low voltage cutoff switch

I am trying to protect my 12 volt air compressor from low voltage damage. I was told that using the compressor without the engine running is bad for the unit because voltage drops below 12 volts after a few min. of turning off the engine. The viair compressor company tech dept. told me this, but I figured that only a couple min wouldn't matter....I found they were right because after running the compressor about 4 different times for about 5 to 10 min. without engine running, the unit is now broken!!!!It will not build up pressure, only blows a tiny bit of air out of it... SOOOOOO, I need to find a low voltage cutoff/turnoff switch that turns the compressor power relay off when the battery gets down below 12V. I am hoping this way I can use the unit for a couple of min. after turning off the engine until the voltage drops below 12V.

Thanks for any help with this matter 'cause I am sending the compressor back to the company after 11 months for the one year replacement warranty....(I am not telling viair corp. that I let the unit run without the engine running sooo shussssss!)

I assume this 12 volt system is from an automobile?
I don't see how it could be damaged from such mild under voltage as it's likely just a DC motor and a compression chamber.

No matter. What you could do it setup an Op Amp as a comparator and have it operate a relay.

Schematic from previous thread You will have to tweak R8 a bit to get 12V...

wow!!!

thanks mikeMI:
i didn't imagine this would be such a contraption!! I will have to study up on this stuff 'cause I am looking@ schamatic andt I don't completely understand this setup..YET...! I will try to make sense out of it as a novice electrical person... I have some knowledge but am always learning...
Any help on making this more understandable would be great.