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  • Electrolytic Cap Voltage

    From UFO@21:1/5 to All on Tue Feb 11 10:38:40 2025
    I replaced a set of 500V / 100uF caps used in a HV doubler off
    a power supply that in the end generates about 900V from the
    typical input voltage.

    I had a set of EPCOS (TDK) 450V / 120uF caps and installed them
    just to see if they were in the limit.

    https://wmsc.lcsc.com/wmsc/upload/file/pdf/v2/lcsc/2211021130_TDK-B43255A5157M_C1607543.pdf

    In initial power up they seem to have about 478V on them with no load,
    with a small load they head down to 470v and under normal operations
    in the product they are as low as 430V.

    We are about 7.8% over the 450V when the math is done.

    The product is a ham radio transciever, so while listening the voltage on
    the caps
    is about 480V max. Transmit def brings the voltage below its rating.

    I have seen test equipment designed with caps that are right at the
    operating voltage of the power supply
    and have the max voltage on them
    last about 35 yrs before failing, so I guess there is more wiggle room near
    the top in some cases?

    In this case, they have a 0.01uF disc cap plus a 470k bleeder resistor in parallel
    with each cap, which I also replaced new. I believe this will help to smooth out
    the initial power spike the bigger caps would see?

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From ehsjr@21:1/5 to UFO on Tue Feb 11 16:48:04 2025
    On 2/11/2025 10:38 AM, UFO wrote:

    I replaced a set of 500V / 100uF caps used in a HV doubler off
    a power supply that in the end generates about 900V from the
    typical input voltage.

    I had a set of EPCOS (TDK) 450V / 120uF caps and installed them
    just to see if they were in the limit.

    https://wmsc.lcsc.com/wmsc/upload/file/pdf/v2/lcsc/2211021130_TDK-B43255A5157M_C1607543.pdf

    In initial power up they seem to have about 478V on them with no load,
    with a small load they head down to 470v and under normal operations
    in the product they are as low as 430V.

    We are about 7.8% over the 450V when the math is done.

    The product is a ham radio transciever, so while listening the voltage
    on the caps
    is about 480V max. Transmit def brings the voltage below its rating.

    I have seen test equipment designed with caps that are right at the
    operating voltage of the power supply
    and have the max voltage on them
    last about 35 yrs before failing, so I guess there is more wiggle room
    near the top in some cases?

    In this case, they have a 0.01uF disc cap plus a 470k bleeder resistor
    in parallel
    with each cap, which I also replaced new. I believe this will help to
    smooth out
    the initial power spike the bigger caps would see?





    The .01's bypass RF; typically "initial power surge" refers to
    the high current a totally discharged cap draws when voltage is
    firsts applied. If so equipped, a "slow start" circuit keeps that
    "initial power surge" much lower. "wiggle room", well ummm
    I guess it's your transceiver so you can take whatever chances
    you want.

    Ed

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)