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repairing a table fan

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mdanh2002

Member
Hi

My table fan dropped from the table to the floor last night (because the fan was at full speed and it moved by itself bit by bit during operation). Now the fan won't spin anymore. Upon taking it apart I observed the following:

1. No aparent physical or electrical damage. The winding seems still intact, no distortion of mechanical parts which would have been a result of the drop. In fact, as I know, fans seldom die from drop.

2, The armature, seems to be working. It stil generates a strong magnetic field when turned on without the axle.

3. Without the axle, the motor generates noises as if it was operating normally.

4. When the axle is put in, the noise generated by the motor reduced, and the axle could not rotate, even if attempted manually. In fact, it's very easy to rotate the axle manually when turned off, but once turned on, it's difficult, if not impossible. If the screws are tight, the whole mechanism just sticks together, perhaps because of the magnetic field and moving the axle would move the whole thing. If the screws are not tight, moving the axle would spin it a bit, but does not start the motor as expected

Any ideas what's wrong? Thanks in advance.
 
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transistor495

Member
Forum Supporter
I'm actually not sure whether a table fan(ac) has a starter capacitor. It seldom fails and I don't think that's the case here..re-check the winding.
 

mdanh2002

Member
I attached some images below.

transistor495, what are the symptoms of winding failure? Will it still generate magnetic field, or nothing at all?

The table fan is running at 220V AC and I can't seem to find any capacitor anywhere inside the mechanism.

If it helps, before it was taken apart, I noticed that the fan wing would spin a few rounds if I manually rotated it.
 

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Mickster

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Most Helpful Member
When the axle is put in, the noise generated by the motor reduced, and the axle could not rotate, even if attempted manually. In fact, it's very easy to rotate the axle manually when turned off, but once turned on, it's difficult, if not impossible. If the screws are tight, the whole mechanism just sticks together, perhaps because of the magnetic field and moving the axle would move the whole thing. If the screws are not tight, moving the axle would spin it a bit, but does not start the motor as expected
&

If it helps, before it was taken apart, I noticed that the fan wing would spin a few rounds if I manually rotated it.
Personally, I would suspect that the motor spindle is possibly bent.

EDIT: Scratch the above......must read more slowly!
 
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Sceadwian

Banned
3v0's probably right, from everything described there's a broken wire somewhere that he's not seeing.
 

mdanh2002

Member
Thanks for all the replies :)

From my understanding, the inductors will generate repelling magnetic fields so the motor shaft will move. There are 2 inductors, the left one will generate a field on the left part of the armature and the right one on the right part. The 2 magnetic fields repel each other and the shaft will move. So the windings in one of them is open, the magnetic field will not be present and the shaft won't move but is instead atracted by the other magnetic field. If I remove the shaft and use a screw driver to test the field, it seems that magnetic field is present on both sides of the armature as the screw driver can be attracted to either the left or the right. Can I conclude that the inductor are still intact?

@ Mickster: by 'spindle', do you mean the removable axle in my picture? If so, I have tested it carefully and there is no apparent damage. I can rotate it freely when power is not applied. Is it possible that it's somehow bent slightly but I could not see?
 

Sceadwian

Banned
If it spins freely by hand it's not bent, at least not enough to affect the motor.
 

Mickster

Well-Known Member
Most Helpful Member
If the screws are tight, the whole mechanism just sticks together, perhaps because of the magnetic field and moving the axle would move the whole thing. If the screws are not tight, moving the axle would spin it a bit, but does not start the motor as expected
This is the bit that made me think something may have been bent...

Can we clarify whether the fan blades can be freely rotated by hand, with the screws tight and no power applied?
 

MrAl

Well-Known Member
Most Helpful Member
Hi,


It's hard to tell what is going on without seeing the actual fan now, but i'll take a few guesses too...

1. When the fan fell it bent the bearing supports and thus one or both bearings are not aligned correctly now. It's pretty hard to bend a shaft like that but i guess you never know for sure unless you have some way to test it for straightness.
Anyway, if the bearing supports bent you can try putting the shaft into the bearing and see that the bearing gives a little and rotates side to side and up and down (not rotating the fan blade). That may help to loosen the mount a little and allow the shaft to turn a little more freely.

2. After making sure both the shaft and the inside of both bearings (especially the front bearing) do not have any black buildup on their surfaces, apply some light oil like 3 in 1 oil. That will free up the mechanism a little more too.

3. If it is a broken wire it may be hard to fix unless you can see the actual wire hanging loose.

4. Check the switch mechanism to make sure it still makes good contact and also provides the correct switching action for any and all circuits involved.

5. If all else fails, go out and buy a new fan <chuckle>. I had fixed a fan i liked for many years as the bearings kept drying out. One year i finally got tired of taking the dang thing apart and went out and bought a new fan for ten dollars (USD).
 
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Sceadwian

Banned
Judging by the size of it I'm not even sure a replacement would cost 10 dollars.
 

Mickster

Well-Known Member
Most Helpful Member
Judging by the size of it I'm not even sure a replacement would cost 10 dollars.
Perhaps so, but what is dirt cheap for us may be expensive for someone else...

Or simply be an exercise in trying understand and repair something just for the experience.

I'd probably just buy a new one and hoard the old one 'In case it came in handy one day', throw it out after two years, then wish I'd scavenged that switch/bearing/armature/mesh....etc.
 

mdanh2002

Member
Thanks all for the comments.

I wanted to repair the fan mostly for learning purposes, and this is my first time fixing a fan.
It's ok if I could not fix the fan, but I will be happy to learn exactly why it stops working :)

I have tested again carefully today and notice that the shaft can move freely within the shaft when no power is applied (with the screws tight). When power is applied, the shaft can actually spin by itself (albeit very slowly) in the bearings if placed at certain positions. When the shaft spins out of its "comfort zone" (which is less than 1 round) , it will stop spinning.

I attached 2 photos of the shaft for clarity. Do you think that the part highlighted in red is worn out and causing the problem? I assume when the fan was new, the highlighted part in the image was not worn out (e.g. flat), so the cylindrical structure of the shaft could spin inside the bearing with no issues. After it has been worn out, there is some imbalance, and the shaft could not spin.
 

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Sceadwian

Banned
Those photos are so out of focus it's hard to tell what you're talking about.
 

mneary

New Member
To get a better close range focus on a cell phone camera, put the lens from a "reading glasses" in front of the camera.
 

Sceadwian

Banned
Nice suggestion Mneary. I took some photo's of birds through my regular digital camera at a decent distance simply putting the lens up to a pair of binoculars, placement was a little tricky, but the auto-focus on my camera is somehow based on the actual image itself so it self corrects if it's possible to focus at all.
 

mdanh2002

Member
I made some improvements. I aligned properly, cleaned and applied some oil to the fan shaft and the bearings and the fan is able to spin normally for a moment. However, after a while when the oil gets dried , the fan becomes noisier and slower and eventually stops.

So I guess that's it. The fan is dying - time to buy a new one :)
 

MrAl

Well-Known Member
Most Helpful Member
Hi again,


Sorry to hear that. I guess it is time to buy a new fan now, and you will be happy to get a new one anyway :)

When i oil mine it usually lasts at least one whole summer until the next year when it needs cleaning and oiling again.
 

mdanh2002

Member
I have bought my new fan :) Actually I am happy since this is the first time I successfully repaired something electrical/mechanical. I am using the new one now, keeping the old one just in case I need it some day.

Thanks all for your help.
 
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