490000uf 35 WVDC - Ideas?

Discussion in 'General Electronics Chat' started by Artfldgr, Jan 12, 2013.

  1. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
    I recently acquired a few interesting large capacitors.
    5 that are 7,900 uf 350WVDC
    2 that are 490,000 uf 35 WVDC (max surge 40V)

    I am hoping they are not blown, I think they were replaced because of an upgrade in which the replacements have to be larger so these were discarded.

    No need for warnings... these are seriously dangerous toys when charged.

    to give a nice feel for how different.
    a disposable camera at max is around 160uf or so (350volts)
    A commercial flash unit for a DSLR can be 10 times as much so that you can take many pictures before waiting for a charge. 1600uf

    you would need around 3000 disposable camera capacitors to match the uf of just one of the large caps... (but voltages are not equal).

    discharge that with a screwdriver and it will not be pleasant...

    I wonder what great hobby project one can use one or more of them for.

    and just to limit the list to something a bit more reasonable
    (as I live in an apartment)

    no sasquatch stunners
    no rail guns
    no tesla coils
    no emp pulse
    no Jacobs ladder (already done it)
    no shrinking coins...

    ok.. I know... took out all the best fun ones...
    but really, how suitable are those for an apartment?

    I also have a collection of some motorized micrometers
    so what I thought of was using a 1amp laser, and pulse it at much higher power, and perhaps make a micro CNC machine.
    [my day job is an applications developer for research computing so the software and such is not the hard part for me, the hardware and such is more so]

    this CNC would not be able to work on anything larger than a postage stamp given the micrometer travel distance.

    how long could one run led lights off of something like that?
    use the cap as a battery with a high cycle life for some solar cells I have laying around?

    I have some weird spare parts that are always looking for a project.
    a nice collection of small vacuum arc gaps...

    well, be interesting to hear what comes up
    if ideas are interesting I may take a picture of the strangest parts for doing things and then see what comes up... but no promises, life has been very busy lately.. :)
  2. ifixit

    Well-Known Member

    Nov 20, 2008
    1. Spot welder.
    2. Door stop.
    Number 2 is the safest for an apartment, but number 1 would be more fun. I built one 20 years ago using two 47,000uF (industrial grade the size of a coke can) in parallel and a heavy duty SCR to dump the charge. Worked well for spot welding steel sheets together.

    If the caps are old they should be formed up before using. If they will be use in a high current discharge application then inclose them in a metal box or chassis in case they explode.

    What current rating do they have?
    What is the physica size? (to get an idea of current rating)

    Play Safe,
  3. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
    A spot welder is a really good suggestion..

    dangerous is ok... nothing in life is safe and i have done some prior high voltage projects...

    i do not like the paper weight idea..

    the Capacitors documentation is here

    as i said, its 490,000 (one more zero than your mention)
    490F technically...

    this one is 35 WVDC max surge 40vdc

    its 3.5 inches in diameter, the size of a fosters beer...

    i have a 35 amp/10 volts transformer for 120 volts
    that would make a hell of a welder too?

    how bout a super low frequency oscillator with a 10 year cycle.. ha ha

    they have no continuity (not shorted)
    but my meter only goes up to 600uf

    i am leaning towards the cutting lazer... somewhere in here i have a half inch thick orange glass plate..
    makes a nice laser sheild for blue lasers of moderate strength...

    a fly zaper from hell?
    Last edited: Jan 12, 2013
  4. ifixit

    Well-Known Member

    Nov 20, 2008
    They are 0.49 Farads not 490 Farads. There is 1 million microfarads in 1 Farad and your caps are 490,000 microfarads. To roughfully measure the capacity you could charge them through a 10Ω resistor from a voltage source and measure the time it takes to get to 63% of the source voltage (TC). Don't forget to discharge using the 10Ω resistor.

    TC = R x C, so T = 10Ω x 490,000uF = 4.9 seconds, or one tenth of a second for every 10,000uF.

    The spec doesn't say they can be used in a high discharge current application, but would likely work for occasional use. The ESR is only 3.5 milliohms, so a screw driver short from 35V would yield 10,000 Amps so don't do that.:eek:

    This is way more than needed for most spot welding. Using an SCR though a length of wire would limit that. Having 100 to 200 milliohms in series would be good.

    Hopefully a better idea will pop up.

  5. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
    thanks for setting me straight on the farads..
    and my post pointed out that a screwdriver is a very bad idea
    I used a ten meg ohm ceramic resistor to make sure they were discharged

    and your comment as to 10,000 amps confirms it would be the bug zapper from hell...

    I think I will probably use one in a led lighting application with solar cells and go for a lot slower discharge than 10k A. I wonder how long 10 white leds would stay lit from a full charge...

    other than slow discharge as a high cycle capacity battery, not much you can do.... the worlds funkiest joule thief....
  6. MrChips


    Oct 2, 2009
    Not very long. Do the math. A 470,000μF capacitor charged to 3V might power a standard LED drawing 20mA for about 30 seconds. The LED just gets progressively dimmer.
  7. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
    Nice blue paperweights so far...


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