Vehicle aircon compressors - how much power do they take?

[Timleech]

I want to adapt a water pump to take an electric clutch. The commercially made clutch pumps are expensive, I've been wondering about putting an aircon clutch onto a pump that I already have. Secondhand aircon pumps are cheap enough, & judging by the size of polyvee belts that are commonly fitted the clutches ought to be man enough, but does anyone know a typical rating?

Thanks

Tim

[JoeBean]

Well, A/C pumps can quite commonly drain 5-10hp at peak, so the clutches have to handle that. And since you shouldn't have any torque spikes on a water pump I'd say any clutch should be fine. If you did have a situation where you could have sudden demands put on the clutch I'd look for one from an older fixed displacement compressor. The newer variable displacement compressors usually ramp up to full power, and so may not deal with spikes well.

That said, what are you trying to achieve? Might a better/more efficient solution be to use an electric pump, as is used nowadays in most autos, especially high-efficiency models?

[Black_Moons]

Well, A/C pumps can quite commonly drain 5-10hp at peak, so the clutches have to handle that.

Wow, Seriously? thats 3,700 to 7400 watts equivilent.. One hell of an air conditioner

Are car air conditioners SERIOUSLY inefficent due to the variable RPM they might be driven at or what?

I recall heating my truck very nicely with just a 1400W heater when it was -10c out, And I know most house AC units move more heat then used in wattage, So I can't see needing 4000W+ of 'cooling' for a car unless they are not recirculating any of the air...

[Timleech]

Well, A/C pumps can quite commonly drain 5-10hp at peak, so the clutches have to handle that. And since you shouldn't have any torque spikes on a water pump I'd say any clutch should be fine. If you did have a situation where you could have sudden demands put on the clutch I'd look for one from an older fixed displacement compressor. The newer variable displacement compressors usually ramp up to full power, and so may not deal with spikes well.

That said, what are you trying to achieve? Might a better/more efficient solution be to use an electric pump, as is used nowadays in most autos, especially high-efficiency models?

Something like this:-
http://www.jabscoshop.com/marine/pum...aded-ports.htm

I have the equivalent pump already, without the clutch.
I don't think the type of electric water pump used on vehicles would be any use, they're probably just a paddle pump designed to assist a closed cooling system.

Tim

[HSS]

I guess this is going to turn into an argument one way or another. When I went to technical school for A/C and refrigeration 40 years ago, I was told that automobile A/C compressors were rated at about 4 tons or 48000 btu's to compensate for the amount of glass in an auto and nearly no insulation.
What kind of head pressure do think you will encounter on your water pump? The clutch will handle a very large load. If you don't believe that, you have never had an auto A/C compressor lock up on you auto. The cluch doesn't slip, it just burns the belt up and that belt is usually wrapped 3/4 the way around the shieve.

[Black_Moons]

Btw, Have you considered not using a clutch on the pump input, But on its output instead? Ie, Just a big bypass valve that lets it pump back into its own inlet with no pressure?

Depends on how much efficency you need and how often it will be turned off....

PS: those 'flexable impeller' pumps tend to smoke themselfs if you ever let them run dry for any signifigant amount of time.

[Timleech]

Btw, Have you considered not using a clutch on the pump input, But on its output instead? Ie, Just a big bypass valve that lets it pump back into its own inlet with no pressure?

Depends on how much efficency you need and how often it will be turned off....

PS: those 'flexable impeller' pumps tend to smoke themselfs if you ever let them run dry for any signifigant amount of time.

It's intended as emergency backup for an existing 3-phase motor driven pump of the same basic (Jabsco) type, general service/bilge pump, might never be used in anger but we need something which isn't reliant on the 3-phase generator. It'll be belt driven from the compressor engine, which has its own 12V supply for starting. They do versions with mechanical clutches, but my experience of those tells me that the mechanical clutch is a weak point.
Yes I'm very well aware that these pumps don't like being run dry!

Tim

[Duffy]

Since you are considering automobile parts, have you thought about cooling fan clutches? I had a Pugeot, (admittedly a loooong time ago,) and it had a magnetic clutch on the fan. It had to be good for over one HP.
York compressors for larger cars were at least 1 1/2 tons, which translates roughly to 1 1/2 HP, and they sure were not "soft start!"

[Willy]

The generally accepted figure I have seen is like JoeBean said 5-10 HP. Depending on compressor design and of course compressor rpm, there will be some variance to this figure.
Also like HSS stated the clutches have enough torque capacity to burn a belt if the compressor stalls/locks up.

Although a simple and robust unit the keys to making them work properly is to have a good electrical circuit supplying the clutch, nothing unusual here, and to have minimum spec air gap when the clutch is disengaged.

[datsun280zxt]

Years ago my wife's car (89 olds with the quad 4 motor) had the compressor lock up. If the car was running and you switched on the a/c it would kill the engine and not even let it crank over. It was a serpentine belt setup and the belt would not slip. I tried cranking the engine over with a breaker bar and couldn't do it (before I realized it was the a/c locked up). They definitely have quite a bit of holding power! I wonder if a clutch off a semi truck would be stronger yet. They typically have an even greater output due to the size of the system to run the cab and sleeper compartments. Maybe the automotive clutch will suit your needs, but if you need a stronger clutch, that may be the way to go.

[bruto]

Since you are considering automobile parts, have you thought about cooling fan clutches? I had a Pugeot, (admittedly a loooong time ago,) and it had a magnetic clutch on the fan. It had to be good for over one HP.
York compressors for larger cars were at least 1 1/2 tons, which translates roughly to 1 1/2 HP, and they sure were not "soft start!"

I had one of those too (a 404) and if the clutch lasted you were lucky. They came with lockdown screws built in so that you would have a fan when it failed. Most fan clutches now are viscous with thermal switches. I'd stick with an automotive AC clutch, in part because they are easy to obtain and replace.

[tdkkart]

Electric clutches are very common on lawn tractors now, they're a bit spendy new, but if you can buy a whole tractor $1-200 you'll have the motor and clutch for your project.

[winchman]

I've used lots of modern automobile AC compressor clutches on my winches for launching RC sailplanes. Several of them were mated to starter motors used on large Chevrolet and Ford engines. I never had a problem with the clutches, and they were getting cycled many times under load during a launch.

[Timleech]

I've just bought a cheap used aircon compressor from ebay to experiment with, if the results are at all interesting I'll post them in due course.

Thanks

Tim