Air compressor modifications and a discovery

With the borrowed gas torch still in my possession it seemed like a good idea to complete some planned modifications to the 12 volt air compressor.  It came with a 12V power lead that had spring loaded battery clips on the end.  I want to be able to connect the air compressor to the vehicle at the rear where I have fitted a 175A Anderson Plug that will supply power to the trailer battery.  Doing this will mean the compressor air hose will reach 4x4 and trailer tyres.  It also means I won’t have to raise the bonnet to connect to the starter battery.

So I cut off the battery clips and fitted a 50A Anderson plug instead.  However the Anderson Plug at the rear of the 4x4 is 175A which is bigger.  So I made an adapter lead.  I didn’t want the throw away the battery clips and connected another 50A Anderson Plug to that end.  The end result looks like this…

A – Adapter lead with battery clips

B – Anderson Plug on the air compressor

C – 175A to 50A adapter lead

Everything appeared to have gone well until I decided to test the setup by connecting the air compressor to the rear plug using the adapter lead [C].  The compressor would run for 5 second and stop… wait 10 second and run for another 5 seconds.  Then it permanently stopped.  After some fault finding I discovered the 100 Amp circuit breaker located by the started battery which protects the cable running to the back of the 4x4 was tripping out.  It has a ‘self reset’ function but was obviously overheating.  This is rather annoying as the vehicle alternator is only rated at 70 Amps and the air compressor doesn’t draw nearly that amount of current.  This means the cheap Chinese 100A circuit breaker is useless.  To confirm my conclusion I used the other adapter lead and connected the air compressor directly to the starter battery where it ran without any issue.  I’ve now ordered a different circuit breaker.  It’s probably better to discover this problem now rather than being somewhere out in the desert.