Arduino + relays

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bigwestwc
 
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Arduino + relays

Post by bigwestwc »

Hi, can anyone help me? i have a app that i created using touch osc + processing and the arduino. i have it all set up on my breadboard so that i can turn on different parts of my house with my ipad or iphone wireless like: tv, fan, electronics bench ect. Have it all working on my breadboard using LEDs to see for debuging. my thing is that i want to wire it all up to a junction box with like (4) 120v wall outlets that i want to put together. i want to use the natural TTL logic from the arduino to control the relays to each 120 wall socket. does anyone know whats the best relay to do this with? something that will withstand over time and be inclosed? needs to be able to run 120v.

i will be running a 1000KHom resistor, a 1n4001 diode and a 2n22222 npn transistor on each relay, to protect the arduino.

thx all help will be appreciated

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adafruit_support_bill
 
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Re: Arduino + relays

Post by adafruit_support_bill »

does anyone know whats the best relay to do this with?
That depends on what you are switching. Some loads are more difficult than others and need a higher-rated relay.

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bigwestwc
 
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Re: Arduino + relays

Post by bigwestwc »

I will be swtching on regular house hold appliances like my flat screen tv, my work bench that has my soldering iron, small fan, and probably a lamp, also a regular 120v room heater and a fan. im guessing you mean whats the Amps that these things require?

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adafruit_support_bill
 
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Re: Arduino + relays

Post by adafruit_support_bill »

No, check the link in my previous post. Some loads like incandescent lights and motors have a very high initial current draw. There are relays specifically rated for motor loads or inductive loads. Or you can just get one rated for 2-3 times the steady-state load.

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bigwestwc
 
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Re: Arduino + relays

Post by bigwestwc »

ok so example. if iam running something that takes 5amps to run, 2-3 times steady state load will be a relay that can handle 10-15 amps? making sure its still rated at 120v of course? sorry if that makes no sense but iam a newbie with things like relays and voltage. thats why i have waited so long to finish up my project.

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adafruit_support_bill
 
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Re: Arduino + relays

Post by adafruit_support_bill »

That's right. It is better to oversize the relay than undersize it. For smaller (< 15A or so) relays the cost differential is typically small, so it is not so expensive to design for the worst-case.

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bigwestwc
 
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Re: Arduino + relays

Post by bigwestwc »

that makes a lot of sense, thank you verry much for all the information and quick replies. i can finally finish out my project and wire it up.

:D :D

Rukbat
 
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Re: Arduino + relays

Post by Rukbat »

Be careful. A room heater normally draws around 15-18 Amps while running (just divide the wattage on the label by the voltage), but if it's a Nichrome element heater the initial surge can be 3-4 times that (or even more) even though it doesn't last long enough to pop the circuit breaker. But even a 1/4 cycle (less than 1ms) surge like that would pop a SS relay. At least you'd free some magic smoke in the process.

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