Relay options for Chargery BMS

[Machthaber]

My system:
4 Phocos 5kw inverters
32 304AH EVE LIPO4 batteries (48 volt)

Based on my system, I see I can pull 20kW through my 48 volt battery bank for around 420 amps. I purchased the Chargery 600 amp BMS to go with my batteries, but did not order a relay for it. In order to utilize the disconnect feature, its my understanding that I need to connect a relay between my battery positive and my inverter but I am having a hard time finding one that is spec'd for such a large size. Anyone have any recommendations for low power consumption relays or any other way I can wire it to accomplish a LVD?

 

[BentleyJ]

When you mention "Relay" I believe you are referring to a golf cart style contactor. Units rated up to 400 amps are readily available but can consume as much as 140mA continuously. That adds up to KWh's over a month. There are a few choices for higher end contactors that use economizer designs where the holding current is reduced quite a bit from initial activation current. In your situation it sounds like a pair of 300A contactors would be sufficient. Still your parasitic load is going to be fairly high.

One possible solution for high current disconnection with virtually no parasitic load are Latching style contactors. Unfortunately both the single or dual coil type require a PCB controller to latch and unlatch the contacts. I've developed a couple of controller PCB's for latching contactors and also a PCB controller that can be used directly with a Midnight Solar Remote Trip breaker. The RT breaker is an elegant solution because it eliminates the need for a contactor but then someone needs to be physically present to reset the breaker(s) if the BMS trips them. Although under normal circumstances this should never happen.

Not sure if any of this is helpful. Let me know if want any more info.

 

[Machthaber]

Hmmm, never made a PCB like that before. Is it comp

When you mention "Relay" I believe you are referring to a golf cart style contactor. Units rated up to 400 amps are readily available but can consume as much as 140mA continuously. That adds up to KWh's over a month. There are a few choices for higher end contactors that use economizer designs where the holding current is reduced quite a bit from initial activation current. In your situation it sounds like a pair of 300A contactors would be sufficient. Still your parasitic load is going to be fairly high.

One possible solution for high current disconnection with virtually no parasitic load are Latching style contactors. Unfortunately both the single or dual coil type require a PCB controller to latch and unlatch the contacts. I've developed a couple of controller PCB's for latching contactors and also a PCB controller that can be used directly with a Midnight Solar Remote Trip breaker. The RT breaker is an elegant solution because it eliminates the need for a contactor but then someone needs to be physically present to reset the breaker(s) if the BMS trips them. Although under normal circumstances this should never happen.

Not sure if any of this is helpful. Let me know if want any more info.

Hey, never made a PCB controller before, is something like that complicated? Are there any contactors you might recommend that have a low passive draw? Also, you mentioned just using 2x 300 amp contactors.. I'm assuming those would just be wired in parallel to split the current and the relay leeds on my BMS would connect to both of them?