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Registered Member #3603
Joined: Tue Jan 11 2011, 11:21PM
Location:
Posts: 11
Hello guys,
I'm thinking of budget ideas for switching my cap bank into my coil gun for firing. Would it be stupid to put copper contacts on a mousetrap (via lots of solder and a mechanical linkage as well) and use the trap as a high-speed switch? My cap bank is 3600uF at ~415v. I have thought about getting an SCR but if something less elegant would work I am all for not waiting for one to get shipped to me.
I like the trap idea right now because it will allow me to be far away from the firing in case something else goes wrong; since I'll be doing a demonstration at school I think that would be best.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
There was this mechanical design I saw one time where someone used two pieces of copper as contacts and used a solenoid to wedge another piece between them. They used something like an 8 degree angle to keep the copper sticking to prevent contact bounce. It worked really well for them and there was no welding as far as I know. I'll see if I can find the page again.
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
The requirement for mechanical switches is maximum contact area and minimum contact bounce.
Remember, most small-signal switches have contact bounce up to 15 msec before it's fully settled. However, most coilguns have an entire firing time of 4 msec or less. Any bounce during this time can cause arcing and welding.
I built a wedge contactor switch from ideas used in high power commercial switching a few decades ago. I've scoped it and found zero bounce (at least at low voltage, lol). However, now I still need to finish the coilgun and see how it performs under load. I plan to return to this coilgun in late summer and see.
Cheers, Barry Technology is a way of studying the universe so man doesn't have to experience it firsthand
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Switching for my coilgun project
