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Total beginner... so I don't know if what I want to do is easy or hard!

Nafnlaus

Sep 14, 2015
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Wow, you all have been writing full of replies since I last responded, lol!

I tried taking the case apart yesterday to get a look inside. There were four long pins holding it closed, and I managed to remove them. The inside of the motor now turns a bit against its housing, but unfortunately doesn't pull out. I'm thinking the cooling fan on the back might be in the way, but I can't remove it (I tried) (I also assume I'd have to disconnect the wires from the wiring box even if it would budge anyway). So no luck looking inside. I mean, I could always fire up my angle grinder to get inside, but I'd seriously worry about damaging it, and I couldn't exactly just weld it back shut again without frying it.

Tha fios agaibh, I have never noticed any sound coming from within when I move it around.

It sounds like the different types of motors have different behaviors when fired up and stopped. Would it help if I did some tests - running it without load, disconnecting and seeing how long it took to stop, bolting on different loads and seeing how it compares, etc?

I'm also open to just guessing on the wiring (see the diagram above) if you think it that the chance of burning the motor out isn't too high (doesn't have to be a zero chance, I got the motor for nearly free). The four white wires are the only wires that go into the motor itself, so there's not a whole lot of possible permutations. I also have a multimeter which I could use if that would be useful, so long as hooking it up wouldn't burn it out or anything.
 

Minder

Apr 24, 2015
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If we assume it is a basic induction motor here is the normal connections, with both windings exiting the motor it is possible to reverse the motor easily, if there is a common coil connection made internally and not as shown then you may be stuck with opening up the motor and digging the connection out, the Centrifugal switch should be shown closed initially in the dwg.



images

Under load I believe it would be 1. My guess is that if it's unloaded it may keep running (3) do to residual magnetism in the field poles.
Chris
No, No2 This is the reason that DC shunt wound field motors generally have a field loss detection circuit, otherwise they have been known to fly apart on field loss.
Not a problem on permanent magnet motors of course.
M.
 

Martaine2005

May 12, 2015
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I think it could speed up until it blows up...
But under load would slow to a stop.
Although both scenarios should at least employ some sort of protection against the massive current draw.
I imagine ring fires, cables melting and shafts shattering..
But I am always a little dramatic.

Martin
 

Minder

Apr 24, 2015
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I think it could speed up until it blows up...
But under load would slow to a stop.
Martin
Partly right, the maximum rpm is governed by the load, no load is the condition where it can fly apart.
It is common in machine tool spindles to decrease the field to obtain a little more top end rpm, but at the sacrifice of torque.
In a shunt wound motor the maximum rpm depends on the field current, the higher the current the lower the rpm for a given applied voltage.
Reducing the field current, reduces the generated BEMF that is opposing the applied voltage.
M.
 
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Martaine2005

May 12, 2015
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Hehe, was that with crystalline (galena) and an earth wire?
one very quiet headphone too?

Martin
 

Minder

Apr 24, 2015
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Hehe, was that with crystalline (galena) and an earth wire?
one very quiet headphone too?

Martin
Yep, string the aerial along the clothes line.:p
Galena has been attributed to the first semiconductor put to practical use in electronics.
M.
 

Arouse1973

Adam
Dec 18, 2013
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This is very interesting.
One other thing I would like to add is, the run away condition will only occur as the field decays towards zero. When the field is zero you will have zero torque but this can take many seconds and the motor could have reached destructive speeds within that time. And as @Minder said the speed torque load relationship will dictate the maximum rpm.

Thanks
Adam
 

Tha fios agaibh

Aug 11, 2014
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Inside of the motor now turns a bit against its housing, but unfortunately doesn't pull out. I'm thinking the cooling fan on the back might be in the way, but I can't remove it
The magnets will make it implode as you pull it apart making it difficult to get back together.
The cooling fan on the back may have a c clip that has to be removed, and many require a gear puller to remove them.
If its plastic its a lot easier. Cast iron may have to be heated before it can be reinstated.
The motorbox (peckerhead) usually has to be removed first.
 

Tha fios agaibh

Aug 11, 2014
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never noticed any sound coming from within when I move it around.

It sounds like the different types of motors have different behaviors when fired up and stopped. Would it help if I did some tests - running it without load, disconnecting and seeing how long it took to stop, bolting on different loads and seeing how it compares, etc?
......The four white wires are the only wires that go into the motor itself, so there's not a whole lot of possible permutations. I also have a multimeter which I could use if that would be useful, so long as hooking it up wouldn't burn it out or anything.
The noise we were talking about was a universal motor.
I don't see the point of doing tests.
If you have 4 leads perhaps you could ohm out the leads to see it they are the start and run windings. The resistance of the start winding is usually higher with smaller size conductors.
Do yourself a favor and keep away the grinder. Also keeping any debris and metal filings away would be a good idea
 
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