Electrically seized fans..whats going on there then?
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baxpoti said:
Never seen one in my life.
ya know what i'm on about though don't ya.
Whats your thoughts baxpoti
N
namsag
So how come if you oil them they can start working if its electrical
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I don't think we're talking about the same fault here?
When no power applied the fan spins freely
With power applied the fan will not move and is held magnetically, along with a lot of humming. Never tried oiling one that's doing this!
When no power applied the fan spins freely
With power applied the fan will not move and is held magnetically, along with a lot of humming. Never tried oiling one that's doing this!
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namsag said:
Ye but , no but,... the ones i am on about will run freely with no power so don't need lubricating.
I had a 1 day old one do it once (sime super 90)
N
namsag
Yeah even when they spin freely with no power and sieze with power have found some that will spin with oil, and always thought this doesn`t make sense
This fault is caused by bearing wear.
What happens is a rotor rotates because a magnetic field is generated by the stator and is a combination of attract/repel forces which cause rotary motion -it's also finely balanced in order to work.
When the bearings are worn this attraction is turned from a rotary motion to a linear one -IE the rotor is drawn towards the stator and hence becomes 'stuck'
Once the electricity is turned off this magnetic attraction is lost and hence the rotor spins freely.
However oil will not nor never can 'repair' this fault as it merely lubricates the bearings not reduces the wear
Cheers
Richard
What happens is a rotor rotates because a magnetic field is generated by the stator and is a combination of attract/repel forces which cause rotary motion -it's also finely balanced in order to work.
When the bearings are worn this attraction is turned from a rotary motion to a linear one -IE the rotor is drawn towards the stator and hence becomes 'stuck'
Once the electricity is turned off this magnetic attraction is lost and hence the rotor spins freely.
However oil will not nor never can 'repair' this fault as it merely lubricates the bearings not reduces the wear
Cheers
Richard
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r.bartlett said:
That sounds very plausible, it fact i bet its spot on, unless anyone knows any different
Sounds good to me.
Actually, TT has got it right because they are usually shaded pole motors.
The shorted turns have to be very low resistance and fatigue can cause internal cracks in the turn, usually at the weld.
You can identify the problem if you measure the impedance of the fan as opposed to just the resistance and compare it with a good fan.
The Ideal Mini C had that fault with a batch of fans and ran out of spares for a while!
There are a very few boiler fans with two windings and a capacitor. I think earlier Sonya Duvals had them for example.
Tony
The shorted turns have to be very low resistance and fatigue can cause internal cracks in the turn, usually at the weld.
You can identify the problem if you measure the impedance of the fan as opposed to just the resistance and compare it with a good fan.
The Ideal Mini C had that fault with a batch of fans and ran out of spares for a while!
There are a very few boiler fans with two windings and a capacitor. I think earlier Sonya Duvals had them for example.
Tony
They're shaded pole motors .
Squirrel cage, as described here in general
http://www.physclips.unsw.edu.au/jw/electricmotors.html#squirrel
and here in particular - the fan one
http://www.phys.unsw.edu.au/hsc/hsc/electric_motors1.html
A break in the laminations of the squirrel cage means that the motor wouldn't be pulled round properly by the rotating field, so it sits there wobbling.
You can also get "shorted turns" in the windings, which cause nasty problems.
Digressing a little, they often fail through lack of lubricant. In plain bearing motors (eg on Profile boilers) they look like this, where the yellow stuff is grease, and the grey part a sintered (porous) bearing. I thought those were only used with oil, and I'm not sire of the best way to get them going again once they've gunged up. Carb cleaner, or even several doses of WD40 helps to clear the goo.
Squirrel cage, as described here in general
http://www.physclips.unsw.edu.au/jw/electricmotors.html#squirrel
and here in particular - the fan one
http://www.phys.unsw.edu.au/hsc/hsc/electric_motors1.html
A break in the laminations of the squirrel cage means that the motor wouldn't be pulled round properly by the rotating field, so it sits there wobbling.
You can also get "shorted turns" in the windings, which cause nasty problems.
Digressing a little, they often fail through lack of lubricant. In plain bearing motors (eg on Profile boilers) they look like this, where the yellow stuff is grease, and the grey part a sintered (porous) bearing. I thought those were only used with oil, and I'm not sire of the best way to get them going again once they've gunged up. Carb cleaner, or even several doses of WD40 helps to clear the goo.
Whilst trying to keep on topic as best as possible, my cooker hob extractor fan has somewhat seized.
After taking it apart as best I could and freeing it up a little by hand, it works again but far from perfectly with the speed fluctuating.
The likely cause of fault is grease I know, but is it really safe to use oil in an electrical fan assembly? Or are you just talking about lubricating the bearing?
After taking it apart as best I could and freeing it up a little by hand, it works again but far from perfectly with the speed fluctuating.
The likely cause of fault is grease I know, but is it really safe to use oil in an electrical fan assembly? Or are you just talking about lubricating the bearing?
The best small motors use ball bearings but the cheaper ones use a poreous bronze bush bearing which is soaked in oil and expected to last the lifetime of the motor. There is usually a felt pad also soaked with oil in contact with the bush to extend the life.
Since oil is an excellent insulator there is no problem using it on a fan. Indeed oil is used to fill high voltage transformers and capacitors as an insulating and cooling medium.
Some oils used in sealed components, mainly capacitors, during the 70s and 80s is extremely toxic!
Tony
Since oil is an excellent insulator there is no problem using it on a fan. Indeed oil is used to fill high voltage transformers and capacitors as an insulating and cooling medium.
Some oils used in sealed components, mainly capacitors, during the 70s and 80s is extremely toxic!
Tony
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