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[on:]

Hello,
Arduino newbie here respectfully bringing my project here for guidance. I wish I knew how to do this, but need help getting going. Want to make sure I do not go down the wrong path. From watching this site, there is some incredible knowledge here, so am hoping to tap into just a tiny bit of that!

• Am building a temperature monitoring system that will use data from one sensor to operate a 1/2 hp 110v electric motor.
• Sensors are DS18B20s.
• Will monitor temperatures from about a dozen DS18B20s.
• Data will go via modified cat6 cable to an Arduino Mega1280. (DS18B20s, time stamp, temp.)
• Data from one of the DS18B20 will operate a relay for ½ hp 110v motor.
• Data will transfer via ethernet shield from Arduino Mega1280 to Ubuntu/Mint/Debian PC for storage/analysis.
• Other sensors will have data read and logged every 30 seconds.

What type of relay works best here?

Regarding the Arduino code, 're-inventing this wheel' makes no sense to me and I learn best using a solid code base to work and learn from.

IMO, having a proven solid code base to start with and then testing / learning / experimenting off of this would be far preferable.

Anybody agree with this? I know I work best starting with a proven thing and using that to learn.

I would be very grateful for any and all suggestions.

Thank you. Looking forward to this.
Clinton

[Reply #1 on:]

What type of relay works best here?

Look at: http://goo.gl/lkfoi  which is rated 1 HP at 120VAC 

Typical 10A rated relays are probably not OK for the startup surge on the motor.


DISCLAIMER: Mentioned stuff from my own shop...

[Reply #2 on:]

Look at: http://goo.gl/lkfoi  which is rated 1 HP at 120VAC.  Typical 10A rated relays are probably not OK for the startup surge on the motor.

Good link. I agree, a 10A relay would not be good. Even if it worked, I do not believe it would last long as it would  be stressed hard.

Now hoping some people have examples of a similar setup with regards to a code base to start from.   

Thank you Terry.
clinton

[Reply #3 on:]

 Agree that a hefty relay is required. Motors require more amps on startup, I recommend a 20amp relay for good safety margin. In fact, I'll be using a RIB2401b "Relay-inna-box" for my own 1/2 horse motor application. I'll be using DS18B20s too. Haven't started yet though so no code advice, sorry...

[Reply #4 on:]

Big electric motors typically use something called a 'contactor' rather than a relay. They seem to be fundamentally the same thing (solenoid operated switch) but are presumably optimised for switching high current inductive loads. The ones I looked at were surprisingly expensive. This may be a good reason to keep looking for an ordinary relay and hope you find one that is up to the job, but I can't help thinking that they're probably expensive for a reason.

[Reply #5 on:]

I to what was stated re: contactors, they can be found on ebay for about the same cost as comparable SSR's

[Reply #6 on:]

Hi guys im interested in doing a small scale version of this. Very bare bones, I'm a hardware guy so i have my circuit set up but im trying to find a piece of code to work off. What I plan on is having 1 Ds18b20 set up to trigger a relay at a set temp limit. I have come across some code but most of it is to log the temps.

Could anyone give me some pointers or point me in the right direction?

Thank You

[Reply #7 on:]

Hi guys im interested in doing a small scale version of this.

Take a look at: http://arduino-info.wikispaces.com/Brick-Temperature-DS18B20

After you have that running, add a variable to hold the value returned by
sensors.getTempCByIndex(0)

And then use an "if" statement like ;
if (temperature > toohot) {//do something } ;

[Reply #8 on:]

What I plan on is having 1 Ds18b20 set up to trigger a relay at a set temp limit.

...

Could anyone give me some pointers or point me in the right direction?

It sounds as if you are planning to emulate a thermostatic switch in software. Why not just use a thermostatic switch?

[Reply #9 on:]

Big electric motors typically use something called a 'contactor' rather than a relay. They seem to be fundamentally the same thing (solenoid operated switch) but are presumably optimised for switching high current inductive loads.....

Grainger has a helpful PDF entitled "Choosing Relays, Contactors and Motor Starters" and clarified some points for me. here is the link: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&sqi=2&ved=0CCwQFjAB&url=http%3A%2F%2Fwww.grainger.com%2Ftps%2Felectrical_choosing_relays_motor_starters_contactors.pdf&ei=Bwt6UI73Dq6p0AHM7YHICg&usg=AFQjCNFTeGMBcA0tosszw9fOhvEOXKdefw&sig2=HW8qHpAJQnmd5B4ve0TJtg

Hope that is helpful. It clarified some stuff for me.

[Reply #10 on:]

You may also want to look at this from the ArduinoInfo.Info WIKI:

http://arduino-info.wikispaces.com/RelayIsolation

[Reply #11 on:]

Thanks guys I'll try that.

[Reply #12 on:]

Updates: I have the brick sketch running fine now, I unsure on how to keep the value from the serial port to compare to my limits. Would i use the math library? Sorry for all the questions

Thanks again