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Triple high voltage...

Discussion in 'High Voltage' started by TaDa, May 30, 2010.

  1. TaDa

    TaDa Member

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    I want to create a high voltage circuit from bits and bobs...
    I have the inverter circuit fom a disposable flash camera - this yields around 300 volts
    But I want 900 volts.

    Could I charge a 900V capacitor from this circuit if combined with a voltage tripler circuit (one made with 3 caps and 3 diodes)?

    Cheers
     
  2. Sceadwian

    Sceadwian Banned

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    Probably but it'd take quiet a while, keep in min those flash charing circuits were only meant to be run for short periods of time.
     
  3. amando96

    amando96 Guest

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    And the components can't handle all that voltage.
     
  4. dave

    Dave New Member

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  5. Sceadwian

    Sceadwian Banned

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    They would if they're rated for it amando, the flash circuit will never see anything but the 300 volts, it's the voltage trippler and everything after it that will see the high voltage.
     
  6. TaDa

    TaDa Member

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    Ok, yes Sceadwian, I see your point about the short term use of the chargers - if I keep burning them out I will have to rethink.
    Hmm, could I run this all off a 12v battery and triple that to 36V, then triple that to 108V, triple that again to 324V before tripling that to my desired 900V (and a bit more)? (With appropriately rated caps/diodes throughout)
    Sounds decidely unlikely but does do away with the flyback circuits - is this a valid way of stepping up or is there a better way I should be using?
     
  7. Sceadwian

    Sceadwian Banned

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    That depends completely on what you're trying to do TaDa, voltage doubling etc.. like that will work for charging up something like a surge generator, but it's not going to be able to ever supply a steady current. I've never gotten my hands on one but a lot of people say neon sign transformers are good for high voltage low current stuff, even a small neon sign transformer will supply 2000 volts at a few ma
     
  8. TaDa

    TaDa Member

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    Hmm, yes, a 'surge generator' is a good way of putting it :)

    So, no, I'm not looking for a steady flow - just a nice great big zap - sounds like the flyback circuit might have been a bit of a red herring for me.
    Thinking about it, voltage multiplying circuits might be more dependable (won't burn out) and, possibly, more suitable.
    More suitable because when the caps have fully charged they'll only take a small 'leakage' current from the power source - and will effectively self regulate whereas I would need to put some sort of switch in place to control the fly back circuit.

    Anyone know a cheap source for bulk purchase of reasonably high voltage (50+V)/capacitance(100+uF) electrolytics? :)
     
  9. vonsproken

    vonsproken Member

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    I made a huge voltage doubler consisting of 60V electrolytic capacitors - costs more than its worth, I didnt get a decent amount of power either.
    I once needed a 1kV supply, I found the cheapest/easiest way was to put a phone charger transformer in reverse to a 12Vac supply, I managed 1.2kV from that alone - couldnt run it for long though.
    Another way is to use the common flyback circuit and wind your own secondary - any voltage can be achievable then.
    I found the best way was to use a 555 timer and a MOSFET, got a good amount of power too.

    Just search for flyback transformer circuits on google search.
     
  10. TaDa

    TaDa Member

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    Hmm, I like the idea of using a phone charger transformer in reverse - that would give me a rather handy 240V AC to start doubling/tripling etc

    It'd only need to run for a minute or so once the 'surge' capacitors were loaded.

    Are there any gotchas i should bear in mind?
    Can anyone suggest a circuit to drive the low voltage end?
    Is there any way I could get a circuit to turn itself off when the capacitors have fully charged?
     
  11. vonsproken

    vonsproken Member

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    I have attached the circuit that I would build. The two transformers I once used were christmas light adapters but make sure that there outputs are AC if your not going to open them up. I built a charger with light adapters and a voltage doubler, I can charge a 1kJ cap bank at 500V in about 7seconds. Warning the transformer can overheat quickly - I melted quite a few.

    I have included a circuit that would turn off the power when it gets to 600V, just change R3 and R2 to adjust this. This can take a max of 1500V if you do not change R1 and R4, 100V for every 1V on the input of the comparator.

    What size capacitor bank are you charging - let me guess its for a coilgun.

    I wont be held responsible if you hurt yourself, capacitors are very dangerous - yet fun
     

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  12. vonsproken

    vonsproken Member

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    I made a mistake in the first circuit, this is the correct one
     

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  13. TaDa

    TaDa Member

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    something like a coil gun :)

    I'm going to be handling this stuff _very_ carefully - I played around with capacitors charged to 300V/600V when i was (a lot) younger and had a few 'surprises' - nasty.

    I fear I'm going to show my ignorance here - why two transformers - is the second just for ballast or to charge a second circuit?
    Doh! I see this only shows the auto cut-off circuit. The two higher voltage windings from the separate transformers are combined (after rectification I presume?) to give the 500V

    I've not finalised my cap bank - but I'm thinking 2kv 100uF which I'm hoping will give me a pretty serious surge - I think this is 0.2kJ so not quite the beast you have :)

    Do you have a schematic for your oscillating circuit you run into your transformers?
    Does it need to match the frequency of the mains (50Hz)?

    I'm only going to run one transformer and my charge time can be minutes if need be I assume the current in the oscillator must be pretty high - is there some way I can limit this to reduce the probability of transformer burnout?

    Or is there a way to limit the draw into the capacitor bank?

    I was thinking of savaging one of those small car inverters - would that be a more suitable source for the step up transformer than a phone/christmas light transformer?

    Cheers
     
    Last edited: Jun 9, 2010
  14. vonsproken

    vonsproken Member

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    I may have forgot to add, the first transformer steps 230v mains down to 24vac, then another adapter in reverse steps this voltage back up to 230V.

    to find energy of capacitor is E = 0.5CV² therefore your capacitor is indeed 200J
    My bank originally was 3kJ but was a bit loose and scary, so I made one in a box - its only rated at 440V but can over-volt it to 500 at exactly 1kJ.

    How much are you willing to spend. Another way I thought of was to use a variac and a microwave oven transformer. I found an alternative to the variac, £20 230V 4000VA 0-230 out , its some module I bought on ebay. I once connected this in series with a light bulb (current limiter) and the transformer, I could get 0 to 2000Vac out - therefore not voltage doubler needed.
     
  15. TaDa

    TaDa Member

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    Nope, I'm drawing the line at mains - this has to be powered by a battery so it will need an oscillating circuit and, potentially quite a pokey one.

    I'm not too sure why 240VAC scares me more than 2kV but there you have it :)

    But it would make it a lot easier - no oscillating circuits etc etc. Hmmm...

    I imagine the initial current drawn into your cap bank must spike pretty high?
    Is this about right?

    Q=C*V=.0001 * 500 = 0.05
    Q=I * t. Using t=7 we get I = 7mA - at the 500v end = 7mA * 500/24 = 0.15A - not that high - I guess it spikes then reduces

    Have i got that right - 150mA doesn't sound too punishing for a christmas tree light transformer yet you say they get terribly warm

    Do I need to limit the current being drawn to minimise the transformers burning out?
    If so would a hefty resistor in series in the 24VAC circuit do it or would I need to do something more clever?
    I should have listened to those inductance lessons! (Would I need to avoid a wire wound resistor for example)

    I like the idea of not needing the doubler circuit - though, for now as a proof of concept I'll stick with the bits I have to hand. For future reference what was the module - £20 is hardly a lot for so many volts and I'm sure the local dump will let me have an old microwave :)
     
    Last edited: Jun 9, 2010

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