Is 63VDC filter cap good enough for 45V rail voltage?

Discussion in 'DIY' started by Alan0354, Jun 15, 2017.

  1. Alan0354

    Alan0354 Super Member

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    As the tittle, Is the 63V filter cap safe to use for 45V to 46V rail? It's about a little less than 75% of the rated voltage.

    I've seen amp using caps rated for 100VDC on 75 to 80VDC rail. That is over 75% the rated voltage. Acurus and Nakamichi PA-7 are two examples.
     
  2. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Just about optimum I would say, most of the time they are ~80% Applied voltage/Capacitor working voltage ratio or thereabouts.

    Personally, I would think nothing about replacing 80V main PSU smoothing capacitors, and using 100V replacements, with applied voltage of 70V.

    Or in your case using 80V rating to replace 63V rating for example, but I definitely wouldn't replace a 63V with a 50V - with applied voltage 46V.

    I hope this helps.
     
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  3. nj pheonix

    nj pheonix AK Subscriber Subscriber

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  4. gadget73

    gadget73 junk junkie Subscriber

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    Just mind the turn-on voltage surge. As long as its not beyond cap rating, you're good.

    As for pushing the limits, the original main filter caps in my Phase Linear 700 were rated for 100 volts. The rails measured at +/- 103 volts. New caps are 160v.
     
  5. Alan0354

    Alan0354 Super Member

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    I did not know you can push this hard. I know they push hard on tube amps in the older days like they use 450V cap on 400V or even a little more. But I chucked it to that's all they can get in the older days.
     
  6. Alan0354

    Alan0354 Super Member

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    Thanks to all. The reason I asked is because I still have 14 of the 10,000uF 63V cap, so I don't have to buy new ones.
     
  7. stoN_Cold

    stoN_Cold Super Member

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    Don't buy. :rockon:
     
  8. roger2

    roger2 . Subscriber

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    I was aware of current surge at start-up. But had not heard of turn-on voltage surge. Could someone elaborate on this please?
     
  9. maxhifi

    maxhifi Super Member

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    Tube equipment has to deal with the fact that the voltages are all a bit high until the tubes warm up and start passing current. Sometimes this goes to extremes, for example needing 500V capacitors when the normal operating voltage is about 300V.

    With a typical complementary symmetry transistor amplifier, the power supply voltage at idle will be as high as it's ever going to be, because bias current is so low relative to full load current.

    I think 80% of the rating is just fine for solid state stuff.
     
  10. gadget73

    gadget73 junk junkie Subscriber

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    yeah I usually dwell in the land of tube electronics, not these weird non-glowing things

    basically stick the meter across the caps and see if its higher when you first throw the switch. More an issue with tubes, but in stuff that might have circuits on a delay there could be lower supply load (and thus higher voltage) until that delay is finished. Under conditions of low load you don't want the voltage to be beyond what the cap is meant to take.

    as for 103 volts on 100v caps, I don't think you'll ever find someone that will tell you its a good idea. Maybe 35 years ago with slightly lower line voltage it was not exceeding the ratings but it had to have been right at the limit. Not sure if it was all that could be had, or maybe attempts to cut costs as much as possible, leaving no margin of safety but its not good practice either way.
     
  11. audiodummy

    audiodummy Active Member

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    Just wanted to also remind, if you're using off-brand caps, you might need a bit more margin as they could leak a bit more current. Also if you find caps with "WVDC" or "working voltage DC" rating, then you can safely go up to that voltage, unlike the ones that just give a voltage without the "working" qualifier.
     
  12. Alan0354

    Alan0354 Super Member

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    This is the cap I have, I bought it a little over two years ago from Allied when they had a closed out sale really cheap, I bought like 50 or 60 of them. It's Nichicon.

    Nichicon.jpg

    Nichicon1.jpg


    Ha ha, I bulk buy stuff when I see it's on sale. I also bought 60 of the "IC" ( I think is Illinois Cap) 4700uF 100V with the same footprint ( 10mm spacing,35mm diameter), just different height.
     
  13. whoaru99

    whoaru99 Epic Member

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    From what I've seen in the capacitor datasheets, applied voltage up to the rated voltage is not a material factor in the life calculation.

    Of course, consideration must be given to the actual circuit voltage variations to ensure the rated voltage is not regularly exceeded. But, on the presumption the rated voltage is not exceed, over-specing the voltage rating does not appear to materially increase life/durability. At least not for an electro cap like the Nichicons pictured.
     
  14. triode17

    triode17 Active Member

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    According to Morgan Jones (former BBC Engineer), studies he did showed lowering the voltage to just 89% of the rating, doubles the life of an electro. cap. You are at 71% so it 's just fine, the cap. should last a long time.
     
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