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Registered Member #4659
Joined: Sun Apr 29 2012, 06:14PM
Location:
Posts: 158
I made a prototype mechanical switch. This thing -
It's two metal rods (iron, because that's what I had, but I'll switch to aluminum or copper for better conductivity if feasible) in a pvc tube with a rubber band around the switch holding them together. There's a window in the pvc tube cut out, and into that window I put a nonconductive stop - a scrap piece of PVC for now. To close the switch, i pull out the stop:
How much current do you think this could handle (at 240VDC for starters)? Will there be sparking (and the associated loss of efficiency)?
Registered Member #1064
Joined: Tue Oct 16 2007, 05:04PM
Location:
Posts: 42
Contacts will probably weld when they close and you will have to use a hammer to open them. Book Reference Data for Radio Engineers, Fusing current of 0.162 inch diameter copper rod 668 amp. Iron rod 205 amp.
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
I think having a high power switch held together with a rubber band is probably unsafe since the band could get cut by the rough edges of your pvc pipe and the electrodes could fall out. A mousetrap might be a better start.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
i think welding/errosion wil be a problem...
A triggered spark gap would be better if possible, best would be a SCR bolt stud type.... why the desire to avoid the SCR's ? gate drive doesnt scare you does it?
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
i think welding/errosion wil be a problem...
A triggered spark gap would be better if possible, best would be a SCR bolt stud type.... why the desire to avoid the SCR's ? gate drive doesnt scare you does it?
I assume there are a few reasons, cost and availability being two. Simplicity is a third.
A better design might be to cut/file the contacting ends at an angle. They would then tend to slide together and not 'bounce'. I've seen other solutions to this problem that utilized a wedge that makes contact between two angled terminals.
I seem to remember the example I saw used a solenoid or something to trigger/operate it.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
if thats true, cost and simplicity, then use the mouse trap idea... you could get several high power shots before it needed to be replaced, even the smallest standard size here in the US would be addequate. And there chaep at the hardware store.
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
You could get a few of these from vishay's sample program. They can take a pulse of 1400 amps and are suitable for coilguns up to a few hundred joules.
Relays aren't too bad either for the energy level you're at. BGmicro has 2 of these left which have some pretty beefy contactors and an open frame which is convenient for if/when they weld together.
Here's one of the wedge type ones that ash mentioned (although the other contact should have a wedge removed from it to accept the copper wedge) and another one i found
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Prototype homemade heavy-duty mechanical switch - how much power do you think this could handle?
