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  1. #1

    need a lesson on capacitors

    Hey guys , I've been a tech for three years now. I don't really know much about capacitors except they fail alot when it gets hot i love capacitor calls because they're quick and easy calls. Moneymaker calls as i often call them.lol. how much do they increase the voltages and what makes them fail so much? Can a 370vac be replaced with 440vac? is the capacitor doing work the whole time the unit is on or is it out of circuit after the start windings are done? Any info would be great and thanks in advance!

  2. #2
    Join Date
    Nov 2011
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    how much do they increase the voltages

    why not measure it and see?

    and what makes them fail so much?

    Made in China

    Can a 370vac be replaced with 440vac?

    yes

    is the capacitor doing work the whole time the unit is on or is it out of circuit after the start windings are done?

    yes, for run caps on PSC motors, no for start caps

    (when the windings are "done"? )

  3. #3
    Join Date
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    They don't increase the voltage. The emf created by the spinning motor does that.

    They fail so much because of low quality, and poor design.

    A 440v cap can always replace a 370v cap of the same microfarad rating.

    The run cap is in the circuit the entire time. A start cap is removed from the circuit after it helps the motor to start by a relay.

    A run cap is essentially a starting cap that is left in the circuit while the motor RUNS. It is filled with oil to help it take the heat of remaining in the circuit. A start cap has no oil, because it is not designed to remain in the circuit.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  4. #4
    Join Date
    Sep 2002
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    Virginia
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    also , they use a run capacitor to help average out the power it needs under certain loads. Its like a booster when the motor calls for help. For instance when the rev valve shifts and the motor suddenly needs a little boost of energy , it sends a little surge of power. Then when its not using extra power the cap temporarily stores it.

    Some caps store that extra energy even after the power is off , and if you touch the terminals it will light your tail up. But most drain the power as the unit shuts down.

  5. #5
    Quote Originally Posted by Snapperhead View Post
    also , they use a run capacitor to help average out the power it needs under certain loads. Its like a booster when the motor calls for help. For instance when the rev valve shifts and the motor suddenly needs a little boost of energy , it sends a little surge of power. Then when its not using extra power the cap temporarily stores it.

    Some caps store that extra energy even after the power is off , and if you touch the terminals it will light your tail up. But most drain the power as the unit shuts down.
    I've always heard they would give you a heck of a jolt. I've been fortunate enough not to receive one yet!. Thanks for the info. Sometimes we have new capacities fail in a week or two. I hate call backs just wandering if there was something we could do to improve situation, but don't look like there is until capacitor manufacturers start putting out better product!

  6. #6
    Join Date
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    Packard capacitor training video http://www.youtube.com/watch?v=TRi5WTntirY
    Aircraft Mechanical Accessories Technician. The Air Force changed the job title to Air Craft Environmental Systems Technician. But I've decided I'll always be a Mech Acc.

  7. #7
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    Aircraft Mechanical Accessories Technician. The Air Force changed the job title to Air Craft Environmental Systems Technician. But I've decided I'll always be a Mech Acc.

  8. #8
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    Nice vids.
    You need to put the phone down and get back to work!

  9. #9
    Join Date
    Jul 2012
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    I usually replace the caps, start and run if there's been any problem with that circuit. Had an issue once with caps on blower motors in the top of the bread ovens at the Subways I work for, eventually had to go up to the higher voltage rated caps. It's hot at the top of those ovens <> 350 degrees.

  10. #10
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    Quote Originally Posted by mainstreamac View Post
    I've always heard they would give you a heck of a jolt. I've been fortunate enough not to receive one yet!. Thanks for the info. Sometimes we have new capacities fail in a week or two. I hate call backs just wandering if there was something we could do to improve situation, but don't look like there is until capacitor manufacturers start putting out better product!
    Start caps are the worst to be shocked by.......

  11. #11
    Join Date
    Oct 2010
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    AZ
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    644
    Some of them fail because they are pieces of junk, but heat also wreaks havoc on them. I have even seen some companies put a hole in the electrical panel so the base of the capacitor slides in the hole into the air return so they stay cooler. You should also check out the other electrical components associated with the bad capacitor to make sure they are in good working condition (bearings, motor windings, etc)

  12. #12
    Join Date
    Jul 2012
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    North west Arkansas
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    Quote Originally Posted by Trehak01 View Post
    Start caps are the worst to be shocked by.......
    Try not to get shocked, always short leads on cap to ground before I do anything, if it'll arc and burn an old screwdriver shaft it can't be good for you. Don't use a screwdriver that you want to keep.

  13. #13
    Join Date
    Jun 2001
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    Moore, Oklahoma, United States
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