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Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Small coil guns can be switched without hardly any noise using primitive mechanical switches. Try a light switch or maybe a relay. If you find a suitable type it will be pretty quiet and not weld the contacts too often,
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
My very first coilgun was triggered by a large-ish rocker switch for automotive use I picked up at the hardware store. No noise other than the "click" the switch makes, and it still works to this day.
Registered Member #1316
Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365
How many amps peak was that? Right now I am looking for a SCR for my demo coil gun and I just want a ballpark guess for the current it will have to switch.
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
For energies less than 150J or so, I prefer the TYN640 SCRs; they're these little TO-220 guys that can handle 600V and 420Apk. I usually buy them 10 at a time on Digikey, since as far as I can tell they're cheap and reliable.
And no I have no idea what kind of current my coilgun was switching. I have a homemade clamp-on oscilloscope CT, using an old probe with the head cut off, a broken ferrite toroid, and a jumper cable clamp. It outputs 100mV per Amp, so the most I can measure on my scope (5V/div max) is +/-250A. Not enough for a coilgun, but then again this was made for SSTCs/DRSSTCs.
Registered Member #1316
Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365
Would 300 amps be in the ballpark for 200 uf of photo flash caps? I am restricted to only things I can get from frys and they have a nice stud type SCR that can switch 300 amps peak.
Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
You could try with it. It makes a bang when switching, but IIRC it wasn't too loud. However, you shouldn't use it with a too big cap bank. Mine was probably 20J. Every time you trigger it the switch welds closed but not badly.
This isn't the most reliable switching method and the switch won't last very long. If you have a change to get a SCR, then get it. It'll be a lot better.
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Flash lamp coil gun
