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Bedini Comparator Cap Dump

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  • JulesP
    replied
    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.

    Regards,

    Jules
    Attached Files

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  • RS_
    replied
    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

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  • JulesP
    replied
    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

    Jules
    Attached Files
    Last edited by JulesP; 01-30-2019, 02:24 AM.

    Leave a comment:


  • Thomas Autark
    replied
    Originally posted by RS_ View Post
    [ATTACH=CONFIG]3128[/ATTACH]

    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 ??

    second:
    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.
    Thomas

    Leave a comment:


  • RS_
    replied
    gabiX87

    Deleted private messages.......

    Leave a comment:


  • gabiX87
    replied
    RS_ has exceeded their stored private messages quota and cannot accept further messages until they clear some space.

    Jame McDonald
    thank you much for the pic. I redraw the SNAGs-002 diagram back to Altium Designer and my friend will help me with PCB design and milling.
    By the way do you have *.PcbDoc or *.SchDoc of yours ? Would help a lot ,I have issues with parts library in altium. The schematic is ok , but the PCB part ,oh boy...

    Thanks
    G
    Last edited by gabiX87; 08-23-2016, 04:24 AM.

    Leave a comment:


  • James McDonald
    replied
    Originally posted by gabiX87 View Post
    Hi everyone,

    currently sourcing the parts for the 12V comparator circuit which RS_ posted (KRL RS revB, 08/12/14). I have a couple of questions guys. I have no formal electro background , just a self learner.

    There are a lot of information in specs sheets which I cant interpret , need some help.

    1. I have all the resistors but I have problem to find D3 1N5242 12V Zener .... can I use 12V/1,3W = BZX85C12; 1N4742A ?
    2. Also none of the supplier have exactly LM741 ,they do have with different specs. Will these do ? LM741CH/NOPB (1MHz; 318VDC; TO99) or LM741H (1MHz; 1044VDC) or UA741 CN = LM741 CN (DIP8) (1 MHz ,Supply Voltage Min 5 V , Supply Voltage Max 40 V )

    3. Also there are variations of IRFP260 MOSFET ... I suspect the higher the A rating the better for cap dump. I have some 3x or 4x IRFP260MPBF (HEXFET; 200V; 50A; 300W) Will these do ?
    or I can order these AUIRFP2602 Transistor: N-MOSFET; unipolar; 24V; 380A; 380W; TO247AD

    4. The capacitors should all be electrolytic ? Do all caps have to have the same Voltage rating ?

    Thanks for help
    Gabriel
    Hi Gabriel --

    For the 12 Volt Zener use the same part number with a "B" added on the end. 1N5242B.
    For the 741 I used the better rated one which has a 44 volt swing. Which means the max
    +/- voltage is 22 volts.
    For the FET's it really depends on how much current you capacitors are going to store before
    you let them dump. I used a part that was rated at 200 volts @ 130 Amps. The IRFP260MPBF
    will be fine if your capacitor total is not to big.
    It is best if all the capacitors are rated at the same voltage. I used four totaling 88,000 ufd.
    The voltage rating was 63 volts. See my completed board assembly running on AC house
    current. It also works off the back of the SG Machine.



    James McDonald

    Attached Files

    Leave a comment:


  • gabiX87
    replied
    Hi everyone,

    currently sourcing the parts for the 12V comparator circuit which RS_ posted (KRL RS revB, 08/12/14). I have a couple of questions guys. I have no formal electro background , just a self learner.

    There are a lot of information in specs sheets which I cant interpret , need some help.

    1. I have all the resistors but I have problem to find D3 1N5242 12V Zener .... can I use 12V/1,3W = BZX85C12; 1N4742A ?
    2. Also none of the supplier have exactly LM741 ,they do have with different specs. Will these do ? LM741CH/NOPB (1MHz; 318VDC; TO99) or LM741H (1MHz; 1044VDC) or UA741 CN = LM741 CN (DIP8) (1 MHz ,Supply Voltage Min 5 V , Supply Voltage Max 40 V )

    3. Also there are variations of IRFP260 MOSFET ... I suspect the higher the A rating the better for cap dump. I have some 3x or 4x IRFP260MPBF (HEXFET; 200V; 50A; 300W) Will these do ?
    or I can order these AUIRFP2602 Transistor: N-MOSFET; unipolar; 24V; 380A; 380W; TO247AD

    4. The capacitors should all be electrolytic ? Do all caps have to have the same Voltage rating ?


    Thanks for help
    Gabriel

    WHY THERE IS NO STRIKE-THROUGH FORMATING/OPTION TO STRIKE TEXT BUT NOT REMOVE IT.
    Last edited by gabiX87; 08-27-2016, 02:53 PM. Reason: updates

    Leave a comment:


  • adys15
    replied
    Your right Tom!....Stilll i always wandered how the cap is able to dump 70A/sec ...advanced book says that...and if we'r using the same power in/out and amps to charge the batt.then whats the advantage?pulsed amps?

    Leave a comment:


  • Tom C
    replied
    Originally posted by adys15 View Post
    Hy guys long time no see....Tom if you compare 1 cap to 3 caps yes you cannot see the diference,but if you add 10caps as i did they would take much longer to charge 3sec instead of 1...

    I am sure there is a point but I was pretty shocked that when we went from 60,000 to double that, nothing changed... all I was trying to communicate is that you want as much cap uF size to get the entire spike, and adding caps till discharging slows down is a good way to figure that value.

    Tom C

    Leave a comment:


  • adys15
    replied
    Hy guys long time no see....Tom if you compare 1 cap to 3 caps yes you cannot see the diference,but if you add 10caps as i did they would take much longer to charge 3sec instead of 1...

    Leave a comment:


  • AlvaroHN
    replied
    Update on this,

    I ended up with a 20k pot in series with C2, and now I can adjust the ON TIME and there for adjust the "cut off" voltage of the dump.

    best,

    Alvaro

    Leave a comment:


  • AlvaroHN
    replied
    I have been playing with the comparator all weekend, trying to find the correct value capacitor for C2, because initially it didn't trigger with 0,1 uf, and I ended using 2.2 uf. But looking at the capture capacitor on the scope, I saw that it was dumping to the battery voltage, so the ON TIME was too much.

    So I started to change cap values, etc, until I ended up with 3 little green caps (224k) in parallel (for C2) which dumped from 26 to 18.

    For the capture cap I added another cap in parallel, 2 caps 3300uf 35v, total 6600uf. And I added a jumper to the positive rail of one of the caps to choose between 3300uf and 6600 uf.

    The thing is that with 6600 uf the cap is discharged until 18 volts, and with 3300uf is discharged until 15.

    It would be great to have a variable capacitor for C2 to change the ON TIME, but the variable capacitors are in the picoFarads range isn't?

    And here comes the question---> Can I simulate a variable capacitor with a potentiometer and a cap in series???? While testing different cap values for C2 I saw that with a resistor in series would change the ON TIME.
    I have also noticed that change in the "cut off" dump voltage depending on what I have for charging battery?, with my little lifepo4 it dumps from 26 to 18, with an old slab it dumps from 26 to 23, and with a alkaline 9v battery it dumps from 26 to 24. I guess it is because of the impedance of the battery.
    best,

    Alvaro
    Last edited by AlvaroHN; 01-14-2015, 10:57 AM.

    Leave a comment:


  • AlvaroHN
    replied
    Originally posted by Tom C View Post
    try it with the SG, you are playing with different electricity with the SG. I would expect the wall adapter to play nice with the comparator and operate in a linear fashion. how are you getting the required voltage? most wall adapters for computers are 24 volts on the output.

    Tom C
    I will try with the SSG and see.

    I have an old HP wall adapter with 2 outputs 15 volts and 32 volts, so I use the 32 volts output to the comparator. the first time I connected the 32 volts directly to the comparator it started to dump super fast and I almost burn the BD243 that is before the mosfets, after that I added 400 ohms between the positive of the 32 volts and the positive input of the comparator.

    best

    Alvaro

    Leave a comment:


  • Tom C
    replied
    try it with the SG, you are playing with different electricity with the SG. I would expect the wall adapter to play nice with the comparator and operate in a linear fashion. how are you getting the required voltage? most wall adapters for computers are 24 volts on the output.

    Tom C

    Leave a comment:

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