building a 12V compressor....

[freeagent]

i've got an air con pump, from a discovery tdi.... and intended to fit it to my new disco to run on board air...

..then i bought a discovery with air-con and that idea went out of the window....

so ive been thinking... is it possible to rig it up, on a mounting plate next to a suitable 12v motor, running a simple belt drive, and treat it as an electric compressor... i know onboardair.com sell a york compressor powered by a winch motor but its £600 and a bit rich for me...

i've got a compressor with clutch, tank, pressure switch and kind of know how to wire it all up/ plumb it in as i know a little about compressors... but i dont know what sort of electric motor i need...

does the compressor when used as an aircon pump spin at engine revs? if so do i need a motor to run at around 2500 rpm?

i dont know a lot about motors, but think a small winch motor, with solenoid control might work...

anyone thought about this..? it could be good as it would be pretty light, and could be swapped between vehicles if it was wired through those large plugs used to charge forklifts....

m@tt.

[LandyManLuke]

why not mount the compressor with the original air con compressor?

just like in the archive here

Luke

[RPR]

Wouldn't a nitrogen or CO2 tank and a pub regulator be cheap and effective? If you really want to build something, I can understand. But nothing is easier than a tank....

[FridgeFreezer]

What about a starter motor? I'd imagine it'll take quite a bit of power to turn it when it's up to pressure, the current will be big so the wiring and mounting would need to be pretty good. And the efficiency of a setup like that is rubbish - burn fuel to turn engine to spin alt to charge battery to power motor to turn pump to compress air

My vote would be to stick a double-pulley somewhere and get inventive with the mounting brackets.

[simonr]

AC pumps take a fair bit of torque to run, particularly as the pressure increases. They will draw up to 10bhp from an engine - so it's a tall order for an electric motor.

However, A winch motor is almost ideal - and is in the reaches of that kind of power & torque. They are expensive however.

Next best thing is indeed a starter motor. Most are between 2 and 4 Hp - and certainly deliver some torque! I think it's worth a go, just watch the motor temperature if you are running it for a long time.

Go for as big a starter as you can, preferably one from a diesel (higher torque).

You will wind up with a compressor which will p155 on just about any 12v electric air compressor you can buy. Certainly worth the cost of an old starter and an afternoons work!

Si

[freeagent]

thanks Si, kind of what i had in mind.

the pub tank or dive tank is fine for challenge events but not easy to recharge on expeditions.

i know the efficiency will not be brill, but i don't want to 'hard mount' it to one vehicle as i regularly use two different Landrovers, and would like to run it in both.

just need to draw something up and get on with it.

i've never realy looked at a starter motor before... is the 'casting' easy to remove at the top of it?

[rtbarton]

The casting contains the mechanism for engaging the starter into the flywheel. I'd be inclined to use an earlier type with an inertial pinion and somehow fix the pinion so it doesn't slide along the sleeve.

I believe one of the national recovery firms used home-made winches using starter motors and the original flywheel bolted to a drum.

[simonr]

It is true that it is not particularly easy to interface to a starter motor - but can be done.

The 'hood' which covers half the cog usually contains a bearing, so you might have to do a little re-arranging of things. Alternatively, make a small pulley to go on the same shaft. A starter will run plenty fast enough to get a decent flow rate with the tinyest pulley driving it.

If you have a lathe, it would not be hard to make a new bearing carrier and just have a drive shaft sticking out. Replace the solenoid with a contactor - as it is this that moves the sprocket forward to engage with the flywheel.

One of the issues with older starters is most are permanent magnet type motors rather than series wound. These run slower and produce less torque than a typical series wound motor.

Si

[freeagent]

thanks Si, i don't have access to a lathe, but do have a place local to us that makes and supplies pulleys in any size and style you can think of for sensible prices.

i'm thinking a winch motor might be easier, as its just about 'plug and play' but more expensive.

i did think the starter motor idea might be too good to be true... especially as they can be found at the breakers for about £20.....

if anyone has a suitable motor, and/or solenoid pack, i'm interested.

i thought if i can do this for sensible money then its worth a couple of sundays, if not then i might just forget it, and treat the aircon pump as a spare......

m@tt.

[rtbarton]

It is true that it is not particularly easy to interface to a starter motor - but can be done.

The 'hood' which covers half the cog usually contains a bearing, so you might have to do a little re-arranging of things. Alternatively, make a small pulley to go on the same shaft. A starter will run plenty fast enough to get a decent flow rate with the tinyest pulley driving it.

If you have a lathe, it would not be hard to make a new bearing carrier and just have a drive shaft sticking out. Replace the solenoid with a contactor - as it is this that moves the sprocket forward to engage with the flywheel.

One of the issues with older starters is most are permanent magnet type motors rather than series wound. These run slower and produce less torque than a typical series wound motor.

Si

I have never seen a starter with a permanent magnet, and I'm going back to 1946! All the mainstream Lucas ones I've seen have a field coil, pre-engaged or inertia type.

I would be inclined to use an inertia type as it is easier to get to the shaft, as all you have is a shaft sticking out of the end

I agree a starter solenoid (like on the Series petrol engines) may not be suitable for continuous duty, use a winch solenoid.

[simonr]

I have never seen a starter with a permanent magnet, and I'm going back to 1946! All the mainstream Lucas ones I've seen have a field coil, pre-engaged or inertia type.

I would be inclined to use an inertia type as it is easier to get to the shaft, as all you have is a shaft sticking out of the end

I agree a starter solenoid (like on the Series petrol engines) may not be suitable for continuous duty, use a winch solenoid.

Never really looked at a LR Inertia type, but seen several PM non LR ones (in a past life)

Si

[darthdicky]

Matt, my brother (Jon W) managed to break the casing on a fairly new starter motor - I think the only bit that broke was the half-cap type bit over the shaft but I didn't have a proper look. Don't think its fixable for our use but might be ideal for what you want? PM him and ask.

Richard

[rtbarton]

Never really looked at a LR Inertia type, but seen several PM non LR ones (in a past life)

Si

Mmmmmmmm Interesting - they'd make a good dynamo for welding ???!!!

[simonr]

For all the nay-sayers (Nick!):

Works pretty well considering how gash it is. Motor is an Iskra 800w 12v item from Ellis Components. It's a Perm Magnet type, but seems to be plenty up to the job.

Develops sufficient torque to get the compressor up to about 300psi (at which point the pneumatic push fitting burst with a 'slight' pop!)

I would say, without a shadow of doubt that pretty much any starter motor will run the thing. It's hard to find a starter motor with less power or torque than this motor.

Si

[SOA 93]

For all the nay-sayers (Nick!):

Works pretty well considering how gash it is. Motor is an Iskra 800w 12v item from Ellis Components. It's a Perm Magnet type, but seems to be plenty up to the job.

Develops sufficient torque to get the compressor up to about 300psi (at which point the pneumatic push fitting burst with a 'slight' pop!)

I would say, without a shadow of doubt that pretty much any starter motor will run the thing. It's hard to find a starter motor with less power or torque than this motor.

Si

Si, I read somewhere, that you were looking at making a conversion kit or something for "On Board Air" using a Sanden compressor, is this true? If it is then I can add it to the list of your gear that is going to go on my disco . Looking at that picture I can see what I think is a grease nipple, any more info, Please .

[simonr]

Si, I read somewhere, that you were looking at making a conversion kit or something for "On Board Air" using a Sanden compressor, is this true? If it is then I can add it to the list of your gear that is going to go on my disco . Looking at that picture I can see what I think is a grease nipple, any more info, Please .

Tis True! However, it is proving difficult to find fittings, filters etc at a sensible price which are not fit for the bin! I've bought lots of stuff from companies all over the world - and most of it is just such poor quality I would not put my name to it!

Most of the kit is sorted, but there are just a few important bits to sort out. Unlikely to happen before Billing now sadly.

It is a grease nipple on top by the way! When I went EFI, I had to remove the compressor. Driving it electrically seems a reasonable alternative until I come up with something more cunning (dimensionally transindental engine bay for example! )

Si