I'm not well versed on transformers, so I don't fully understand how that's going to work. I guess it steps the voltage up by ~15%? That would be very handy while the beans are still green and heavy, as long as the fan motor can handle a little higher voltage.
It steps the voltage up by 15 volts, but that's probably close to 15%. It was used by Ron in his modification to up the voltage to the fan. He says the fan handles it fine over time. Here's the thread: "My popper"
Dana Leighton - Espresso hack and CoffeeGeek moderator
The thermocouple is suspended from the mounting. Actually, hot air leaks between it and the mounting to the inside of the popper. If you've taken the popper apart, you can see moulded portrusions around the heater chamber. I ground down one of the portrusions until it was level with the top of the heater chamber and drilled a hole straight down big enough for the thermocouple. I don't have a tap set so I used a nut on the inside and sealed the threads with silicone sealant. I should seal the thermoucouple so there are no leaks, maybe next time I take it apart.
Posted Sun May 24, 2009, 2:04am Subject: Re: (Another) Poppery PID controller project
I'm waiting for some components to arrive in the mail, so I thought I'd take a shot at designing the front panel for the control box.
I had the idea to make the PID and temperature monitor thermocouple input switchable. I am concerned that the switch would introduce some error in the TC measurements, since TCs use such small current load. There are special switches for TCs, but they're expensive. Any experience using standard off-the-shelf switches?
(Click for larger image)
Dana Leighton - Espresso hack and CoffeeGeek moderator
JGG Senior Member Joined: 31 Mar 2006 Posts: 1,343 Location: Kentucky, US Expertise: I like coffee
Espresso: PID Silvia; PID Alexia Grinder: Mazzer Mini E (A), SJ; Rocky... Roaster: Hottop D w/PID; Thermometric...
Posted Sun May 24, 2009, 6:21am Subject: Re: (Another) Poppery PID controller project
dana_leighton Said:
I had the idea to make the PID and temperature monitor thermocouple input switchable. I am concerned that the switch would introduce some error in the TC measurements, since TCs use such small current load. There are special switches for TCs, but they're expensive. Any experience using standard off-the-shelf switches?
No direct experience with using switches of either kind, but I can't think of any reason it would not work in this application.
I believe that the primary reason for using special t/c switches is to avoid introduction of 2 additional junctions. This introduces an error that is approximately equal to the temperature difference between the junctions. With the special t/c switches, all of the junctions are alloy-to-alloy, so this source of error is eliminated.
For a roaster application, you might find the introduced error to be acceptably small, especially if the environment inside the enclosure is fairly homogeneous.
I had never considered the effects of the additional resistance before reading your post. This may be more important than I am leading you to believe, but I think the input impedance of the instruments might be high enough so that the switch resistance is negligible.
I'm waiting for some components to arrive in the mail, so I thought I'd take a shot at designing the front panel for the control box.
I had the idea to make the PID and temperature monitor thermocouple input switchable. I am concerned that the switch would introduce some error in the TC measurements, since TCs use such small current load. There are special switches for TCs, but they're expensive. Any experience using standard off-the-shelf switches?
I like your control panel, you have control of all the circuits. I don't know if your themocouple switches will work, in addition to the junctions where the thermocouple wire will contact the switch, there are the contacts within the switch. I would allow a bit more room for the fan dimmer. Where are you going to roast? I'm going to re-do my control panel this summer and yours gives me a couple of ideas. FYI, I use 2 different house circuits to roast, one for the heater and one for the rest. This way I won't overload the circuit if I have too many things going at once. Luckily, an outlet for one circuit is close to my porch and I use a long extension for the controller and fan. Keep us posted.
I don't know if your themocouple switches will work, in addition to the junctions where the thermocouple wire will contact the switch, there are the contacts within the switch.
Yes. I also found out the rotary switches are expensive -- around $15-20 each. I then went to slide switches, which are a couple bucks each. I am now thinking about abandoning the switches altogether, since it will only be during my testing that I will ever want to switch the TCs. I think I might go ahead and install the switches, try it out and see if error is introduced. That way we will know for sure.
I would allow a bit more room for the fan dimmer.
Yes, I was thinking about that. I was hoping to find some kind of low-profile dimmer switch that would fit, but if I want an off-the-shelf dimmer from Walmart, it'll have the standard light fixture mountings. I also considered buying a rheostat instead. We'll see.
Where are you going to roast? I'm going to re-do my control panel this summer and yours gives me a couple of ideas. FYI, I use 2 different house circuits to roast, one for the heater and one for the rest. This way I won't overload the circuit if I have too many things going at once. Luckily, an outlet for one circuit is close to my porch and I use a long extension for the controller and fan. Keep us posted.
I roast outside on the porch. I have a plug near the door. The panel was going to have one plug coming out, and into the wall. The electronics in the panel draw a pretty small amount of current, but adding the transformer might make it overload the circuit. I did not think about that. Did you have problems with that, Ron?
Dana Leighton - Espresso hack and CoffeeGeek moderator
I was hoping to find some kind of low-profile dimmer switch that would fit, but if I want an off-the-shelf dimmer from Walmart, it'll have the standard light fixture mountings. I also considered buying a rheostat instead. We'll see
Inspired by Dana's project, I recommissioned my P1 over the weekend. First, I removed the permanent t/c sensor from the roasting chamber. It was poorly placed, and trapped a bean each time I roasted.
Instead, I used the bare bead sensor that is epoxied in place between vanes. It measures the temperature of the heated air just as it enters the roasting chamber. This MET sensor was then connected to the PID to use for controlling the heater. I disabled the ramp/soak features in my controller, and instead performed temp profiling by manually varying the setpoint on the PID.
I did two roasts, each consisting of ~165g, or 1 mounded 8 oz measuring cup of SM Sulawesi beans.
Next roast, I tried an even more abrupt MET profile:
0:00 - 6:00 : 300F
6:00 - 12:00 : 425F
12:00 - end of roast : 440F
Results (below) show an even lumpier bean temperature profile.
These test roasts were pretty valuable to me, however, in helping understand the relationship between MET and bean temperature. Using these two profiles, it should be a little easier to develop a ramp/soak program on the MET that will give the desired bean temp profile.
I'm not sure I'll take this any further, at least not immediately. But I think it is interesting data. Hopefully Dana, or the next PID projectmeister, can use it as a starting point for programming their PID.
BTW, the bean temperature sensor is a 1/8" diameter stainless steel sleeved t/c probe sticking straight down into the bean mass from above (it is mounted to the soup can chimney on my P1). The tip of the probe is around 1" above the base of the roasting chamber.
Interesting data, Jim. As might be expected, the more numerous your set point steps, the smoother the bean temperature curve is. I wonder how it would look if the bean temperature thermocouple were above the bean mass, not so close to the bottom of the chamber. Jim Schulman is of the opinion that best estimates of bean temperature is the temperature of the air exiting the bean mass. I expect that would temper the rapid rise at the beginning of each step.
What are you using to datalog the temperatures? Does the software from Delta for the PID do that? What device are you using as a transducer for the bean mass temperature? I didn't want to spend much more money, but dammit, Jim, that dual probe plot would sure be handy for profiling...
Dana Leighton - Espresso hack and CoffeeGeek moderator
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