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

http://www.metalworking.com/dropbox/...s/welder00.txt

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

On Sat, 03 Mar 2012 15:22:01 -0800, JR North
put finger to keyboard and composed:

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

http://www.metalworking.com/dropbox/...s/welder00.txt

I blew the switching IC in the unit ...

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.

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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