Go Down

Topic: Propane Fired Smoke House (Read 159 times) previous topic - next topic

bigredsmokehouse

I am a total noobe to the Arduino and am having a lot of fun.  I am no electrical engineer but am learning.  I am fine with logic and C programming.

I build a smoker out of a 1948 Philco refridgerator and used the Auber plug and play PID (www.auberins.com).  I am now building my ultimate smoker and want to build my control system.  These are my ideas and I would love to hear from the experts.

I tested the MAX6675 / K termocoupler and it works quite nice.  This definitely needs some type of an offset for calibration and I am hoping it is a linear problem for an easy fix.  Any ideas why it is 4-5 degrees off?

I am going to use an oven burner assemply in my smoker with a pilot thermocouple.  I will get the pilot safety as an added bonus.

My plan was to use a simple servo motor to run a needle valve on a typical turkey cooker.  This does not appear to be a big deal.

My question arises around the PID algorithm to control the flow of propane.  I could just control a valve to be on or off and this should not be too difficult in a PID algorithm.  Does anyone have suggestions on how to design/program a PID to regulate the gas flow?  Is it even worth it to try a variable gas flow or should I just stick to an on/off solenoid.

Any recommendations on potential equipment (regulators, valves, etc) would be helpful and recommendations on an approach to a PID algorithm for temperature control using this variable gas approach.


lukeg22woo

Hey Smokehouse,

I built something really similar for my house - it's a simple propane heater that I modified to have an Arduino-controlled thermostat. I have a pilot light with a thermocouple and MAX6675 chip reading the pilot light temperature. A different thermocouple monitors the temperature inside the house and actuates a brass solenoid to let propane flow into the burner, igniting with the pilot light. The pilot light is also a safety feature - if it drops below a certain temperature (I have this set to 300 degF after some testing), it indicates the pilot light went out and the program shuts off the gas.

It's a "bang bang" controller, so it's either on or off. That works just fine for me, but it also takes about half an hour for the house to cool 1 degF on a cold night, so temperature changes can happen very slowly.

Whether or not you need a PID controller depends entirely on your application. How controlled do you need the temperature to be? Even if you need it stay within +/- 5 degF, for example, could you still achieve that by switching the gas on and off fairly often? I think the implementation of a bang-bang controller will be much easier than a PID in this application.

I'm using a low-pressure, 2-stage, auto-changeover propane regulator that connects to a TWO standard 20-lb propane tanks (like the kind on grills) and delivers 11 inches water column (~1/2 psig) of propane vapor. The two tank set-up is optional and just allows for a backup cylinder when the first one runs out without leaving me freezing in the middle of the night.

I'm using this exact solenoid. No issues in 6 months of use, although it does get hot when held on for more than a few minutes continuously.
https://www.amazon.com/Electric-Solenoid-Normally-Solid-U-S/dp/B00APDNPXG/ref=sr_1_1?ie=UTF8&qid=1510722974&sr=8-1&keywords=us+solid+solenoid&dpID=41u-Om3NIIL&preST=_SX342_QL70_&dpSrc=srch

The relay seems like a pretty standard option - you can find a million of them on Amazon or eBay. The one I have is a "srd-05vdc-sl-c". It IS a mechanical relay, which can get annoying as there's a very audible click when it switches on or off. In hindsight, I would have gone with a solid state relay. But, either one works.

Hope that helps. I can supply more info in you're interested.

dave-in-nj

a thermocouple is like a measuring tape.
high accuracy is like thin paper.
the two are mutually exclusive.
when you are near 1,200 degrees, being a few degrees off is not an issue.
typically within 5 degrees is expected.


if you want to smoke at anything less than water boiling, use a different sensor.
there are a lot of options that will be accurate to better than 1 deg C.


gas flow is controlled by one of two things.
either pressure of orifice size.
most of the adjustable regulators I have seen use the aluminum body with a steel screw.  these will wear as the steel is not polished and the alunumun is soft.
and control is constant. you can either plan for the wear, or re-do the threads for minimal wear.


you should be able to get a stepper to control the pressure, but would need some sort of feedback.  either pressure in inches or BTU output, or gas flow input.


another option would be the needle valve.  you might be able to get a stepper on a needle valve to regulate orifice size.

another option is a two burner. small and larger.   the small one would output 1x heat, the larger one 2x and combined 3x.  then use a simple on/off solenoid valve.

Go Up