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Bedini Comparator Cap Dump

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  • Originally posted by RS_ View Post

    Here is a 12V version of Bedini's Comparator Trigger Cap Pulser......

    hope this helps every one build them at 12V
    Hello RS
    Thanks for all that information and the 12V Circuit.
    I have 2 Questions please:
    I am not sure how the Opto is connected.
    Pin5 -> + charging
    Pin4 -> Base Q1
    Pin6 -> "nothing"
    Pin1 ??
    Pin2 ??

    Is there a different if i use my SSG with or without the cap dump on the charging battery? Charges faster or what does it do?

    Thanks so much.


    • Cap Dump Circuit for 36V system

      Hi RS,

      I'm late to the party but have been developing a solid state generator (attached) and am at the stage where I wish to compare the battery charging when feeding the HV pulses (attached) directly to the two 36V battery stacks to when some cap dump system is used. The HV scope traces were taken with a 45:1 voltage divider so the pulses are around 700V, although will be around 8,000V when I have switched to a different set of coils with high permeability cores.

      I was sent your circuit by another member but, as relatively new to some of these things, I wondered if you could ask some questions re the circuit (attached).

      1. I would like to be able to run the cap dump from the drive batteries and not some external power source so can I ignore the FWBR on the left and connect directly to my 12.7v supply rail?

      2. This circuit uses an optocoupler that I have heard said can impair the fast switching of the FET. Is this something you recognise or is it insignificant?

      3. Which components allow one to set the discharge voltage threshold (I assume the discharge rate will be a function of that and the cap value)

      4. Can one build in a simple means of indicating that the main cap is charged (LED?) and also of safely discharging it after the main generator is turned off?

      Thanking you

      Attached Files
      Last edited by JulesP; 01-30-2019, 02:24 AM.
      'Consciousness came First'


      • Hi Jules,

        I am sorry that i have not seen your post any sooner....

        got a new puter before x-mas and just now logged back into this site

        The Cap Dump compairtor circuit is powered from the energy that is coming into the dump cap, no need to power it with the drive battery's

        I don't know why you would want to ignore the FWBR, and connect directly to the 12.7v supply rail, this would just fill the dump cap to 12.7V and never do any thing else.... The FWBR should be on the out put of your oscillator, to feed the spikes into the dump cap, to fill up the cap till the comparitor trips and dumps the cap, and then repeats....

        The H11D1 is what JB has always used. There are newer faster Opto's out there, and they can be used in place of the H11D1.

        R10 pot adjusts the voltage that the circuit discharges at....

        the discharge rate is a function of the amount of energy coming into the Dump cap, and the discharge rate will vary as the input energy vary's.
        Such as the primary discharges, etc....

        The comparitor's output could be fed to another Opto that can kill the trigger of your oscillator during the cap dump if needed


        • Hi RS,

          Thank you for your thoughts.

          Since writing that post I have had a chance to get to understand the circuit better and have drawn my own version of it (attached) that I find helpful as a preparation for a build and which incorporates my battery swapper and an LED off the LM741 to indicate activity. I now recognise that the timing control power supply is from the energy delivered to the main cap but even so, from the SG Intermediate handbook*, I read that the FWBR is not required as the HV pulses are unidirectional anyway and to save on voltage drop. That is why my circuit brings the HV feed straight to the 15,000 (or greater) cap.

          *"p30-31: The full-wave bridge requires the output pulse to travel through two diodes that each have a voltage drop of about .6 volts. . . . . .So, it seems clear that collecting the output pulse from the main coil winding (MC) and using a single diode (D2) to direct that impulse to the capacitor (C) is more efficient."

          With regard to the charge and discharge voltage levels that a cap dump system working with 36-38V batteries should be adjusted to, I understand that the upper threshold should be about 48V and the lower around 40V? I have displayed this in the attached graphic and wondered if you think those are reasonable.

          My battery charging experiments with the solid state generator indicate that as the frequency increases the charging benefit declines and is certainly not a liner function of frequency. I'm thinking that as the interval between succesive pulses gets shorter and shorter the battery is unable to fully 'process' them. I'm hoping that a cap dump circuit in between will be better able to absorb the hot and cold aspects of the HV pulses and relay them more effectively to the batteries and that increasing my cap to 60,000uF will be useful too.


          Attached Files
          'Consciousness came First'