Cooker fan motors

[steptoesyard]

This one is really beyond me........

The motor recently died on my ageing Belling cooker, no problem I thought, I`ve got some spares up in the loft. One was old but unused, two I bought from a guy on Ebay, they were used but in good shape and clean, and another which I can`t remember the origins of.

All of these motors were totally free running, smooth, and had absolutely no play in the bearings which is why I kept them.

Now after two weeks of faffing around with this I have given up on all four. Same story every time - I fit the motor, fire up the oven and all is good until it starts to get hot, then the motor starts to drone/rumble, and the higher the oven temperature, the worse it gets. It`s clearly not a friction thing because at high temperatures the fan is still very free running (if I switch the oven off it spins for ages) and still very fast.

Anybody else experienced this? It`s not a minor noise, it`s enough to be intrusive over the tv in the next room!

I`ve lost the will to live with now and am buying a new cooker as this has driven me nuts!!

[Malcolm G6ANZ]

Probably the grease is melting and allowing a rough bearing to be heard.
Malcolm

[Goldie99]

Seems unlikely that 4 different motors would all have rough bearings / the same symptoms.

Could there be something physically fouling the fan(s) ? e.g., some part expanding to touch the fan as it heats up ?
Alan

[Boater Sam]

Its excessive end float on the shaft when hot. Well known problem, the motors are rubbish and the end float on new ones is set with fibre washers usually, these wear and the motor stack expands with heat.

[McMurdo]

I've fitted brand new ones that drone and drum at higher oven temperatures after only a few hour's use.

[steptoesyard]

Brand new ones that do it?

That really is poor, the motor that failed had been in there, and ran quietly and smoothly for 30 years. This has really put me off having a fan oven to be honest, I`m sure it`s down to bad design

[Radio Wrangler]

Some of the self-cleaning ovens go up to 500c for 2 to 3 hours. Do they have a better grade of fan motor?

David

[steptoesyard]

Originally Posted by Goldie99

Could there be something physically fouling the fan(s) ? e.g., some part expanding to touch the fan as it heats up ?

No nothing fouling the fan, the noise was definitely within the motor.

[Mike Phelan]

I'm sure the last one I dismantled had ball races rather than sintered bronze bushes, however if the latter, it's quite possible that a new unit could be noisy:

Had no lubricant or the wrong lubricant been applied the motor would run freely but could be noisy - the chalk squeaking on the blackboard syndrome.

[vidjoman]

Originally Posted by Radio Wrangler

Some of the self-cleaning ovens go up to 500c for 2 to 3 hours. Do they have a better grade of fan motor?

I had a Pyrolytic oven for 25 years and the cleaning cycle took about 90 minutes. The oven had 2 fans, one for the heat circulation and the other to keep the cabinet and kitchen cabinets cool. The heating fan did sometimes get a little noisy but a drop of oil every few years soon silenced it. The cabinet fan which was a long cylinder type normally ran slowly but ramped up its speed, and noise, when on the cleaning cycle. Oil didn't make any difference to that one. Although the oven reached 500 Deg C the triple glazed door remained touchable.

[Radio Wrangler]

The cabinet cooling fan pushes cool air between the outer two panes of glass in the triple glazed door on mine. It takes 2.5 hours for a cleaning cycle, which is a task I reserve for cold days

David

[McMurdo]

The same type of shaded pole motors are used on a well-known make of audio amplifier fan. The drumming that soon develops seems to be caused by the rotor moving cyclicly in and out of the pole pieces after the shaft/bearing sleeve have been run-in. They are supposed to be self-centering in the field but maybe the fan load is interacting somehow

[mole42uk]

Maybe there's some Curie point effect going on?

[steptoesyard]

Which amplifiers have these things as cooling fans? Just out of interest.

[Radio Wrangler]

You need to read "The care and feeding of power grid tubes" by William I Orr and the staff at Eimac-Varian.

It takes a lot of care to stop the wrong things cooking in big transmitters.

David

[vidjoman]

Originally Posted by steptoesyard

Which amplifiers have these things as cooling fans?

You'd be surprised how many amplifiers have cooling fans these days. Most are small computer types and are cheaper to fit than to use a larger metal heat sink. Many are the slim amplifiers but some are in the larger and more expensive types. Some are temperature controlled but cheaper makes run all the time. Usually quiet when new, but gradually get noisier with continued use.