Help with battery cutoff

[krell313]

Hello all, I need some help with a diy lifepo4 24 volt battery bank. I am going to make a 2p8s 560 amp battery and I am trying to work out the protection circuits. The output of this bank will be fused at 200 amps which is more than I will ever use. Also this is an offgrid setup.

I am going to use an Orion Jr BMS because of it’s programmable outputs (and I have one in another build so I’m familiar with it). For over voltage cutoff I plan to use normally closed relays for the solar input to the charge controller and the same for the input to the AC charger.

The problem is in the low voltage cutoff circuit. I do not want a mechanical relay because it must be active all the time and if a low voltage event occurs, the relay will power down and not drain the bank further but it will on 99.999% of the time which seems like a waste. Also with the heating of the relay being on constantly, over time in may fail and not open and destroy my bank.

I would like to use a solid state relay to disconnect the bank and use a separate diode across that relay so the bank can accept a charge when the relay is open. All of these components must be rated at or above 200 amps.

I have looked around for a stand alone SSR like one that would be in a Daly or JK bms but I can’t find one. I could make one but then I would have to trust my design.

Any suggestions?

 

[BentleyJ]

You could use something like a Victron Battery Protect it has its own voltage monitoring circuit, you wouldn't need to use the Orion output to trigger a shut down. Since the device is unidirectional it would work well in your application. As far as a bypass diode you should be able to safely build one yourself and size the diodes for 200% of continuous current. Should be reliable enough.

 

[krell313]

As I recall, Victron did not want you to run inverters off of their battery protect devices and I need the Orion to trigger a generator and other things at different SOC points. I will recheck the Victron specs.

 

[BentleyJ]

Plan B you could use a magnetic latching contactor that doesn't have any standby current draw. That's what I have set up my DIY battery. This does require a simple custom control board to release the contactor if the signal is lost from the BMS. The down side of this is its an active system not passive.

 

[Suijkerbuijk]

As I recall, Victron did not want you to run inverters off of their battery protect devices and I need the Orion to trigger a generator and other things at different SOC points. I will recheck the Victron specs.

It have a relais switch that you can use to program.
This way you can do what you like to do with.

That relais is make the to switch Victron inverter on or off.
But if you stuff have a onboard switch than you can use that