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What the ?!?!?!


Bobster
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Just happened here?

My system has occasionally shown this sort of behaviour before, but not as egregiously as this. 76% to 100% in 5 minutes.
image.png.1b7c4285d27a3f9d2d7e48437f06ac58.png
Which figure do I believe? The 76% of the five minutes later 100%?

Goodwe ES inverter. Revov batteries with a BYB BMU and the Goodwe configured to "see" a BYD B-BOX.

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5 minutes ago, Bobster said:

Goodwe configured to "see" a BYD B-BOX

Sounds as if the inverter gets its SOC from the battery.

BYD batteries can drift quite a bit, because their current sensors can't sense well below 2A (per module, multiply by number of modules). So if your batteries have been subject to a low charge or discharge currents (in this case I suspect slow charging to be the culprit), the battery SOC might well have been higher than the BMS estimated... until the cell voltage suddenly went up and the BMS realised it had to reset.

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19 minutes ago, plonkster said:

Sounds as if the inverter gets its SOC from the battery.

BYD batteries can drift quite a bit, because their current sensors can't sense well below 2A (per module, multiply by number of modules). So if your batteries have been subject to a low charge or discharge currents (in this case I suspect slow charging to be the culprit), the battery SOC might well have been higher than the BMS estimated... until the cell voltage suddenly went up and the BMS realised it had to reset.

Thanks. So I believe the 100% then?

Don't know about the slow charging. We had good sunshine, but the pool pump was running and then appliance was piled upon appliance and certainly it would have got to 100% SOC later than usual.

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9 minutes ago, Bobster said:

Thanks. So I believe the 100% then?

There is always some sort of algorithm in the BMS that it uses to decide when to go to 100%. Usually it is something like 1) all cells above 3.45V and 2) at least one cell just spiked above 3.5V. One reason why seeing per-cell voltages, or at least the lowest and highest voltages, is a very good diagnostic tool.

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  • 2 weeks later...
On 2020/08/17 at 2:47 PM, plonkster said:

One reason why seeing per-cell voltages, or at least the lowest and highest voltages, is a very good diagnostic tool.

Is it possible to see this in a blue system? MPII, Venus, 4 * pylontech us3000...

 

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54 minutes ago, Ironman said:

Is it possible to see this in a blue system? MPII, Venus, 4 * pylontech us3000...

 

Ask Pylontech if the firmware that implements this is available yet... 🙂 I know they were working on it.

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On 2020/08/17 at 2:02 PM, Bobster said:

Just happened here?

My system has occasionally shown this sort of behaviour before, but not as egregiously as this. 76% to 100% in 5 minutes.
image.png.1b7c4285d27a3f9d2d7e48437f06ac58.png
Which figure do I believe? The 76% of the five minutes later 100%?

Goodwe ES inverter. Revov batteries with a BYB BMU and the Goodwe configured to "see" a BYD B-BOX.

This is pretty normal, like @plonkster explained. If happens once a while then it's okay.

But, if that happens everyday, then it means that the real capacity of the cells is much lower than what's hardcoded in the BMS FW.

Everyday jump from 90% to 100% is okay. Everyday jump from 76% to 100% is not.

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  • 2 weeks later...
On 2020/08/30 at 11:11 PM, Youda said:

This is pretty normal, like @plonkster explained. If happens once a while then it's okay.

But, if that happens everyday, then it means that the real capacity of the cells is much lower than what's hardcoded in the BMS FW.

Everyday jump from 90% to 100% is okay. Everyday jump from 76% to 100% is not.

It is occasional.

Thanks all for the input and information. 

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  • 10 months later...

Necro post.

This is still happening and the trigger for the big jump in SOC (usually from mid 70s to 100) is when SOC drops to the 40% that I have reserved for load shedding. But now this morning I see this for the first time - a sudden DROP. In this case from 48 to 40. There is a spike in the load there, but not unusually high for this time of day in my house (kettle being turned on whilst the heat pump is still running) and the spike was 3.2 kw. Note that later on I get the sudden big increase in reported SOC.

I don't know whether to worry or not.

image.png.68aec3a6e25121cfbce72aa6ec96b396.png

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