Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil

Hi Jon;

Your mention of interaction in widely separated devices reminds me of an
incident I had years ago.

Back then I was involved in maintenance of some lathes that required
holding tolerances on some parts to within a couple of microns. This
was a production environment with parts being knocked out in under 30
seconds all day long. As you an imagine we had to deal with all sorts
of physical issues along with the electric.

One day one of the techs came to me indicating that he had a lather that
would loose 2 microns position every time the spindle was cycled from on
to off. Sure enough that was exactly what was happening. Eventually
the problem was traced to two relays inside of the spindle drive that
where un protected. That is no transient suppression at all, ended up
having to solder two diodes to the PC board traces.

When dealing with any sort of digital electronics connected to a machine
tool it is a good idea to make sure from the start that all solenoid and
relays are installed in a electrically sound manner. Don't rely on
vendors of electronic hardware to do this either. It doesn't manner
if your dealing with a digital readout or a full CNC system, one little
relay parked feet away can make any of these devices unstable or
unsuitable for operation. The amount of isolation you think you may
have isn't always as effective as it seems. The spindle drive
described above did not have any electrical connections to the CNC
controller.

Dave

On Sun, 2004-01-11 at 22:39, Jon Elson wrote:
> Paul Davis wrote:
>
> >I've had it happen in circuits before. Maybe, though, it was the back emf spike which caused the circuit to re energize the coil? In any case it's a good idea to have the diode.
> >
> >Paul Davis
> >
> >
> >On Sun, 11 Jan 2004 16:13:56 -0600, Jon Elson wrote:
> >
> >
> >> Paul Davis wrote:
> >>
> >>
> >>
> >>
> >>> Diodes are a good idea for DC even if you don't care about the
> >>> spike caused by the back emf. The relay will remain latched
> >>> until it dissipates it's magnetic field. Assuming it doesn't
> >>> destroy your driving electronics or short it's coils it can cause
> >>> the relay to remain latched for a few seconds after the input is
> >>> removed. So for the sake of speed it's a good idea to have the
> >>> diode.
> >>>
> >>>
> >>>
> >>>
> >> Huh? With the diode, the field dissipates slowly, but it is
> >> usually done in tens of
> >> milliseconds. Without the diode, the field dissipates VERY
> >> rapidly, unless it
> >> arcs over in the coil, and the field collapses in microseconds.
> >> So, the diode slows it down, rather than speeding it up.
> >>
> >>
> Oh, yes. Uncontrolled switching spikes are FAMOUS for causing totally
> unpredictable malfunctions in digital circuits. I have seen amazing
> interactions,
> where a relay being turned off in one unit triggered bizarre malfunctions
> in equipment that seemed quite remote to the circuits that were connected to
> the relay. And, even experts have sometimes been stymied in finding the
> cause of the problem.
>
> 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@... davemucha@... [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
>
>
>
> Yahoo! Groups Links
>
> To visit your group on the web, go to:
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/
>
> To unsubscribe from this group, send an email to:
> CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>
> Your use of Yahoo! Groups is subject to:
> http://docs.yahoo.com/info/terms/
>
>
>