to say day for day as I’m a shift worker and my wife is out of town for work a lot so it can fluctuate. I’ve never looks at battery load average but right now I use about 5 to 7kwh a day according to my inverter.

It seems like my night time load is around 100-140 watts.

I only have a very small hrv, a ceiling fan on low, a router, and the occasional small fridge load as the only things pulling amps at night besides standby over loads

I hope this helps answer your question. I will try to get a more accurate draw tonight for the nighttime draw with a clamp meter
 
PapaK said:
Hard to say day for day as I’m a shift worker and my wife is out of town for work a lot so it can fluctuate. I’ve never looks at battery load average but right now I use about 5 to 7kwh a day according to my inverter.

It seems like my night time load is around 100-140 watts.

I only have a very small hrv, a ceiling fan on low, a router, and the occasional small fridge load as the only things pulling amps at night besides standby over loads

I hope this helps answer your question. I will try to get a more accurate draw tonight for the nighttime draw with a clamp meter
Click to expand...
6 batteries would need a combined hourly load of 200+ watts to guarantee that the BMS will recognize the load and adjust the SOC accordingly.

If by chance your were running an old BMS firmware, those firmware versions would need a combined load of 600 watts or more, before the BMS would adjust SOC.
 
Interesting. Thanks for the info! It’s crazy home much stuff you have to find out on your own
 
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