Manual low voltage cutoff solution 48v

[Sterling9250]

I have a 4 kw solar system running a SAJ solar inverter with two, 100 ah 48 v lifepo4 batteries. Sparing you all my complaints about SAJ inverters (they are terrible), the inverter low voltage shut off doesn’t work. I have it set to 42volts currently. When i gets close to 42 volts the inverter shuts off (mostly), and the inverter knows it shuts off, but there’s a constant drain of 0.3 to 0.5 amps after the low voltage shutoff. The drain continues until my batteries are so low that my battery BMS kills the connection. SAJ support is horrific.

Is there a manual solution I can put in place, such as installing my own low-voltage disconnect module? I found one from Victron called the BatteryProtect but it says not to install it between the battery and the inverter, which is exactly where I would want one to go.

 

[Rocketman]

Two step- use the Victron Smart Battery Protect (Smart so you can control it with your phone) then this drives a contactor Tyco EV200AANA that is in the positive leg of the inverter.

Actually that relay is a 9-36v one - they have a 48v one - Battery Hookup is selling them used $15 - so it may be cheaper/easier to drop the voltage from 48v to 12v to run the contactor.

My BMS uses that contactor for its critical shutoff. (Except I paid new price).

The am sure there are other ways of handling it too.

 

[hwy17]

Are the batteries 16S or 15S?

42v is a very low cutoff. If you set it at more like 45v or 48v you would have more reserve capacity to avoid it going into shutdown.

Also, running into the low voltage cutoff shouldn't be a regular occurrence in the first place, so it would be best addressed by avoiding that. Decreasing loads, or increasing battery, or increasing solar, as appropriate.

 

[Sterling9250]

Are the batteries 16S or 15S?

42v is a very low cutoff. If you set it at more like 45v or 48v you would have more reserve capacity to avoid it going into shutdown.

Also, running into the low voltage cutoff shouldn't be a regular occurrence in the first place, so it would be best addressed by avoiding that. Decreasing loads, or increasing battery, or increasing solar, as appropriate.

Agree, but 42v is the highest I can do with this piece of junk inverter. They literally won’t let me go any higher than 42 V.

 

[hwy17]

Agree, but 42v is the highest I can do with this piece of junk inverter. They literally won’t let me go any higher than 42 V.

Oof. Ok yeah that sucks.