How do i charge my coil gun capacitor?

I have a working coil gun, but i fried the circuit that charges my cap that i took out of a disposable camera.

How can i make on of those myself?

Does anyone know where i can find schematics on how to build a cap charging circuit that charges up to about 300v using AA or 9v batteries?

The simpler the better. In fact, assume i don't know anything about electronics.

8 Answers

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  • Gary H
    Lv 6
    1 decade ago
    Favorite Answer

    If you've got enough savvy to whip up a coil gun out of wire, some caps, and a disposable camera, I think you can handle this - a mechanical step-up inverter, no chips and only 4 diodes (or a single fullwave bridge diode pak).

    Start with a battery holder that can hold at least 6 cells (AA is okay) in series, but start out using only 3 initially, otherwise the voltage might get so high that you blow your caps. Just jumper across the empty battery spots. From Radio Shack, get a 12-volt center-tapped (MUST be center-tapped)transformer and a 5-volt, DPDT (double-pole, double-throw) relay, 1 10-ohm, 10W resistor, and 5 one-amp 1000-volt diodes (something like a 1N4007, I think RS has them). You might also want a pushbutton momentary switch so you can press-to-charge, rather than hooking and unhooking the battery plus lead. And a piece of perfboard big enough for the transformer, battery box and other components is highly suggested.

    I suggest you create a schematic from the description before you start.

    We're going to hook the transformer up backwards from it's normal config, applying power to what is usually the secondary (the 12V side), and draw the power from what is normally the primary (the 120V side).

    The relay has 8 pins total. 2 are for the coil, 3 are the normally-open (NO), normally-closed (NC), and common(COM) of switch A (SWA), and the last 3 are the NO, NC, and COM of switch B(SWB).

    Start with the batteries removed from the holder and keep them out until finished building.

    Connect the battery (-) to both the neg. terminal (or either terminal if it isn't polarized) of the relay coil and to the COM pin of switch B of the relay.

    1) Connect the (+) battery output to one contact of the momentary switch.

    2) Connect the other momentary switch contact to the NC contact of SWA, and to one end of the 10-ohm, 10W resistor. The 10-ohm resistor is to limit charging current to a safe level for the circuitry.

    3) Connect the other end of the resistor to the center-tap of the 12V side of the transformer.

    4) Connect one of the 12V transformer wires to the NC contact of SWB, and the other 12V transformer wire to the NO contact of SWB.

    5) See

    http://en.wikipedia.org/wiki/Bridge_rectifier

    if you need to for how to connect 4 of the diodes in a bridge, with the AC ("~") coming from the 120V wires of the transformer. Email me if not clear.

    6) Connect the "band" end of the last diode to the relay coil contact that is connected to battery (+), and connect the other end to the other relay coil contact. This is to protect the coil from large inductive spikes that would occur when the relay opens.

    7) Now go back to step 1 carefully checking each step for accuracy.

    Install the batteries. connect your caps to the bridge rectifier output, making sure to hook "+" to "+" and "-" to "-".

    Do you have a meter? Monitor the DC output voltage of the bridge rectifer (+ and -). Press the momentary switch for just a second while you monitor the meter. The relay should start buzzing and you should get intially a low voltage on the meter, rising fairly rapidly unless you have a really HUGE capacitor arrray. If the voltage tops out too low, add another battery to the battery box and try again. Don't blow your caps, and for God's sake, this is very high energy - be careful, don't let the thought of batteries fool you, this thing can kill a man. SERIOUSLY!!! All standard disclaimers apply, don't electrocute yourself or anyone else, this is NOT a toy!

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  • CB
    Lv 7
    1 decade ago

    What you need is a boost power supply. I'm guessing your input voltage is from portable batteries. (AA, AAA, C, D etc.) Depending on the current you need their are many designs and topologies, but you need a lot more information. I'll add a link to a Texas Instruments application note about boost supplies to help you get more acquainted with the circuits that are out there.

    By the way I'm a design engineer with a major power supply manufacturer.

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  • 1 decade ago

    If you can deal with the fact that this is dangerous and will only charge your cap bank up to ~170v (if you live in the USA), just use a diode bridge with a series resistor (about 100 ohms, rated 10W or so).

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  • 1 decade ago

    any capacitor can be charged by passing current into it... but i dont know what is a coil gun capacitor...

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  • 1 decade ago

    assuming you don't know anything-

    i'd say just go down to walgreens and ask for one of the disposable cameras that have been used. use the circuit from one of them.

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  • Anonymous
    1 decade ago

    If you are going to charge anything you will have to start by reading the miranda rights.

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  • 1 decade ago

    you mean like a Tesla Coil? you can find schematics online I suppose.....

    Source(s): my cerebral cortex
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  • Anonymous
    1 decade ago

    electronics goldmine often has those kind of goodies and they are cheap.

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