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Subject: Re: Zener Diode
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Date: Tue, 10 Sep 2002 17:48:50 -0700
NNTP-Posting-Date: Tue, 10 Sep 2002 17:44:19 EDT
Organization: Optimum Online
All relays will have a "Pull in " and a "Drop out" voltage.
If this is a "one off", first determine what the pull in voltage is normaly
for the selected relay. That value should be fairly consistent, try it
several times to see if it is. Chances are the relay will "Pick" at 8 - 9V.
If this is not aceptable, add a series resistor: If the relay picks at 9V
and the current is 50ma, then add a 20 ohm resistor in series. The resistor
will drop the additional 1 volt, to add up to a total of 10V.
This circuit may not be accurate for your needs, you did not offer any
spec's. However it does offer a quick and dirty solution.
"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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