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-   -   450 mfd capacitor replaced by a 370 mfd (https://www.askmehelpdesk.com/showthread.php?t=213464)

  • May 7, 2008, 08:27 AM
    gelagasse
    450 mfd capacitor replaced by a 370 mfd
    I don't very much about capacitors but I have a supplier that insists that a 40 mfd 370 VAC rated running capacitor can adequately replace a 40 mfd 450 VAC rated one. Based on what I read, a starting capacitor can vary by up to 10% but that running capacitors must be matched perfectly.
  • May 7, 2008, 11:35 AM
    KISS
    They are both 40 uf and operating off a 240 volt source. Just fine. Give him a beer for giving him such a hard time. He's right.
  • May 7, 2008, 01:24 PM
    gelagasse
    So that I can advise customers in the future, where on this capacitor does it say 240 volts? I see 450 VAC, 50/60 Hz
  • May 7, 2008, 02:46 PM
    KISS
    Well, since this is a DIY board, and domestic voltages are 240 VAC, so I assumed 240.
    The voltage rating of the capacitor must be greater than the line voltage. Hence 370 and 450 V are greater than 240, so your OK. The higher voltage introduces a higher safety and likely the lower voltage has a lower ESR (Effective series resistance). This will not likely matter.

    The start cap uf value is more critical than a run cap, if used. The run cap may change the speed.

    Extension cords, for instance, come in 300V and 600V ratings.
  • Nov 23, 2013, 03:04 PM
    Ken66220
    Many 450VAC capacitors are used on the secondary side of a transformer (lighting ballast) where the voltage is 400+VAC. While the supply voltage is from 120 to 277VAC a 370VAC capacitor is not adequate. While in this situation a 370 VAC capacitor may work, it is really not adequate protection for the real voltage incurred. I would use caution when the substitution is not up to OEM specs.

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