RE: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Posted by
Jeff Goldberg
on 2004-01-10 20:53:47 UTC
Jon:
On D.C. side, I'm not using transistors (sounds too much like electronics),
but there's no harm in putting $.35 diodes there anyway.
On A.C. side, the capacitor and resistor go in series across the coil
(sanity check)?
Thanks,
Jeff
-----Original Message-----
From: Jon Elson [mailto:elson@...]
Sent: Saturday, January 10, 2004 11:13 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
washcomp wrote:
conduct when the normal polarity is applied to the coil. When a
presumably transistor circuit turns the supply voltage off, the coil,
by its inductive nature, wants to continue conducting current. This can
destroy the transistor that drives the relay due to the large voltage that
can be produced when you try to abruptly stop the current in the coil.
The diode provides a safe path for the current to circulate in the coil,
and the coil's own resistance dissipates the energy in milliseconds.
The same problem exists for AC, and can cause sparking of contacts
when one relay's contacts break the path to another relay's coil.
But, since the AC supply provides both polarities, a diode would
short out the supply every half cycle. There are devices called snubbers,
arc supressors, transient voltage supressors, etc. They generally use
a capacitor and a resistor in series. You can make your own with
these two parts. For a 120 V AC coil, something like 22 Ohms in
series with a .01 uF capacitor will work in most cases. These values
can be tuned for the particular coil.
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/
On D.C. side, I'm not using transistors (sounds too much like electronics),
but there's no harm in putting $.35 diodes there anyway.
On A.C. side, the capacitor and resistor go in series across the coil
(sanity check)?
Thanks,
Jeff
-----Original Message-----
From: Jon Elson [mailto:elson@...]
Sent: Saturday, January 10, 2004 11:13 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
washcomp wrote:
>Back when I was a kid learning about relay circuits on the jobOn relays energized by DC, you use a diode connected so it will not
>(1960's), most of the control circuits I got involved in used low
>voltage A.C. and I don't ever remember seeing a diode. I just found
>out that it's good practice to put a diode across the coil of relays
>to keep them from chattering due to the current stored in the coil
>inductance. Question is: Only on D.C. relays or is this supposed
>to be done on A.C. relays as well?
>
>
conduct when the normal polarity is applied to the coil. When a
presumably transistor circuit turns the supply voltage off, the coil,
by its inductive nature, wants to continue conducting current. This can
destroy the transistor that drives the relay due to the large voltage that
can be produced when you try to abruptly stop the current in the coil.
The diode provides a safe path for the current to circulate in the coil,
and the coil's own resistance dissipates the energy in milliseconds.
The same problem exists for AC, and can cause sparking of contacts
when one relay's contacts break the path to another relay's coil.
But, since the AC supply provides both polarities, a diode would
short out the supply every half cycle. There are devices called snubbers,
arc supressors, transient voltage supressors, etc. They generally use
a capacitor and a resistor in series. You can make your own with
these two parts. For a 120 V AC coil, something like 22 Ohms in
series with a .01 uF capacitor will work in most cases. These values
can be tuned for the particular coil.
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/
Discussion Thread
washcomp
2004-01-10 18:05:55 UTC
Relay question about diodes across the coil
Dave Fisher
2004-01-10 18:20:23 UTC
RE: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Greg Jackson
2004-01-10 18:35:09 UTC
RE: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Jeff Goldberg
2004-01-10 18:40:34 UTC
RE: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
archie & kathy
2004-01-10 19:44:28 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Harvey White
2004-01-10 19:45:38 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
JanRwl@A...
2004-01-10 19:56:50 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Harvey White
2004-01-10 20:05:19 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Jon Elson
2004-01-10 20:18:23 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Jeff Goldberg
2004-01-10 20:39:19 UTC
RE: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Jeff Goldberg
2004-01-10 20:42:51 UTC
RE: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Jeff Goldberg
2004-01-10 20:46:40 UTC
RE: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Jeff Goldberg
2004-01-10 20:53:47 UTC
RE: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Harvey White
2004-01-10 21:24:23 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Harvey White
2004-01-10 21:27:04 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Paul Davis
2004-01-10 21:37:09 UTC
RE: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
David A. Frantz
2004-01-11 02:33:13 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Jon Elson
2004-01-11 14:16:55 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Jon Elson
2004-01-11 14:19:07 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Paul Davis
2004-01-11 17:22:40 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
Jon Elson
2004-01-11 19:44:20 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
washcomp
2004-01-11 20:06:18 UTC
Re: Relay question about diodes across the coil
JanRwl@A...
2004-01-11 20:28:29 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil
David A. Frantz
2004-01-12 11:24:51 UTC
Re: [CAD_CAM_EDM_DRO] Relay question about diodes across the coil