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370 vac vs 440 vac capacitors ?

Discussion in 'Residential' started by prokefah, Nov 6, 2013.

  1. prokefah

    prokefah New Member

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    What is the difference between 370 vac and 440 vac capacitors

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  2. Bob Hubbard

    Bob Hubbard Professional Bicker er

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    I only buy 440 caps ..... You can always use the higher v cap on a lower volt but not the other way around .....;)
     
  3. prokefah

    prokefah New Member

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    can u explain why i cannot
     
  4. Chuck

    Chuck SSP

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    440 caps rated for higher voltage. Here is link to a chart that shows how much cap life is affected by applying too much voltage.

    https://db.tt/QDQVLqdk
     
  5. flange

    flange Act like you care and do SOMETHING!!

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    its the insulation and materials classification. you can use higher numbers in place of lower, but not lower to replace higher.
     
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  6. Catpower

    Catpower The Crowd Pleaser

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    Yes it is the difference of the dielectric strength

    That being said, how come a lot of 480V single phase motors list a 370 V run cap?

    It makes no sense
     
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  7. Hot Gas

    Hot Gas Woof! Woof!

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    The answer is in the lattice. It's always the lattice.
     
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  8. flange

    flange Act like you care and do SOMETHING!!

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    do you have 460 volts on a single leg, or two hots at lower voltage converging at the winding?



    The voltage rating on a capacitor is the maximum amount of voltage that a capacitor can safely be exposed to and can store.
    Remember that capacitors are storage devices. The main thing you need to know about capacitors is that they store X charge at X voltage; meaning, they hold a certain size charge (1µF, 100µF, 1000µF, etc.) at a certain voltage (10V, 25V, 50V, etc.). So when choosing a capacitor you just need to know what size charge you want and at which voltage.
    Why does a capacitor come in different voltage ratings? Because you may need different voltages for a circuit depending on what circuit you're dealing with. Remember, capacitors supply voltage to a circuit just like a battery does. The only difference is a capacitor discharges its voltage much quicker than a battery, but it's the same concept in how they both supply voltage to a circuit. A circuit designer wouldn't just use any voltage for a circuit but a specific voltage which is needed for the circuit. For one circuit, 12 volts may be needed. A capacitor with a 12V rating or higher would be used in this case. In another, 50 volts may be needed. A capacitor with a 50V rating or higher would be used. This is why capacitors come in different voltage ratings, so that they can supply circuits with different voltages, fitting the power (voltage) needs of the circuit.
    Take note that a capacitor's voltage rating is not the voltage that the capacitor will charge up to, but only the maximum amount of voltage that a capacitor should be exposed to and can store safely. For the capacitor to charge up to the desired voltage, the circuit designer must design the circuit specificially for the capacitor to charge up to that voltage. A capacitor may have a 50-volt rating but it will not charge up to 50 volts unless it is fed 50 volts from a DC power source. The voltage rating is only the maximum voltage that a capacitor should be exposed to, not the voltage that the capacitor will charge up to. A capacitor will only charge to a specific voltage level if fed that level of voltage from a DC power source.
    Keep in mind that a good rule for choosing the voltage ratings for capacitors is not to choose the exact voltage rating that the power supply will supply it. It is normally recommended to give a good amount of room when choosing the voltage rating of a capacitor. Meaning, if you want a capacitor to hold 25 volts, don't choose exactly a 25 volt-rated capacitor. Leave some room for a safety margin just in case the power supply voltage ever increased due to any reasons. If you measured the voltage of a 9V battery supply, you would notice that it reads above 9 volts when it's new and has full life. If you used an exact 9-volt rated capacitor, it would be exposed to a higher voltage than the maximum specified voltage (the voltage rating). Usually, in a case such as this, it shouldn't be a problem, but nevertheless, it's a good safety margin and engineering practice to do this. You can't really go wrong choosing a higher voltage-rated capacitor than the voltage that the power supply will supply it, but you can definitely go wrong choosing a lower voltage-rated capacitor than the voltage that it will be exposed to. If you charge up a capacitor with a lower voltage rating than the voltage that the power supply will supply it, you risk the chance of the capacitor exploding and becoming defective and unusable. So don't expose a capacitor to a higher voltage than its voltage rating. The voltage rating is the maximum voltage that a capacitor is meant to be exposed to and can store. Some say a good engineering practice is to choose a capacitor that has double the voltage rating than the power supply voltage you will use to charge it. So if a capacitor is going to be exposed to 25 volts, to be on the safe side, it's best to use a 50 volt-rated capacitor.
    Also, note that the voltage rating of a capacitor is also referred to at times as the working voltage or maximum working voltage (of the capacitor). So when seeing the (maximum) working voltage specification on a datasheet, this value refers to the maximum continouous voltage that a capacitor can withstand without becoming damaged
     
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  9. newtech

    newtech 636

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    Must be a Carrier, I see that alot.
     
  10. Catpower

    Catpower The Crowd Pleaser

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    2 hots at 277 each, but why is the back EMF so much lower on a 480 motor, almost every 480 volt motor I have installed they always used a 370 V run cap
     
  11. flange

    flange Act like you care and do SOMETHING!!

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    If I were smart enough ot know all of the answers to life's questions, I would be in a different line of work. With that kind of brainpower, I could have answered my own question at eighteen when I was living in my car, which was....what the f*** do I do now?
     
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  12. Chuck

    Chuck SSP

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    The back EMF you read at the cap will change as the load changes. It is basically a generating effect so the faster the motor spins the more voltage is generated. If you measure 370v under full load and then decrease the load, you will read a higher voltage.

    But I don't know why a 480 volt motor would have lower back emf, Cat.
     
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  13. Snoring Beagle

    Snoring Beagle Need Little - Want Less - Love More

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  14. Texas-Tech

    Texas-Tech Official Geezer*

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    duhh
    All Trane caps on their 480v cfms are 440v, 10x and 25x440.
     
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  15. prokefah

    prokefah New Member

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    that was very useful
    thank u