I'm bench testing a new replacement AC clutch coil before installing it in a van. The coil was placed on a large iron girder and when power (12V) was applied the coil magnetized and after a minute or so was very hot to touch although the 14 gauge test wires were not hot. Is this normal?
Thanks

 

When in use does it have a continuous 12V across it?
It may (I have no idea) get 12V to pull it in, then something less than 12V to hold it in.

 

Typically they are continuous duty rated at 12 - 15 VDC input and exhibit a ~ 2 - 4 amp draw depending on their physical size.
Given the mechanical loads those clutches have to carry I do not know of any that lower their power once engaged simply due to the inherent risk of clutch plate slippage. Their magnetic field strength is all that's keeping the plates held together under load.

If yours is running hot after a minute it's more than likely it has something wrong with it like a partial short between windings.

 

I'm bench testing a new replacement AC clutch coil

The last time I looked a clutch coil needs about 3 amps, which is 36 watts, and a piece that size should be able to radiate 36 watts without melting. Check the amps. If they are reasonable looking, hook it up and let it ride, just to see if it smokes. It's going to be a lot hotter under the hood, so give it a chance to betray itself.

 

Yes- 14V to 15V continuos (always from alternator) @ about 3.5A. I like the concept of letting the part "betray itself" but I don't want to do many hours of labour myself without the right (expensive) tools or pay a mechanic $500.
I suspect it is normal heating. I'm only talking very hot to touch- I can hold it if I jossle it around a little. I'm hoping someone has "hands on" experience with this.
I realize I need to measure the draw as the 3.5A is per a service manual. I can also just plug it into power without installing it proper. I'll stick it on a vertical surface driving where it can hit the road if it betrays me.

 

I don't want to do many hours of labour

Maybe I assumed too much. Us nerds have power supplies laying around to just connect the clutch, go about our business, and check it later. I think you could find a battery or a battery and a battery charger, put all this outside where it can't hurt anything if it catches on fire, and come back after lunch to see if the current is stable and the clutch is unharmed...in spite of the fact that they normally run hot.

I have felt some very hot clutches, but I assumed they were hot because of the under hood temperatures and their connection to a compressor that can possibly use 5 HP to do its job. Five is a lot of HP to convert to heat in something the size of a compressor. Maybe I was fooled.

 

Keep in mind that a compressor clutch is not continuosly running, but cycling all the time depending on pressure and ambient temperature. It also has air cooling itmconstantly . I would say if it is a brand new clutch and it is war, to the touch, it is fine. Install it and be done and dont forget the air gap.

 

Thanks for your comments. With engine running and jumper wires I tested it next to the vehicle so I had full alternator voltage instead of just 12V and also this allowed a test of the remainder of the actual circuit that will be used.
It will cycle on and off but with the extra engine & compressor heat air cooling won't cool it down more than my orig. bench test. It was more than warm- like a very hot coffee cup you couldn't just hold without shifting around.
I agree I could just put it in but as I said that will be tuff or even impossible for me without the proper tools. A shop that said they would install the clutch kit yesterday for $215 booted the price up to $500 when they popped my hood open and said "but you have plumbing in the way". So this question really ends up relating to money- coil supposed to be hot it goes in, just supposed to be warm a return it to EBay and get another. I have 1 shorted coil and with the tiny varnished windings want to avoid a 2nd.
Thanks again

 

Not sure what type of compressor or car you have, but many clutch coils fit over a iron 'spigot' on the pulley. without that iron in the center of the coil it may cause the coil to over heat. Like when a transformer bobbin is activated without the lamination's inside of it. Or a solenoid coil activated with no plunger in it, will over heat. Just putting it on a beam isn't enough, it needs the iron inside of the coil.

 

Not sure what type of compressor or car you have, but many clutch coils fit over a iron 'spigot' on the pulley. without that iron in the center of the coil it may cause the coil to over heat. Like when a transformer bobbin is activated without the lamination's inside of it. Or a solenoid coil activated with no plunger in it, will over heat. Just putting it on a beam isn't enough, it needs the iron inside of the coil.

Except that it's a DC coil so the current depends only on the coil resistance. The core will make no difference to that.

 

The last 2 posts put it together for me. Yes, the core shaft will have all to do with the temp.. Research has indicated to me the "geometry and material" of the core has everything to do with maximizing magnetic force while limiting heat emmision.
The core may not have anything to do with the amount of current but it does have to do with what proportion of that electrical energy ends up as magnetic force or heat.
So yep- I just need to get it in.

Thanks

 

The core may not have anything to do with the amount of current but it does have to do with what proportion of that electrical energy ends up as magnetic force or heat.

The core may or may not help to conduct the heat away from the coil but it will not change the amount of heat produced at all.

 

The core may or may not help to conduct the heat away from the coil but it will not change the amount of heat produced at all.

I am in no position to and have no desire to dispute this at all. Below is are 2 samples of the info I looked at that gave me the impression the core might affect temperature;

1) Project with electromagnet produces way too much heat!!;

https://forum.allaboutcircuits.com/...es-way-too-much-heat-help-please.83951/page-1
Quote (post 17);
""Ever apply power to a induction motor with the rotor out of it? The coils get hot real fast.""
--------------------------------------

2) The Electromagnet;

http://www.electronics-tutorials.ws/electromagnetism/electromagnets.html

Quote;
""...The magnetic field strength of the electromagnet also depends upon the type of core material being used as the main purpose of the core is to concentrate the magnetic flux in a well defined and predictable path. So far only air cored (hollow) coils have been considered but the introduction of other materials into the core (the centre of the coil) has a very large controlling effect on the strength of the magnetic field.""

 

Except that it's a DC coil so the current depends only on the coil resistance. The core will make no difference to that.

I disagree with this. I have burned out a starter solenoid by not having the plunger in it. I was attempting to use it as a powerful DC electromagnet. They are made like the clutch coil and are made to have a metal core in place.

 

without that iron in the center of the coil it may cause the coil to over heat. Like when a transformer bobbin is activated without the lamination's inside of it. Or a solenoid coil activated with no plunger in it, will over heat. Just putting it on a beam isn't enough, it needs the iron inside of the coil.

I am in no position to and have no desire to dispute this at all. Below is are 2 samples of the info I looked at that gave me the impression the core might affect temperature;

1) Project with electromagnet produces way too much heat!!;

https://forum.allaboutcircuits.com/...es-way-too-much-heat-help-please.83951/page-1
Quote (post 17);
""Ever apply power to a induction motor with the rotor out of it? The coils get hot real fast.""
--------------------------------------

2) The Electromagnet;

http://www.electronics-tutorials.ws/electromagnetism/electromagnets.html

Quote;
""...The magnetic field strength of the electromagnet also depends upon the type of core material being used as the main purpose of the core is to concentrate the magnetic flux in a well defined and predictable path. So far only air cored (hollow) coils have been considered but the introduction of other materials into the core (the centre of the coil) has a very large controlling effect on the strength of the magnetic field.""

That's for a AC powered coil/solenoid induction motor systems not a DC ones. AC inductor theory does not apply to DC electromagnets outside of when they first turn on or turn off and inductive impedance effects are in play. Beyond that they are just a wire wound resistor and how hot they get is determined by how much heat they can dissipate.

Which BTW if you feed a AC coil or solenoid or induction motor DC at the same amperage it draws when on AC it will not overheat either regardless of whether the core or rotor is in place or not. Total dissipated wattages will for the given input amperages be the same.
Only the input voltages will be different and the cores will at best only aid in cooling due to thermal conduction. Magnetic properties will be irrelevant.

 

Thanks for all responses to my original post. They gave me the confidence to "do the hard labor" (for me anyway) and install the clutch coil even though it got very hot when bench tested before installation. My AC has been working fine and I took away the following from this forum and others;

• The coil wire creates resistance and therefore heat is a byproduct and as wound that heat is concentrated and can't be as readily disapated when the coil is tested freestanding without the metallic clutch bearing attached and and air flow created by the quickly rotating pulley to help cool it. Also the duty cycle of the compressor will not allow the coil to be continuously energized again allowing it to cool off some.

• A metallic coil core as opposed to air core affects the configuration of the magnetic field only and not the heat produced in the coil. The metal core doesn't increase overall magnetism but concentrates it.

Finally I noticed with the engine running everything attached to the engine block was substantially hotter than the coil alone had been on my bench test so there was no doubt the coil could withstand a lot of heat.
Anyway even if I'm off a little in my conclusions above I've got AC in S. Fl. and will start saving money now to keep one of the world's greatest inventions running.