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Relay used to control home appliance

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
 
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

Call me dense, but why would you want to turn on/off a freezer like
it's a light ?

GG
 
D

DJ Delorie

Jan 1, 1970
0
Call me dense, but why would you want to turn on/off a freezer like
it's a light ?

I'm guessing you turn it on when the inside is too warm, and off when
the inside is too cool. I.e. thermostat.
 
J

Jasen Betts

Jan 1, 1970
0
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).

the easiest type of relay to hook to a basic stamp and used to controll a
mains powered appliance is a solid-state relay.

radio shack is not a good place to buy electronics parts, look in the yellow
pages if you want to find a nearby place.

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?

that one's not really suitable, you want a relay that operates off a low
DC voltage rather than a high AC voltage.

nominal current is the current the relay is designed to use in the coil,
max continuous voltage is the most you can give it and be sure not to blow
it up. pull in is how much it needs to turn on, drop-out is howw little you
need to give it for it to turn off.

Bye.
Jasen
 
P

petrus bitbyter

Jan 1, 1970
0
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

John,

I understand this relay is meant to be powered by 110VAC, and able to switch
on/off appliances that require 110Vac at up to 10A. The maximum 250Vac can
be considered the space you need to stay on the safe side like you mentioned
already.

As you want to power the relay with 5V (or maybe 12V?) it's of no use for
you.

I advise to use a solid state relay. One with a build in opto coupler.
Digi-Key has a lot of them in the catalog but a lot of that lot are not on
stock.
But a 425-1223-5-ND for instance may fullfill your needs at an acceptable
price.

petrus bitbyter
 
R

Rich Grise

Jan 1, 1970
0
I'm guessing you turn it on when the inside is too warm, and off when
the inside is too cool. I.e. thermostat.

Aren't they kind of "built-in"?

Thanks,
Rich
 
Rich said:
Aren't they kind of "built-in"?

Thanks,
Rich
The stamp based thermostat is actually a piece of a larger project but
in short the freezer is being turned into a refridgerator and so would
require a new thermostat, an upright freezer is being used because its
cheaper, the correct dimensions, and much more aesthetically appealing
for the project then a refridgerator.
 
E

ehsjr

Jan 1, 1970
0
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
 
R

Rich Grise

Jan 1, 1970
0
The stamp based thermostat is actually a piece of a larger project but
in short the freezer is being turned into a refridgerator and so would
require a new thermostat, an upright freezer is being used because its
cheaper, the correct dimensions, and much more aesthetically appealing
for the project then a refridgerator.

How does the existing thermostat control the motor? Does it have a relay?
If so, you could use that one. Or if the thermostat itself is doing the
switching, then, of course, you'd go back to your original idea.

I would look for a relay that's specifically designed for motors, though;
maybe even a contactor, but you might not need that much heft.

Good Luck!
Rich
 
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