Lamona Cooker Hood - HJA2500 aka LAM2502/3 - capacitor

[David]

Things have been progressing slowly due to the winter lurgi which seems to have hot everybody over the holidays.

I now have the cooker hood main unit off the wall, but I haven't fully taken it apart yet because it is covered in several years of grease.

I can now see inside it properly, and it has a capacitor along side the motor. The bits I can see are labelled

CBB61#

2uF +/- 5%

450V AC

50/60 Hz A/C

A quick search shows that these are common for fans of all sorts.

I have no idea if this is the problem, but I was wondering what function the capacitor serves.

Initial searching suggests that it is a run capacitor not a start capacitor because of the 2uF/450V rating. Also, the fan is only 140W so I am guessing it doesn't need a boost to start spinning.

The extractor hood is about 5 years old; how long do capacitors normally last. Roughly.

I'm wondering about the advisability of testing (if I can) or just replacing. The capacitor is about £12 but the whole motor assembly is around £150.

In a day or so I should have most of the grease off and the fan motor and wiring extracted from the hood so that I can do a little testing and tracing.

Recap of problem.

Lights work.

Buttons for 3 fan speeds seem to work - power indicator in control panel goes on and off.

Fan doesn't work at any speed.

Now I have access, the fan spins freely when flipped with a finger.

The layout is power cable -> switch panel -> wiring box on side of motor.

Wires to the lights and capacitor come back out of the wiring box.

First question is how you test that the capacitor is working?

Cheers

Dave R

[tabbypurr]

£12 seems very high. Try rapidonline. I'd sub the cap with one from the junkbox, and I'd test the cap there with a component tester, but you have neither. If you put the 2uF cap in series with a LED bulb it should dim it some. No light = dead cap.

NT

[Andy Burns]

£1.69 delivered from eBay

[David]

Thanks.

I'm still struggling with conflicting information on t'Internet but if it is a starting capacitor then there should be a switch somewhere to take it out of circuit which is another point of failure.

I can't get a clear picture on a capacitor used for both starting and running; it looks as though a single phase motor must have a start capacitor or it won't start but it isn't clear if the same capacitor can be used as a run capacitor as well.

It looks as though the motor should run if started by hand if the start capacitor is duff. However it is not clear if it would run with a flick start of it relies on a run capacitor.

The £12 tag is probably because instead of the usual little black box it is a tube with a stud in one end which is used to fix it into a bracket on the motor housing.

One strange thing - the nut and washer holding the capacitor appears to be corroded much like a failed battery but the rest of the capacitor seems fine.

No doubt all will become clear in time.

Cheers

Dave R

[tabbypurr]

The corrosion probably doesn't matter. It'll cost you £1.69 to find ou t what's up. afaics you don't really need to know if it's a run or start ca p.

NT

[John Rumm]

If you have a start cap you will hear the centrifugal switch click out as the motor gets up to speed. You will also hear a definite click as it spins down. It would be unusual for a cooker hood to have a start cap.

(run caps are usually higher voltage rated - they typically want to be over 1.5 x RMS voltage)

You can have a motor that has just a start cap and no run cap, and also the reverse.

If it has just a start cap and that has failed (usually the motor just sits there and hums at you, you can manually spin it (in either direction) and it will run fine once its got started.

Run cap motors won't run without them, and will also only run in the proper direction.

Most of them have that...]

[David]

Thanks.

My education progresses. :-)

The bit that I am now (currently?) failing to understand is how a single phase motor will start without a start capacitor.

The #101 guides suggest that a single phase motor without a start capacitor will just sit and hum, as you describe.

I can remember from my childhood the hobby electric motors (DC admittedly AFAICR) which needed a quick flick to start them in either direction.

Cheers

Dave R

[Harry Bloomfield]

David expressed precisely :

That does not apply to a DC motor, they rotate in a direction depending on the polarity of the supply and do not need any help to start.

The very small AC motors (used in clocks), would run randomly in either direction - if the direction of run was important, they would have a pawl and spring arrangement, to force them to run in the required direction.

[John Rumm]

The run cap in effect creates a second phase leads the primary one, crating field progression or rotation in the stator.

Hobby electric motors are typically DC with a single winding and a simple two terminal commutator. Hence they are not self starting in all rotational positions. However the run direction will be dictated by the polarity of the supply / orientation of the permanent magnetic field.

[damduck-egg]

My younger brother got given a model Spitfire aircraft around 1969 manufactured by Dinky . It had a propellor rotated by an electric motor and to start rotation you flicked the propellor so although it may not have been common such a flick starting DC motor did exist although AFAIK it only rotated in one direction. I guess it may have only had two poles and the prop gave just enough flywheel action to maintain rotation once started. In truth it wasn't used much as the battery was an N type not as easily found in shops as they are now and the nearest town that had a stockist was only visited a couple of times a year.

G.Harman

[Brian Gaff]

However I'd have expected at least some kind of buzz if you try to flip the fan while its on, which worries me a bit. Brian

[Brian Gaff]

Not really its used to shift the phase so it actually rotates, and goes the right way, at least the one we had was like that. How many wires coming from the motor? Brian

[Brian Gaff]

If you look at an electric clock motor you often find a little spring ratchet thing that engages if the direction its incorrect and the spring flicks back and makes it go the right way. Besides one could with an induction motor arrange the windings so that the phase as perceived by the rotor is actually biased one way. What I'm not getting though is how the thing that selects the speed works. At least not from your description. Brian

[Brian Gaff]

Most self starting motors for models have odd numbers of poles on the armature, 3 5 7 etc, the more poles the slower but the smoother it runs. Brian

[David]

I haven't got to the stage of connecting the now removed cooker hood back up to the mains, and testing the "flick" approach.

Some "ick" degreasing is called for first.

I didn't fancy reaching up far inside the hood assembly to try and find a fan to flick when it was still mounted on the wall and powered up.

As far as I can recall there was no hum, which would have suggested a failed start capacitor.

[tabbypurr]

No it doesn't. Motors that use start caps, which that is not likely to, still get power when the cap fails.

NT

[Harry Bloomfield]

Brian Gaff explained on 20/01/2018 :

The one I had, which the fan fail a couple of years ago, had three speeds and from what I could see - used different motor windings to produce the speeds. My tests suggested it had built into the motor failed thermal fuse, so I abandoned the attempt to repair it.

[David]

O.K. now I'm really depressed. :-(

I assume that if the design is similar to yours then it must be a common component which has failed otherwise two of the three speeds would still work.

Cheers

Dave R

[tabbypurr]

If the fan's dead maybe you could fit an extractor fan onto the outlet in there. What does a multimeter on its connections tell you?

NT