Re: SS Relays - Revisited

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "cutthroatplasmaco"
<cutthroatplasmaco@y...> 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?
>
> Please someone help!
> Chris

Hi Chris,

Which model # ? the AC units are strictly and only AC output, and
the DC are strictly and only DC, each has a specific model #.

If I am reading the spec sheets correctly, there are two very
different units listed.

The AC units have a very high voltage to turn on at 90 volts. So if
you are using an AC voltage unit, you need to switch with more than
90 volts.

DC is different in that is uses a very low voltage to switch, but
then it will only switch DC voltages on the output.

If I read you correctly, you mentioned that you are using 18VDC as
the power and are trying to power the torch trigger.

Also, If I am reading the DC connection properly, the wiring diagram
is hard to read.

the power supply shows that your positive torch connection would go
to the power supply positive and the torch negative would connect to
the relay positive. think series connection.

the DC neg of the power supply and the relay are connected directly.

This means the torch control is always hot, and you are switching the
negative, typical NPN trainsistor control.

Re-draw your circuit so you can really see how the current flows.

and, if you are still not sure, give us the model #

Dave