Simgo Thanks for you input
daveomak is using one of these which is what you're talking about I think. I like the idea of the elements not turning off and keeping a very steady temperature. Any reason shouldn't is one of the ends. There are less than $20.
I couldn't see the item linked in your post, but viewing at subsequent post by Dave, I see he is using a phase control gadget. Basically, a high power dimmer, as we've been discussing.
The advantage of his setup is that it's inexpensive, and gives efficient power control to his heating element. He's got it marked with settings to achieve various temperatures.
However, the disadvantage is that this is not an actual "temperature control". Instead, it's a "heat control" or "power control".
Think of this as being like the heat control for an electric burner on a typical range. You can adjust the average power to the burner, but you must determine by trial and error what setting gives you what you want. There is no actual monitoring and self-adjustment of the system to achieve any particular temperature.
On the other hand, a temperature control system uses some sort of self-monitoring or "feedback" to actually control the temperature to the setpoint the user enters or dials-up.
This is like a thermostat for a furnace or oven. You set the temperature you want, and the controller (thermostat) adjusts the power to the heater to achieve and maintain that temperature "setpoint".
As folks have pointed out, you can spend quite a bit and buy a pre-built PID temperature controller that comes with everything you need. Or you can build one yourself, rounding up the necessary parts, and do it for considerably less. It depends on how much of an electrical or electronic do-it-yourselfer you are, and how comfortable you are with your skills in that area.
To the points about wasting power. The phase controls like Dave's won't waste much power at all. They're quite efficient because of the way they switch the power on and off.
The old rheostat setups would waste quite a bit of power, but as we've established, nobody is actually using a rheostat, so that's a moot point for our discussion.
Neither a dimmer like Dave's or a fancy PID system will
have to cycle the power to the heating element slowly enough to see any "ups and downs" in the cooker's temperature.
Even with a dimmer like Dave's, the TRIAC or SCRs switch the power to the heater on and off fully. This fully on and fully off switching is what makes these devices power efficient. The power control elements are either conducting fully, or switched completely off. Yes, there's a little bit of voltage drop across them in their "on state", but only a few volts worst case. So the power wasted is tiny.
These dimmers are called "phase control" devices because of how they switch the power on and off. With both SCRs and TRIACs, there is a trigger input that can cause the device to begin conducting. Once you've triggered the device "on", it cannot be shut off. However, because the power being controlled is AC, it shuts itself off at the next available zero-crossing point in the current waveform.
So if you trigger the device "on" when the phase of the available voltage is halfway through its half-cycle, the device will remain on for the rest of that half-cycle, then shut itself off. So you will get one half of one half-cycle, or 1/4 of a full power cycle.
So these dimmers employ a simple setup using a DIAC, resistor, and capacitor to develop a triggering pattern that lets you adjust when, in each cycle of the mains power, the TRIAC or SCRs are triggered. This cycle of switching the power on within each available power cycle is repeated every 120th of a second (once for each half-cycle of the 60Hz mains power) (50Hz if you're in England).
If you have the adjustment potentiometer set fully clockwise, the circuit will trigger the SCRs or TRIAC very early in each power cycle so that the conduction takes place over almost all of the full half-cycle each time. If you set the potentiometer closer to counter-clockwise, the device will be triggered nearer to the end of each available half-cycle.
Thus, you can adjust the average power to the load over a wide range. But it's important to realize that the power
is being switched on and off. It's not continuous power being fed to the load.
But at 120 pulses per second, the typical heating element appears to be powered continuously simply because its mass is great enough that it cannot vary in temperature much at all in such a short period of time. So the effect is smooth heating with little or no observable "on-off" effect.
A detail often overlooked is that because the typical dimmer control circuit provides a linear adjustment of the
timing, the actual power delivered to the load is NOT linear with the position of the potentiometer. That's because the waveform of the incoming mains power is a sine wave, and you're triggering the SCRs or TRIAC at different points in each half-cycle of that sine wave. Obviously, at the extreme ends of the pot rotation, you're getting less of an effect on the average power than you do near to the middle of the range because the power waveform is nearly zero at the beginning and end of the half cycle, but quite high when you're near the center of the half cycle.
But if we're not actually controlling the temperature, but instead controlling the power with the pot, we need to use trial and error anyhow, so it doesn't matter too much. But just be advised that there will be a lot more adjustment happening when you're near the middle of the pot's rotation than when you're at the extremes.
This is a drawback of phase control. There are fancy systems that take this non-linearity into account and translate the user's power pot adjustment into a modified timing scheme to try to simulate linear power control, but at that point, you're now paying a lot more for the circuitry.
OK, now we get to various actual temperature controllers.
No mater what sort of controller we use, we still need to control the power to the heating element. And to be efficient, we'll have to switch that power on and off fully if we want good efficiency.
This can be done with a mechanical relay (as my
Masterbuilt unit does) or a solid-state relay.
A mechanical relay has a limited cycle life, so to make it last longer, designers choose a relatively long cycle time. That cycle time can be so long that the heating element actually does change temperature. At the extreme, as with the stock MES controller, the power is switched on and off to the heater over a very long cycle time. This achieves two things for the MES.
One is that it makes their mechanical relay last longer.
But the other, more subtle effect, is that it allows their chip burner to function to deliver smoke.
To get the chips hot enough to smolder, the heating element needs to be on "full blast" for time periods long enough to let it get red hot and stay there for a while.
But that also leads to large swings in the temperature of the smoker itself. There's no way to get around that. If you want the chip burner to work, you must use a long cycle time for your control system so that you'll get the heating element red hot for long enough to ignite the chips every so often.
So people often complain about the way their MES's temperature cycles up and down. But unless you use a different smoke generating system, you're stuck with those temperature swings in this design.
But people here often use something different to get their smoke, anyhow, because we often find the chip burner to not work as well as we'd like. So if you're going to use a separate smoke generator, you are no longer married to those large temperature swings.
So at that point, you can use a dimmer like Dave's using, or any of the various temperature controllers to set your smoker's temperature.
PID controllers are popular because they can be "tuned" to provide tight, but responsive temperature control. There's a lot to that. But suffice it to say that a PID controller has the potential to work quite well for our smokers.
And also note that in the setup of the PID controller, you can select the cycle time or "period" for the controller. So you can choose a short enough cycle time that the heating element doesn't cycle noticeably in its temperature. So the heat can be just as smooth and "continuous" as with a dimmer (which, remember, also switches the power to the element on and off - just very quickly so that it appears to be continuous).
In many PID controllers, choosing the cycle period is part of tuning the control just as the P, I, and D terms are. PID loop tuning is an interesting subject to say the least! :)
