Question about failing starter capacitors on electric motors

[Rod Out Back]

Folks,

Do starter capacitors ever fail gradually, or do they either work or not work?

I have a rooftop evaporative aircon, which is playing up. The motor starts, but
accompanied by loud humming and the fresh smell of burning electrical
insulation.
Starter capacitor in the control box (it is a variable speed controller) is
nominated as 25uF (+- 5%), and reads with a multimeter as 22.74uF. No bulges or
deformities on the starter cap.

Should this reading be exactly as printed on the cap?

I have checked all the wiring into the control box, and out to the various
accessories (fan motor, water pump motor & downstairs control box -with the
user-selectable switches in it for the aircon), and there dont seem to be any
problems there.

Water pump starts happily, with no humming, and no burning electrical smell.


My suspicion is I have a fan motor about to expire. The electrical smell doesnt
manifest itself in the rooftop control box, and only appears when the fan is
started.

Info on the death of starter capacitors appreciated.



-----------------

Cheers,

Rod.....Out Back


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[Lord Garth]

Folks,

Do starter capacitors ever fail gradually, or do they either work or not work?

I have a rooftop evaporative aircon, which is playing up. The motor starts, but
accompanied by loud humming and the fresh smell of burning electrical
insulation.
Starter capacitor in the control box (it is a variable speed controller) is
nominated as 25uF (+- 5%), and reads with a multimeter as 22.74uF. No bulges or
deformities on the starter cap.

Should this reading be exactly as printed on the cap?

Exactly as printed + or - 5%

 

[Mr.T]

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.

 

[Bob Parker]

Folks,

Do starter capacitors ever fail gradually, or do they either work or not work?


Info on the death of starter capacitors appreciated.



-----------------

Cheers,

Rod.....Out Back

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

Bob

 

[Ross Herbert]

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.

 

[Rheilly Phoull]

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

Bob

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 .

 

[Phil Allison]

"Ross Herbert"

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

** 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

 

[Bob Parker]

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

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

 

[Bob Parker]

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

 

[Rod Out Back]

Question about failing starter
capacitors on electric motors",

"Rheilly Phoull" <[email protected]> ordered the talented chickens to
cluck & peck the following:

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 .

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

 

[The Real Andy]

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

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

 

[Bob Parker]

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.

 

[The Real Andy]

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?

 

[ron]

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?

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

 

[budgie]

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?

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

 

[Clifford Heath]

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.

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.

 

[Phil Allison]

"Clifford Heath"

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

** Not a great lot

The Mk2 has better protection for the meter .

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

** 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

 

[Geoff C]

..au:

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.

Hi Bob,

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

http://www.anatekcorp.com/testequipment/esrcompar.htm

 

[Phil Allison]

"Geoff C"

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

** 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

 

[Geoff C]

"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

Good to know, thanks.