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From C to 2kV (and beyond)...

Discussion in 'High Voltage' started by TaDa, Jun 16, 2010.

  1. TaDa

    TaDa Member

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    Since an average C cell battery has >30k Joules (which seems a lot but numerous site suggest this is the case)

    and my 2kV/100uF capacitor bank holds a mere 200 Joules

    Is it practically possible to power up the bank using 1 C cell without using a flyback transformer?
     
  2. mneary

    mneary New Member

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    Can you think of other ways?

    A transformer does a nice job of converting low voltage high current into high voltage low current.
     
  3. Pommie

    Pommie Well-Known Member Most Helpful Member

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    An alkaline C cell discharged at 1A will last about 1 hour (capacity 5400J). At 2A you'll get about 20 minutes. To charge your capacitors in 1 minute will require 2¼A assuming 100% efficiency. You'll be lucky to achieve 50% efficiency and so you'll be drawing about 4½A out of the poor little C cell and it'll be flat in about 6 minutes (total capacity a mere 2400J). So, in theory yes but in practice not really. However, make a bank of C cells to produce a higher voltage and you could manage it.

    Note, the above is all pure guess work and probably wrong.:D:eek:

    More.

    Mike.
     
    Last edited: Jun 16, 2010
  4. dave

    Dave New Member

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  5. TaDa

    TaDa Member

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    Ok,

    So, assuming its possible, how can it be done - speed is not the important part :)

    If need be i can have a few more batteries - to get 6V say or even 12V - or some in parallel to give more current.

    Can it be done without transformers - with repeated osscilating circuits and voltage doublers?

    Failing that, what is the easiest way to turn the DC battery into an AC source suitable for passing into a chain of transformers?

    Cheers
     
  6. Sceadwian

    Sceadwian Banned

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    Why batteries at all, and why are you trying to avoid transformers? There is no solid state circuit I can think of that would allow you to make a working circuit without a transformer for those voltages. The transformer is far more practical.

    Turning a DC source into an AC Source is pretty simple, you just turn it on and off, the output from a 555 timer can be directly used to power mall transformers, and you generally don't chain transformers together in the first place you use the right one from the start.

    You seem to be going out of your way to make something that's not that complicated very difficult.
     
  7. TaDa

    TaDa Member

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    Sadly I seem always to overcomplicate things.

    With this project I'm trying to be cheap - ultimately I'll be giving this high voltage generator away and I don't want to spend a lot.
    I have access to diodes and capacitors and various 240V (to 24, 12, 6, 5 volts) transformers.

    The battery is, mostly, because I'm concerned about plugging my home made stuff into the mains but also because in use the charger may be away from main usage. The batteries I have are normal D, C, AA and AAA and a 12v battery out of a strimmer :)

    I want to charge a bank of capacitors to 200J at 2kV.

    If I stop asking inane questions can someone just give me the solution :)
     
  8. Blueteeth

    Blueteeth Well-Known Member

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    200J bank to 2kv eh?

    As Sceadwian said you're going to need transformers for that sort of voltage. I guess for stupidly low efficiency a boost converter with a single inductor, followed by many cockroft/walton multiplier stages will manage it. But with all the losses your C cell will be dead before it finishes charging.

    Most batteries with low self-discharge have the highest capacity when discharged at a low current. That means low wattage for a long time. With your 100uf cap bank, as low as that seems, by the time you've boosted your little battery to a significant voltage, the amount of current delivered to the capacitor will be silly. Also note capacitors don't hold charge forever.... so if the uA you're supplying to it doesn't over come the self discharge, your caps voltage won't go very far :/

    Some numbers, just for 'fun'. Single cell boost with 90% to 5v. Max output 100mA (battery supplies 550mW). thats a half a watt. Joules = watts*secconds. For 200, thats 400 seconds, or just under 7 minutes. To boost 5v to 2kV... thats a pretty large ratio transformer you're looking at. So with 50% efficiency (which is optimistic) it'll take twice as long = 800 seconds, or 13 and a half minutes. Working backwards (I'm cool, I've avoided any specific circuits here!) Q=CV=IT, I=CV/T

    CV = 100u * 2000 = 0.2. 0.2/800 seconds = 0.25mA. - you better make sure you have no resistors in parallel with the cap bank. A megohm resistor would take most if not all that current at 2kV.

    Theoretically yes. Practically, naaaa
     
    Last edited: Aug 6, 2010
  9. Martel

    Martel New Member

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    ---"The battery is, mostly, because I'm concerned about plugging my home made stuff into the mains"

    PLEASE !!!!! Buy or build a good lab category power supply !!!! Unless i want to show a project to a friend outdoors, i NEVER use batteries.

    A good power supply will generate the voltage you want, will be 100% short-circuit proof (You can actually adjust a lab supply for it's maximum output amperage) and will supply you (YES ! with a TRANSFORMER !!!) the required electrical isolation between the mains and your project).

    BTW, ALL UL / CSA approved power supply WILL provide you that primordial isolation...
     
    Last edited: Sep 26, 2010
  10. Martel

    Martel New Member

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    ...And BTW, 100µF charged at 2kV IS LETHAL !!!

    Take great care !!!
     
  11. Pommie

    Pommie Well-Known Member Most Helpful Member

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    Yup, 200 Joules can kill. But you'd have to be pretty unfit.

    Mike.
     
  12. Blueteeth

    Blueteeth Well-Known Member

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    All depends on the voltage, your skin, hydration, electrolytes. When thinking about 'electricity can kill' one realises that the human body can be both extremely fragile, as well as ludicrously tough. The latter was found out when folks designed 'the electric chair', but there have always been stories of people recieving a somewhat 'mild' shock and either dying from the direct effects (heart stopping) or secondary effects (falling over and banging ones head).

    As long as one has a healthly 'fear' of voltages above around 80v, its all good. It is easy for the experienced to say 'I've worked with high voltages and I'm fine', but its better to be safe than sorry. I guess I have been lucky, I have been zapped by a 120Joule cap bank, charged to 800v, and it hurt like hell (burned my finger too). As well as a few mains shocks (my own stupidity). But I doubt I made a decent connection in any of the above situations, so as luck would have it, I didn't conduct much current.
     
  13. Gary B

    Gary B New Member

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    Actually, you can do it without a step up transformer. You need to build an inverter that will run on your C cell. The output feeds a series of cascade voltage doubler circuits of diodes and capacitors in a ladder arrangement. Each pair adds the original voltage to the total. I don’t consider it very practical but, it is possible.

    FYI, the national electrical code considers anything over 50 volts to be high voltage and 50 to 60 Hz AC is the most dangerous because it is in the range of signals the heart uses to control it beat (or at least so I have been told).
     

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