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View Full Version : Homemade Digi-Q?


BigBellyBen77
04-04-2013, 09:44 AM
My friend has a WSM and is looking at adding a Digi-Q to it. We got to talking though and were wondering if anyone had made their own using a thermostat power switch and a small fan. Any thoughts?

willbird
04-04-2013, 10:25 AM
My friend has a WSM and is looking at adding a Digi-Q to it. We got to talking though and were wondering if anyone had made their own using a thermostat power switch and a small fan. Any thoughts?

I would think you would use a PID temp controller, they can be had really cheap these days. Most have a mode where they are just on-off depending on temp, or usually better a fuzzy logic system that will alter the on-off times based on what happened over some time frame.....it adjusts to the pit more or less.

Here is an example of a PID but it's included SSR (solid state relay) is not up to running a 12 volt fan like many folks use...and it's input voltage would be a PITA too.

Ideally you want 12 volts input voltage and an SSR that will run a 12 volt fan....but looking at the example will give you some ideas.

http://www.auberins.com/index.php?main_page=product_info&cPath=1&products_id=14

I know you can dig around on the web and find one that will do what you need, searching here on the forum for "PID temp controller" will probably net some part numbers and other folks builds too.

IMHO the real niche for the home brewed systems may be when you already have an auber or digiq, and power supplies and fans, etc, etc and want to play with cheaper options.

I have the auber myself and love it....but I have all the stuff to build a raspberry pi/heatermeter setup too, just need to get the soldering done :-).

Bill

willbird
04-04-2013, 10:27 AM
Many of these type projects require you to get parts from several sources, there is no "one stop shop" for everything....and when you add up shipping and sales tax, and messing around you see that the folks that sell the whole shebang really offer a fair price for what you are getting.

Bill

VA-Dave
04-04-2013, 11:02 AM
Many of these type projects require you to get parts from several sources, there is no "one stop shop" for everything....and when you add up shipping and sales tax, and messing around you see that the folks that sell the whole shebang really offer a fair price for what you are getting.

Bill

Bill is right.

Also, thermocouples (temp probes) are not linear. The microvolts they generate are not a linear function of temperature, so you have to have an algorithm that compensates for this non-linearity.

There are components you can get from digi-key whose output are a linear function of temp, but they are usually limited to 300 degrees F.

A thermostat with a power switch can be done, but there are adjustments you would need to make to prevent overshoot, undershoot, etc. I wouldn't recommend it if you're not familiar with it.

PID controllers are so cheap now (I have 2 Aubers, 36 bones each) that you're better off buying them off the shelf.

Dave

willbird
04-04-2013, 11:29 AM
There is also a thermostatic controlled DAMPER concept, that uses no fan that might be simpler, there is a thread over on the Virtual Weber forum.

http://tvwbb.com/showthread.php?35582-Blue-Sky-Stepper-Damper-thread-Breakout-from-RaspberryPi-LinkMeter-blue-sky&highlight=damper

It should work well if they have it all sorted out (I have not kept tabs on it).

If there was a market for it I bet a simple self contained damper about the size of a pitmaster IQ would not be an expensive proposition at all. But the fans being used are not super expensive either.

Bill

ButtBurner
04-04-2013, 11:37 AM
right now, Auber has the complete system for a WSM on sale for about $125

cant beat that, I have one and it works great

BobM
04-04-2013, 02:24 PM
By design, a mechanical thermostat is going to have a somewhat large temperature swing. A PID controller will be much more stable.

As others have said, there are several ATCs on the market that are inexpensive and work well.

BigBellyBen77
04-04-2013, 03:40 PM
Thanks everyone. Very helpful.

woodpelletsmoker
04-04-2013, 05:47 PM
You can buy a 12 VDC thermostat from eBay @ $13, probe $5, AC/DC adapter 12 VDC 2 amps $10, 12 VDC 10 CFM fan $5, You may need to make fan adapter by yourself. total price $33 plus fan adapter, let's say total $50.
as said above auber $125
or Golden-DOG $99, http://www.bbq-brethren.com/forum/showthread.php?t=146531