Daly BMS after a low voltage shutdown…

Delta3

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I have read thru a lot of posts here and no one is describing my issue. I have a 4s 60amp Daly bms. Everything was working fine until I tested the low voltage cutoff. It did cut off, then after the battery rebounded some it cut back on in say 10-30 seconds. Result is my 12v inverter cuts on and off and on and off. How can I get it to remain off after the low-voltage condition is met?

thanks
 

mmame

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On some smart BMS, the recovery voltage can be adjusted. In case of a thumb BMS, recovery voltage is fixed. In case of large currents, OC battery voltage might trip recovery voltage level, so there is imho no solution...
 

Delta3

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On some smart BMS, the recovery voltage can be adjusted. In case of a thumb BMS, recovery voltage is fixed. In case of large currents, OC battery voltage might trip recovery voltage level, so there is imho no solution...
So I guess your saying I’m out of luck. That seems a little off for a BMS to do that. Don’t understand the logic.
 

mmame

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Well... It depends if several low voltage cutoff/on cycles are an issue for your given use-case or not. From battery health perspectives, some on/off cycles aren't a big issue as long as the low voltage cutoff level is properly choosen.

Btw, I'm unsure how other BMS models/brands react to low voltage cutoff: I guess some are more "smart" and prevent such a restart (independent from actual cell voltage) as long as no charge voltage is applied.
 

Delta3

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Thanks for your reply. I understand what your saying, but for an inverter, it’s ridiculous.
 

Sharky722

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Is this a smart bms can any adjustments be made?
I had a similar issue but at the other end on hvd when charging.
The time delay was to short and the recover voltage was to high. Charger was on off repeatedly.
I suspect yours is similar but with low voltage.
Can the inverter LV be set higher?
 

Delta3

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It is a smart BMS, but the standard BT app will not let me change any rebound values. Can’t even see if it has any.
 

Sharky722

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It is a smart BMS, but the standard BT app will not let me change any rebound values. Can’t even see if it has any.
While I'm not familiar with these smaller bms units, is there a possibility to connect the sinowealth software to make the changes?
If not, then the next point of interest would be the inverter set point. Set that above the bms set point.
 

OTRwSolar

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Have you checked the input DC voltage to the inverter when it cycles on and off?

Constant voltage means the inverter itself is cycling off and on. Could be due to an internal inverter problem, or the inverter itself is activating its own low-voltage disconnect due to low input voltage (typically <11v).

If the input voltage to the inverter cycles off and on, then the BMS (actually anything in-between the cells and the inverter input) is suspect. If the cells are in a low SOC, the BMS may be simply cycling between low voltage disconnect/cut-off (voltage sag with inverter load) and LVD release (voltage recovery after the inverter load is removed). If you fully charged the cells after the LVD, then it's obviously another issue.

Not having access to the BMS's parameters/faults leaves you with few options in terms of troubleshooting the BMS. Have you checked voltages of the individual cells with a voltmeter for any anomalies?
 

Delta3

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It could be low voltage on the inverter, but as I watched the voltage it was cutting off on exactly what I have it set to.

I’m including a picture of the BMS.
 

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OTRwSolar

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It could be low voltage on the inverter, but as I watched the voltage it was cutting off on exactly what I have it set to.
Did you happen to make (and record) any of the voltage readings I mentioned/suggested (while the inverter cycles off and on)? These readings should confirm whether the BMS, or inverter, is cycling off and on.

If you confirm the BMS is cycling, what are the individual cell voltages when it cycles? Cell voltages should help determine whether the BMS is currently at a low SOC, cycling between LVD and LVD release (or not, as the case may be).
 

Delta3

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I haven’t tested that test again. But I will. The stated voltage on the inverter is 10v-15v. I can remember seeing one of the cells bottom out at 2.5v and then rebound. So I believe it was the BMS. I also know that it happens at the top when charging as well. It will shutdown when a cell hits 3.65, but will rebound lower and restart the BMS. I have confirmed that it does not reset if it reaches pack maximum. Prob the same for pack minimum.
 
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