What is Rdis of a capacitor and is it important? « on: December 28, 2019, 08:24:11 PM » Author: Fluorescent05
I got a 100 watt CWA mercury vapor ballast for Christmas and it says "10 microfarad 240 volt cap" (which are readily available as fan capacitors) but it also says "2.60 MEGOHM MAX Rdis". What does this mean and will it affect performance of the ballast?
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	Re: What is Rdis of a capacitor and is it important? « Reply #2 on: December 28, 2019, 09:02:32 PM » Author: Fluorescent05
Thank you! That sounds very plausible!
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	Re: What is Rdis of a capacitor and is it important? « Reply #3 on: December 29, 2019, 03:16:34 AM » Author: Medved
It is for safety reasons: To make sure when the power is disconnected, there is no unsafe voltage (so the capacitor discharged) after a given time limit. The time depends on the voltage the capacitor could be exposed and the time constant of the capacitoance and the discharge (aka bleeder) resistor.
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	Re: What is Rdis of a capacitor and is it important? « Reply #4 on: December 29, 2019, 09:48:35 AM » Author: Rommie
Usually for a PFC capacitor across the supply as we have here, it is to ensure there is no unsafe voltage (≯50V) after approximately 1 minute.
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	Re: What is Rdis of a capacitor and is it important? « Reply #5 on: December 29, 2019, 03:31:51 PM » Author: Fluorescent05
So if I were to use it without the discharge resistor, it wouldn't damage the ballast at all, but I could get shocked?
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	Re: What is Rdis of a capacitor and is it important? « Reply #6 on: December 29, 2019, 06:12:42 PM » Author: Rommie
Quote from: Fluorescent05 on December 29, 2019, 03:31:51 PM So if I were to use it without the discharge resistor, it wouldn't damage the ballast at all, but I could get shocked? Only if you touch both the capacitor terminals
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Ria (aka Rommie) in Aberdeen
Administrator, UK & European time zones. Any questions or problems, please feel free to get in touch

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