|
Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
|
Thread Tools |
12th Oct 2018, 1:03 pm | #1 |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
|
Faulty motor run capacitor.
I have just ordered a replacement 6uF motor run capacitor for my Zanussi tumble dryer.
The original component had gone down in value to 3.5uF. The mechanism of loss of capacitance in class X capacitors is well known, but do motor run capacitors use a similar technology to class X types and loose capacitance by a similar mechanism or does something quite different cause loss of capacitance in motor run types? I realize that "motor run" is a description of the of the capacitor's application and not necessarily its construction technology. There may be different technologies used for them and therefore different modes of failure. |
12th Oct 2018, 8:02 pm | #2 |
Nonode
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
Posts: 2,350
|
Re: Faulty motor run capacitor.
I have a large number of motor run, 450v AC rated capacitors, and checking against the nominal value on the cans, I find very little difference between claimed and measured. I also have some 240v AC rated ones, with unusual values eg, 120UFd - 160UFd. All measured somewhere within their stated ranges.
The only failures I have had have been very loud exploding failures. As I am using these in connection with rotary converter developments, I now double all values with two in series. No exploders since. I do have a few smaller block like ones in the 1UFd to 5UFd range, will check them sometimes. I don't think I have used any of them yet. Les. |
12th Oct 2018, 8:11 pm | #3 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,580
|
Re: Faulty motor run capacitor.
My experience of motor-run capacitors is that they lose value. My old tumble dryer used an 8uF 450VAC capacitor and the first symptoms were reluctance of the drum to turn usually accompanied by a low humming noise. The first one I removed had gone down to around 3.5uF. That replacement was replaced about 5 years later and the value had dropped to around 4uF.
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
12th Oct 2018, 8:50 pm | #4 | |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
|
Re: Faulty motor run capacitor.
Quote:
I was just interested if anyone knew the mechanism of failure that caused the capacitor to loose capacitance. In class X capacitors it is the "self repairing" mechanism that causes gradual loss of capacitance. Perhaps its the same with motor run types? |
|
12th Oct 2018, 8:57 pm | #5 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,274
|
Re: Faulty motor run capacitor.
well..the spec sheets call them Metallised Polypropylene, as are most x caps.
These days they usually have a safety release that cuts off the power if the vent cap lifts
__________________
Kevin |
12th Oct 2018, 10:20 pm | #6 |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
|
Re: Faulty motor run capacitor.
|
12th Oct 2018, 11:11 pm | #7 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
|
Re: Faulty motor run capacitor.
And before that, most were metallised paper sporting the same self healing properties.
|
13th Oct 2018, 5:21 pm | #8 |
Heptode
Join Date: Feb 2003
Location: Garnant, near Ammanford, South Wales, UK.
Posts: 657
|
Re: Faulty motor run capacitor.
Motor run capacitors used to be very reliable, and held value well, I have equipment that's 40 years old and the caps measure fine.
Then 10 years or so ago they suddenly became unreliable, loosing value very quickly. When I worked on commercial dishwashers, glasswashers etc we used to fit new ones at every annual full service, they are that bad. I now work on whitegoods, including tumble driers etc and regularly change them on machines that are only 2 or 3 years old. Richard
__________________
BVWS member. |
13th Oct 2018, 5:45 pm | #9 |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
|
Re: Faulty motor run capacitor.
That's an interesting observation Richard. I wonder what's going on there?
A reduction in the quality of new capacitors? An increase in the amount of noise and spikes on the mains supply? Both? |
13th Oct 2018, 6:06 pm | #10 |
Dekatron
Join Date: Jan 2006
Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex.
Posts: 5,817
|
Re: Faulty motor run capacitor.
I had the Engineer round for a previous T Dryer. The 8uF had failed under warranty. He consulted the service details on his gadget and said "That's funny it shows a 16uF replacement!" I said "Maybe this is why?" He agreed, it never failed again and as the back was all metal it was very safe anyway!
Dave W |
13th Oct 2018, 8:50 pm | #11 |
Octode
Join Date: Apr 2005
Location: Peterborough, Cambridgeshire, UK.
Posts: 1,898
|
Re: Faulty motor run capacitor.
I recently changed one on a mate's compressor, about 4 years old but to be fair it is used all day 5 days a week. the cap was strapped to the motor body against the cooling fins in the airflow of the cooling fan. I put the failure down to the hot summer and in my opinion bad siting of the capacitor.. But reading this maybe not...
Rich. |
13th Oct 2018, 10:40 pm | #12 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,554
|
Re: Faulty motor run capacitor.
We have a local scrappy and he had a little compressor of the kind sold by pretty well all the DIY sheds.
It was humming and he was patting the plastic cover. I told him to whip the cover off and look for a capacitor with its guts spilled out. We found one with a split in it. We got it before it had all spilled out. |