Air moving fan troubleshoot

[Robbox]

Have an air movement fan, big 30cm blade, for cooling etc. Tried it out the other day, after many months in the loft, worked fine for a couple of days then just stopped.
Replaced the fuse, still not working.
Opened up the fan and there's not much to see. A multi-gang switch to give three speeds and a large cap (which I assume is the starter cap?).
Here's a pic of the innards....
I did a search for the cap and Amazon came up with ceiling fan in the description. Reviewers said replacing it fixed their fan, so I'm assuming here that these things do go bad...

 

[Burnerman]

The capacitor is to prevent TV interference, you can remove it if you like.
It seems that the incoming live wire (brown) goes to the switch terminal which is slightly remote from the others, and when the switch is turned it will connect into the different windings of the motor.
I think I'd do some testing with a multimeter first if you have one, just to see what's happening within the switch.
John

 

[Robbox]

Hi John, I have an MM, what should I expect when I connect across the terminals?

I did put the MM across the cap and that returned an infinite value in ohms. (Have to say I don't really know what I'm doing or what to look for....)

 

[Robbox]

Off= no circuit
1= starts off with a small resistance then goes to zero
2= ditto
3= ditto

 

[Burnerman]

The capacitor won't show continuity so that seems fair enough.....try disconnecting it if you like but I don't think it'll make any difference.
Try your resistance test again, using the lowest resistance on the meter you can?
Are you happy to try some readings with the unit live, and the meter set to 250v AC? I would have thought you would get some sort of a result unless the motor windings have called it a day. Did the motor smell at all?
John

 

[Robbox]

how about if I short out the cap? that would at least eliminate one thing. I could just put a crocodile clip across the bare end of the cap wires. One thing I did notice, when the unit is plugged in and fab set to three, there is more resistance on the shaft.
Not really happy with testing at 240v

 

[Robbox]

motor smells greasy. no burning smells...

 

[Burnerman]

how about if I short out the cap? that would at least eliminate one thing. I could just put a crocodile clip across the bare end of the cap wires. One thing I did notice, when the unit is plugged in and fab set to three, there is more resistance on the shaft.
Not really happy with testing at 240v

I can't see you have anything to lose, but if I'm doing stuff like this I use one of those plug in circuit breakers just to keep things safe and damage free.
John

 

[Robbox]

I did short out the cap and still nothing. I guess next step maybe putting 240v across the actual motor. I'm assuming here that the way the fan achieves three speeds is by having three windings, or something like that...

 

[bernardgreen]

The capacitor is to prevent TV interference,

A 1.5μF capacitor is a bit large for a suppressor capacitor and it would be connected across Live and Neutral and not in series with one of the wires going to the motor. Hence I would suggest it is a starting or run capacitor which, together with one of the motor windings creates a magnetic field that is out of phase with the field from the main winding and thus determines which way the motor will start to turn.

I did short out the cap and still nothing

If it was a suppression capacitor then the fuse would have blown. If it was a starting capacitor then the start winding would be in phase with the main winding and hence no oout of phase magnetic field to start the rotation.

Hi John, I have an MM, what should I expect when I connect across the terminals?

When you touch the ohm meter to the capacitor it will show as a dead short for a split second until the capacitor is charged from the meter's measuring current. Then it will appear to be open circuit. many digital multi-meters will not respond fast enough to show that transient "dead short".

To test the capacitor charge it by connecting to a 9 volt battery. Remove the battery and measure the voltage. It should reduce slowly down from 9 volts as the capacitor discharges through the multi-meter's measurring circuit

 

[Robbox]

To test the capacitor charge it by connecting to a 9 volt battery. Remove the battery and measure the voltage. It should reduce slowly down from 9 volts as the capacitor discharges through the multi-meter's measurring circuit

OK, I did this as you suggested and the voltage went down to almost zero in a matter of seconds. I mean by the time I'd disconnected the battery and attached the MM, it was already 5v, then seconds late it was 0.
Does that sound like the cap is a dud? On Amazon they are not expensive, maybe I should just replace and see.

 

[bernardgreen]

OK, I did this as you suggested and the voltage went down to almost zero in a matter of seconds.

The CBB61 is a metallized polypropylene film capacitor ( low leakage type ) so I would expect it to hold voltage for more than just few seconds.

 

[Echo the husky]

Just replace the cap, those CBB caps are awful chinese crappy things and fail all the time. I usually replace them with something made by a better brand.

 

[Robbox]

going to do that, would you suggest a different type of cap or still the metallised pp variety?

 

[Echo the husky]

Still metallised, but one that doesn't have CBBxx printed on it.