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

GG

Reply to
stratus46

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

Reply to
DJ Delorie

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.

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

Reply to
Jasen Betts

schreef in bericht news: snipped-for-privacy@y43g2000cwc.googlegroups.com...

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

Reply to
petrus bitbyter

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

Thanks, Rich

Reply to
Rich Grise

Well, my furnace had a built-in one too ;-)

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Reply to
DJ Delorie

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.

Reply to
jalamia

Thank you jasen and petrus, I think the information you two gave should set me on the right path.

Reply to
jalamia

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

Reply to
ehsjr

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

Reply to
Rich Grise

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