Overvolt when battery reaches full charge

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So, I seem to have an issue with either my BMS or inverter.

100Ah 24V battery with an 8S Overkill BMS
2000W Giandel Pure Sine inverter
2 Epever SCC (one 40A with 1050W array, one 30A with 500W array, both same charge settings)

When my battery reaches full charge and charging stops, the BMS shuts down charging due to one cell hitting max voltage. When that happens, I hear a beep on my inverter for a moment and then nothing. It appears that my inverter stops outputing AC for a moment and it is causing a quick blackout on my AC equipment. I do see on the SCC that it shows max voltage of the battery hits something like 31 or 36V for the day.

1. Is there a setting in the BMS or the SCC I should consider changing to prevent this possible overvolt trigger?
2. Should I hook the inverter to the B- side if the BMS, and only have the C- side to the SCC? (following all safety precautions of course)

The latter is not what I personally think will fix it and I will lose function of the discharging switch. What other details are needed?
 

sunshine_eggo

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So, I seem to have an issue with either my BMS or inverter.

100Ah 24V battery with an 8S Overkill BMS
2000W Giandel Pure Sine inverter
2 Epever SCC (one 40A with 1050W array, one 30A with 500W array, both same charge settings)

When my battery reaches full charge and charging stops, the BMS shuts down charging due to one cell hitting max voltage. When that happens, I hear a beep on my inverter for a moment and then nothing. It appears that my inverter stops outputing AC for a moment and it is causing a quick blackout on my AC equipment. I do see on the SCC that it shows max voltage of the battery hits something like 31 or 36V for the day.

1. Is there a setting in the BMS or the SCC I should consider changing to prevent this possible overvolt trigger?
2. Should I hook the inverter to the B- side if the BMS, and only have the C- side to the SCC? (following all safety precautions of course)

The latter is not what I personally think will fix it and I will lose function of the discharging switch. What other details are needed?

What you're describing is normal for behavior with a BMS cut off.

1. Yes. Stop allowing the BMS to trigger protection. This is a safety device, not a means of terminating charge routinely.
2. Never bypass the BMS. Ever.

You likely need to top balance your cells. If want to try to get the BMS to passively balance it instead, which might take weeks, recommend you reduce absorption voltage by 0.2V until it stops behaving like that. Set BMS to balance above 3.40V, 20mV difference, and only during charge.
 

DThames

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You can get an RS485 to USB cable for the EPEver and connect it to a PC, then set the charge to voltage a bit lower. There is also a little plug in interface box "MT50" that will allow some settings to be made. I prefer the PC interface but it takes a little PC knowledge and some work to gain a proper understanding to use it.
 

Any name you wish

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I use the USB cable and a single Atom PC to monitor it. 27.8V is the boost charge voltage. Boost charge duration of 120 minutes. 0 min equalisation. Float voltage of 26.8V.

I have to do a screenshot from my phone for the battery. Give me a few for that.

*edit: Wrote incorrect float.
 

GXMnow

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I agree with the other posts here. You have an out of balance pack which is allowing the one cell to "run away" when it passes the knee voltage.

The first thing to do is set your absorption voltage a little lower in the charge controller. Then set it to float at a safe voltage. Hopefully, the balance is close enough that the BMS balancing can bring down the high cell during the float time. If the problem persist, then you may have to manually top balance the cells. But even when perfectly balanced, you should still have the charge voltage stop a couple volts below the BMS shut off voltage.

27.8 volts for an 8 cell LFP is not pushing it too high if the pack was well balanced, so you must have a runner that is a bit out. Do you have all the specs for the BMS balancing and cut off voltages? You can try backing it down to just 27 volts even, that would be 3.375 volts per cell if they were balanced. But you have to be sure it is getting high enough to trigger the balancing. Oops, that is below the 3.4 volt balance trigger. It should still come on when a cell starts to run, but that is already too late.

The high voltage reading in the charge controller could be from when the BMS disconnects. The voltage will jump up when the load of the batteries is removed. So I am not that worried about that.

Do you know which cell in the pack is going too high? Is it always the same cell? When it shuts off, measure all the cells right away. Can you connect a load o the high cell and drag it down a bit? I find 12 volt 55 watt fog light bulbs seem to work pretty well. When cold, they will pull over 2 amp from a 3.5 volt cell. Use a bulb to rain off charge from each cell to bring them down to the voltage of the lowest cell. Depending on how bad the balance is, you may need to do this a few times.
 

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This is disturbing. Are you sure this isn't array voltage? Have a pic of this showing high battery voltage?

What does your 500W array consist of?
500W array is two 250W panels in Series. 1050W array is 2S2P. 3 are 250W panels, 1 is 300W but near identical voltages.

Lg Voc - 40
Lg Vmpp - 32.1
LG Impp - 9.52

Csun Voc - 37.3
Csun Vmpp - 30.1
Csun Impp 8.31

LG is the 300W panel.
 

Any name you wish

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I agree with the other posts here. You have an out of balance pack which is allowing the one cell to "run away" when it passes the knee voltage.

The first thing to do is set your absorption voltage a little lower in the charge controller. Then set it to float at a safe voltage. Hopefully, the balance is close enough that the BMS balancing can bring down the high cell during the float time. If the problem persist, then you may have to manually top balance the cells. But even when perfectly balanced, you should still have the charge voltage stop a couple volts below the BMS shut off voltage.

27.8 volts for an 8 cell LFP is not pushing it too high if the pack was well balanced, so you must have a runner that is a bit out. Do you have all the specs for the BMS balancing and cut off voltages? You can try backing it down to just 27 volts even, that would be 3.375 volts per cell if they were balanced. But you have to be sure it is getting high enough to trigger the balancing. Oops, that is below the 3.4 volt balance trigger. It should still come on when a cell starts to run, but that is already too late.

The high voltage reading in the charge controller could be from when the BMS disconnects. The voltage will jump up when the load of the batteries is removed. So I am not that worried about that.

Do you know which cell in the pack is going too high? Is it always the same cell? When it shuts off, measure all the cells right away. Can you connect a load o the high cell and drag it down a bit? I find 12 volt 55 watt fog light bulbs seem to work pretty well. When cold, they will pull over 2 amp from a 3.5 volt cell. Use a bulb to rain off charge from each cell to bring them down to the voltage of the lowest cell. Depending on how bad the balance is, you may need to do this a few times.
I have top balanced the cells about 1.5 months ago. They are cylindrical cells from battery hookup and not prismatic ones. I was looking at adding the Neely? active balancer on this to help with cell drift but haven't seen the complete need yet.
 

sunshine_eggo

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500W array is two 250W panels in Series. 1050W array is 2S2P. 3 are 250W panels, 1 is 300W but near identical voltages.

Lg Voc - 40
Lg Vmpp - 32.1
LG Impp - 9.52

Csun Voc - 37.3
Csun Vmpp - 30.1
Csun Impp 8.31

LG is the 300W panel.

Your 1050W array is more likely a 950W array. Your LG is limited to the same current as the Csun. The mismatch in voltage also plays a part.

I have top balanced the cells about 1.5 months ago. They are cylindrical cells from battery hookup and not prismatic ones. I was looking at adding the Neely? active balancer on this to help with cell drift but haven't seen the complete need yet.

It didn't take or it didn't hold.

Yes you have. It's why you posted.
 

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The load is pretty low. about 24Ah per day unless I am dumping the excess into my car. 1.3A during the night is the draw from the battery. 0.8A during the day (running cameras and network equipment)
 

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Your 1050W array is more likely a 950W array. Your LG is limited to the same current as the Csun. The mismatch in voltage also plays a part.
The array is well within the tolerances of the SCC voltage of 100V. The panel was newer and completely free. This should not affect the charging of the battery or the high voltage once cell protection kicks in.
 

sunshine_eggo

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The array is well within the tolerances of the SCC voltage of 100V. The panel was newer and completely free. This should not affect the charging of the battery or the high voltage once cell protection kicks in.

I made no mention of it affecting charging. It's simply incorrect to refer to the array as a 1050W array as it's not possible to get that out of it due to the 250W panels forcing it to run at a lower current.
 

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27.8 volts for an 8 cell LFP is not pushing it too high if the pack was well balanced, so you must have a runner that is a bit out. Do you have all the specs for the BMS balancing and cut off voltages? You can try backing it down to just 27 volts even, that would be 3.375 volts per cell if they were balanced. But you have to be sure it is getting high enough to trigger the balancing. Oops, that is below the 3.4 volt balance trigger. It should still come on when a cell starts to run, but that is already too late.
It is currently at 99Ah and balance is now at 0.050V. Maybe I got a runner here...
 
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