Re: Relay used to control home appliance
- From: ehsjr <ehsjr@xxxxxxxxxxxxxxxx>
- Date: Thu, 15 Jun 2006 05:01:40 GMT
jalamia@xxxxxxxxx wrote:
Hi, I'm working on a project in which I need to be able to switch on
and off an upright freezer. I'm trying to control the relay via a
transistor controlled by a basic stamp (as I assume this is really the
only way its going to get done). Unfortunatly I have been researching
relays for the past four hours or so and understand the theory behind
them very well but not how to use them / how to select the proper relay
for this project. Stopping by radio shack on my way home from work
today I saw a relay (electromechanical) that claimed a contact rating
or 10A at 110VAC, which seemed around the correct range (A upright
freezer I had looked at said it only drew 5A at 110VAC) and that its
maximum operating voltage was 250VAC, well enough to not fry incase of
any spikes. the rest of it I'm not exaclty sure what to make of, It
said the nominal coil current is 8.4mA, the continuous coil voltage is
132VAC, that the Pull-in voltage was 9.6VAC and that the Dropout
voltage was 36VAC. What i'm trying to determine is simply does this
relay require 8.4mA to maintain its position and 9.6VAC to switch? or
36VAC to switch or 8.4mA of current to switch?
If someone could shed some light (or atleast point me in the direction
of where specifically I could find this information) on what the
Pull-In voltage, Continuous Coil Voltage, Nominal coil current, and
Dropout voltage indicate I would greatly appreciate it.
Thanks,
John Alamia
As others said, you really want something different.
My reply will address your questions about relay
operation. First, however, there is a typo in
the Pull-in voltage spec - you said it was 9.6 VAC
but the correct figure has to be 96 VAC.
Short answer:
Continuous coil voltage - the voltage you should apply
to the coil to energize the relay
Pickup voltage - the minimum voltage that will cause
the relay contacts to transfer to the energized
position
Dropout voltage - the voltage at an energized relays
contacts will transfer to the de-energized position
Coil current - the amount of current the coil will draw
to the continuous coil voltage
Long Answer (some detail):
The relay you are talking about is an electromagnet
with a movable armature. When the relay is de-energized,
a spring holds the armature at some distance away from
the electromagnet. When you energize the magnet it
takes a certain amount of magnetic attraction to reach
across the distance to the armature to pull it toward
the magnet. When the magnet is energized and the armature
is in contact with it, the amount of magnetism to hold
the armature to the magnet is much less, as it does not
have any distance between.
The continuous coil voltage is the voltage that
will be applied to the relay in normal circumstances.
The coil can operate with that voltage without damage.
The pull-in voltage is the voltage at which the armature
will move to the magnet.
The drop out voltage is the voltage where the spring
overcomes the strength of the magnetic field and the armature
moves away.
The nominal coil current is the amount of current the coil
will draw when energized by the continuous coil voltage.
Ed
.
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- Relay used to control home appliance
- From: jalamia
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