Stoneridge Engineering Home |
Hello Roger, I assume you are using something similar to a starter solenoid/relay to do the switching of Ultracapacitors? Options for relay type switching would be making a custom high current relay that uses large diameter tungsten contacts - the high melting temperature of the tungsten should be a bit more difficult to weld. You will need to use a high pressure air cylinder in order to quickly develop the contact pressure necessary to prevent magnetic forces from trying to separate your contacts under load (which will overheat and weld them). Another alternative is a commercial high current relay, such as Ross Engineering GA, GB or GD series. These are specifically designed for high voltage capacitor discharge applications (much higher voltages than youre using). Unfortunately these are probably overkill, as well as being quite expensive - see the following URL to see what these look like: A bank of high current SCR's or IGBT's (a type of high power transistor) might also work, but this option would also be fairly costly unless you were able to find some less expensive devices on the surplus market. Recently, some very high current SCRs and IGBTs have been appearing on eBay at fairly good prices. Commercial capacitor discharge welders avoid the problem of having to switch ultra high currents by using a higher voltage capacitor bank to drive a step down transformer (with a very heavy low voltage secondary winding) in order to generate a low voltage, very high current pulse. The capacitor bank is switched using either and SCR or (in earlier times or higher power systems) a special mercury vacuum tube switch called an ignitron. By switching a higher voltage, but lower current, pulse on the primary side of the transformer, the welder can develop an extremely high current low voltage pulse on the secondary side. This avoids the problem of trying to switch kilo-ampere currents at low voltages. You didn't mention how you were charging your capacitor bank. A small controller could be designed to properly sequence charging, welding, and unloading/reloading material, The controller could be as simple as some electromechanical relays, a microprocessor and interface hardware, or a small industrial programmable controller. Itll take a bit of engineering to pull it all together though. Good luck and best regards, -- Bert --
: I've built a Spot Welder using a 2 Farad Capacitor & using a Automotive
: DC Relay to Switch the Charge to the Electrodes & Spot Weld the Sheet
: Metal.
: After each Spot Weld the Relay contacts Fuse together & need to be
: Phyically Separated inorder to Do another Spot Weld.
: Can you suggest a Swtching Setup that will not Fuse the Contacts & a
: Wiring Setup to Turn off Power after each Weld, when the Contacts Don't
: Fuse Together.
: Now the Power has to be Shut off after the Weld is Made, the Work removed
: from the Electrodes, then the relay Contacts Separted, Setup the New Work
: to be Welded & then Turn On the Power to Charge the Capacitor, &
: Close the Switch to Weld.
: Thank You for Considering my inguire.
: What a Great Web Site you have.
: Sincerely,
: Roger Laghezza
:
http://www.rossengineeringcorp.com/high_current_switches.htm