Re: SS Relays - Revisited

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "cutthroatplasmaco"
<cutthroatplasmaco@y...> wrote:

> Thank you all for the replies to my original question, but I am

still

> completely stumped.
> I drew upt this quick diagram of what I have if someone could look

at

> it and tell me if that makes sense, then what might be the issue...
> http://cutthroatplasma.com/wiring.gif
> Thanks,
> Chris
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Moore" <pminmo@c...> wrote:
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "cutthroatplasmaco"
> > <cutthroatplasmaco@y...> wrote:
> > >
> > > > 1. What is the part number of the crydom?
> > > The model # is DC60S3
> >
> > DC Input model so thats ok
> >
> > > > 2. What are you using to turn it on?
> > > I'm using a campbelldesigns.com breakout board to trigger the
> > relay -
> > > 12VDC
> >
> > Should work
> >
> > > > 3. What is each wire of the crydom hooked to?
> > > so, the +12Vdc from the breakout board is hooked to the

positive

> > side
> > > of the input on the relay, the gnd side of the breakout board

is

> > > hooked to the other (I guess it would be referred to as gnd)

side

> > of
> > > the input on the relay. +18Vdc side of the torch trigger is
> hooked
> > to
> > > the + side of the relay output. The other side of the torch
> trigger
> > > is hooked to the other side of the relay output.
> > >
> > > I had originally purchased an AC SSR and it worked, wired
> basically
> > > as I had wired this new crydom (except I wasn't using a

breakout

> > > board at that time). The problem with that was when I shut the
> > relay
> > > off, it took up to a few seconds for the torch to shut off. So
> > after
> > > reading those past messages from Jon and others explaining why
> that
> > > happens, that's when I bought the dc relay... so, I'm fairly

sure

> > > that it's wired correctly...
> >
> > As I not familiar with the torch trigger, does it supply the
> 18VDC?
> > I would expect that the minus side output of the ssr to be
> connected
> > to the return of the power source, and the plus side to the

device

> > (torch) minus and the device plus hooked to the plus of a DC

power

> > source. If the trigger plus is really the low side of the load
> then
> > what you described is ok.
> >
> > > > 4. What is the DC power source for the load you are

switching.

> > > Not exactly sure what you mean here?... The Plasma cutter has
> 18Vdc
> > > on the ttorch trigger...
> > Is there an 18Vdc power supply that is part of the torch trigger?
> >
> > Who/model of Trigger?

Seems to me that a simple 12vDC small relay with at least one set of
NO contacts in parallel with the two switches would work a lot better
than an SS relay (which contains active devices and has some of the
normal leakage current issues listed. We use little PCB mount 12V
relays that draw about 40ma on activation in our THC circuit (also
available from Bob) to activate the torch and to feedback the arc
good signal. The 18VDC is just part of the internal torch voltage
and the trigger input may well be a high impedence logic input that
draws such a small current that normal SSL's will have trouble
turning off of where a small amount of leakage current creates long
decays. If the input were a FET type then even small currents will
cause turnon.

By sticking with a mechanical relay you have the same type contacts
you have in the switches in your schematic. Hook it up so the coil
of the relay is driven by the breakout board with the plus of the
coil to +12 pin and the minus to the signal pin. Be sure to put a
small diode (1N4001 or equiv) across the coil of the relay with the
cathode (striped) end on the plus and the anode on the negative.
This supresses any negative voltage pulse when the relay is turned
off and the colapssing field generates a voltage spike.