Black Cat Mk 2 - Propane smoker controller

[JC in GB]

Good day all. I have started my latest project of marrying up my Black Cat Mk2 controller to a gas fired smoker. I have thus far gotten a functional diagram started and am fine tuning the functional logic. I have also started putting together the Bill of Materials for the prototype build.

The design so far has a single burner controlled by a PID controller. I am going to hand craft the first burner assembly. The burner will be ignited using a silicon nitride style igniter.

Once the basic function is going, I plan on adding an idler burner to the set-up. The idler will be on most of the time with a boost assist burner for bringing temps back up quickly.

One of the cool things about this project is that the control function is fairly simple so I am going to be using some old school TTL logic to run the control function.

Stay tuned....

JC

 

[OldSmoke]

Keep us posted. I am very happy with my propane/PID mods, but always looking new ways to skin that cat.

 

[JC in GB]

So after doing much more research on gas fired control systems, I came across a flame sensor device that rectifies AC current to DC in the presence of a flame. I also noticed that some systems use IR sensing to detect flame present.

My alpha-prototype is designed using metallic snap action switches. This seems like the Occam's razor method of doing things but I am always wary of using mechanical switches as they tend to wear out before most other parts. These switches should last for 12 years doing 50 cooks a year for 12 hours at a time. Assuming the data sheet was accurate at a 100000 cycle switch life. I have the prototype design completed and am mulling over ordering parts for this configuration or should I go with a different design idea? IR or flame sensor instead of thermal switches?

The flame sensor and IR sensor design would require more circuitry but would last a very long time and be less susceptible to mechanical failure. These approaches would also likely cost more for the end product.

So, here is my question... As a user of a gas fired smoker, what kind of flame detection system would you feel most comfortable using?

Thanks,

JC

 

[OldSmoke]

My experience tends toward the simplest solution as they tend to be the most reliable. Smokers live outdoors usually, and get operated in bad weather so durable wins the day.

As far as longevity, I doubt the cabinet will last much past ten years. Certainly the burner will need replacement several times. By then I’ll probably build a better one or go electric.

If your flame sensor is to detect flame outages, I support that safety feature. I have one propane tank with a sensitive OPD valve. As the solenoid valve controlling the burner opens, it trips the OPD valve shut.

If the snap switch controls the flame, how will you get the flame to start, before the snap switch gets warm and takes control?

 

[JC in GB]

My experience tends toward the simplest solution as they tend to be the most reliable. Smokers live outdoors usually, and get operated in bad weather so durable wins the day.

As far as longevity, I doubt the cabinet will last much past ten years. Certainly the burner will need replacement several times. By then I’ll probably build a better one or go electric.

If your flame sensor is to detect flame outages, I support that safety feature. I have one propane tank with a sensitive OPD valve. As the solenoid valve controlling the burner opens, it trips the OPD valve shut.

If the snap switch controls the flame, how will you get the flame to start, before the snap switch gets warm and takes control?

The way I have it planned so far is I have a thermal switch on the ignitor that will turn on the gas valve when a flame command is issued from the PID and the ignitor gets hot enough. Once the ignitor is hot enough to light the gas, the gas valve opens and the burner lights. Once the burner has been detected as ON, a thermal switch on the burner tells the ignitor to turn off.

If the burner switch gets too cold, the gas valve will close even with a PID command to open. This will avoid blowouts and blowups.

The trick is to get the material and spacing for the sensors so they operate in the time frame I am hoping for.

Here is the simplified function.

IG = Ignitor
G = Gas valve
PI = PID command
TC = Burner ON switch
TB = Ignitor ON switch

IG = PI * /TC

G = PI * (TC + TB)


JC

 

[OldSmoke]

Sounds like you have it well thought out!

What kind of temp probe are you using?

 

[JC in GB]

Sounds like you have it well thought out!

What kind of temp probe are you using?

I was planning on using a k-type thermocouple for the PI control.

JC

 

[OldSmoke]

I’m looking forward to your progress, thanks for sharing.

 

[JC in GB]

So, after deliberating this for a day or two, I am going to use the mechanical bi-metal switch approach for my alpha-prototype unit. I will be putting the parts order in after Xmas. I have most of what I need for a burner so I will craft that first.

JC

 

[OldSmoke]

Are you using a solenoid valve?

 

[JC in GB]

Are you using a solenoid valve?

Yes I am.

JC

 

[Fueling Around]

JC
Not a pro at this but which bimetal switches are you considering?
Light duty rising temp units do not take temps much over the trip point.
Hot source ignitors are a weak link in furnaces.

 

[JC in GB]

JC
Not a pro at this but which bimetal switches are you considering?
Light duty rising temp units do not take temps much over the trip point.
Hot source ignitors are a weak link in furnaces.

I was wondering about the heat tolerance of these sensors. I was planning on using one of the sensors listed below.

Mfr. #: 1NT01L-7952
Mfr.: Sensata Technologies
or
Manufacturer: CANTHERM
Manufacturer Part No: F20B15005ACFA06E

I wanted to use a hot source ignitor as it is the current state of the art. Also, I think the duty for use in a smoker may be less abusive than a furnace. If it doesn't work, I can always switch to a piezo spark type ignition.

I may rethink using the thermal switches. I will have to look into the flame rectification sensor or IR flame sensors.

JC ​

 

[JC in GB]

I have done some more research on using an IR detection scheme for ignition and flame detection. This approach will cost roughly the same as using the bi-metallic switches. It will also be less prone to failures.

I will be working on the circuit diagram for this configuration today.

JC

 

[Fueling Around]

1NT01L-7952​

Max temp 240°C or 460°F​

F20B15005ACFA06E​

Max temp (switch) 175°C or 350°F

Call me old school but I much prefer systems with a standing pilot.
Probably because I know how to work on them

 

[JC in GB]

1NT01L-7952​

Max temp 240°C or 460°F​

F20B15005ACFA06E​

Max temp (switch) 175°C or 350°F

Call me old school but I much prefer systems with a standing pilot.
Probably because I know how to work on them

That is the fun and challenge of using new technologies to achieve the same end result. A standing pilot system has been used reliably for many years and would likely work just fine.

JC

 

[JC in GB]

Ah the fun pf prototype designing.

So, now I have finished my alpha prototype design concept for the propane burner controller. After looking at available technologies, I decided that I wanted to go with close to state of the art while also keeping a eye on cost.

Here is what I came up with.

Black Cat II PID controller for thermal control
IR receivers to detect ignition and flame.
Hot surface igniter (Silicon nitride)

This configuration will also be the easiest to interface together.

I have started ordering parts for the project.

JC