Re: SS Relays - Revisited

I'm presuming that you simply have the trigger lead of the plasma
cutter going to the (+) output lead of the SSR and the (-) SSR going
to the plasma cutter ground, right? No other supplies involved?
That is how it should be connected (presuming the cutter triggers by
simply grounding its trigger input -- very standard).

It seems perhaps the trigger input is overly sensitive and is being
triggered simply by leakage current of the SSR... spec'd to be 0.1mA
max. Try your test again but with the INPUT leads to the SSR shorted
together just to ensure the relay is definitely not turning on.

If it still happens, try connecting something like a 47k resistor
(1/4 watt is fine or anything you find) across the trigger input to
ground. Does that trigger the plasma too?!? If so, then probably
it's the SSR leakage current doing the errant triggering.

This problem is easily solved if you have access to the +18v power
source from within the plama cutter... but perhaps you don't want to
mess inside there? What you would do is simply connect a resistor
(I'd use something like 2.2k ohms) between the trigger input and this
+18v source. This will provide the leakage current to the SSR and
avoid false triggering. It will also make the trigger input more
noise immune. It will not affect normal/manual triggering either.

I find it hard to believe they use such a sensitive (high-impedance)
trigger input.... so it may be something else... but this gives you
something more to check.

Good luck!
Russ

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> cutthroatplasmaco wrote:
>
> >Jon, someone, anyone please shed some more light...
> >
> >I ordered one of these
> >http://www.crydom.com/pdf/dc60.pdf
> >I hook it up, power up the input.
> >I'm no electrical engineer, so I don't know the proper
> >terms/techniques or anything here, but I set my voltmeter to ohms
and
> >touch the output poles and it shows a reading... i shut the input
> >off, take another reading and nothing. So, from my limited
knowledge,
> >everything looks good. I then hookup the output sides to my plasma
> >trigger (that's what I am using it for, to fire my plasma cutter)
I
> >turn on my plasma cutter, and it shows a fault... so I'm
> >thinking 'ok, I did something really dumb here and cooked my
plasma
> >cutter'. I then proceed to disconnect one side of the relay... the
> >relay input is powered off this whole time, I turn the plasma
cutter
> >back on, and of course the fault is gone. The relay input is still
> >off, so I reconnect the output and 'IT FIRES THE TORCH!!! (and
scares
> >the bajeezers outa me)'.
> >
> >So, my question is why would a closed (off) relay act as though it
> >were on? The torch trigger shows about 18VDC. I have the positive
> >18VDC connected to the + side of the relay output and the relay
input
> >is turned off. The only thing I didn't check is what the amperage
is
> >on that 18VDC on the torch trigger. Could that possibly have
anything
> >to do with it, if the amperage on that 18VDC were higher than the
> >rated load current range of the relay?
> >
> >
> I really can't answer this. Are you sure you have the polarity of
the
> SSR correct with respect to the polarity of the torch control?
> The SSR may well have a diode to protect the SSR against reverse
> polarity on the output terminals. That would be my best guess.
>
> Jon