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From: "Reg Edwards"
Subject: Re: Zener Diode
Date: Tue, 10 Sep 2002 15:12:23 +0000 (UTC)
Organization: Private individual
NNTP-Posting-Date: Tue, 10 Sep 2002 15:12:23 +0000 (UTC)
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You havn't provided enough information to solve whatever problem you have.
But it should be remembered there are THREE important parameters of a
magnetic relay -
Operate current. The lowest current at which the relay MUST operate.
Hold current. The lowest current at which the relay must NOT release.
Release current. The highest current at which the relay MUST release.
Which are all very different from each other.
A reputable manufacturer will state these values in performance
specifications. If not then the circuit designer can expect the unexpected
The specification, of course, can be written in terms of operating volts. V
= I*R where R is the relay coil resistance.
It may be of interest that relay timing is a function not only of coil
resistance but also of inductance. Coil inductance can be very large (many
turns of fine wire on an iron core), which with coil and external circuit
resistance greatly affect operate release times.
"Redd" wrote in message
> I wanted to energize a 12 volt relay coil only when my
> supply voltage rises to 10 volts or higher so I place
> a 10 volt zener diode in series with the relay coil.
> The relay will not energize when the zener turns on.
> the voltage across the zener is 10 volts but only 2
> volts across the relay coil. The relay coil only needs
> about 35 milliamps to turn on, after that the contacts
> will latch the supply voltage across the coil.
> What am I doing wrong and how can this be accomplished.
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