FINDING CAPACITOR MFD RATING

[Bobice]

 

 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.

[JJDH]

Cool..

[ACtechGUY]

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.

[applianceman18007260692]

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

[Bobice]

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

[Bobice]

[user=57399]ACtechGUY[/user] 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.

[J5*]

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

[Bobice]

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

[ACtechGUY]

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.

Thank you , I now step off the retaliation box.

Feel free to throw some more rocks at me :shock:

[Bobice]

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.

[AmTec Services]

   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

[Bobice]

[user=66622]AmTec Services[/user] wrote:

   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

Amen.

[JJDH]

If a cap is rusted beyond reading and failed, I call the manufacturer and find what it needs to be.

[Bobice]

At 9:00 PM at night ?

[JJDH]

[user=43030]Bobice[/user] wrote:

At 9:00 PM at night ?

We have resources when needed.

[Bobice]

[user=70229]JJDH[/user] wrote:

[user=43030]Bobice[/user] wrote:

At 9:00 PM at night ?

We have resources when needed.

The multimeter is one of the best resource.