using an Air conditioning magnetic clutch

[madderscience]

Random technical musings
(oddly enough)

has anybody tried using an air conditioning compressor magnetic clutch as a way to implement some sort of belt driven accesory but in such a way that the accessory only runs when necessary and not at all (including the belt) when not engaged to avoid any parasitic drag?  This would require putting the clutch on the motor tailshaft and running it "backwards" so that the normally driven member would become the driving member.   

It's theoretically possible of course but I am wondering about things like how much horsepower one of these things can transmit and what kind of starting loads it can handle, since this thing could well engage when the motor is doing several thousand RPM.

Ideas for things to drive would be an automotive alternator for small amounts of regen (only makes sense on a series DC car of course) or a mechanical vacuum pump that only engages when you are on the brakes anyway and other intermittent loads that could only be engaged when you are slowing down anyway to take advantage of inertia that you would otherwise be throwing away as brake heat.

[leitmotif]

Mag clutches are used for all kinds of things.  Just make sure that you always have power in on the power in side of it and same for power out side.  Automotive air conditioning is often a hard starting load like many compressors so it should have a good starting torque.  My guess for HP rating is around 3 maybe 5 - course those may be Detroit HP so divide by 5.

The problem with adapting automotive stuff is it is so customized to that application that it may be difficult to fit up to anything else.

Bolt your desired load to a piece of 2 x 6 mount the clutch however you want and drive with a motor with suitable RPM and HP.  Then you will know.  The other option is to buy one thru Grainger.

Dan Bentler

[madderscience]

grainger is a good thought, thanks.  I might even be able to find specifications on one from there.

I have one off of a new VW beetle and mechanically it looks like a relatively easy mod to make it fit the tailshaft of and advanced DC as I described on my original post, but it would require driving it "backwards" as in driving it off of the driven end and taking load off the driving end.  I could run it the other way too but then I get bearing friction though it would be very minimal.  Nothing but windage the way I was thinking about it.

THanks for the idea, I'll check out grainger.

[leitmotif]

Grainger is a really handy book.  They have sections on how stuff works that cover the basics.  The other good thing it is for is to get an idea of what cost is for equipment.

 You may be able to drive backward for all I know - if you only have $5 into it what the heck try it out.  I believe the driving sheave will require a bearing because it always turns.  the driven end may get its "bearing" from whatever VW meant it to drive.

You are in So Park right??  I would have to see clutch before I mouth off further.

Dan Bentler

[StorminN]

You guys in Seattle also have the luxury of stopping by Pacific Industrial Supply on 4th Ave S and seeing what they have there. I'm pretty sure they will have something that would work, those clutches are commonplace (in all sorts of sizes) on the belt-driven hydraulic pumps and other accessories that a driven off of ship's diesels.

-Norm.

[madderscience]

Yep, I'm in SP.

The way I would like to install it is to build a sleeve that supports the outer pully (part that would have always turned when installed on ICE, and which has a big idler bearing already in it) that goes over the tailshaft.  The inner "driven" member originally hooked directly to the A/C compressor shaft would now be attached to the tailshaft of the motor.  With this setup the driving/driven roles would be reversed from the original usage, but the upside is zero additional friction when disengaged, unless you want to count miniscule wind drag and inertia on the driving member.

Only issue with this is the clutch I have seems to be designed to run CCW under load and my motor will drive it the opposite way which would probably make it chatter like crazy when engaging.    This is total theory of course I've only poked at it on the bench.

I should probaby try to get one off of a honda as their engines turn the other way.

This is all theoretical at this point I'd have to play around with the setup before I decided if it was reliable enough to justify the additional weight of the clutch and whatever it runs.   Also, the electro magnet wants 50W of power when engaged so whatever I do needs to justify that as well.   However, if an A/C clutch can transmit several HP of power then maybe mild regen with a rewound 100A car alternator would work.  You'd probably want to find a way to ramp it up after engaging it to avoid a jolt to the belts and clutch when first engaged.

[leitmotif]

Coupling the clutch driven end to the driver may work IF you can ensure proper lineup ie shafts are parallel to within 2 to 3 thou.

Some clutches will care about rotation others (mag friction) often do not.
Yes it would be nice to have the prints and all for the clutch design but that may be difficult.  I get the idea this is out of the junk box so try it out and see what happens.  If you destroy it you have still gained cause now you know what does not work.

Dan

[Dink]

If the clutch spins freely in both directions without being engaged, your good to go. Sprags, can be drive and direction sensitive.