Getting high voltage DC from portable sources. (various ideas read more)

[XOIIO]

Hey all, one of the things that has always interested me is making a coil gun/rail gun, or even a mock tazer (getting nowhere near the 10kv+ required to spark like a real one)

Now, the issue with these is that they use capacitors, and you need to charge them.

One of the best ways I can think of is using a voltage multiplier, can't recall what it's called exactly, but it is the one with the principle of having a series of capacitors and diodes hooked up, rectifying each wave of AC, the longer the chain, the higher the voltage.

It seems like it would be a good way, though probably not very compact, of perhaps taking a power source like a 9 volt battery, converting that to an AC signal, then rectifying and multiplying the voltage to what you desire.

All just ideas bouncing around in my head right now stopping me from sleeping at the moment, but figured I would throw it out there to see if anyone has any ideas. I'm sure there are better options and there are some badass looking coil gun projects already out there (made by people with far more manufacturing capabilities at their disposal), I'm sure I could grab a system from them, though I think the one I have in mind uses camera flash charging circuits hooked in parallel.

Those circuits are fantastic though, a nice fairly consistent 300v+ from a 1.5v battery, I wonder if I have any transformers laying around or could salvage one from the HV supply of LCD monitors that I could use to create a more robust version capable of handling a larger battery/more current, that would be a pretty great and compact solution. Maybe someone has a bit more understanding of the specific transformer needs for these circuits? I've never really touched transformers in any of my electronics projects but I feel there is a lot of potential for this sort of application.


Anyways, that's my idea dump for the night I suppose, always nice to burn some sage, listen to some good music, and get this stuff out of your head.

edit: also, if anyone knows of good ways to find transformers for the specific uses you need, that would be neat, I figure searching ebay might be tough to find one, unsure of if digi-key does much with transformers at all.

[XOIIO]

Something else intriguing about the camera flash circuits (in most cases) is they have one main larger transformer, which is most likely for the initial conversion (along with transistor, diode and capacitor) from low voltage to high voltage DC, for the bulb itself they seem to have a second small transformer, though I have seen it as another style setup (waxed cylinder of sorts with 3 leads) and this always has a flying lead from the top of the device to the center of the flash tube. I am guessing it is to reduce the breakdown voltage of the filament in the bulb but aside from that it confounds me.

[daqq]

One of the best ways I can think of is using a voltage multiplier, can't recall what it's called exactly, but it is the one with the principle of having a series of capacitors and diodes hooked up, rectifying each wave of AC, the longer the chain, the higher the voltage.

It seems like it would be a good way, though probably not very compact, of perhaps taking a power source like a 9 volt battery, converting that to an AC signal, then rectifying and multiplying the voltage to what you desire.

The more stages the multiplier has, the less "hard" it is - the less current you can source from it. Also, you have to take into account the voltage drop per diode - there's a finite amount of multiplier stages you can source of a converted 9V. However, multiplier are used for this, but the voltage is first increased by a transformer (fed by a to AC converted low voltage, say, your 9V), then multiplied.

Something else intriguing about the camera flash circuits (in most cases) is they have one main larger transformer, which is most likely for the initial conversion (along with transistor, diode and capacitor) from low voltage to high voltage DC, for the bulb itself they seem to have a second small transformer, though I have seen it as another style setup (waxed cylinder of sorts with 3 leads) and this always has a flying lead from the top of the device to the center of the flash tube. I am guessing it is to reduce the breakdown voltage of the filament in the bulb but aside from that it confounds me.

This configuration uses two transformers - one for actually charging the cap to the somewhat high voltage (hundreds of volts). The other one (wax sealed) generates the trigger impulse of several kV.

For cap charging you might consider a switched DC-DC converter - reasonably simple, efficient, clean. Google for nixie tube switched power supply for an example.

By the way... be careful. You're dealing with potentially lethal stuff.

[Recyclojunk64]

For transformers you could use a TV flyback transformer (if it's too big they come in small versions; from really small TVs). A new primary can be easily wound arround the exposed ferrite core. They can be driven by a lame single-transistor driver that gets really hot, or a 555-timer based oscilator. The best choice though would have to be a ZVS driver, such as this one. Low parts count, and they produce heaps of current, but not quite as much voltage as it's driving it with a sine-wave (unless it's supplied with several hundered watts, think li-poly batteries)

Of course that may be way to big and powerfull for the applications you're interested in, if you're not planning on electrocuting anyone changing your capacitor instantly, you could just use the single-transistor inverter circuit from a portable fluorescent lantern (they will run at 9V). Or if you can live with an even slower changing time; the simmilar-but-smaller circuit from an electronic bug-zapping racket (usually run off about 3V). These will probably produce in the range of a couple of kV; an easy way to turn this into invididual sparks of maybe several tens of kV the output can be fed into a stove-lighter transformer via the included storage capacitor and spark-gap. There's no need to make a 'mock tazer' when you can make a real one . They do hurt somewhat, but they're not dangerous.

For example, a fluorescent lantern transformer combined with a stove-lighting transformer. I know the build-quality looks shocking but it was a while ago that I built it. It could be made much smaller with a 9V battery


But if you're after a more DIY solution there's no reason why you couldn't rewind any old ferrite core and build a scaled-down version of a 555 or ZVS based TV flyback driver. Better than having to convince your enemy to wait the 5 minutes for you coil-gun to charge with camera flash inverters.

[XOIIO]

Ah yes, forgot about flyback transformers from TV's, I have a very small one from an old camera baby monitor, and could get a smaller one from one of those plasma balls, however all the guides I have seen wrap around the ferrite, and these ones do not have it exposed. Haven't found a pinout on them yet.

Never dealt with re-winding a transformer at all but I do see it mentioned a lot, sounds tough though, I'd probably need a lot more knowledge to know what exactly I need to do to get the desired results.

[Skimask]

Anything wrong with an old school ignition coil from an auto engine?

[XOIIO]

I also have a few HV circuits from old scanners that power the CCFL tube inside, they use the transformers I was thinking of, I need to study that circuit.

Also, since my old one was lost in packing I made a small shocker again from camera flash components, I also grabbed a 68uf cap, threw some copper tape on it and soldered the leads to it, figuring hey, I'll charge it, toss it to a friend and say "catch". Still tempting, but it wasn't fully charged, and even then that extra capacitance gave a pretty impressive spark when I shorted it with some needlenose pliers. Currently reconsidering the capacitor part lol.

those small film ones hold enough for a little jolt, I need to find a larger one and that would be a better option than an electrolytic.

This circuit does work great though, if I could find the same type of transformer but larger, and use a larger transistor/resistor it would be fantastic for higher input voltages, this one puts out almost 500v with 1.5v input.

[amyk]

Just get a CCFL inverter.

[David Hess]

A simple boost or flyback converter can drive a voltage multiplier directly and the high starting voltage makes the loss do to forward voltage drop of the diodes insignificant.  Feedback is needed however to limit the output voltage.

For higher power, I would drive the voltage multiplier with a saturable inverter or Royer converter.

[echen1024]

If you don't need high currents, a high voltage module from someone like Ultravolt would work really well. Just input LV DC, hook it up to a Vref source, and bam, HV out.

[NiHaoMike]

Get one of those extra cheap power inverters and it's very easy to tap 170V or so from the voltage boost stage. On some (generally the high wattage units), it's possible to rewire for 340V or so.