Pages: [1] 2   Go Down
Author Topic: Help With BBQ Smoker Temperature Control Project  (Read 6813 times)
0 Members and 1 Guest are viewing this topic.
0
Offline Offline
Newbie
*
Karma: 0
Posts: 19
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi all,

I'm new to the Arduino land and small electronics in general and am looking for some help/validation from you knowledgeable folks out there.  I'm constructing a BBQ smoker and plan to use the Ardunio to control the temperature, with two temperature probes as input (meat and pit) and a 1500w heating element.

The smoker is approximately 60"x26"x18" with an aluminum frame, sheet metal doors and sides with high-temp insulation.  The heating element will be placed at the bottom of the smoker.

So far I've purchased the Uno and got it up and running and reading the temperature from one of the probes via analog input.  I've read a bunch about controlling 120V AC via the Arduino and it sounds like for my application a SSR is the way to go.  1500W / 120V = 12.5 amps, so I'm thinking I need at least a 15 amp relay, maybe 20 or 25 to be safe?

I know the community generally frowns upon a noobie attempting a project involving AC so any recommended input, reading materials, safety precautions, etc would be greatly appreciated.

Jeff
Logged

0
Offline Offline
Newbie
*
Karma: 0
Posts: 19
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Sorry couldn't put links in first post, but some references I'm using are http://www.smokingmeatforums.com/forum/thread/90085/the-how-to-for-making-an-arduino-controlled-smoker and http://hruska.us/tempmon/.

For the relay I was thinking something like this or this maybe?
Logged

Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 514
Posts: 31553
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
maybe 20 or 25 to be safe?
Yes defiantly, an SSR is very unforgiving of over current and while your heating element might be a certain value when it is hot, it is a much lower resistance when it is cold and so likely to take a lot more surge current. I would suggest you measure the DC resistance when cold.

Generally speaking make wiring neat and physically secure and well insulated. Keep mains out of contact with anything conducting unless there are two different layers of insulation. Always have a 3mm gap of air and 5mm exclusion on any PCB tracks.

Quote
the community generally frowns upon a noobie attempting a project involving AC
Consider your self frowned on.
Logged

0
Offline Offline
Jr. Member
**
Karma: 0
Posts: 50
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
I know the community generally frowns upon a noobie attempting a project involving AC

It's only dangerous if you don't take the time, effort, and care to make sure it's done safely.  

Logged

Phoenix, Arizona USA
Offline Offline
Faraday Member
**
Karma: 36
Posts: 5519
Where's the beer?
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

jeffesonm - you might check out this project:

http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=119

While it doesn't use an SSR for control, instead opting for a standard relay, the tutorial is still something worthwhile to read. Plus, you might give some thought to using a standard relay instead of an SSR; it will be less expensive, plus you won't have to heatsink the relay (SSRs sometimes have to be heatsinked, depending on the amount of current they are switching).

This tutorial, for example, can probably be done in total for under $20.00 USD (that would include buying the parts from SparkFun, plus the parts needed from Home Depot, etc - things like the outlet, cords, etc).

Regardless, it offers other tips and techniques for working with AC.

If you've ever wired a lamp or installed a ceiling fan, outlet, etc - then you have the basic knowledge needed. Just do a lot of googling and such to find out more and study everything carefully. Double check all your work before plugging it into the wall. As long as you take your time, inspect your work, and respect what you are working with, it should all work out ok...

Good luck with this project; I'll be keeping an eye on it and/or the thread - I have a propane-based smoker I use often - something electrical might be interesting to try...

 smiley
Logged

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

0
Offline Offline
Newbie
*
Karma: 0
Posts: 19
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Thanks all for the feedback.  I will be sure to do some more research on good wiring practices before actually hooking anything up.

That last article was particularly interesting and looks like a good design approach.  I like the idea of wiring up an outlet to the switch, so I can use it for something else in the future if I choose.

I've been reading a bunch on SSR vs EMR and it seems like the main benefits of SSR are increased reliability and switching speed.  Benefits of EMR seem like price and that if it fails, it will more likely be in the open position.  I saw an advertised average EMR lifespan of 1,000,000 switches, which with 1 switch/minute for 10 hours/smoke, running the smoker every day, it would last 5 years, so basically indefinitely in my application.  It also sounds like heat is primarily an issue with the SSR, so I would not have to worry about a heatsink with the EMR.

Any other thoughts about EMR vs SSR?
Logged

0
Offline Offline
Sr. Member
****
Karma: 4
Posts: 310
Posts: 40382
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

FYI, if you ever have an AC project that deals with 10 amps at the most, a beginner can use this: http://powerswitchtail.com/default.aspx  It's like the sparkfun product, you turn it on and off like an LED.  
Logged

Ontario
Offline Offline
God Member
*****
Karma: 20
Posts: 835
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The audible noise a conventional relay makes may bother you.  Or you might find it reassuring.  A conventional relay will make a little RF noise while switching and the electronics to operate the coil are a few cents more complicated than for an SSR.
Logged

0
Offline Offline
Newbie
*
Karma: 0
Posts: 19
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

So after much research I think I'll be going the SSR route... I liked that SparkFun project but it wasn't clear the PCB can handle the load I would be putting through it and I'd prefer to play it safe when dealing with main voltage.

I've gathered all parts except for the relay and last night did my first ever soldering 8-).... got the ET73 temp probe hooked up and am printing the readout on a 16x2 LCD.  Next up I'll be connecting the Ethernet/SD shield and working on the sketch.  Will be sure to post some diagrams/pictures as I get closer to wiring up the relay so you all can double check my wiring work smiley  Thanks for the help.
Logged

0
Offline Offline
Newbie
*
Karma: 0
Posts: 1
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

wow.. I'm out googling the almost EXACT same project.  I have a Traeger that I want to have wifi control and logging of and stumbled onto the arduino's and now your thread(s).  

I'll be running a auger to feed the pellets into the firepot instead of the electric heating element but you've already solved some of the issues.  I'll be very interested in your code and results.
Logged

0
Offline Offline
Newbie
*
Karma: 0
Posts: 19
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Okay well I've made some good progress and am about ready to hook this all up.  Attached is a picture of the switched outlet box I put together... I took a 12g extension cord and cut off the one end... hooked it up to a 25A SSR and then to a 15A GFCI outlet.  Hard to tell from the pic but there's a CPU heatsink attached to the SSR too.  I've also got another box with the arduino, LCD and jacks for thermometers... will be running one additional +5V/ground to the switch side of the SSR.

Can you have a look at the wiring below and let me know if it looks okay before I go plugging this thing in?

Logged

Greenwood, Indiana
Offline Offline
God Member
*****
Karma: 0
Posts: 508
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

This seems adequate. The black has been cut and wired to the SSR. The GFI is a nice touch. The crimps on the spade lugs look good.

I would suggest a barrier over the 3-30V input when you've installed wires to it. Also use a separate opening for those love voltage wires in case they break and touch AC or the AC wires break and touch them. Dress them away from any AC outside the box.

I think the heatsink is outside the box? If so I believe you should tie that to ground just in case you get a catastrophic failure and one of the AC lines break and touch it or the SSR fails in a way the manufacturer will swear is impossible.

The most common failure I see on industrial controls is a wire breaking and falling where it should never go if dressed and tied down properly.

On commercial and consumer equipment low voltage inputs and outputs; transorbs are commonly found to keep high voltage transients and induced currents out of them.  If you use them use a fuse in series.

http://en.wikipedia.org/wiki/Transient_voltage_suppression_diode
http://www.opencircuits.com/Input_protection
http://forum.allaboutcircuits.com/showthread.php?t=6784

Logged

If it was designed by man it can be repaired by man.

Phoenix, Arizona USA
Offline Offline
Faraday Member
**
Karma: 36
Posts: 5519
Where's the beer?
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
On commercial and consumer equipment low voltage inputs and outputs; transorbs are commonly found to keep high voltage transients and induced currents out of them.  If you use them use a fuse in series
.

Also look at Omron's Industrial Automation site for more info on SSRs:

http://www.ia.omron.com/index.html

They have a bunch of great information about usage; I found the site after I had purchased at a hamfest yesterday a large heatsink with 16 25A/240VAC SSRs attached to it; between the output contacts of each was a varistor, so I was trying to understand the need for a varistor across the contacts (prevents current spikes from inductive loads from damaging the SSR, among other things).

Make sure that you have your hot lead and neutral lead connected to the right terminals on your plug; you don't want these to be swapped, because if there is a failure somewhere in the controlled appliance or elsewhere, an electrocution hazard can present itself. It looks like you have things wired OK, but we can't see where the wires go to the terminals on the outlet...

Logged

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

0
Offline Offline
Newbie
*
Karma: 0
Posts: 19
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Okay I've grounded the heatsink just in case.  Also made up a quick schematic for how this is all laid out (actually stole and modified one from here)



I'm thinking it might be nice to add an LED that indicates when the heating element is switched on... would I just wire that to the same +5 and ground as is going to the SSR?
Logged

Phoenix, Arizona USA
Offline Offline
Faraday Member
**
Karma: 36
Posts: 5519
Where's the beer?
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
I'm thinking it might be nice to add an LED that indicates when the heating element is switched on... would I just wire that to the same +5 and ground as is going to the SSR?

Should be OK as long as you don't exceed the current requirements for a single pin (under 20ma should be safe); remember your current limit resistor for the LED, and check the spec on the SSR for the current needs of the control side - but you should be OK.

 smiley
Logged

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Pages: [1] 2   Go Up
Jump to: