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Homeroasters - Home Roasting Coffee Community » DATALOGGERS - CONTROLLERS - RATE OF RISE METERS » Dataloggers/Controllers/Rate of Rise Meters

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AC fan control
mg512	#1 Posted on 07/11/2018 4:41 AM
1/4 Pounder Posts: 189 Joined: March 04, 2018	Hi all, I have had a few people ask about AC fan control with a CR3 / TC4, and the need for a ZCD. I've been making the CR3 board since the TC4 isn't available anymore, but I am extremely reluctant about making a ZCD due to all the issues that would come with tapping directly into mains voltage. Which leaves anyone wanting to build a roaster around an AC fan hanging. So I have been thinking about that a lot recently, and I was wondering if someone more familiar with the matter might want to weigh in: In my practical experience with my own popcorn machine roaster, I have not really had a strict need to set multiple different fan levels. During the roast, I have the fan set to a fixed duty cycle, and let Artisan control the heater duty cycle to get the temperature profile I want. For cooling down the beans I sometimes set the fan to 100%, but that isn't strictly needed, just makes the cooling process marginally faster. So for my own setup, I could really get away with an AC fan controlled via a regular zero-crossing SSR that just turns it on or off entirely. A <100% duty cycle could still be set with a hardware dimmer switch if needed. Is this the same for larger hot-air fluidbed roasters? Could people get away without a ZCD with those? How does it work with drum roasters - do you control temperature purely through the heating element, or do you need to control airflow as well? Could you do slow PWM on an AC fan for those maybe?
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greencardigan	#2 Posted on 07/11/2018 6:13 AM
1 1/2 Pounder Posts: 1185 Joined: November 21, 2010	I definitely need fine control of the blower in my smaller electric air roaster. It's running quite close to capacity and I have to turn the blower down gradually to get enough heat but without stalling the circulation. It's a fine line sometimes. A hardware dimmer will work, but values are not logged as they are when using a TC4 and ZCD.


renatoa	#3 Posted on 07/11/2018 6:54 AM
Administrator Posts: 3005 Joined: September 30, 2016	Aren't AC motors wildly nonlinear when controlled using a dimmer ? At least this is my experience... very little RPM change until 70%, then sudden stop, and not restarting until PWM back at least to 80%... There is a PWM controlled dimmer, using an octocoupler to tap into mains, maybe you can inspire from the schematic to adapt to your needs, or embed in CR3.1 https://www.tindi...r-mpdmv41/


mg512	#4 Posted on 07/11/2018 6:54 AM
1/4 Pounder Posts: 189 Joined: March 04, 2018	Ah, okay, I see. Thanks for clarifying. I was really only thinking of the hardware dimmer if one single, constant fan level would be enough (e.g. you want it around 70% all the time). Controlling it that way would defeat the purpose of the whole Arduino setup. I suppose you could increase the heating capacity? But that would be a bit overkill just to get around the lack of ZCD availability as well. I will keep thinking about it, maybe I will find a way to offer one after all. If anyone here is a lawyer or knows about the legal aspects (certification and liability and anything else I'm not thinking of) of selling mains-connected hardware, let me know. ;)
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mg512	#5 Posted on 07/11/2018 6:57 AM
1/4 Pounder Posts: 189 Joined: March 04, 2018	Quote renatoa wrote: Aren't AC motors wildly nonlinear when controlled using a dimmer ? At least this is my experience... very little RPM change until 70%, then sudden stop, and not restarting until PWM back at least to 80%... There is a PWM controlled dimmer, using an octocoupler to tap into mains, maybe you can inspire from the schematic to adapt to your needs, or embed in CR3.1 https://www.tindi...r-mpdmv41/ Oooh, that is a great pointer. It might be possible to just connect one of those to IO2/3 and be done with it! That would make it a lot easier. Thank you! And interesting point about nonlinearity with dimmers, I'll have to look into that. I thought a random-fire SSR was working in the same way as a dimmer, but maybe I was oversimplifying things in my mind.
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Will2	#6 Posted on 07/11/2018 7:04 AM
1/4 Pounder Posts: 154 Joined: March 24, 2015	For popcorn roaster, gradual reduction of airflow is almost necessary, otherwise you have not enough power for heating. The value for decreasing the air flow is 1% down in steps, so that the PID temperature control can be more responsive: Similarly, it is with AC motors. I have not published detailed information, but it is possible to regulate the AC motor with the help of a regulator connected to the IO3. I've tried it successfully: https://www.tindi...50hz-60hz/ Viliam


mg512	#7 Posted on 07/11/2018 7:21 AM
1/4 Pounder Posts: 189 Joined: March 04, 2018	Quote Will2 wrote: For popcorn roaster, gradual reduction of airflow is almost necessary, otherwise you have not enough power for heating. (...) I have not published detailed information, but it is possible to regulate the AC motor with the help of a regulator connected to the IO3. I've tried it successfully: https://www.tindi...50hz-60hz/ Oh, cool, that one looks even nicer. I might get one of those to experiment with. I think something like this would be a _much_ better option than the ZCD approach. And interesting; For mine as I said I've been fine with the fan level constant; But then my heating element is probably also slightly overpowered, plus I tend to do fairly light roasts so I'm not pushing it too far. Are you adjusting the fan speed with alarms in Artisan or similar? Or manually?
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Will2	#8 Posted on 07/11/2018 7:51 AM
1/4 Pounder Posts: 154 Joined: March 24, 2015	If I use TC4 in stadalone mode or Android mode, then I use manual fan control. In these cases it is not otherwise possible. Of course, with Artisan roaster scope, I fully use the option of automatically controlling the fan with alarms. Viliam


AMRoberts	#9 Posted on 07/11/2018 8:13 AM
Newbie Posts: 30 Joined: March 24, 2018	FWIW, this is the AC controller I use for manual heating element control of my hacked popcorn popper: https://www.amazon.com/gp/product/B00MFEA5AE/ Take a look at the pictures, and you'll notice that the control element is a small panel with a digital display (of duty cycle, 0-100), with a 4-conductor ribbon cable connecting to the driver board. I got mine, gave some thought to how to wire it for controlling 120V, tried it with a lamp test load and it worked; so I had no need to try and figure out how the control head was signalling the driver. If you have the tools to understand it (a DMM might do it, scope would probably be better), you might (or might not) find you could use an analog-out from an Arduino or Pi in place of the control head. More complicated (I suspect) would be to keep the control element as a visible duty-cycle display, and hack it to allow an Arduino/Pi to "push the buttons" using digital output pins. I don't really trust the power ratings of parts like this, but provided you have some airflow over the heat sink it seems like it would control a lot of fan.


renatoa	#10 Posted on 07/11/2018 9:52 AM
Administrator Posts: 3005 Joined: September 30, 2016	Quote mg512 wrote: ...If anyone here is a lawyer or knows about the legal aspects (certification and liability and anything else I'm not thinking of) of selling mains-connected hardware, let me know. ;) Isn't the heater also mains-connected? Why a fan could be more dangerous than a heater if both have good case insulation ? Edited by renatoa on 07/11/2018 10:06 AM


renatoa	#11 Posted on 07/11/2018 9:58 AM
Administrator Posts: 3005 Joined: September 30, 2016	Quote mg512 wrote: Oooh, that is a great pointer. It might be possible to just connect one of those to IO2/3 and be done with it! That would make it a lot easier. Thank you! And interesting point about nonlinearity with dimmers, I'll have to look into that. I thought a random-fire SSR was working in the same way as a dimmer, but maybe I was oversimplifying things in my mind. If IO2/3 are open collector transistor, yes, you can connect directly and also a pot, to fine tune the zero point. If they are Arduino GPIO, an additional transistor is needed, I can detail the purpose. A dimmer fire each half sine in the same point in time, chopping them in precise slices, while a random fired SSR allows to pass very random quantities of power, depending a lot of the fire frequency, and the sync with the sine wave.

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