250A BMS with low-temp charging cutoff?

[John Frum]

@smoothJoey How do i size SSR or is DC60S3 SSR enough? Thinking for my 12kw inverter 48v battery (12000 watts /.85 conversion factor / 48v low cutoff = 294 dc amps). Buying a 500a bms costs over $300 but using SSR gives me huge savings.

This is the datasheet for a similar part

https://www.sensata.com/sites/default/files/a/sensata-dc60%20series-panel%20mount%20relay-datasheet.pdf

It can only handle system side voltage of 3.5-32 volts direct current.
You need one that can handle up to 60 volts on pins 3 and 4.

Please provide a product link to your inverter so we know what we are dealing with.
You mention its a 12000 watt inverter at 48 volts.
I'm guessing its a Growatt all-in-one but would need to confirm.
Also since you mention the service amps are ~294 I wonder if you understand that the solid state relay will not be in the high current path.
Also you need some pretty stout battery to handle ~294 amps service current even if you do bypass the bms.

 

[alvirtuoso]

This is the datasheet for a similar part

https://www.sensata.com/sites/default/files/a/sensata-dc60%20series-panel%20mount%20relay-datasheet.pdf

It can only handle system side voltage of 3.5-32 volts direct current.
You need one that can handle up to 60 volts on pins 3 and 4.

Please provide a product link to your inverter so we know what we are dealing with.
You mention its a 12000 watt inverter at 48 volts.
I'm guessing its a Growatt all-in-one but would need to confirm.
Also since you mention the service amps are ~294 I wonder if you understand that the solid state relay will not be in the high current path.
Also you need some pretty stout battery to handle ~294 amps service current even if you do bypass the bms.

Yes, it's Growatt. I'll have 32 of 304ah Catl LiFEPo connected in parallel first then 1 series. With my limited knowledge, I gathered that SSR bypasses bms to my battery negative instead of BMS P- will go straight to inverter.

Growatt 250V Dual PV Input – 48V 12000T MPV 12kW Split Phase 120V/240V output (100A at 120V ,50A at 240V) – here in Dec – Watts247.com

watts247.com

 

[John Frum]

Yes, it's Growatt. I'll have 32 of 304ah Catl LiFEPo connected in parallel first then 1 series. With my limited knowledge, I gathered that SSR bypasses bms to my battery negative instead of BMS P- will go straight to inverter.

Correct.

I can't tell by the product link if the Growatt has the correct type of power switch to be controlled by an ssr.
Does it have a simple switch?
Maybe it has provision for external switching, confirm?

 

[John Frum]

I have concerns about this setup.
Because the unit is an all_in_one you may have a lot of scenarios where you end up dead in the water because disconnecting the discharge path also means you disconnect the charge path.
If it were me I would really need to test things to determine how these units really work to see if this setup is viable.
Do you have any other charge sources?

 

[alvirtuoso]

Correct.

I can't tell by the product link if the Growatt has the correct type of power switch to be controlled by an ssr.
Does it have a simple switch?
Maybe it has provision for external switching, confirm?

The Growatt 12K has a remote port, which i figured makes it easier to connect SSR. I've attached pic

 

[John Frum]

The Growatt 12K has a remote port, which i figured makes it easier to connect SSR. I've attached pic

Before I bought an ssr I would bodge together a simple control mechanism using an rj-x and a simple switch.
Or reverse engineer the remote control if you have it.

 

[alvirtuoso]

I have concerns about this setup.
Because the unit is an all_in_one you may have a lot of scenarios where you end up dead in the water because disconnecting the discharge path also means you disconnect the charge path.
If it were me I would really need to test things to determine how these units really work to see if this setup is viable.
Do you have any other charge sources?

No I do not have any other charge sources.
My alternative plan, if SSR is not viable, is to use 2 of my 200a BMS(with built-in relay) on 2P 2S 48v cells. In that way, i don't have to buy a single 500a bms(expensive) for 1 series battery bank. With SSR, i thought that i could lower the high amperage bms.

 

[John Frum]

No I do not have any other charge sources.
My alternative plan, if SSR is not viable, is to use 2 of my 200a BMS(with built-in relay) on 2P 2S 48v cells. In that way, i don't have to buy a single 500a bms(expensive) for 1 series battery bank. With SSR, i thought that i could lower the high amperage bms.

Understood.
I still think you should test with a rj jack and a simple switch.
I'm a fan of incremental development.

 

[alvirtuoso]

Before I bought an ssr I would bodge together a simple control mechanism using an rj-x and a simple switch.
Or reverse engineer the remote control if you have it.

Understood.
I still think you should test with a rj jack and a simple switch.
I'm a fan of incremental development.

That's a wonderful idea. I'll try that first

 

[John Frum]

test 001
See if you can disable discharge via remote port

test 002
see if you can disable charge via remote port

Then when you get the ssr

Test 101
See if the ssr will command the remote port to disable discharge

test 102
see if the ssr will command the remote port to disable charge