Relay Help

General project help for Adafruit customers

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yo1dog
 
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Relay Help

Post by yo1dog »

I bought this relay from radio shack to use with a temperature controller I am building.I have isolated the relay by itself and I am trying to get it to switch but with no luck. Here are the stats from the package:

Continuous coil voltage: 132VAC
Power consumption: 1/10VA max.
Rated Voltage: 110/120VAC
Coil resistance: 4.430 ohms max.
Pull-in voltage: 96VAC max. 36VAC min.
Nominal coil current: 8.4/8.2mA
Contact rating: 10A at 110AC or 24VDC
Maximum operating voltage: 250VAC/125VDC
Minimum load: 100mA 5VDC

I tried connecting the two coil terminals to a 6v 4.5 Ah battery and to a 5v 350mA power supply but still no luck.

Any ideas?
Thanks,
- Mike

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yo1dog
 
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Re: Relay Help

Post by yo1dog »

Oh and I am following this diagram.


... couldn't find the edit button.

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zener
 
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Re: Relay Help

Post by zener »

mikeem wrote: Continuous coil voltage: 132VAC
Do you know what this means?

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yo1dog
 
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Re: Relay Help

Post by yo1dog »

Sure don't :)

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zener
 
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Re: Relay Help

Post by zener »

That is the voltage that operates the coil. In this case probably the maximum. So it's nominally a 120VAC coil.

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yo1dog
 
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Re: Relay Help

Post by yo1dog »

So does that mean I can use the current straight from the wall?

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zener
 
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Re: Relay Help

Post by zener »

You are not following your diagram very well. The diagram shows a Solid State Relay with 3 to 32 VDC control, controlled by 3-32 VDC. You have substituted an electromechanical relay with 120 VAC control, and a 5 or 6 volt battery. So that is not going to work. I do not recommend attaching anything the wall power without knowing very well what you are doing. I do not believe your thermostat will survive trying to switch 120 VAC. I would recommend following the diagram more closely. You could use an electromechanical relay with a 5VDC coil and your battery.

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yo1dog
 
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Re: Relay Help

Post by yo1dog »

Wait, so whats the point of a relay that can control 120VAC when it takes 120VAC to switch it??

Where can I get a relay that allows me to control 120VAC with around 5V?

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zener
 
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Re: Relay Help

Post by zener »

Relays have a lot of specs. They have a full data sheet, except if you get one from Rad Shack then it has no data sheet unfortunately...

A couple of the main things to understand is that there is the contact rating (what it can switch), and there is the coil rating (how you control the relay). These are two unrelated things.

It appears you want a relay with a 5V coil, and contacts rated for a 120VAC load of some kind. To pick an actual relay you need to know the exact load you will switch, not only how many volts, but also how many amps it draws, and what kind of load it is, inductive, resistive, capacitive, motor, etc. Then you can go to Digikey of somewhere and hopefully find a relay that will work for your application.

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easternstargeek
 
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Re: Relay Help

Post by easternstargeek »

Hi, Mikeem-
I wonder if this question is related to your cooling fan project and cheap Honeywell thermostat, down-thread? If so, I kindly encourage you to give us the big picture, because to me, it looks like you're just taking random shots at the problem. Selecting the right parts to build a system is often an iterative process, and the folks here will be able to help you much better if you tell us:

1. What, exactly, are you trying to build?
2. For what purpose?
3. What must it do?
4. What are the major components that you are trying to control?

Context is always helpful in cases like this. Looking forward to hearing from you.

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yo1dog
 
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Re: Relay Help

Post by yo1dog »

Yea sorry about that. As I am in the learning stage of all this I like to break down the project into it's individual problems so that I can get more information about each part.

I am building a temperature controller for my kegerator I made from a freezer. It needs to keep the liquid temperature inside the freezer at 38° F by cutting and restoring power to the freezer. Sense my last post I have gotten a lot done. I have gotten the correct relay and everything works great. Only problem is that the thermostat I bought only goes down to 50° F. I decided to use my Ardunio instead. I already have a thermistor that I purchased with the board. I still have to purchase a transistor and a diode to complete this circuit for controlling relays with Arduino.

Regarding said circuit, I am using a 12v/10A relay with a 12v power-supply. I am not good at reading these diagrams yet, here is me attempting:

Starting at AURDUINO_DIGITAL_OUT, this is obviously one of the digital pins (like pin 13).
Then it goes to a 1KΩ resistor.
It then connects to the "base" pin of the transistor.
The "emitter" pin goes to 12v power-supply's ground.
The ground terminal of the relay goes to the same place as above.
The "collector" pin connects to the diode and ?? whatever that box with a slash is?? Can someone tell me what that is?
The ends of the diode and the ?? slash box?? connect to the power terminal of the relay.

So here are my questions:
1. What is that box with a slash and 16 and 1 on either side? And what is the S1 01 P1 K1 with the dashed line to the slash box?
2. Where does the 12V+ from the power-supply connect in the circuit?
3. Radioshack (the only electronics store around me) does not carry TIP102 transistors. This is there selection. I am not sure what I should be looking for. Can someone point me in the right direction?

Perhaps if someone could draw me a "circuit for dummies" that maybe even included small descriptions of what each part does. That would be extremely helpful.

I appreciate all the help so far!
Thanks,
- Mike

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brucef
 
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Re: Relay Help

Post by brucef »

mikeem wrote: 3. Radioshack (the only electronics store around me) does not carry TIP102 transistors. This is there selection. I am not sure what I should be looking for. Can someone point me in the right direction?
TIP102 is a Darlington transistor. The only Darlington I see on that list without checking every spec is the TIP120, which has lower voltage and current ratings than the TIP102. I'm not even going to venture an opinion on whether that might be a suitable substitution in your case because it sounds like you're messing around with mains power in a potentially wet environment. That's more danger than I'm comfortable playing with, myself.

Have you considered using something like a powerswitch tail instead of creating your own circuit on the 'hot' side?

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easternstargeek
 
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Re: Relay Help

Post by easternstargeek »

OK, Mike- that is much better. I can do something with your information.

First, to answer your questions:
1. The box with the slash is the standard symbol for a solenoid coil, which in this case, represents the coil (electromagnet) in your relay. The 1 and 16 are just the pin numbers for the coil, probably for small DIP relays. Since you are using a bigger unit, your can ignore them.
2. "S1" is the reference designation for any kind of switch. "01 P1" not sure where these came from- you can ignore them. "K1" is the reference designation for the relay, itself. The symbol next to that stuff is a generic switch contact symbol, in this case, representing the power contacts in your relay. Your relay will likely be different.
3. The dashed line between the coil and switch contact symbol shows that there is a relationship between the coil and contacts (they are magnetically coupled).
4. The 12+ terminal from your power supply will connect to the "Relay Power V+" and the negative terminal will connect to the "Relay Power GND"

As far as transistors go, please see this thread: http://forums.adafruit.com/viewtopic.php?f=8&t=23203
The transistor you need depends on how hungry the relay coil is. Pick the relay first, then find a suitable transistor. I agree with the Arduino folks- a 2N2222 or TIP102 are both excellent choices for the hobbyist. My bet is that a 2N2222 will work fine for you. That transistor can drive a 12V, 6 watt coil , and that's a BIG coil!

Some more tips for you:
I wouldn't necessarily assume that your 10A Radio Shack relay is adequate for controlling the freezer. The compressor probably pulls way more than that when it starts, leading to premature contact failure. When poorly rated contacts fail, they usually fail welded-shut, which will make the freezer run non-stop. Please consider the potentially serious consequences!

To be on the safe side, please write down everything on the spec plate of your freezer (at least volts, amps, HP, watts, etc- whatever may be listed) and post it here.

See also this forum topic:
http://forums.adafruit.com/viewtopic.php?f=8&t=19146
My contributions to that thread include a very in-depth explanation of relays for applications like these, including some part numbers and where to get them. The relay I recommend ( http://search.digikey.com/us/en/product ... -ND/254527 ) would be a much better match for your freezer, most likely. If you want to use this part, don't forget to order the special crimp terminals for it. Everything you need is in the thread, so please read all of it.
Pay particular attention to the warnings regarding wiring practices for AC circuits. Even though I managed to survive my childhood (I've been playing with this stuff since I was 8 ) a certain amount of that was luck! Please be careful, because of the considerable hazards that can lead to shock, fires, and equipment damage (possibly leading to beer damage, too- and you wouldn't want that!)

Also, I strongly recommend that you stay away from Tar-Paper Shack. They are OK in a pinch, but a lot of the parts are pretty junky and cheap. If you want to make things like the pros do, you need industrial-grade components. (Besides, any company that rips-off consumers by charging almost $40.00 for a firewire cable doesn't deserve your business) I rely on Mouser and Digi-key for the things I can't buy from Adafruit. The selection can be plenty bewildering at first, but bazillions of folks use them regularly, and you'll get the swing of things the more you build.

Finally, get yourself some good books on basic electricity, home wiring (for good tips on the AC stuff) and basic electronics. They are handy references, and reading them is a pleasant way to pass the time while waiting to see the Triage Nurse at the Emergency Room. :mrgreen:

Have fun with your project!

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yo1dog
 
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Re: Relay Help

Post by yo1dog »

Wow! Thanks for the time and good info!

I forgot to add that I am trying to get this done quickly. Stupidly of me I thought I would be able to get it this done quickly and I already have the kegs sitting in my friends fridge... who wants them out lol. Hence why I am purchasing everything from Radio Shack.

I read the whole transistor thread but I was lost during most/all of it. I still do not know what terms like "sourcing" and "sinking" mean... I promise I'm trying! If someone could recommend which one of these I should get I can hopefully get those kegs out of his fridge tonight (he is threatening to take them out regardless!).

I could not find any specs on the fridge but I did find this on the compressor:
1NP 115V 60Hz

I hope that is enough information. I was talking to my dad and my uncle (both experienced with electronics) and they seemed to think that 10A was huge and would be enough and anything more than that risked filliping the breakers.

I attached my revision of the circuit please let me know if everything is correct.

Thanks again,
- Mike
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relayCircuit.png
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yo1dog
 
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Re: Relay Help

Post by yo1dog »

I have been doing some research and it looks like most 7.5 cu ft freezers are rated at 5A. So my relay should be fine.

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