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From: "John Jardine"
Subject: Re: Driving a coil-driven relay
Date: Tue, 10 Dec 2002 20:46:01 -0000
NNTP-Posting-Date: 10 Dec 2002 20:33:40 GMT
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
Michael Starks wrote in message
> Hi all,
> I am having fits trying to troubleshoot a circuit. Perhaps some ideas
> will help.
> The circuit is designed to drive the Open and Close coils on a 800A DC
> contactor. This thing is bi-stable and has a permanent magnet inside.
> When you hit the open coil with 24V (requiring about 300mA in
> steady-state), it opens. When you hit the (oppositely-wound) close
> coil with 24V (requiring about 2A in steady state), it closes.
> Any ideas as to where to go with this? I have the current; I have the
> voltage; I have the pulse lengths; yet the close cycles still don't
> close it properly.
> Thanks for any thoughts. I've got 3 days into this thing and all I've
> done is eliminate possibilities. Still no answers.
> Michael Starks
I'd think that using caps as the switching supply is the problem. As soon as
the caps are connected they start discharging at an exponential rate. The
voltage to the coil starts off OK but is out of spec' a moment later.
The opening cap bank size has not enough sustained energy to do the
changeover job and would need increasing in size (substantially!).
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