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Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
you can use a mosfet driving chip or a transistor 'totem pole' to drive the gate of the mosfet from nearly any signal strength. Using a gate drive transformer (GDT) can get you higher or lower gate voltages/currents as needed, and can also be used to switch multiple mosfets at ~the same time so parallel/series becomes an option.
a low current coilgun will certainly work for testing purposes but i wouldn't limit yourself to only 35 amps when a hundred or two is easily doable with mosfets. Also bear in mind that you'll be using the fets to switch short pulses, so you can use a current value closer to the peak current rating from the datasheet rather than the continuous.
while relays might not be usable for the high current switching, you could possibly use them to alter the coil configuration in between shots. you could have several layers on your coil that could be included or removed from the circuit by the switching of relays. If the relay is already closed when the high current comes through, it should act more like a wire and (hopefuly) not explode/weld itself.
Registered Member #4306
Joined: Tue Jan 03 2012, 02:42PM
Location:
Posts: 9
Okay, so a month and a science project later, I've learned that, Really, my approach was wrong the whole time. If any future ambitious hobbyist finds this thread, please heed this warning:
Do not try to use a programmable micro control board (such as my arduino and a compatible shield) for coilguns, EVER... Due to several manufacturing problems, the Arduino Power Driver Shield Kit short curcuited when applied with 6 Volts at 3 amps for around 2 seconds... (They were rated for continuous 12 Volts and 8 Amps). How? I'm not quite sure, and I don't mean to discredit the manufacturer, but I got TWO of them and both fried the same way...
I ended up using an Industrial PLC and using its own Assembly Language to operate an IO card which drives reed relays, which in turn, runs the relays that use it. In order to compensate for the fact that the machine language doesn't keep time well at all, i'm using a Osciliscope (a bit more complicated version of a voltage meter) to time the circuit.
I hope I can help any future hobbyists that become interested in Open-Circuit coil guns, IMO there are too many "closed system" ones, and those just take the fun out of the process!
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Multi-Stage Coilgun Project Help
