Question: Easier to stoke up or choke down?


 
j biesinger

j biesinger

TVWBB Platinum Member
I did my maiden run with a new PID controller from Auber Instruments. I had just under a 1/2 bag of charcoal to do some spares, which I thought was plenty. I made a minion start with about 15 fully lit briquettes, as I normally would. The stoker did ok, but it was blowing pretty much nonstop getting up to temp. And at one point,I came back and it was under temp, and blowing hard again. I stirred up the remaining coals and pushed them towards the stoker and she was good again.

I figured I need to start with a bigger fire and see how it goes. I'm thinking it might work better if it has the opportunity to do both stoking and choking.

Suggestions?
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">What size/type of smoker do you have and what size fan are you using? </div></BLOCKQUOTE>

18" wsm + 6 cfm blower
 
I have an 18" WSM and Stoker with 5 CFM fan. I use lump charcoal. After filling the ring, I use a propane torch to light a couple pieces of lump that are closest to the Stoker fan. Once I have them started, I turn on the Stoker. I leave the top vent 100% open for the initial ramp up, then close it down to roughly 25% open when I get close to the target temp. I start shutting it down around 200-210 if shooting for 225 temp. On higher heat cooks, I need to leave the top vent open more.

I find it easier to control on the way up rather than trying to slow it down after overshooting your target temp.
 
Two things...
first
Most process controllers don't have the smarts to transition from start up to in process, so getting the process into the control band before engaging the controller is a good idea.
second
Fire size will make a big difference to the tuning parameters. When you start from cold the draft will over size the fire trying to get up to temp, then be unable to throttle it back, this will cause the system to oscillate.
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Two things...
first
Most process controllers don't have the smarts to transition from start up to in process, so getting the process into the control band before engaging the controller is a good idea.
second
Fire size will make a big difference to the tuning parameters. When you start from cold the draft will over size the fire trying to get up to temp, then be unable to throttle it back, this will cause the system to oscillate. </div></BLOCKQUOTE>

makes a ton of sense, thanks!

I was wondering if the controller takes the ramp up into consideration. I was confused if it only learns during an "autotune" phase or during the entire time.
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by j biesinger:
makes a ton of sense, thanks!

I was wondering if the controller takes the ramp up into consideration. I was confused if it only learns during an "autotune" phase or during the entire time. </div></BLOCKQUOTE>
Depends entirely on the controller, Typical cheap auto tune PID boxes tune once then keep the settings. You might try bringing it up to temp with a fire size you like THEN running the tune to get good parameters for in-process control. You will get better control that way while cooking, but you will probably still need to have some over sight during startup, but perhaps not.
Throttling the intake of the fan might allow you to come up to temp with out over heating the fire if the controller doesn't have provision for this.

It just sounds to me like your fan has too much capacity.

Part of the problem is that you have two process inputs, fire size, and air supply. You have no control over the fire size except in the initial construction of the fire. So you need to be careful in how much air you give it...and the controller doesn't know that.
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> It just sounds to me like your fan has too much capacity. </div></BLOCKQUOTE>

that's ironic. The auber came with a 7 cfm and the nano came with a 5. It was a deciding factor.
 
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