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From: Tony Williams
Subject: Re: Driving a coil-driven relay
Date: Tue, 10 Dec 2002 13:40:02 +0000 (GMT)
NNTP-Posting-Date: Tue, 10 Dec 2002 13:58:12 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article <email@example.com>,
Michael Starks wrote:
> The problematic driving circuit charges large banks of caps to 28V
> through diodes and a current limiting resistor. It is then fired for
> 250ms by a monostable, which turns on a MOSFET and shorts the
> capacitors across the appropriate coil. We use 8800uF for the Open
> coil and 88000uF for the Close coil.
A quick sum suggests that (to be compatible with the
Close cap) the Open cap should be about 12500uF.
> I have discovered through a lot of testing that the Open circuit is
> 100% reliable if you always close the contactor by manually resetting
> it (pushing it closed). If you ever close it using the Close circuit,
> something funny happens inside and the Open circuit cannot open it,
> despite the fact that it did close and latch. The only thing that
> will open it is +/-15V from the brick. Clearly my problem lies with
> the close cycle.
Whether the problem is in the Close or Open
cycle is not really certain yet.
Note the suggested increase in the Close cap.
Any chance that the Close circuit (even though
passive at that time) is interfering with the
The coils on maglatch relays have to be driven with
the correct polarity. Any chance you have this wrong?
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