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FINDING CAPACITOR MFD RATING

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Posted: Sat Sep 4th, 2010 01:03 am

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1^st Post

Bobice

Joined:	Sun Nov 30th, 2008
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Using a good multimeter you can determine a capacitors Micro Farad (mfd) rating

mfd = 2650 x amps / volts

amps = start winding amps of compressor or motor

volts = volts measured across the capacitor terminals.

____________________
Retired US Army Refrigeration Specialist / NYC Board of Education HVAC/R (Retired)
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Posted: Sat Sep 4th, 2010 02:31 am

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JJDH

Joined:	Fri Aug 27th, 2010
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Cool..

Last edited on Sat Sep 4th, 2010 02:31 am by JJDH

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Posted: Sat Sep 4th, 2010 04:41 pm

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ACtechGUY
Master Appliantologist

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COOL formula , but mostly useless in the real world. :shock:

When do you really need to know the capacitance value of a capacitor? Yes that's right , when it has failed. But when it has failed the formula is useless....

I was excited years ago and tried the formula when I first came across it. But have not used it since, as a failed cap cannot reveal its capacitance rating via a formula.

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Don't know much. But learned early on, once you let the smoke out of a something electrical, you can never put it back in!! :oops:

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Posted: Sun Sep 5th, 2010 11:52 pm

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4^th Post

applianceman18007260692
Fellow, Academy of Sublime Masters of Appliantology

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GUY don't they have digital meters that measure MFDs on the market?

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Posted: Mon Sep 6th, 2010 01:03 am

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5^th Post

Bobice

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There are digital meters that have that capability.

However I think it is a good idea to learn "Ole School" as I believe that knowledge is a Beautiful Thing. JMO

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Posted: Tue Sep 7th, 2010 01:24 am

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6^th Post

Bobice

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ACtechGUY wrote: COOL formula , but mostly useless in the real world. :shock:

When do you really need to know the capacitance value of a capacitor? Yes that's right , when it has failed. But when it has failed the formula is useless....

I was excited years ago and tried the formula when I first came across it. But have not used it since, as a failed cap cannot reveal its capacitance rating via a formula.

Is it really ? Are most formulas usless ? I think not Do you know how many "Technicians" I have interviewed that know how to just keep replacing parts without knowing why ? The numbers are staggering.

Prime example of this is a company who shall remain nameless doing warranty work

having to send back technicians six times before getting to the real problem.

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Posted: Tue Sep 7th, 2010 01:36 am

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7^th Post

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every cap i have seen has the ratings on the can or can be found on a diagram

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Posted: Tue Sep 7th, 2010 02:50 pm

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8^th Post

Bobice

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Not always. Many times the rating has worn off.

I cannot count the times wiring diagrams were missing.

The formula is two fold.

1. An exercise in using a test meter

2. Diagnosing

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Posted: Tue Sep 7th, 2010 11:57 pm

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9^th Post

ACtechGUY
Master Appliantologist

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OK guys, Maybe you misunderstood what I was a typing.
(sorry for the delay, I had not internet for the last 4 days, darn AT&T and the holiday)

When I said the formula was useless , I was referring to the rash of failed(open, exploded, shorted) RUN capacitors that have been showing up for the last 5 to 10 years.

I do have a $300 FLUKE meter VERY capable of reading capacitance, IT however DOES NOT READ A DEAD CAPACITOR!!! Nor does any Multimeter.

In condensing units, water vapor manages to get in and rust the outside of some capacitors, rendering the value printed on them unreadable(it happens,). A/C manufacturers NEVER list the rating of compressor caps anywhere one the unit( I speak of Lennox, Carrier, Trane and their sub brands.)
If you have a cap that is dead and rusted beyond reading you HAVE TO go to the manufacturer to determine the cap that goes into that unit.

I don't know where you guys get your capacitors , but you really need to send us some down here. Because when ours fail (and it happens every, day) they can't tell us their values , regardless of how much we threaten them with a formula that can't possible work on a capacitor that is so dead it won't start a motor.

:soapbox:

Thank you , I now step off the retaliation box.
Feel free to throw some more rocks at me :shock:

____________________
Don't know much. But learned early on, once you let the smoke out of a something electrical, you can never put it back in!! :oops:

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Posted: Wed Sep 8th, 2010 12:28 am

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10^th Post

Bobice

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No rocks intended, but guess what ? A dead compressor is dead yet we check it with a good meter do we not.

I am just trying to get "Apprentices" as well as others use to Troubleshooting.

Makes them more valuable.

Last edited on Wed Sep 8th, 2010 12:29 am by Bobice

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Posted: Wed Sep 8th, 2010 01:11 am

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11^th Post

AmTec Services

Joined:	Sun May 16th, 2010
Location:	Tampa, Florida USA
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That formula is useful to check the cap under load. That is the real truth about whether a cap is good or not. It may check good with the cap meter, but be out of specs under load.

Bobice is right on, our new generation of techs need some real world trouble shooting skills. We need to instruct them on how to recognise and repair,not condemn and replace. JMHO :shock:

...................AmTec

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Posted: Wed Sep 8th, 2010 07:01 pm

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12^th Post

Bobice

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AmTec Services wrote: :soapbox:

...................AmTec

Amen.

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Posted: Wed Sep 8th, 2010 09:48 pm

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13^th Post

JJDH

Joined:	Fri Aug 27th, 2010
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If a cap is rusted beyond reading and failed, I call the manufacturer and find what it needs to be.

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Posted: Thu Sep 9th, 2010 09:03 pm

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14^th Post

Bobice

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At 9:00 PM at night ?

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Posted: Sat Sep 11th, 2010 12:02 am

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15^th Post

JJDH

Joined:	Fri Aug 27th, 2010
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Bobice wrote: At 9:00 PM at night ?
We have resources when needed.

____________________
Model sears kenmore 41744052400

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Posted: Sat Sep 11th, 2010 01:27 am

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16^th Post

Bobice

Joined:	Sun Nov 30th, 2008
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JJDH wrote: Bobice wrote: At 9:00 PM at night ?
We have resources when needed.
The multimeter is one of the best resource.

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Current time is 12:52 am
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