Can Daly BMSs be connected in series?

Venezuela Solar

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Just that, can I make 2 identical batteries with Independent and identical BMSs in series, let's say 4 280Ah Lifepo4 cells with a 100A bms and other battery identical in series for a 24v battery bank? This is all DIY by the way, I know some BMSs can be adjusted but the second BMS would have voltage readings out of the range right?
 

FilterGuy

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but the second BMS would have voltage readings out of the range right?
No, the BMS only reads voltages relative to the most negative cell so that is not a problem. However, if the BMS has to turn off the current, the voltage across it's FETS will be the full voltage of the bank of series batteries. In the example you described the voltage across the FETs could go to 28-30V if the cells are fully charged and the BMS decides to turn off.

I do not know what the Daly limits are, but this is the typical limiting factor for putting FET based BMSs in series.
 

Venezuela Solar

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No, the BMS only reads voltages relative to the most negative cell so that is not a problem. However, if the BMS has to turn off the current, the voltage across it's FETS will be the full voltage of the bank of series batteries. In the example you described the voltage across the FETs could go to 28-30V if the cells are fully charged and the BMS decides to turn off.

I do not know what the Daly limits are, but this is the typical limiting factor for putting FET based BMSs in series.
Didn't completely understood what you said, if one bms would shut down the input, assuming it is a common port BMS, the voltage would go to 28-30v, on the FETs of the BMS?
 

FilterGuy

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Didn't completely understood what you said, if one bms would shut down the input, assuming it is a common port BMS, the voltage would go to 28-30v, on the FETs of the BMS?
Think of the FETs in the BMS as switches. Each 12V pack will be ~ 14.4V when fully charged.

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When one of the BMSs turns off, that 'switch' will have the full voltage of both batteries across it. If the FETs are not designed to handle switching that level of current and voltage, they will burn out.
 
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