Re: [CAD_CAM_EDM_DRO] SS Relays - Revisited

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