Question about failing starter capacitors on electric motors

work?

starts, but

is

bulges or

Exactly as printed + or - 5%

Yes, and when coupled with the uncertainty of the multimeter figure, it may, or may not be, in spec :-)

MrT.

I've been told that some air-con technicians/mechanics use ESR meters to identify motor start caps which have gone bad....

Bob

An ideal use for your ESR meter Bob. Polypropylene (MKP) starter caps measure very low when they are in good condition.

In another life I used to work in a motor rewind and repair shop, personally I would regard the reading you got as reasonable (meter accuracy etc.) but the burning smell is a worry since it comes from overheated windings. Once that happens a few times there is every chance your motor is fritzed ! The situation really needs checking by experienced persons which is not easy for you out there, also it may well be the cost of a new motor and controller would be similar to that of a callout. Perhaps you could send the parts into town for testing and take it from there. Incidentally technically that is a "Run" capacitor and of different construction to a "start" cap. Run caps usually last longer than start caps. Hope you find a solution Rod .

--
Cheers .......... Rheilly P

"Ross Herbert"

** It weird how poly film caps sometimes go high ESR.

It aint like there is any liquid electrolyte in there to dry out.

Got a 22nF Wima class X cap here now that measures about 5 kohms in series with 2 nF.

Not visibly damaged.

Pulled it out of a Marshall amp, was driving output valve grids.

........ Phil

As Phil said, it's weird that this kind of cap would fail with high ESR. BTW and just for everyone's info, DSE are flogging all their kits at ridiculously low prices at the moment. The ESR meter is just under $25 when at one time it was up near $80.

Cheers Bob

its probably a failure of the end-cap metallisation. If I had access to ABSE I could post a photo of a partially assembled film cap - I have one here, its 80mm OD, 100mm long and measures 109uF on my Fluke 12.

If the metallisation process is poorly controlled, the metallisation-foil interfaces wont be very good (high resistance) and thumping great wads of current can blow them open. Its a runaway kinda thing too....

wow, I'll see if I can get one here in NZ for that sort of price! I cant find it on the NZ website though...

Cheers Terry

I dunno what's going on with the Kiwi DSE website. I can't find the ESR meter by catalog number. All I managed to find by searching for 'ESR' was the chart for the first version's front panel. I couldn't find the K7205 LOPT tester either. Looks like DSE's not stocking a lot of their kits over there now. Does anyone know anything about this?

Bob

On Wed, 31 Jan 2007 15:10:44 +0900, and after reading the post titled " Re: Question about failing starter capacitors on electric motors", "Rheilly Phoull" ordered the talented chickens to cluck & peck the following:

Thanks to all who offered suggestions. I spoke to the electrician (original installer of the aircon), and his assessment is it sounds like the motor is dying. The fan motor cops a hiding in it's location (pretty corrosive bore water used in the aircon), and I replaced the same motor about 4 years ago.

I ran into town this arvo and got a new motor. The whole fan/motor assembly comes out of the aircon in about 5 minutes, and the connections are clearly marked on the control board(also took plenty pics before removing connections as well), and on the side of the motor.

MY next 'challenge' was removing the plastic fan off the old motor shaft. I hadnt remembered the compressible collet that sits between the fan & shaft, and of course it fell apart as we remove the cover plate. No chance of making one up, so I expect we will be in touch with electrician again tomorrow....sigh.

Thanks again for all the ideas. I might pick up another capacitor as well when picking up the collet. May as well change it out, and then I know they are both right to go.

Cheers,

Rod.....Out Back

I'll probably never use it, but I am going to go and buy one if they are still at that price!

There might be other really cheap kits you'd have more use for? The ESR meter is awfully specialised. If you decide to get one, be aware that DSE's selling the Mk1 (1996) version of the meter for the same price, and the Mk1 and Mk2 cartons tend to get mixed up on the shelf.

Thanks Bob. I will go and have a look today. Its one of those tools that occasionally you say 'I wish I had one of those'. Whilst i very rarely have anything to do with hardware it does still arise from time to time.

Are DSE clearing out all there kit stock?

I think DSE NZ don't stock this kit. I purchased one a year or so ago and had to use mail order from DSE Australia. It's proved to be a useful addition to my workshop.

cheers, ron

Sounds like they need more shelf space for the farting ashtray lines ;-(

There were two of each on the shelf in the Box Hill (Melb) store, tagged at $49.95 - but the counter check showed they were $25. Thanks for the heads-up, I almost bought one six months ago at >$70. Now I have a MK2 to build.

What're the main differences in capability between the MK1 and MK2?

What else can it be used for apart from testing electro's?

Clifford Heath.

"Clifford Heath"

** Not a great lot

The Mk2 has better protection for the meter .

** Resistors from 0.01 ohms to 100 ohms - but must be non-inductive, lengths of wire or coils are out.

The ESR of cells and batteries - indicates condition, plus approximate state of charge or remaining capacity.

Just perfect or button & lithium cells etc.

Do a Google search - plenty of stuff on Bob's site and elsewhere.

...... Phil

Bob Parker wrote in news:45c0725d$0$13520$ snipped-for-privacy@per-qv1-newsreader-01.iinet.net .au:

Hi Bob,

I came across this review website and wondered if you think the comments and tests on your design are fair?

"Geoff C"

** How about this quote then:

" But a good 1 ufd, 200 volt aluminum electrolytic can have an ESR of 100 ohms or more. That is beyond the measurement range of all of the meters listed above! "

I just checked a number of old but unused electros bought from WES in a bulk pack.

Values ranged from 0.47uF to 1.0 uF with voltages from 250 to 400 volts - physical size all about 12mm by 8mm dia.

None tested more than 30 ohms on Bob's Mk1 meter.

Any that test over 100 ohms are FAULTY !!!

........ Phil