Not really "Engine Tech", but it runs off of an engine accessory. The system can be build at around $150.

if you are into that that's awesome. i'm building a portable type 2.5 hp briggs with the york compressor going into two one gallon tanks and a 250 amp alternator for welding. still need a pig tail to hook up to the truck but you can put it into multiple rigs and loan it out .

It can be done a lot cheeper. I had about $75 into mine