Calling the motor experts

[JM2]

I've replaced (due bad bearings) the motor assy from my domestic (single ph 230v) cooker hood extractor with a same numbered model second hand motor unit.

Now the switching is such that is off (0) or slow/med/fast (1-3). Wiring swapped one for one (I know, heard it before) and drawn out - I agree with myself!

The problem is on medium (2) the fan motor is unhappy and vibrates badly - like miswired/windings incorrect. Slow is good, fast is good.

See what you think, on slow L-Grey & N-Black; on medium L-Grey & N-Blue; on fast L-White & N-Blue.

I'm thinking the windings are okay, the wiring is okay, so what can be wrong - or do I have the windings to simplified? What is normal for such a simple motor?

Basic dc loop (resistance) metering gave me each wire's resistance to each other, from that table I've hopefully duduced correctly the motor windings are like this:-

Untitled

• JM2
• 20 Feb 2013
• 1

 

[IJWS15]

May not be electrical, may be that something is loose and is resonating at the frequency matching that speed.

These are generally DC motors and you switch in resistors to vary the speed.

 

[bhm1712]

Cooker hoods are not usually DC motors, but 3 speed AC motors with tapped windings. The speed switch actually switches the line voltage onto one of these tap-ins on the winding to achieve the 3 different speeds. Speed 3 or full speed is usually straight onto the main full winding, with speed 1 and 2 going through a tap-in.

Your motors tap-ins are on the Grey, White and Blue wires. One of those will be the full speed main winding so not actually part of the tap-ins.

If you have wired it like for like which you say you have, that would lead me to suspect that the seconds hand motor may have a dodgy second speed winding. How do you know that the 'new' motor is actually a good one?

other things to consider may be the possibility of a capacitor problem, but without seeing this motor in person its hard to say.

 

[bhm1712]

if the old motor was only broken due to bad bearings, then i suggest you also measure the resistance across the same windings on that motor to see if that pinpoints a problem with speed 2 tap-in on the new motor.

 

[JM2]

Yes, I'm thinking W-B is the full speed winding.
And is is used always.

Could be capacitor issue but but again, okay at the extremes?

Should have measured the old one (doh!) but is was physically stiff to rotate (and squealled when cold) so was happy it was the bearings gone and I've thrown it.

Could eaily be a doggy motor (same age) but I can't explain how that could only play up in '2' - medium speed.

I've "rewired" the netural portion of the switch and now have 0-1-0-3 which at least stops the thing vibrating.