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Registered Member #1523
Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97
I am continueing to work on mt first coil gun.
But i have yet again ran into an interesting problem.
I have built my capacitor bank, charging circuit, coil and physical switch.
I then tuned my coil to my capacitor bank, all with the switch.
So far, exept for some charging circuit issues, everthing was working better than fine. (Putting large dents in putty)
NOW however, I have swtiched from a physical switch, to an SCR.
This is the ONLY change I have made, and yet, now, the coil wont fire.
I have a voltmeter hooked up, and I can charge up to my target voltage (270), I then hit the trigger to activiate the SCR. Which discharges the capacitors through the coil.
I see the voltage drop from 270 to .9 volts.
AND YET
it does not fire the projectile. (a BB)
I find it strange that by switching switches, my gun is no longer opperational.
Has anyone any ideas? or better yet, has anyone encountered this before?
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
The reason a BB is not a good projectile is that best performance occurs when the coil is about the same length as the projectile. There are huge practical problems designing a coilgun with a coil that's only a few mm long.
By using a 1" nail, for example, you can build a 1" coil and it will have a much greater chance of working well.
Cheers, Barry Forecast for tonight is alcohol, low standards and seriously impaired judgment.
just an idea, but the mass and the overall area of the BB may be so low the magnetic field has nothing to "grab" and accelerate. I use a cylinder type projectile which is longer than the dia so the mag field can grab it and accelerate it.
Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
My guess would be that the SCR is either not fast enough or not turning on all the way. I would probably guess a little of both. If you have an O-Scope I would check and see if there is an RF spike when you pull the trigger or just listen for a POP on the stereo.
Registered Member #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
He's given us two different clues here that mostly seem to have been ignored.
It worked with a light switch, but doesn't now (with the same projectile).
The voltage drops, so the power is going somewhere.
I have a couple theories, but need a little more info. Can you sketch up a quick schematic of your circuit? Is there a protection diode in the circuit? Also, do you know the part number of your SCR? Its possible that you aren't switching it on in quite the right way for that particular device. Its unlikely that the SCR is 'too slow', as it doesn't really have a conducting state below maximum like a FET does. It also is likely MUCH faster than an average mechanical switch when you factor in several hundred microseconds of mechanical bounce.
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Wierd Coil Gun problem
