Latching Chargery DCC off

Ai4px

Solar Enthusiast
Joined
Feb 20, 2021
Messages
77
Given that the chargery DCC does not do soft start when commanded off and back on, I'm seeking ideas to make sure it stays off if it is shut down for low voltage on the discharge mode. I've got a HUGE battery and if it goes dead, I got bigger problems.... I don't mind if the inverters stay off.... heck they are sunny islands and if they power down, they will not auto start unless the user holds the "start" button down... so there is no need to have the DCC surge and charge those huge caps when the inverters won't autostart anyway.....

So, I've thought of using a SSR for 12v inline with the DCC control cables... using the SSR as a latching relay and the user has to press a button to make the relay latch on.

So start up sequence would look like this...
1 make sure the DCC is OFF
2 power up the BMS and wait for it to assert the DCC interface pins.
3 press my "latch start" button on the latching relay
4 flip the manual power switch on the DCC.

Anyone else got any ideas?
 

Bob B

Photon Sorcerer
Joined
Sep 21, 2019
Messages
3,342
The other option would be to automate a pre-charge circuit that would be external to the DCC .... just treat the dcc like a regular SSR.
 

Doug

Solar Enthusiast
Joined
Apr 14, 2020
Messages
21
Location
Australia
I don't have a DCC, I'm using a ABB shunt trip breaker. Tripped from a 12v NO relay.
@Danner could you please explain how you activated the shunt trip from the 12V NO relay? What outputs does your BMS have?

A Chargery BMS has a relay output that is activated in an ok state, and deactivated when there is high voltage and the same for low voltage. How would this drive a pulse/continuous current to the shunt trip breaker when the relay output is deactivated? Do you have some circuitry to do this? Or am I missing something?

I know a Batrium BMS has custom relay outputs that can trip the shunt trip breaker. A ZEVA BMS is similar to a Chargery and would therefore experience the same issue in tripping a shunt trip breaker, but the difference is that it doesn't provide power for the relay, just a switched output. I don't know about others.

I'm wondering if a normally closed relay would work, i.e. an LVC or HVC condition would deactivate the relay which would close and provide current to the shunt trip, tripping it, but I'm unsure how it would work during BMS startup. I'm guessing the BMS starts up with the relay disengaged, so something would need to be done to prevent this tripping the shunt trip breaker till the relay can be engaged as per "battery ok" operation. A time delay sounds dangerous, should an actual battery issue be present at BMS startup. The shunt trip circuit would also have to be powered through the shunt trip breaker itself to prevent the circuit continually drawing a small amount of power after tripping, which could over discharge the batteries after a LVC condition. Or am I over thinking this?
 

Danner

New Member
Joined
Sep 27, 2019
Messages
18
Doug, typo on my part, you're thinking in the right direction. The 12 volts from the BMS is continuously powering a 12v relay,
I have a separate 24 volt power supply that runs to the normally closed portion of the relay. The BMS would have to be manually reset in order to reset the relay.
 

Doug

Solar Enthusiast
Joined
Apr 14, 2020
Messages
21
Location
Australia
Doug, typo on my part, you're thinking in the right direction. The 12 volts from the BMS is continuously powering a 12v relay,
I have a separate 24 volt power supply that runs to the normally closed portion of the relay. The BMS would have to be manually reset in order to reset the relay.
Thanks Danner for explaining. This makes more sense now.
 
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