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I've found a few mercury wetted relays and was thinking of using them to fire a railgun, but I have no datasheets and don't have any experience with these types of relays. How will they perform under large current pulses? I know they have very low contact resistance, which would be nice.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
They typically can handle a lot of current, and have nearly infinite life. However with any type of relay, there could be arcing and thus slow switching. I would use an SCR. Super high current ones are readily available, and they are "accurate" unlike relays. If your building a multiple stage coil gun timing is everything.
Oh wait, railgun? Yeah they could work. Part numbers?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Can we see a picture? Are these small-signal relays, or mercury displacement contactors with a couple cc of liquid Hg in a capsule inside a solenoid?
The latter are meant for very durable, infrequent switching of mains voltage at 10's of amperes. Heaters, motors, etc. I would not worry about brief kiloAMP pulses within the device's voltage rating (as with large SCR's). But who knows what they do when open circuit voltage is in the kV? I hope not break down and dissipate kJ of capacitor bank energy. Better to have a cratered SCR than 10 or 20 grams of mercury sprayed around your lab. [edit] I bet you can find datasheets that cover electrical-code-compliant protection of the relays against short circuit overcurrent faults. See "Proper Fusing is Required" in reference above.
What they have over SCR's is bilateral conduction, low resistance even around zero volts, and (maybe) tolerance of occasional electrical abuse. The first two are not important in railgun.
An ignitron might serve you well. They are rated for kV and kA.
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mercury wetted relays?
