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Electronics Need about 200v DC, any help?

Discussion in 'Modding' started by M2k3, 17 Apr 2007.

  1. M2k3

    M2k3 Wired to the Core

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    Well for a little project I've decided to build a coilgun. The design is easy and I've already got a small working prototype but it's simply not powerful enough. Right now I'm using nine 16v 2200µF capacitors in parallel and I am able to launch a small metal projectile (the projectile is about the equivalent to a .30 caliber bullet) down a large straw. But I am itching to use some of the 200v capacitors I got out of some old power supplies, the problem is I simply do not have anything that puts out 200v DC to power these capacitors. I am only using a computer PSU to power the capacitors (only puts out 12v) and I need to get that to 200v or at least 150v DC.

    Is it possible to combine a bunch of PSU's to get more voltage output or is there another way to build something similar? I have a large amount of PSU's and many other electronic goodies at my disposal I just need help finding something that will work. I would strongly prefer not to buy anything since I have so much junk sitting around here right now that needs some using.
     
    Last edited: 17 Apr 2007
  2. Xiachunyi

    Xiachunyi What's a Dremel?

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  3. crazytyler34

    crazytyler34 What's a Dremel?

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    What do you know about circuits. Because you would get more farads out of those capacitors if they were in parallel instead of series. Capacitors work the opposite way of resistors, they add in parallel.
     
  4. M2k3

    M2k3 Wired to the Core

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    I think that will work, but I am confused about how much it will increase the voltage. For example if I had 4 stages in the voltage multiplier and I was using a 12v power supply would it do 12x4 (48v)? Because to get that I want (at least 150v) I'd need more than 10 stages and on the site it says more than 10 stages don't work.

    Ah yes, I just got confused between the two terms. They are in parallel.
     
  5. Xiachunyi

    Xiachunyi What's a Dremel?

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    You could change it to AC and then feed it through a step up transformer. After doing so, you can then tack on the voltage multiplier array.
     
  6. Confused Fishcake

    Confused Fishcake Minimodder

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    You could always use the high voltage circuitry out of a disposable camera. Go to any shop which processes disposable cameras (WITH flash) and ask for some old processed ones. You can usually get about 8, not that you need that many. Simply open them up, there is a small circuit board in it which produces 300VDC and a matching 80uf capacitor. I have built a working coilgun from a single camera, but connecting about 4 caps in parallel to one HV power supply seems optimal.

    EDIT: If you're using PSU caps, I don't think they're meant for sudden huge discharges. Flash caps are, and you can get them easily. Be careful though, without caps, the 300v hurts like ****, but with a meagre 240uf I was literally thrown backwards across the room :eeek:
     
    Last edited: 17 Apr 2007
  7. M2k3

    M2k3 Wired to the Core

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    I like the idea of a step up transformer but I don't know where I'd find one of those. I think I'll try getting the camera capacitors if PSU caps aren't going to work as well.
     
  8. legoman666

    legoman666 Beat to fit, paint to match.

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    I can testify to that. Back in high school, someone had a dismantled disposable camera PCB. They tossed it to me, and I not knowing what it was, caught it. Damn that hurt, left 2 little black marks on my finger where the leads of the capacitor touched.
     
  9. profqwerty

    profqwerty What's a Dremel?

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    I made a coilgun for my physics A2 investigation.
    I had 20*10000uF caps @50V, arranged to charge up to 400V.
    You don't want the farads, you want as high a voltage as possible (P = V^2 / R) (EPE = 0.5CV^2)

    So an increase in V is a huge increase in the energy dumped into the coil - putting the caps in series increases the V, but BE CAREFUL. If one of them fails then IIRC the lot die.

    Also increase in V = high current, so the whole circuit needs to comfortably take this current.

    I used a proper HV PSU which could only do 400V @ 30mA; it took ages to charge them.
    How are you switching them? above about 50V, you need a DECENT thyristor + protection diode, or the reverse EMF pulse (>1000V) will blow the lot up.

    I looked into charging, and what you want is a cheap bridge rectifier (look in the PSU might have some), rated for mains, and that will output about 320V in DC pulses. Put a large resistor on the output, and charge the caps straight from it!

    a load of camera flash caps in parrallel would do good, as they are rated to like 400V. I don't know if the charge circuits could be connected in parrallel - it charges in pulses so if they're not synced something bad could happen.
    Otherwise it would take a while to charge.

    I second touching one of those flash things.

    fish:
    yeah, the larger caps are really designed for surge currents, but more for stablising large current applications.

    Hope this helps, pictures / advice just ask!
    profqwerty
     
  10. Snipes0990

    Snipes0990 What's a Dremel?

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  11. ChromeX

    ChromeX Minimodder

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    Building on that idea why not power it off the mains, here in the UK we use 240. Build a regulated supply using the bridge rectifier, some smoothing caps and a regulator (prob a zener or something). When I built my coilgun thats how I did it.
     

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