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Author Topic: 1100 watt, PID and Fan alteration  (Read 1837 times)

Offline David E

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1100 watt, PID and Fan alteration
« on: August 06, 2015, 12:07:40 pm »
Important note: It is very easy to add the 1100W finned strip heater, fits better than the 900W and has lower temperature per sq inch. But – without extreme care you will melt / burn the insulation in your smoker or worse - - -. You do any heat mode at your own risk.

I live in Arizona and my 6 rack Bradley Smoker does not make enough heat even in the summer. To improve the temperature performance and regulation I have made three major changes, learned from these, and did them all over again. I think my third generation is worth sharing.
•   Changed the heater to an 1100W finned strip heater.
•   Added a fan to move air in the heat (bottom) chamber.
•   Built a PID controller.
I initially made mistakes with
•   the heater, (mounting it too close to the back and burnt the insulation)
•   the PID controller, (purchased Centigrade only PID controller from China)
•   and with the Fan, (mounting and size of fan were not optimal)
I was motivated to solve the heat problem when it took 30 minutes to heat up and then, when you load the smoker, it takes a very long time to recover. This is not the stall expected in the meat internal temperature, but a failure to reach and regulate temperature to my satisfaction. It is easy to see how crummy the temperature control is with the Bradley, just observe the temperature changes on the smoke generators oven temperature. However, if you put a thermistor in the center of the oven you will see it is even much worse. The built in temperature gauge is mounted to a wall, sometimes the actual temperature is much higher in the middle of the over, (like when first warming up), and sometimes much lower, (like after adding meat). I use a thermistor that I can move anywhere I like, I hang it from a rack. You still only measure one point but it is any point you pick. Add PID control, and the 30 and 40 degree swings at the wrong place become 2-5 degrees where you want to measure. I recommend keeping the Bradley thermistor in place, it is a nice double check and if the PID should fail it is a nice backup to finish a cook. IMO, no heater change should be made without a PID and care that you do not burn your house down! In fact, a limit my PID to 90% on time to make my 1100 watt heater last and reduce even father the watts per sq inch.
Parts that I am now using
•   1100W finned strip heater, Zoro part number G1034862, $38.53 with shipping
•   Broan 162, 164 Bulb Heater Replacement Vent Fan Motor, 3200 RPM 120V, $27.16
•   4mm, .7pitch, 70mm long screws to replace the screws in the fan
•   Aluminum Fan Blade, 3 inch diameter
•   Homemade dual channel PID controller, AC 110-240V PID Digital Temperature Controller+40A SSR+ Thermocouple Sensor, $23.59 each
•   1 PCS 110V AC 22mm Diameter Yellow Red Green 3PC LED Indicator Light with Buzzer, $6.00
Lessons learned, heater
I previously used a 900W finned strip heater. Got lots of great service from this. I mounted it to the ceramic blocks by adding metal tabs that I placed between the two sections of the original ceramic blocks. This burnt all the insulation in the smoker behind the heater. In the next version I added a fan, removed the heat deflector that fits to the original heater, mounted the 1100 watt heater on top of both halves of the original ceramic blocks. This gave me much more room to the back wall. It is also a lot easier to mount, just drill two holes in the longer 1100W heater. The 1100W heater actually has a much wider finned area and has a lower W per Sq inch then the 900W. But, just to be extra sure, I added lava matt to the back wall behind the heater. This is pretty much just because I had it left over from a motorcycle heat insulation project. I also added a fan motor outside the chamber with the blade inside the heat chamber. Tons of heat well distributed and with the PID well controlled. Details on the heater:
Finned Strip Heater, Voltage 120V, Overall Length 14 In., Mounting Dimension 13 In., 1100 Watts, Watt Density 37W/sq. in., Terminals Each End, Element Width 1-1/2 In., Sheath Material Seamless 304 Stainless Steel, Material Nickel Plated Steel, 1 Phase, H x W Across Fins 1-3/8 x 2 In., Max. Sheath Temp. 1200 Degrees F, Mounting Type Surface Mount, Slotted Hole Length 1/2 In., Slotted Hole Width 5/16 In., Screw Size 10-32, Standards UL Recognized, Includes Mounting Tabs
I don’t use the mounting holes in the heater strip. I held the heater up to the ceramic blocks and marked two holes to drill through the heater ends. My Bradley had plenty of wire, with the back removed it is easy to adjust the length of the heater connections.
Lessons learned, fan
My first fan was adequate to move the air around the heater, but as the case expanded it would sometimes bind on the bushing that keep it well sealed. So my 900W burner burned out when my fan seized. Second fan is more powerful, but more important, I provided a little extra margin for the shaft, I simple removed the sleeve that seals the shaft and left a small air leak. The fan is overkill, but I will never have to worry about it stopping as the case heats up. I drilled sloppy holes as my Bradley does not fit on my drill press. If I did it over, I would drill a 2x4 on my drill press as a template to get the mounting screws and the shaft hole exactly aligned and parallel. Since the fan motor is external to the Bradley and the fan is inside, (right side toward the back), the fan motor does not heat up. The new fan motor also has a longer shaft that allows better fan positioning.
Lessons learned, PID controller
I purchased two PID controllers from China, had to wait a month, but the cost savings was significant. I designed my own enclosure and had it 3D printed. I do not think in degrees Celsius and that is all the cheap PID controllers from China give you. I think in terms or Fahrenheit. I am replacing my PID controllers but the deal from China is pretty compelling, as it came with the heat sink, the correct relay, and a K type probe. If I did it over again I would not build a two channel, just a single. I might build two so that I have a backup for oven control and use the other one to alarm when the food is done. If there is interest I will update my SketchUp design and post on so others can have a PID housing 3D printed. PID programming has a learning curve. The REX C-100 from China has English translation problems and is missing features. So you need a non-knock off version with a manual written in English or you will need to study the real PID manual to understand the features that may or may not exist in the Chinese version.  Spend $10 more and get a Fahrenheit capable unit with a manual written originally in English.
Lessons learned, Thermistors
I use K types. I used connectors from Omega, in the back of my PID controller, and mounted one in the back of the Bradley cabinet to let me plug in a meat thermometer. So my meat thermistor has two connections, internal to the oven and at the back of the PID. I have a high temperature nylon bushing that is a pass through for the thermistor wire for the oven temperature. I have lots of issues with thermistors, polarity, connectors, and grounding. Ideally, the thermistor wire should be used from the sensor to the PID controller.  The oven thermistor works great, even with the connector on the back of the PID. The two connector to the meat thermometer is flakey. Sources of K type pointed meat thermometers is very limited, and the ones with the yellow wire melt!  So, my suggestion, run the thermistors through the vent holes at the top. Don’t use a PID to measure meat temperature, use a ChefAlarm from Thermoworks. A DIY meat thermometer is not worth the trouble. A DIY PID for oven temperature is well worth the trouble. Under no circumstances use a bigger heater without a PID and then test it carefully!
I attempted to add images, but failed. Email me if you want a pdf version returned.

Offline TedEbear

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Re: 1100 watt, PID and Fan alteration
« Reply #1 on: August 07, 2015, 04:44:28 am »
"I attempted to add images, but failed. Email me if you want a pdf version returned."

Host them on Photobucket and then copy/paste the IMG link in the Photobucket box (you'll see it) for each pic in a new message on here.

Offline piratey

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Re: 1100 watt, PID and Fan alteration
« Reply #2 on: August 07, 2015, 08:49:34 am »
definitely like to see pictures added.  Thanks for posting your lessons learned.