Micromark FAN heater - UK Vintage Radio Repair and Restoration Discussion Forum

ColinB · 18th Aug 2020, 4:09 pm

Hi,

I've got a Micromark MM30115 fan heater here, all of which works as expected, apart from the fan...

It is getting voltage applied to it (the motor gets hot and a bulb connected in parallel with it lights when the fan should run), it is fairly free to move - but it will not turn!

What can I do to make it run?

Cheers,
Colin

paulsherwin · 18th Aug 2020, 4:20 pm

Have you had a look inside the motor?

Refugee · 18th Aug 2020, 4:21 pm

Replace the motor capacitor.

ColinB · 18th Aug 2020, 4:30 pm

Quote:

Originally Posted by paulsherwin

Have you had a look inside the motor?

Yes, there isn't much to see really, just a rotor and what look like two coils.

ColinB · 18th Aug 2020, 4:31 pm

Quote:

Originally Posted by Refugee

Replace the motor capacitor.

I don't see any capacitor?

Refugee · 18th Aug 2020, 4:51 pm

How many wires does the motor have?

ColinB · 18th Aug 2020, 5:40 pm

Just the L and N going in, as far as I can see.

Presumably the rotor is a permanent magnet? As you say, even with two coils, one would have to lead (or lag) the other, and so would need a cap. but I can't see anywhere one might be hiding...?

broadgage · 18th Aug 2020, 6:07 pm

These motors are very simple with only 2 wires and no capacitor.
Probably a shaded pole induction motor. These produce a rotating magnetic field from a single phase supply without use of capacitors or split windings.

The starting torque is very small indeed, and a slightly stiff bearing will prevent starting.
Try spinning the fan by hand, whilst energised this might start it. Do of course take care whilst trying this.

It should be possible to lubricate the bearings, but IME this provides only short term relief.
These cheap fan heaters are a more or less disposable product.

ColinB · 18th Aug 2020, 7:40 pm

Quote:

Originally Posted by broadgage

These produce a rotating magnetic field from a single phase supply without use of capacitors or split windings.

Yes, that makes sense, but how do they manage that? Not questioning what you say, but keen to understand, even if it doesn't help with this particular problem...

Quote:

Originally Posted by broadgage

It should be possible to lubricate the bearings, but IME this provides only short term relief.
These cheap fan heaters are a more or less disposable product.

Yes, this one is headed for the skip I'm afraid. It was a free gift to me, so it doesn't really matter too much, but I had hoped it would work, as it has a thermostat, fan, timer, adjustable heat levels etc, so would have been useful for another project I've got coming up (building a drying room for outdoor gear, if anyone is interested...) but Hey-ho, these things happen.

Thanks to everyone that has contributed, but I think it's time to write this one of as just yet another poorly made piece of junk - totally the opposite of the 1920's fan in another thread on here....

AC/HL · 18th Aug 2020, 8:02 pm

If the motor (as distinct from the element) is getting hot it suggests shorted turns. Same outcome though!

broadgage · 18th Aug 2020, 9:10 pm

Shaded pole induction motors use a single coil of wire on a ferrous former, this would produce a pulsating rather than a rotating magnetic field.
Part of the ferrous former has a "shading ring" of copper or aluminium attached. This retards the growth of the magnetic field at each mains cycle, and thereby produces a slight rotating effect.
The non shaded part will be "leading" the shaded part.
The coil is often divided into two parts, connected in series, this gives a more compact design but does not in itself give a rotating field.

This type of motor is popular when least cost is important, fan heaters, desk fans, small fans in fridges, operating the turntable in microwave ovens.

duncanlowe · 18th Aug 2020, 9:41 pm

I have come across motors that look like this that fail because of a thermal fuse embedded in the windings. Are you sure the heat is from the motor?

usradcoll1 · 22nd Aug 2020, 5:15 pm

Quote:

Originally Posted by broadgage

Shaded pole induction motors use a single coil of wire on a ferrous former, this would produce a pulsating rather than a rotating magnetic field.
Part of the ferrous former has a "shading ring" of copper or aluminium attached. This retards the growth of the magnetic field at each mains cycle, and thereby produces a slight rotating effect.
The non shaded part will be "leading" the shaded part.
The coil is often divided into two parts, connected in series, this gives a more compact design but does not in itself give a rotating field.

This type of motor is popular when least cost is important, fan heaters, desk fans, small fans in fridges, operating the turntable in microwave ovens.

That is the best explanation of the theory of operation of shaded pole induction motors. I know a bit of theory about rotating machines, but you learn something new every day. Thanks!
Dave, USradcoll1.

ColinB · 22nd Aug 2020, 5:32 pm

Quote:

Originally Posted by broadgage

Shaded pole induction motors use a single coil of wire on a ferrous former, this would produce a pulsating rather than a rotating magnetic field.
Part of the ferrous former has a "shading ring" of copper or aluminium attached. This retards the growth of the magnetic field at each mains cycle, and thereby produces a slight rotating effect.
The non shaded part will be "leading" the shaded part.
The coil is often divided into two parts, connected in series, this gives a more compact design but does not in itself give a rotating field.

This type of motor is popular when least cost is important, fan heaters, desk fans, small fans in fridges, operating the turntable in microwave ovens.

Thanks, that's interesting, I was never clear how just one coil with 50Hz applied (no caps, no other phases etc) was able to produce rotation...

Glowing Bits! · 22nd Aug 2020, 7:26 pm

I've been following this post for a while, no one has yet mentioned the bearing assembly.
If the motor is rotating fairly easily, that doesn't mean a vast amount, a simple test as to how free the shaft is would be to fling it by hand, it should do 3 - 4 rotations before stopping, any less would suggest it needs oil.
There should be some felt washers near the bearing/bush, these should be a gray colour, a light grey or cream colour suggests they're dry, start by checking these first.
Whilst assembling it, use the shaft in the bush assy (it's a self levelling gimbal), give it a wiggle around, this may be what the problem is, it will rotate by hand if things are not centred properly but will likely stall under mains operation.
Try these things first.
In regards to the motor getting hot, it probably will if it ain't rotating. Some heat will be produced in operation, the winding will be acting as a 20 watt light bulb.

broadgage · 22nd Aug 2020, 11:49 pm

To add to the above, shaded pole induction motors are one of those technologies that do not "scale up" at all well.
A significant percentage of the input energy is wasted as heat due to eddy currents in the shading ring.

With a total input of say 5 watts, the loss of say 2 watts in eddy current heating is of little consequence. And in the specific case of a fan heater, these losses are completely irrelevant, as producing heat is the purpose of the appliance.

In a large motor with an input of say 1Kw, the loss of say 400 watts in a shading ring would be unacceptable. It not only represents a significant energy cost, but getting rid of an extra 400 watts of losses in addition to other losses would be a design challenge. The shading ring might even melt !

In all but very small sizes, a universal type commutator motor would be more efficient though more costly. In a very small motor, the frictional losses in brush gear can be significant, and perhaps comparable to eddy current losses in a shaded pole induction motor.

A split winding motor with a capacitor in series with one winding is more efficient, but in small sizes adds significantly to manufacturing costs.
Shade pole motor=only one coil with two connection, not polarity sensitive.
Split winding motor=at least five connections more chance for error in unskilled assembly.

18th Aug 2020, 4:09 pm	#1
ColinB Heptode Join Date: Apr 2003 Location: Newton Abbot, Devon, UK. Posts: 761	Micromark FAN heater Hi, I've got a Micromark MM30115 fan heater here, all of which works as expected, apart from the fan... It is getting voltage applied to it (the motor gets hot and a bulb connected in parallel with it lights when the fan should run), it is fairly free to move - but it will not turn! What can I do to make it run? Cheers, Colin

18th Aug 2020, 4:20 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,934	Re: Micromark FAN heater Have you had a look inside the motor?

18th Aug 2020, 4:21 pm	#3
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Micromark FAN heater Replace the motor capacitor.

18th Aug 2020, 4:51 pm	#6
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Micromark FAN heater How many wires does the motor have?

18th Aug 2020, 5:40 pm	#7
ColinB Heptode Join Date: Apr 2003 Location: Newton Abbot, Devon, UK. Posts: 761	Re: Micromark FAN heater Just the L and N going in, as far as I can see. Presumably the rotor is a permanent magnet? As you say, even with two coils, one would have to lead (or lag) the other, and so would need a cap. but I can't see anywhere one might be hiding...? Attached Thumbnails

18th Aug 2020, 6:07 pm	#8
broadgage Nonode Join Date: Jan 2010 Location: North Somerset, UK. Posts: 2,129	Re: Micromark FAN heater These motors are very simple with only 2 wires and no capacitor. Probably a shaded pole induction motor. These produce a rotating magnetic field from a single phase supply without use of capacitors or split windings. The starting torque is very small indeed, and a slightly stiff bearing will prevent starting. Try spinning the fan by hand, whilst energised this might start it. Do of course take care whilst trying this. It should be possible to lubricate the bearings, but IME this provides only short term relief. These cheap fan heaters are a more or less disposable product.

18th Aug 2020, 8:02 pm	#10
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Micromark FAN heater If the motor (as distinct from the element) is getting hot it suggests shorted turns. Same outcome though!

18th Aug 2020, 9:10 pm	#11
broadgage Nonode Join Date: Jan 2010 Location: North Somerset, UK. Posts: 2,129	Re: Micromark FAN heater Shaded pole induction motors use a single coil of wire on a ferrous former, this would produce a pulsating rather than a rotating magnetic field. Part of the ferrous former has a "shading ring" of copper or aluminium attached. This retards the growth of the magnetic field at each mains cycle, and thereby produces a slight rotating effect. The non shaded part will be "leading" the shaded part. The coil is often divided into two parts, connected in series, this gives a more compact design but does not in itself give a rotating field. This type of motor is popular when least cost is important, fan heaters, desk fans, small fans in fridges, operating the turntable in microwave ovens.

18th Aug 2020, 9:41 pm	#12
duncanlowe Nonode Join Date: Jan 2016 Location: Stafford, Staffs. UK. Posts: 2,531	Re: Micromark FAN heater I have come across motors that look like this that fail because of a thermal fuse embedded in the windings. Are you sure the heat is from the motor?

22nd Aug 2020, 7:26 pm	#15
Glowing Bits! Octode Join Date: Oct 2011 Location: Wrexham, North Wales, UK. Posts: 1,457	Re: Micromark FAN heater I've been following this post for a while, no one has yet mentioned the bearing assembly. If the motor is rotating fairly easily, that doesn't mean a vast amount, a simple test as to how free the shaft is would be to fling it by hand, it should do 3 - 4 rotations before stopping, any less would suggest it needs oil. There should be some felt washers near the bearing/bush, these should be a gray colour, a light grey or cream colour suggests they're dry, start by checking these first. Whilst assembling it, use the shaft in the bush assy (it's a self levelling gimbal), give it a wiggle around, this may be what the problem is, it will rotate by hand if things are not centred properly but will likely stall under mains operation. Try these things first. In regards to the motor getting hot, it probably will if it ain't rotating. Some heat will be produced in operation, the winding will be acting as a 20 watt light bulb. __________________ Rick, the annoying object roaming the forum. Last edited by Glowing Bits!; 22nd Aug 2020 at 7:35 pm.

22nd Aug 2020, 11:49 pm	#16
broadgage Nonode Join Date: Jan 2010 Location: North Somerset, UK. Posts: 2,129	Re: Micromark FAN heater To add to the above, shaded pole induction motors are one of those technologies that do not "scale up" at all well. A significant percentage of the input energy is wasted as heat due to eddy currents in the shading ring. With a total input of say 5 watts, the loss of say 2 watts in eddy current heating is of little consequence. And in the specific case of a fan heater, these losses are completely irrelevant, as producing heat is the purpose of the appliance. In a large motor with an input of say 1Kw, the loss of say 400 watts in a shading ring would be unacceptable. It not only represents a significant energy cost, but getting rid of an extra 400 watts of losses in addition to other losses would be a design challenge. The shading ring might even melt ! In all but very small sizes, a universal type commutator motor would be more efficient though more costly. In a very small motor, the frictional losses in brush gear can be significant, and perhaps comparable to eddy current losses in a shaded pole induction motor. A split winding motor with a capacitor in series with one winding is more efficient, but in small sizes adds significantly to manufacturing costs. Shade pole motor=only one coil with two connection, not polarity sensitive. Split winding motor=at least five connections more chance for error in unskilled assembly.