SmartBMS inrush current problem

Q&A and troubleshooting
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1 
   I am having an issue with a battery protect relay when I power up my system. When I turn the system power on the relay will throw an error (E1) and not turn on. The only devices connected to are a Antaira 12\~36 volt POE network switch and a cell modem and nothing is connected to the network switch. I believe it is the network switch pulling an inrush of current which freaks out the relay not allowing it to turn on. If I unplug the POE switch and wait for the system to power up and then plug in the POE switch it works. Has anyone seen any issues like this before? If I put an inrush limiter on the power feed to the POE switch it seems to work. It doesn't do it on every switch, just seems to be random. If I convert my system to 24VDC it doesn’t seem to do it but my systems are typically setup for 12volts.

Aside from the inrush limiter or moving to a mechanical relay or going to a 24volt setup does anyone have any ideas or suggestions? I am also working on a different brand of POE switch. Also recommendations for a mechanical relay would help if anyone has one in mind.

Thanks!

2

A pre-charge circuit could solve this problem.

You take a power resistor e.g. 1Ohm/5W and a button switch in series to this resistor. This is then connected in parallel to the the “power on switch”.

Now the scenario is, the battery is off, and you want to turn it on, then you first push that button for e.g. 5 seconds, and then all the connected loads will be pre charged softly without high inrush current peaks, as the current is limited through the 1Ohm resistor.

After this 5 seconds you turn on the main power/battery switch. With this you can avoid inrush currents for a little price.

3

Thanks for the suggestion however in my application this won’t work because it is a unattended solar platform. If it shuts down due to low battery no one would be there to do the pre-charge. We have established just putting a in-rush limiter on the power feed seemed to work but was just wondering if there were any other options such as the one you gave. I have another brand poe switch that I will be trying to see if the same issue occurs. Thanks!