JK BMS percharges inverter

Just want to share an observation.

I have a 600w microinverter connected to 24v system which is supervised by JK BMS 40A.

I used to use a resistor to pre charge the inverter but lately found that if I disable "discharge" in BMS and connect the Inverter, there is no need to pre charge it separately.
The inverter power light comes up after couple of seconds indicating that the capacitors are charged.

Only then I turn the "discharge" of the BMS.

Would like to understand of there is anything I should worry about in the long run.

harsha31 said:

Just want to share an observation.

I have a 600w microinverter connected to 24v system which is supervised by JK BMS 40A.

I used to use a resistor to pre charge the inverter but lately found that if I disable "discharge" in BMS and connect the Inverter, there is no need to pre charge it separately.
The inverter power light comes up after couple of seconds indicating that the capacitors are charged.

Only then I turn the "discharge" of the BMS.

Would like to understand of there is anything I should worry about in the long run.

Click to expand...

I have done that a few times, myself. I don't know how it could damage anything, but maybe.
I have also used a chargeverter to take care of it.
But now, I have plenty of battery. So, it's no longer a thing.

Interesting. So the BMS is leaking current.

DIYrich said:

Interesting. So the BMS is leaking current.

Click to expand...

According to my meter, it does. But not enough to run a load. (Milliamps)
I only know this, because I was trying to add a relay to indicate if it shut down. (Was unsuccessful)

If you look at the bottom diagram, the 16S JK BMS has a pre-charge that limits it start up current to about 125A (for 48vdc system) and takes about 50 milliseconds to charge typical inverter input capacitor.

It only works when the BMS is first activated from an off state. Once BMS is active it provides no surge protection, like if you turn off then on a series DC breaker after inverter discharges its input capacitors.

I guess you found an easy way to get the BMS power up sequence with its pre-charge circuit to operate.

The 8S model does not have this separate pre-charge circuit. There are places on the 8S PCB for the extra MOSFET and resistors but they are not populated on PCB. Guess they discovered the 8S battery voltage is not enough to damage the MOSFET's so they can do without it on the 8S model. There is some soft start, with a lot of tolerance variability, in just turn on time for the regular high current series MOSFET's.