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Black Forest
12-02-2012, 12:39 PM
I tried to find out what I have via google. Really I tried. I have read all about DC motors from brushless to brushes to step to servo and controllers and and and and.....

I have a small squirrel cage fan on my coffee machine. It is 24v DC. It consists of a coil that is connected to a bunch of thin plates all stuck together. There is a hole in the middle that the armature goes through. There are no brushes. It gets hot and stops turning after about two hours. This fan is continuous duty so long as the machine is switched on which is always except for cleaning. It has just some type of metal bushings for bearings. I replaced on bushing with a ball bearing and it helped but after 6 hours it stopped and was very hot. My next step is to replace the other bushing with a ball bearing also. From my very eloquent description can you tell me what type of motor this can be? The armature looks like it has windings on it also.

Evan
12-02-2012, 12:43 PM
Are you certain that it runs on DC? If the armature looks like it has windings what are they connected to?

Black Forest
12-02-2012, 12:56 PM
They aren't connected to anything. Could there be permanent magnets in the armature?

Evan
12-02-2012, 01:06 PM
Are you sure it's DC?

Black Forest
12-02-2012, 01:40 PM
Are you sure it's DC?

I wouldn't bet my life.

MaxHeadRoom
12-02-2012, 01:43 PM
Sounds like AC to me.
One way of testing for P.M. on the rotor is to short the stator wires together and try and spin the fan, if there is significant difference in resistance between shorted and not, it has P.M. rotor.
It could be a split phase AC motor using a shading ring to obtain the split ph, if the rotor looks like it has copper conductors on it, they could be the rotor conductor bars natural to an induction motor?
Max.

Black Forest
12-02-2012, 02:01 PM
It is 24 volt dc. The same transformer that powers the 24volt dc magnetic valves runs this motor. I just went and looked.

MaxHeadRoom
12-02-2012, 02:16 PM
Are you sure the motor is hooked into a DC supply side?
IOW, after a bridge rectifier etc, often now 24v DC solenoids have a small bridge in them in order that they can be supplied with AC or DC.
Max.

Evan
12-02-2012, 02:39 PM
It is probably connected to the unrectified output of the transformer. It would be done that way for safety reasons. Better than having 220 floating around in the machine. In that case it is most likely just the remaining bearing. That kind of motor has practically no starting torque and if overloaded slows way down. It will then get very hot. However, they are usually impedance protected so they will not burn out even if stalled, just get hot. Fix the bearing and see what happens.

Black Forest
12-02-2012, 02:41 PM
Are you sure the motor is hooked into a DC supply side?
IOW, after a bridge rectifier etc, often now 24v DC solenoids have a small bridge in them in order that they can be supplied with AC or DC.
Max.

OK, Is there a way for me to check whether it is 24 DC or AC? My extensive electrical testing devices consist of two digital multimeters!

Evan
12-02-2012, 02:43 PM
If you test it on the DC setting it should read near zero.

Black Forest
12-02-2012, 02:44 PM
Thanks Evan. I will put it on my list of things to do.

darryl
12-02-2012, 03:34 PM
What you're describing is an ac motor. They can be wound to run on any voltage, so it's not surprising that it's a 24 volt motor, probably done for safety reasons as suggested. By far the most common failure mode is the bushings seizing up. If one goes bad, it's almost a certainty that the other will be bad as well. In many cases, you can oil them and all will be fine for a year or two, but often enough you have to get all the old oil residue out so it doesn't turn the fresh oil into goo and seize it up again. There's also often some kind of felt washer in there which is supposed to hold oil, and it's often sealed in by swaging part of the bearing retainer. A metal working enthusiast :) would probably get rid of both bushings and put in ball bearings.

J Tiers
12-02-2012, 09:04 PM
Essentially THIS THREAD IS WORTHLESS WITH NO PICTURE

Might easily be a DC motor, driven by what amounts to a tiny inverter...... many millions of small cheap computer cooling type fans are made that way. See if there is any little circuit board associated, it only takes one IC and a sensor or two to run it.

if you cannot provide a picture, then at least determine if the 24V is supplied to it as AC or DC.

Regardless, if it is running, odds are that the other bearing gave out, and replacing it will likely do the trick.

CCWKen
12-02-2012, 09:25 PM
It sounds like a common shaded pole AC motor. What's not common is the voltage.
What's the coffee maker brand and model number? It may be easier to go from that angle. If it's UL listed, there should be a diagram inside somewhere.

Most will look like this:

http://www.mobilehomerepair.com/media/img/bathfanmot1.jpg

Evan
12-02-2012, 11:04 PM
Might easily be a DC motor, driven by what amounts to a tiny inverter...

Not very likely. Why would a brushless motor have windings on the armature connected to nothing? It's an induction motor.

Black Forest
12-03-2012, 12:32 AM
The picture CCWKen posted is nearly identical to the one I have. Mine has no printing on the coil though.

EVguru
12-03-2012, 04:44 AM
It will be the bearings. They're just oilite sleeves and often haven't really been well impregnated in the first place.

J Tiers
12-03-2012, 08:26 AM
Now that BF has agreed the motor is something which is COMPLETELY DIFFERENT FROM THE DESCRIPTION.........


Not very likely. Why would a brushless motor have windings on the armature connected to nothing? It's an induction motor.

The description, was , frankly, almost non-understandable, it could have been either. BLDC, or some form of induction motor. BLDC are actually CHEAPER than induction these days, and way cheaper than brush motors, which is the other type which has rotor windings.

Rotor windings were mentioned, but it isn't clear that such a description is more applicable to a squirrel cage motor than any other type...... the "windings" are a cast in feature.

I did not trust any part of the description since it is somewhat self-contradictory, just as the descriptions are for many or even MOST similar internet questions. One picture of any quality would settle the matter without this sort of asinine bickering

THIS THREAD WAS WORTHLESS WITHOUT A PICTURE

The reply from BF shows the absolute worthlessness of the thread and all the guessing...... I KNOW BF had a camera, and they are not expensive, even if the SIL still has the first one.

Black Forest
12-03-2012, 09:55 AM
Mr. Tiers, you seem to have a problem! Maybe the thread was worthless to you but not to me. As to the thread not being up to your standards, well tough sh!t! I guess we should all send you PM's with our posts to make sure they qualify and meet your criteria as to worth-fullness! Or at least I should as I am seemingly an idiot and not capable of expressing myself properly.

becksmachine
12-03-2012, 11:01 AM
Now that BF has agreed the motor is something which is COMPLETELY DIFFERENT FROM THE DESCRIPTION.........
Rotor windings were mentioned,

As a point of curiosity, could you point out where BF first mentions anything about rotor windings?

It seems a classic case of someone saying something that could be possible and then someone else taking it as the absolute truth.

In hindsight, the OP description matches the CCWKEN photo very closely, given the DC description is probably wrong.

Just sayin. ;)

Dave

Evan
12-03-2012, 12:19 PM
Armature windings are mentioned in the original post. "The armature looks like it has windings on it also." It may well have copper conduction bars on the rotor, especially considering that it seems to run on 24 vac.

CCWKen
12-03-2012, 08:07 PM
I have a small squirrel cage fan on my coffee machine. It is 24v DC. It consists of a coil that is connected to a bunch of thin plates all stuck together. There is a hole in the middle that the armature goes through. There are no brushes.

I was able to deduce from that description that it was more than likely the type I pictured. Let's get beyond that now that we know the type.

What's still up in the air is the voltage but perhaps a cleaning and oiling will fix the problem. As already mentioned, these usually have oilite bearings. They dry out and get dirty and gummy. I haven't much luck trying to clean and re-oil those types of bearings. I think when they start to dry out, they smear the inner surface and close off the pores. Seems they still drag down after a short period. You can try to clean the other bearing but a motor replacement would be a sure fire way to get back to making coffee.

J Tiers
12-03-2012, 08:58 PM
In HINDSIGHT, with all the posts visible, it is much easier to see how the description fits the actual device..... But, as can be seen from the various posts, a number of people got different mental pictures of the motor, from the "word picture" given.

It is often very easy to answer the question when you already have seen the answer. Just as it is easy to see the answer to the "brain buster" puzzles in the newspaper once you get the next day's edition,.... then you see how obvious it was.


Mr. Tiers, you seem to have a problem! Maybe the thread was worthless to you but not to me. As to the thread not being up to your standards, well tough sh!t! I guess we should all send you PM's with our posts to make sure they qualify and meet your criteria as to worth-fullness! Or at least I should as I am seemingly an idiot and not capable of expressing myself properly.

Not at all... You are taking an offense which is not there to be taken. A magician you must be ;)

You don't know much about electric motors.

I don't know much about sheep.

You don't know what the important parts to describe about a motor are, to determine what it is. Consequently you are not able to give a good description, and a picture is desperately wanted to make what is a guessing game, into an easy identification. It is no reflection on you, it is just that nobody can know everything.

I would be no better, and maybe worse if I were describing the illness or other problem of a sheep, and you might be saying bad words about that and wishing also for a picture which would make everything perfectly clear to you.

In each case, the person, you, or me, would be very much better advised to take a picture and SHOW the thing which is in question. So many times it is NOT what is SAID that is the problem, but rather what is NOT said...... With a picture, it is possible to look at everything that is in the picture, and maybe see an important detail that a person who is not familiar with the subject could easily miss.

This is not about you, it is inherent in a person trying to make words describe a thing without having the knowledge to be able to correctly identify the important features of the thing described.

There is a reason why a picture is worth a thousand words.

Evan
12-03-2012, 09:15 PM
Using 24 volts ac for that motor also makes the product very easy to sell internationally, especially the US and Canada. By doing it that way all they need to do is change the position of a couple of wires inside for it to run on 117vac. The heaters would be two 117 vac elements in series or in parallel depending on line voltage and the transformer would be series or parallel primaries. The transformer is needed anyway to run the solenoids.

Evan
12-03-2012, 09:19 PM
There is a reason why a picture is worth a thousand words.

The really interesting thing about that saying is that is about the number of binary bits it takes to represent either one.

J Tiers
12-03-2012, 10:44 PM
The really interesting thing about that saying is that is about the number of binary bits it takes to represent either one.

An interesting commentary then about the actual "information content"...... about equal, if I understand the reference correctly. Strange how the folks who made up those old sayings may have been smarter than it seems.