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Darold Petty

help needed, electrical theory issue !

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Darold Petty

I am retired, but was a carpenter, plumber, and home improvement contractor.  I am quite well versed in residential wiring and circuit breaker panels but I know nothing about electrical theory. 

(Why do electrical motors posess such immediate and full  torque?)

  I use this model of small humidifier for my 200 sf hobbyist greenhouse.  Recently it died and I purchased a replacement.  Afterwards I decided to disassemble the defective unit.  I quickly recognized the bad part as a 'capacitor' based on the exploded drawing from the new unit.  I contacted the manufacturer only to learn that it does not offer replacement parts.  The 'support' person told me to purchase a capacitor on-line with the same specifications.  Just how I would access this info from the melted unit was not clear, but I did get the specs from the new, replacement unit.

  Anyway, I need a 250 vac  8.0 uf (-5/+10%) capacitor,  these seem to both common and cheap online.   However, I could not locate the exact brand and model used in my humidifier. 

I have read the Wikipedia entry for capacitor twice but I still don't understand what this component actually does.  So my questions...

1)  What does the capacitor do ?

2)  Why has the bad one appeared to have shorted out, with the eruption of melted plastic?

3)  The bad one had two terminals; with a red and a blue wire connection,  but the aftermaket ones have no color designation to the two terminals.  Does this matter ?

  Thanks very much if you can educate me about these three questions !

 

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Palmarum
Just now, Darold Petty said:

... 1)  What does the capacitor do ?

2)  Why has the bad one appeared to have shorted out, with the eruption of melted plastic?

3)  The bad one had two terminals; with a red and a blue wire connection,  but the aftermaket ones have no color designation to the two terminals.  Does this matter ? ...

 

That cap had fun for a short while.

 - Basically the capacitor stores a charge and when needed (power applied) the charge kicks the motor into gear to get it going. This charge helps the motor to speed up quickly and to break inertia. Some motors will not start spinning without a working capacitor. It would just sit there and go 'Hummm' and not spin. The larger the motor the larger the capacitor. I work with the ones on electrical sprinkler pumps now and then and other motors all the way back to manufacturing and electrical class in high school.

 - There is a capacitance gel-like substance within the capacitor that holds the charge. It can only hold so much, usually measured in farads or more likely megafarads. Too much power and well, you know the result. The symbol is (MF) next to a number. Sometimes if there is a short, there is no path for the capacitor to direct its charge and it overloads.

 - The connectors should have a positive and negative designation on them. Be wary of online substitutions that may be too low quality or it may happen again. Usually its a straight-up replacement deal. Many manufacturers will not sell you replacement parts because they want you to buy a brand new machine again and again...

This is a basic description and there can be more to it than what I added here.

P.S. - We used to charge a capacitor by hand by touching it to a running motor, then walk around and Zap! people with it by touching it to their skin. We would use the big capacitors too, like the size of a spray paint can. I do not recommend this unless you know the target well or can run fast.

Ryan

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Darold Petty

Ryan,   thank you very much ! 

Some of the aftermarket capacitors rated at 8 uf are listed as 250 vac and some at 450 vac.  Would the 450vac one work, and would it be more durable and less likely to fail ?  

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Just now, Darold Petty said:

Ryan,   thank you very much ! 

Some of the aftermarket capacitors rated at 8 uf are listed as 250 vac and some at 450 vac.  Would the 450vac one work, and would it be more durable and less likely to fail ?  

I am not sure, but I would say no. It would sound like it would be more durable but it may not work at all as the voltage would not be sufficient to charge the capacitor. Also, the 450vac cap' could be designed to work only on that voltage and I would imagine at 450 vac, (with the same uF) the charge would be much more powerful than what is needed. Also not sure, but the 450 vac cap' could be for a 3-phase electrical motor, not a regular 2-phase situation. Depends on how much experimentation you like to do.

I would try to find the most identical replacement by a reputable company. Talk, phone, email, etc. to the company before buying and ask them all the questions you can think of. I like to do my research that way and if they like to answer questions as much as I like to ask them, then I will try ordering from them.

Ryan

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Darold Petty

Thanks again, I feel more informed about selecting the replacement. 

This seems almost criminal, that the humidifier manufacturer won't sell a $10 part,  attempting  to trigger a $325 replacement purchase.   :rant:

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1 hour ago, Darold Petty said:

... This seems almost criminal, that the humidifier manufacturer won't sell a $10 part,  attempting  to trigger a $325 replacement purchase. ...

I agree as many companies seem to function the same way. I wonder if you dig deeper, you may find that others have had the same problem with the same model.

Ryan

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WestCoastGal

Let us know how you make out. The manual made specific capacitor reference to 250V/60HZ and I would stick to that.

We needed a capacitor on our A/C unit this past summer. A/C repair company came out and had part in his truck. The same part online was like $20 but he charged over $100. His time was billed separately so it was just the part. My husband called to ask if they had made a mistake on the invoice and promptly told no. 

 

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Darold Petty
On 2/22/2021 at 12:51 PM, Darold Petty said:

3)  The bad one had two terminals; with a red and a blue wire connection,  but the aftermaket ones have no color designation to the two terminals.  Does this matter ?

  

I spent an additional hour diving down the internet rabbit hole, and learned that if the capacitor has only two terminals, then it doesn't matter how they are connected to the appliance wiring.

Success !  I have repaired a $325 appliance with a <$10 replacement capacitor.  Always check this part first !!  :greenthumb: 

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2 hours ago, Darold Petty said:

... Success !  I have repaired a $325 appliance with a <$10 replacement capacitor.  Always check this part first !!  :greenthumb: ...

Fantastic!

It's always fun when you can fix something and get it back to working the way it should. It is the best kind of high. B)

I am searching for a pressure cleaner part at the moment so that is my next "fix".

Ryan

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