Omron SSR G3NA-240B

I'm using this Omron SSR in my homebrew spot welder-documentation here:

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I blew the switching IC in the unit, overloading the welder while doing some heavy duty spot welds during rebuilding of my Datsun Roadster. The welder has languished unrepaired under the bench for 6 or so years. Finally decided to resurect it. I designed the switching system for simplicity, not cost when I built it. The timing module is AC, and the SSR is the AC model, switched by

120V on the input. The AC SSRs are 4X as expensive as the more common DC switched units of comparable rating. In retrospect, I guess I should have designed in a rectifier/transfomer to run the switching on 12 or 24V DC. In attempting to repair rather than replace the SSR, I found it's not that easy to dissassemble. The case comes apart OK, but the output IC is bedded in ceramic on the inside of the bottom heatsink, and the terminals project upwards through the circuit board. I found the IC sinks so much heat I could not effectively wick the solder from these connections, and it took me an hour to slowly work the board up by alternately heating each connection. Anyway- to the point: I can't tell if the output IC is a pair of SCRs or some flavor of Triac. Anyone know? Google provided plenty of datasheets, but no disscusion on the internal components. The circuit board is OK, and what I want to do is mount a couple SCRs or a Triac on an external heatsink, and trigger them with the board from the SSR. I can get these 40 amp ICs for 4-5 bucks on Ebay, and would be cheap and easy to replace if I fried them again. Thoughts? JR
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JR North
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On Sat, 03 Mar 2012 15:22:01 -0800, JR North put finger to keyboard and composed:

There may be a more convenient solution. Would it be possible to convert the timer to output a DC control voltage so that you could use the cheaper SSR with DC input?

AISI, the timer is a microprocessor based device, so it must derive a regulated DC supply from the AC input. If the output is switched by a relay, then it should be a simple matter to wire the DC supply to the relay contacts. Otherwise, if the output is switched by a triac, then you could add a simple NPN transistor switch. If done properly, you wouldn't need to make any changes to your external wiring or construction.

- Franc Zabkar

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Franc Zabkar

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