Temperature Fluctuations #2

[hansville]

Hi there,

I'm new to the forum but have had one of the old models for awhile.  I just received a six rack digital model today thinking it would be much more precise, even and hands off during the smoking process.

When I seasoned the smoker I set the temp at 150 as instructed.  The actual temp read 178 and seemed to stay there.  I put a manual oven thermometer in to double check the temp and it read about 178 as well.

Now I am trying a single tray of salmon.  The recipe I have calls for 140 for the first hour and then hotter after that.  So I set it at 140.  There was a little click when the unit hit 140 but the temp kept rising until it reached 164.  It then dropped down to 128 before climbing back to 164 again.  It took quite a while to make the cycle.

So this machine seems to be plus 24-28 degrees and about minus 12 degrees from the set point.  This does not seem satisfactory to me at all and I am wondering if this is the nature of the beast or if this is unusual.

Any thoughts or advice will be greatly appreciated.

Thanks, 

Steve

[icerat4]

This is the nature of this 6 racker.Lil LEARNING curve but just keep an eye on the internal temps of the food inside and all should be ok. ;)

[hansville]

Thanks for the info.  I don't find it very reassuring or even acceptable given the price of this unit.  Last night I did another smoke.  Plus 25 degrees and minus 16 degrees.  That is a 41 degree temperature swing.
There are lots of thermostat controlled heating devices around and none of them are this erratic.  In particular, it seems to me that if the lower cut off were closer to the set temperature then the upward swing would not be as bad.  It is clear that the heating unit is either full on or full off rather than having the capacity for variable heat output.

I am pretty surprised and disappointed and hope that my unit is not an example of all of them being produced.

Steve

[iceman]

Hi Steve;
Sorry to hear about the temp swing issue you are experiencing. I personally don't have a digital but would like you to try a simple test that seems to work on all my other smokers. When I'm testing the temp settings I make sure the unit is 1/2 to 3/4 full of something. You could use bricks or pans or whatever is handy. This seems to keep the swings down to a minimum as opposed to an empty smoker. I have no idea if this will help but it might be worth a try.
Good luck and I hope things work out for you. ;)

[robs]

Hi Steve;
Sorry to hear about the temp swing issue you are experiencing. I personally don't have a digital but would like you to try a simple test that seems to work on all my other smokers. When I'm testing the temp settings I make sure the unit is 1/2 to 3/4 full of something. You could use bricks or pans or whatever is handy. This seems to keep the swings down to a minimum as opposed to an empty smoker. I have no idea if this will help but it might be worth a try.
Good luck and I hope things work out for you. ;)

I would think that a full water bowl will help too for box mass.

From what I've read on the forum, this is normal for the digitals. Like OldMan said, your kitchen oven probably has the same swing. Not that it makes it right, just something to think about.

God only knows why they didn't just wire a cheap PID in that damn thing.

[hansville]

Thanks for the feedback.  I have not had it full and I'm guessing that would make a difference.  I don't remember wild swings like this with my old Bradley.  It seemed to me it was more constant but with old age and failing memory I may be mis-remembering.  Is there a difference in how the heating element operates and is activated with the manual Bradleys?  If so, why couldn't they just have replicated it in the digital?

Thanks,

Steve

[robs]

I'm not an expert, but from what I understand, it works pretty much just like an electric oven.

It gets up to set temp and then shuts off (it's dumb and doesn't know or care that the temp will keep rising).

Same thing happens on the down swing. When the temp is coming back down (from the 20 deg overshoot) it hits the set temp and decides it's time to turn the bulb on again. This is fine and dandy except that the bulb is already cooled off and will take some time to warm up again. This is the undershoot.

Endless cycle!

PID controllers are different. The aren't on/off. They are on (0-100 output). They will maintain the temp usualy withen a degree or two.

So with a PID controller, the bulb doesn't have time to cool down, it's not off as often. Instead of off, it might go down to like 5% on or 25% on.

Did you buy it local? Can you return it? It doesn't sound to me like you are going to be happy with that temp swing...

Good luck!

rob

[iceman]

God only knows why they didn't just wire a cheap PID in that damn thing.

Funny you would mention that robs. Olds and I were just talking about that yesterday. Seems to me that would be the way to go. ;D

[hansville]

Thanks for the info Rob.  I looked up a PID Controller and that seems very interesting.  I am getting an education here.  Will have to get a little more experience with the unit.  Talked to Bradley this morning and they said a 20 degree swing was normal but I am experiencing a 40 degree swing that may take 15-20 minutes for the cycle.  I'm not certain what that does to the food.  So I just have to study some more and get more experience with the unit,.

We live out in the boonies in Washington State and the digital unit was not available within quite a range so I got in over the internet so i guess that complicates thi ngs if I really don't end up liking it.

Thanks again for the excellent information and advice.  This may just be a case of having too much information.  I'm reminded that sometimes indeed, "Ignorance is bliss".

steve

[robs]

Glad to help. Think of it this way - have you ever ruined dinner in your oven because of the temp swing? Probably not. I think oldman may have also said something along these lines.

I know how you feel though. It's probably just not what you expected. Throw a butt or brisket in that thing for 12+ hours and that temp swing probably won't make a huge difference. Say your set point is 225, and it's swinging from 200 to 250. I guess the average temp is 225 right?

I think your original question was "is this normal?" For the Bradley digital - yes it is.

Oh yeah - glad to see you here. Keep us updated on your cooks...

rob

[bubbagump]

hansville,

Iceman is right, filling with food will help the drastic temp. swings. But like rat mentioned, temp. swings are the nature of the beast.

I would also agree with the others here who find it hard to believe Bradley just didn't go ahead and install a simple PID. With the quantities they would buy their cost would be next to nothing.

Robs - Just to clarify, the PID is actually on - off control. It cycles its output repeatedly to maintain setpoint. That's why you need a solid state relay (SSR) to do the switching. A mechanical relay wouldn't hold up cycling that often.

Bubbagump

[robs]

hansville,

Iceman is right, filling with food will help the drastic temp. swings. But like rat mentioned, temp. swings are the nature of the beast.

I would also agree with the others here who find it hard to believe Bradley just didn't go ahead and install a simple PID. With the quantities they would buy their cost would be next to nothing.

Robs - Just to clarify, the PID is actually on - off control. It cycles its output repeatedly to maintain setpoint. That's why you need a solid state relay (SSR) to do the switching. A mechanical relay wouldn't hold up cycling that often.

Bubbagump

Bubbagump- you're right, bad choice of words on my part. I was trying to verbalize somehow that the heating element would never get as cool because it doesn't allways shut off or stay off for a long period of time, but rather it will be on but with low power.

So it is on/off - but on is (1-100% power). I was also trying to make the point that it's not a clear on/off control (although they can be if configured.)

Thanks for the clarification.

[Arcs_n_Sparks]

With all the arcin' & sparkin' going on, I'll add my 2 kilovolts worth... :D :D :D

Hansville: welcome to the forum. As you can see, a lot of good stuff and knowledgable people.

Regarding PID, that is a control scheme. As was mentioned, this is different from the classic "thermostatic" control. A thermostat has a setpoint with a certain amount of hystersis (deadband). Your house thermostat has a one or two degree deadband. Easy to do, since the house mass is large. One reason for the comment about loading the BS.

Now, the PID controller can implement it's algorithm in basically one of two ways. A rapidly changing on/off approach (that is why a Solid State Relay (SSR) is required). This tries to smooth the application of 0% or 100% power over a short period of time. The second method involves "phase control" of the A.C. power. This is basically how a light dimmer works; a smooth cycle-by-cycle application of power from 0% to 100%.

Arcs_n_Sparks

[hansville]

Thank you all for your help.  Wish I had known about the forum before I bought!  I am VERY impressed with the depth of knowledge and helpfulness of everyone here.  My first time really using one of these lists (or whatever you call it) and I can see it as a tremendous resource.  Only problem know is how to find the time and technique to mine all this information!

Thanks again,

Steve

[Arcs_n_Sparks]

My first time really using one of these lists (or whatever you call it) and I can see it as a tremendous resource.  Only problem know is how to find the time and technique to mine all this information!

Thanks again,

Steve

Steve,

That is the classified aspect of PID controllers. You tell the wife you have to "watch" the smoker (I imagine you run out every 5 minutes when burning steaks on the Weber). In the mean time, you are checking this board and see what is left in the adult beverage refrigerator in the garage on the way to the smoker. I figure I have another 15 years before she catches on.... :D :D :D

Arcs_n_Sparks