Adjustable 12v Pressure switch

Something like this?

Pressure switch

Graeme,

Suggest in the interests of safety, leave the existing pressure switch in place. This will allow you access to the present 120-150 PSI supply too which might be useful for air tools.

Drawing from that 120-150 PSI point I'd add a second pressure switch such as this one . It's a 30-50 PSI switch on Ebay, so that link probably won't work for ever. It's intended for mains voltages but could be used to control a high current relay to switch the 12V supply.

One problem you might face is that any pressure switch will have significant hysteresis, meaning that if it turns off at say 150 PSI, it won't come back on again until the pressure has dropped to 120 PSI. Likewise off at 50 and back on again at 30. You may need a bit of storage capacity to smooth out the supply/demand cycle too.

Cheers

John

a couple ofvthings to think about.

Do you have a reciever or tank in your air system?....this makes any air system more efficient and makes working with a regulator more effecive.

Reducing the air pressure to 40 psi will make tyre inflation very very slow....to achieve air transfer you need a considerably higher source pressure than you wish to inflate to for it to happen with any sort of speed.

Any presseure switch you plan to use should use a realy to do the heavy 12 volt switching which will be in the area of 30 to 60 amps.
That means just about any pressure switch will do the job, if used with an appropriatly rated relay.

Yes there is the issue of hysteresis....all pressure switches will have a significant difference between when they cut in and out..this is unavoidable and in fact desirable, because it stops the switch from hunting and making too many stops and starts.

Most adjustable pressure switches will have either upper and lower limit adjustments or a pressure adjustment and a window or hysterisis adjustment..

personally I'd be adding a tank and a regulator.

This will reduce the number of compressor starts and stops increasing the life of both the compressor and the pressure switch, giving a smpoother air flow and the ability to have a small amount of air stored when the engine is stopped and compressor is not running.

The tank will also drop a lot of moisture and oil out of the air a filter reg will help here too.

The regulator will give you accurately regulated air pressure where a pressure switch will not.

cheers

I had an application that required pumping up to only 5psi (airbag suspension) which was very difficult to do with a compressor (too powerful) or a footpump.

So I bought that automatic inflator gadget that Ryobi sells at the big hardware stores.
The gadget's compressor is just a toy so I discarded that - I was after the electronics.
I rigged the gadget's pressure sensor into an air manifold to my compressor with a shutoff solenoid.
All I need to do now is connect the airhose to whatever needs pumping up - or deflating - and dial up the required pressure. Hitting the on switch does the job for me automatically now, the compressor stops when the selected pressure is reached.

Its a bit of a tinkerer's job but works fine for me, I was wondering why ARB or any other aftermarket gear company haven't come up with something similar yet. It sure makes it easier to change the tyre pressure for different terrains, one can enjoy that cuppa without having to watch a pressure dial like a hawk.
V8Troopie