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Thread: cap dump schematic questions

  1. #31
    Hi Gary,

    Do you recall - once the correction was made to the sch. - if the 555 version ever performed well for other experimenters?

    I'm getting ahead of myself, but just as you did, I want to build another SG, as the one I’ve made doesn’t have matched transistors and resistors, and I didn’t true the bike wheel with a spoke wrench - all of which will limit what it can do. When I get that one made I'll also switch to a comparator.

    Thanks for the advice to use enough FET’s to handle the total capacitance I’ll be dumping. I get a rough idea of the number of FET's to add just reading what you did, but how do you calculate how many FET’s to use in relation to the capacitance?

    I’d prefer to just run the SG and charge batteries directly from it (assuming that’s what generator mode means) but I want to start a business restoring dead vehicle batteries so I'll need to condition them with a cap dump.

    On a bit of a tangent, I saw a post once saying that if one connected multiple batteries on the output side (apparently in series) that those after the first battery would be conditioned by it and thus would work as run batteries/batteries that would accept hot current later. Is that correct?

  2. #32
    Forgot to add, thanks for the photos!

  3. #33
    Hi Cmor,

    Quote Originally Posted by Cmor View Post
    Hi Gary,
    Do you recall - once the correction was made to the sch. - if the 555 version ever performed well for other experimenters?
    Sorry, I don't recall. A search of old posts might answer that, or maybe someone else remembers.

    how do you calculate how many FETís to use in relation to the capacitance?
    I just go by what John Bedini did. He used 4 "matched" FETs to dump 60,000 uf of 80 volt capacitors. So that would be one FET for each 15,000 uf. Each dump is well over 100 amps at that capacitance level. If I hold a magnet next to the leads from the cap dump to the charge battery on mine, each discharge pulse will strongly pull the magnet in my hand!

    On a bit of a tangent, I saw a post once saying that if one connected multiple batteries on the output side (apparently in series) that those after the first battery would be conditioned by it and thus would work as run batteries/batteries that would accept hot current later. Is that correct?
    Sorry, I've never heard that one and never tried it myself.
    Gary Hammond,

  4. #34

    Number of FET's

    Hi Gary,

    Quote Originally Posted by Gary Hammond View Post
    I just go by what John Bedini did. He used 4 "matched" FETs to dump 60,000 uf of 80 volt capacitors. So that would be one FET for each 15,000 uf.
    Since I'll have (4) 18,000 uF caps, it seems like I should put in 4-5 (unmatched - my only option for now) FET's. Do you know if there's an advantage/disadvantage to having 5 instead of 4?

  5. #35
    Hi Cmor,

    The idea is to divide the discharge current up as evenly as possible (hence matched) and stay well within the current and voltage ratings of the FETs. The discharge is pretty rapid, so whichever FETs trigger first will carry the bulk of the current. Four might work and five might be better. I placed mine in European style terminal strips so I can replace them easily in case some of them blow.
    Gary Hammond,

  6. #36
    Thanks Gary. That's what I needed to know. I'll go with 5.
    Given that they won't be matched there will be one that triggers first and conducts the bulk of the current. I imagine it will thus be more likely to burn out. At least now I'll know why.

    You mean you attach them to one of these?
    Strip.jpg
    If so, do you attach them with the screws rather than solder?

  7. #37
    Senior Member John_Koorn's Avatar
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    Quote Originally Posted by Gary Hammond View Post

    I just go by what John Bedini did. He used 4 "matched" FETs to dump 60,000 uf of 80 volt capacitors. So that would be one FET for each 15,000 uf. Each dump is well over 100 amps at that capacitance level. If I hold a magnet next to the leads from the cap dump to the charge battery on mine, each discharge pulse will strongly pull the magnet in my hand!
    Slight correction - JB used 5 matched FETs in the Bedini Large Comparator... so about 12,000uF per FET



    Picture taken from http://www.teslagenx.com/research/tx...egory=research

    John K.

  8. #38
    Hi Cmor,

    Quote Originally Posted by Cmor View Post
    Thanks Gary. That's what I needed to know. I'll go with 5.
    Given that they won't be matched there will be one that triggers first and conducts the bulk of the current. I imagine it will thus be more likely to burn out. At least now I'll know why.

    You mean you attach them to one of these?
    Strip.jpg
    If so, do you attach them with the screws rather than solder?
    Maybe you'd better go with six FETs. (72000/12000 = 6) Sorry about my miscounting. My bad. I didn't look at the picture again before posting , and was just speaking from faulty memory.

    Yes, those are the kind of terminal strips I used on my last cap dump with the comparator. And yes, I attached the FETs with screws so they would be easy to replace.

    The FETs were soldered into my first (555 based) cap dump as you can see in the photo album I linked to earlier. Replacing them was not easy!
    Gary Hammond,

  9. #39
    Hi John,

    I'm not ready to build my "next" cap dump, since I haven't even built the first one, but...planning ahead for when I do, does TeslagenX sell matched Mosfet's in addition to the matched BJT's?

  10. #40
    Hi Gary,

    That it a great tip. I'll do that too. As for specifics, to get good contact, did you wrap the Mosfet legs around the screws before screwing them in?

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