How to diagnose a faulty motor start capacitor?

[p38arover]

Our clothes dryer won’t start spinning unless we give the drum a hand to start.

As you can imagine, this is a bit inconvenient - put a pencil into the hole where the door catch is, wiggle it around until one hears the microswitch operate, press start, when one can hear the motor buzzing, spin the drum with the other hand to get it spinning. Then, while it’s spinning close the door whilst removing the pencil - and hope the drum continues spinning.

It usually doesn’t, so try again - and again - and again...

Then, when the timer stops it to rotate the drum in the opposite direction, do it all again.

The dryer is long out of warranty but has had very little use so I’m not looking to replace it. My wife is! :)


I’m wondering if the motor start capacitor could be faulty. I’m not looking forward to getting this thing off the wall and out to the garage.

[Tins]

Sure sounds like a start cap to me.

[JDNSW]

Try replacing the capacitor - unless it is unusual they are not that expensive.

[Tote]

Just pull it apart and replace the cap. It might be split or swollen or it might not. be aware it might be a run cap rather than a start cap, regardless replace it with one of the same type and you should be good. I hjate dismantling driers though, the drum is usually mounted on the back panel making it a PITA to put back together.

Regards,
Tote

Our clothes dryer won’t start spinning unless we give the drum a hand to start.

As you can imagine, this is a bit inconvenient - put a pencil into the hole where the door catch is, wiggle it around until one hears the microswitch operate, press start, when one can hear the motor buzzing, spin the drum with the other hand to get it spinning. Then, while it’s spinning close the door whilst removing the pencil - and hope the drum continues spinning.

It usually doesn’t, so try again - and again - and again...

Then, when the timer stops it to rotate the drum in the opposite direction, do it all again.

The dryer is long out of warranty but has had very little use so I’m not looking to replace it. My wife is! :)


I’

[p38arover]

Thanks chaps.


I hate dismantling driers though, the drum is usually mounted on the back panel making it a PITA to put back together.

Yes, I know what you mean, I had to do that a few times with our old Simpson. My wife doesn't like this Aldi dryer, she thinks the old Simpson was better.

[Bosco15]

Definitely a faulty capacitor.
I have picked a few driers up, from side of road, and this has been the reason that they were thrown out.
Easy fix. Find a capacitor in an old TV or drier, on the side of the road.
I love to recycle.
I now let the wind dry my clothes.

[scarry]

As others have said,it is probably a run capaciter.
Once you get it out,put a pic up we will be able to tell.

We get them from somewhere like Element 14,but we generally buy 50 or 60 at a time.

The freight for one will be a killer so picking one up locally is the go.

[BradC]

To answer the thread title, I use a capacitance meter or often just the capacitance setting on my multimeter. I'd lay a decent bet it doesn't have a start capacitor, but it's a permanent split-capacitor motor with a run cap that is as dry as a nuns.

Last one I had was a 32uF cap that measured 6uF. I had a 20uF handy so I put that in until I could get the correct cap.

[p38arover]

Yes, I was going to put my capacitance meter on it when I get it out of the laundry. I just need a mate who can help me lift it off the wall bracket and lower it to the ground.

Is the capacitance value important? It's been some years since I studied electric motors at tech.

[BradC]

Is the capacitance value important? It's been some years since I studied electric motors at tech.

Yes. The combination of the capacitance and inductance of the winding produces the 90 degrees phase shift required to get the thing cranking. Having said that, my AC was running along from the 32uF cap right until it dropped to 6uF. What I noticed on my power meter trace was as the cap degraded the start current progressively increased until it reached a point it was tripping a 10A breaker. The run current hadn't increased significantly but the compressor was running for longer, so I expect it had less torque and the rotor was "slipping" more.

Best replace whatever comes out with the same (or similar given most are between 10-20% tolerance). Like I said, I subbed a 20 for a 32 and that ran ok until I could get the correct part.

[p38arover]

I got it out. It's a 9uf 450v (I assume it's 9+9uf). My capacitance meter measures the capacitance at 109+113pf (checked the meter against a couple of other caps). (I don't have a multimeter that measures capacitance, only a multipurpose testing unit ex-China - it tests resistors, diodes, transistors (and identifies the pinouts), caps, and inductors.)

My wife doesn't want me to replace it as she want a new dryer - she says this one is too slow compared to the old Simpson (which was about 20-25 years old when replaced). I don't want to buy a new dryer. This one is 10 years old and has had very, very little use. New dryers are not cheap but I am.

[scarry]

So sneak off and grab a 10mf,run cap,a 9 is probably more difficult to find.
Or an 8mf will probably do.
And a similar voltage.

[p38arover]

Yes, I’ll try the local electrical wholesalers tomorrow. I assume it’s a 9+9 uF for start and run.

I’ve probably got some 450v non-polarised polyester or similar caps in my parts drawers but nothing higher than 1uF. Not something I needed in my electronics work.

[BradC]

Yes, I’ll try the local electrical wholesalers tomorrow. I assume it’s a 9+9 uF for start and run.

I’ve probably got some 450v non-polarised polyester or similar caps in my parts drawers but nothing higher than 1uF. Not something I needed in my electronics work.

Yeah, don’t use those. NPOs are not self healing so the first couple of surges will set fire to it, then you’ll really be up for a new dryer.

[p38arover]

^^ My wife would like that.

[p38arover]

Well, it seems it was just a run cap, not a dual start/run cap. I bought one this morning from a local electrical wholesaler (he told me it was a run cap only). Installed and the drier is operational and back up on the wall (I had to get the apprentice concreter neighbour to help me put it back up on the wall mount.)

[Old Farang]

I stumbled across this while looking for something else. The following may be of interest, even though it turned out to be just a run capacitor.

Cheap split phase single phase motors:
All single phase motors need some form of starting assistance compared to a 3 phase motor.
A start winding consists of a similar number of turns to the run winding but is of thin wire and therefore high resistance. It is placed in slots 90 degrees apart from the run winding but will only give about half of that displacement electrically, resulting in very poor starting torque.

Capacitor start motor: In an attempt to improve starting torque a capacitor is placed in series with the start winding, which because of its electrical properties will give a much better electrical displacement resulting in improved starting torque. The windings are usually the same as previously. The important thing to note here is that a start capacitor is an electrolytic capacitor, and as such cannot be permanently connected. As it is connected in series with the start winding it is disconnected along with the winding, which occurs as before, at around 75% of the motors rated running speed.

Capacitor start, capacitor run: In this case another capacitor is connected in parallel to the starting capacitor and the start winding. This capacitor is of the "paper" variety and can be permanently connected. The starting capacitor ONLY is then disconnected as before, leaving both the run capacitor and the start winding permanently connected. This arrangement has several advantages in addition to improved torque. The vectors and the math's involved are not of concern here!

Permanent split capacitor motor: PSC. This type of motor still has two windings, but it does not have any switch as both the start winding and run capacitor are permanently connected, the capacitor again being of the "paper" oil filled type. It also has a few advantages, such as higher pull out torque, efficiency, and power factor, but it may have lower starting torque.

In my day this last type was very unusual, maybe not even in existence. I used to rewind all types of both single and three phase motors, and don't recall them. I served my time in a farming area where at the time, the rural distribution grid to farms was single phase, 500volts. In some states this system used a single wire earth return (SWER), but where I lived the system did have a return conductor.

The main point here is that we used to get a lot of repulsion induction motors in for service from dairy farms. These 500 volt motors (mostly 5 hp) have a rotor that looks just like a DC generator or motor armature, even being fitted with carbon brushes, albeit for a different function.
Skimming and under cutting the commutators, being a time consuming job, became my function as a form of cheap labor! Always a rush job as well, as the dairy farms needed them back the same day!

The point here being that those motors had good starting torque.

And to answer the question: We used a 500 volt megger to charge up a capacitor as a test. No big fat discharge spark meant a failure!

[p38arover]

I studied all this when I did training for the Broadcast Operator's Certificate of Proficiency 20+ years ago (to work as a tech at a radio station). I've forgotten most of it.

I never thought to use my Megger as described.

500v distribution in the country. I'd never heard of that!