Re: [CAD_CAM_EDM_DRO] SS Relays - Revisited

Hi Chris
Take a look at the schematic on the crydom spec page. See how the + supply
voltage is hooked to the load, in this case your plasma cutter, and the the
load is hooked to the + terminal on the ssr and the - terminal on the ssr is
hooked to negative (or ground). If it's possible to wire it this way, do
so. I believe it will work just fine. If it's not convenient to wire it
that way, there may still be something that can be done. I would need to
know how much current actually flows through the plasma trigger circuit and
some idea of how much current the 18vdc supply is good for. Hope this helps
Bob

----- Original Message -----
From: "cutthroatplasmaco" <cutthroatplasmaco@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, December 12, 2003 10:32 PM
Subject: [CAD_CAM_EDM_DRO] SS Relays - Revisited


> 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
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
> >
> >
> > mrpootoo wrote:
> >
> > >Ah! I ran into this problem and couldn't figure out what was going
> on
> > >for the life of me.
> > >
> > >What type of relay do you use for switching DC?
> > >
> > >
> > There are solid state relays for DC use. Crydom, Omron, etc. make
> > these. If you want a mechanical contact relay, those are
> available, too.
> > The problem with DC is there is no zero crossing to allow the arc to
> > break. Some DC contactors have magnets to bend the arc in a loop,
> > others use insulating barriers that pass between the opening
> contacts.
> > And, of course, if space permits, they just open the contacts wider.
> >
> > Jon
>
>
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
> Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@...,
timg@...
> Moderator: pentam@... indigo_red@... [Moderators]
> URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
> List Owner
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>