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Is Seplos BMS precharge sufficient for Multiplus II 48/5000?

kumpactor

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May 24, 2022
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Germany
Does anyone use a Seplos BMS 200A Lifepo 16s with a Multiplus II 48/5000 and has experience with precharge after BMS disconnects?

If you are offgrid and BMS disconnects battery for any reason, inverter is shutdown, inverter capacitors are drained.
If BMS connects battery again (after error condition has gone), seplos BMS will activate precharge first, than - after configured precharge time - activate discharge MOSfets.

Seplos manual contains no details about precharge current or maximum capacity of inverter caps that can be charged. If caps are not charged up enough, inrush current could still exceed current limits, BMS may disconnect battery for safety.
Has anyone successfully used Seplos precharge with Multiplus?
 
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I was told by their rep to increase the pre-charge timer to 3secs, though am yet to try it.
 
Precharge is set by time required to make it work. To find right amount of time you will need to experiment with your setup.
 
JK active balancer BMS for 16s/24s model does BMS reactivation pre-charging, 8S model does not. PCB pads are there on 8S model but not populated.

For 51 vdc battery, it limits turn on surge current to about 125 amps with 50 milliseconds to settling supply voltage on typical 48v inverter. Only for BMS reactivation, does not help for turning independent circuit breaker on.

A battery/BMS system needs a voltage sense detection on inverter DC input side of breaker to know when to control current limiting on a manual circuit breaker turn-on surge current. For a manual circuit breaker, you want a lower turn on surge current to avoid degrading breaker contacts. Most BMS designs stay away from manual circuit breaker surge current limiting because there are too many variables out of their control on inverter requirements.

16S full board pre-chg picture.jpg
 
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Why not just set it at the max. I don't care if I have to wait 2 versus 5 seconds. Is there any other drawbacks?
Some inverters may not like a slow voltage rise. It can even damage inverter. Also, any inverter that jumps right into active inverting operation (not recommended) may collapse supply and shut down, possibly just oscillating on/off in a continuous start-up attempt.
 
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