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Author Topic: Magnetic Clutch???  (Read 6319 times)

evilpsych

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Magnetic Clutch???
« on: January 05, 2007, 03:03:45 PM »
Has anyone toyed around with the idea of using a magnetic clutch (such as is used on automotive A/C compressors to engage the connection between generator and your flywheel? I was working on my jeep york-powered 10cfm onboard air-compressor system yesterday, and it hit me. If your lister was to be used for more than just power generation, i.e. pumping water, or driving something else, like a seed press.. it would seem to be simple to have two clutches, one for each device, and as you needed extra electricty as your battery banks died down, a simple relay would kick in, disengaging the mechanical device you were running, and engaging the gen-head. All with a minimum of work necessary to do so.

I'm not sure just how powerful the clutch would have to be in one of these situations, but they're just simple electro-magnets and the concept has been used for years in other technologies..

What say you?

rcavictim

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Re: Magnetic Clutch???
« Reply #1 on: January 05, 2007, 04:00:34 PM »
Sounds worth exploring to me!  A big auto aircon compressor is capable of about 3 ton I think.  That would easily carry the power of a 6/1 to a 3 kW gen head, certainly so I think if the head is a 2 pole 3600 RPM unit where torque would be lower than on a 4 pole 1800 RPM head.

No innocent numbers were crunched in coming up with my above statement, just gut feeling.
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evilpsych

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Re: Magnetic Clutch???
« Reply #2 on: January 05, 2007, 04:12:29 PM »
yeah! i just realized that you could have an induction motor running co-gen, and when the power- fails, and your cutout system engages, automatically trip the clutches to transfer to your ST generator! Add some UPS equipment to any sensitive equipment and you'd have virtually zero downtime!

Guy_Incognito

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Re: Magnetic Clutch???
« Reply #3 on: January 05, 2007, 09:16:42 PM »
Was looking at doing this , but in reverse for a starter motor.

It's quite do-able - small A/C compressors pull about 3kW at approx 3000rpm. And lets not forget the shock load when they engage. Might be a bit of a concern with the inertia of a generator though - I'd probably recommend a york compressor (the 2 cylinder version) clutch, they're pretty solid.

You can get new automotive clutches fairly cheap, and your local auto electrician / auto AC guy will have a pile of dead compressors about 3 foot high that you can snitch a clutch from.

Things to note:

- You need to do a bit of machining. The idler pulley normally runs on something like a 1.5" or 2" dia cylinder that is part of the front of the compressor, so you need to whip up one of those to suit your clutch and to sit on the front of the thing that you're driving.

- The coil sits underneath the idler. Best way would be to weld that cylinder above to a small plate then fix the coil to plate.

- Maybe you should just hacksaw off the front half of a compressor, it might be easier.  ;)

- The clutch plate is splined to the compressor shaft it's normally 10mm or so for small compressors. It's shimmed in and out at that point to get the proper clutch clearance (that is, minimal). You'll need to adapt that spline to drive whatever it is you want to drive.

- They've all got to have the same centres with a fairly close tolerance - idler/clutch/coil are all pretty tightly packed. There's a bit of give in the clutch plate , but too far off-centre and you'll scuff the friction plates.

- Make sure the switching voltage is either on or off via a relay. No gradual ramp up/down - that slips the clutch and burns it out. Ditto for DC fans on the same circuit (eg condensor fans) - as they spin down, their back emf makes the clutch disengage too slowly and burns it out pretty quick.


evilpsych

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Re: Magnetic Clutch???
« Reply #4 on: January 05, 2007, 09:37:41 PM »
ditto on the york, I've built many OBA systems with them.. you can find them in 1980's volvo station wagons (those come with v-belt pulleys tho) at pick-a-part places for around $25-$40 depending.... or.. you can get brand new clutches with serpentine belt configuration from http://kilbyenterprises.com/compressors.htm (no, i don't work for him, but i have met him and gone 4x4ing with him. Nice guy.)

It wouldn't surprise me if there was a larger A/C clutch available from a diesel-reefer trailer that might hold stronger.. also perhaps you can run more voltage through them (it's just an electromagnet folks!) to get more power.

On the drive-shaft, perhaps you could get a custom-machined adapter to mate the larger generator shaft to a smaller shaft that would direct-fit the existing clutch that you found.. This would make replacing the clutch easier if you burnt one out. (although it's not the grabbing action that wears these out, it's the initial startup-friction)

theboss

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Re: Magnetic Clutch???
« Reply #5 on: May 14, 2007, 10:55:19 PM »
there are heavy duty magneticl clutches available ready made. 24-48VDC

for even heavy duty use..look at some hydraulic ones pressurized by air or oil.

Ironworks

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Re: Magnetic Clutch???
« Reply #6 on: May 14, 2007, 11:13:00 PM »
I was thinking about using an Ogura electric PTO clutch off a riding lawn mower.

mobile_bob

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Re: Magnetic Clutch???
« Reply #7 on: May 15, 2007, 12:25:14 AM »
the york/tecuseh style clutches are built to handle between 60 and 75 ft/lbs of torque which is a butt load of torque
for such a small package, the inertia of an st head might cause some grief, but i don't know for sure.

i do know they will handle the power requirement of a 10 cu/in york driving r22, which will net 60k btu without a problem

the york and tecuseh compressors i am familiar with all have a tapered shaft, 1 in 10 or 12 inches,, i cannot remember for sure.

it might be an interesting experiment to mate one to an st head, they do a heck of a job coming on against head pressure on an ac compressor

might be better suited to a 3600 rpm unit such as the harbor freight units, as far as inertia goes.

bob g
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kltrider

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Re: Magnetic Clutch???
« Reply #8 on: May 15, 2007, 07:07:21 PM »
Hey troops:
Here's a thought for you all to ponder; I own a Kubota 3100E tractor.  3 cylinder, 22 HP. It has a magnetic clutch on the front of the crankshaft used to drive a belly mounted 48 inch rough cut mower. This has 3 18 inch blades, and will stall the engine if there is too much power demanded. I have engaged it at full throttle and stalled also. This will easilly handle a 5KW or even, probably 10KW, genny. My B6000E Kubby also has a clutch like this, same P/N, and drives a 4000 watt DC genny I used to start the dragster. It would really load the tractor engine, but that one was a small 2 cylinder. I used the generator along with the battery pack, because sometimes I needed to motor the J79 for a short time to cool after a hot start, and this would deplete the batteries below the level I wanted. 
Yes, I think this would connect either a genny, or a starter.
Just my 3.7 cents, Wayne

rbodell

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Re: Magnetic Clutch???
« Reply #9 on: May 15, 2007, 08:00:07 PM »
If you care around the ocean, try checking with some marine mechanics that work on big boats like shrinp boats and comercial fishing boats.. They use those magnetic clutches on large boats for deck hose and fire pumps.