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From: Pat Weston <peweston@teleport.com>
Subject: Re: Master relay
There is no
increased power generated from the coil or the contacts due to frequently
energizing and de-energizing the relay.
I disagree
At no time is the
current more than that in the steady state, thus the power (current
squared
times coil resistance) greater than when the set up is in the steady
state.
Do you mean to say that the pull in current is never more than the hold in
current. My understanding of a coil, solenoid or contactor is that pull-in
in current is greater and the hold-in current less due to the increased
inductance due to the magnetic circuit being closed. Also it is a positive
design feature as as the pull-in forse is greater than the holdin forse. a
contiuous cycle of opening and closing would give an overall aversge
increased power consumption. Increased power consumption = increased power
that needs to be dissipated.
Thus a relay being turned on and off dissipates less power than one in a
permanently on state.
The heat from the contacts is produced only when the contacts are closed,
a
load is applied and a current is flowing, thus if a relay is turned off,
there is no heat from the contacts.
I tried to explain this in laymans terms as much as possible to simplify
it to the average reader. May be I have miss understood something. Your
comments contradict what have learnt in college, experienced in practice and
information researched in ctalogue from Allen Bradley to Sprecher and Shuh.
I am interested to read your comments.
Sean Walker
Checkpoint Engineering and Electrical Service
Gunnedah, Australia
cpeng@mpx.com.au
LML homepage: http://www.olsusa.com/Users/Mkaye/maillist.html
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