The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: John Popelish
Organization: This space not available for advertising.
X-Mailer: Mozilla 4.7 [en] (Win98; U)
Subject: Re: Driving a coil-driven relay
References: <email@example.com> <3DF5A911.8F493BED@earthlink.net> <firstname.lastname@example.org>
Date: Tue, 10 Dec 2002 19:28:46 GMT
NNTP-Posting-Date: Tue, 10 Dec 2002 14:28:46 EST
Michael Starks wrote:
> Hi, Robert. Thanks for the reponse. I have rechecked with the
> manufacturer, and this contactor is supposed to be driven by 24V DC.
> I should also mention that it is bi-stable, but normally-open (i.e.,
> the springs help you open it; you work against them to close it.)
> I have done further testing; I charged a bank of 88000uF to 26V and
> discharged it across the OPEN and then the CLOSE coils. In all cases,
> the operation was 100% reliable in both directions.
> Therefore, the problem lies with my driving circuit. There are only
> four ways the driving circuit differs from the directly discharging
> 1. The current flows through a MOSFET, which we have already proven is
> turning on and off fully.
> 2. The coils have blocking diodes across them.
> 3. Each coil is always connected to its driver circuit, rather than
> hanging free when its partner is being energized.
> 4. Four feet of 20 ga. wire between driver and contactor.
> I suspect that during the CLOSE cycle, current induced in the OPEN
> coil initially by transformer action and then induced by the motion of
> the core (and permitted to circulate through the coil by the blocking
> diode) is somehow preventing the mechanism from throwing closed all
> the way, thus ending us up in the "closed but stuck" limbo state.
> I plan more tests using the capacitors, this time including blocking
> diodes on one or both coils.
> Any ideas in light of this new information would be appreciated.
I think you have hit on the cause of the problem. With the diode,
mosfet (and its internal body diode) and cap bank connected to the
winding not being energized, I suspect there is a transformer action
between the coils that is dumping your energy somewhere other than
into the magnetic field needed to operate the relay. Measure the open
circuit voltage produced by the non energized coil, when the other is
being operated, and then look at the rest of the circuit to see that
that voltage would do.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup