controlling 2 6K heating elements using ssr, heat sink(s), potentiometer

Thread Starter

Glide Consulting

Joined Feb 27, 2018
7
Hello and thanks in advance for any and all help with a project I am working on. Specifically heat control. I am building a fluid bed coffee roaster. It works by roasting the green coffee beans using hot air. The heated air is provided via either electric or gas fired heat being blown over them by a blower fan. My particular project uses electrical heating elements that use 220v AC and each running at 6k I will be working off of a 40 amp dedicated breaker. I am wanting to control the level of heat with a potentiometer. This would allow me to raise and lower the output temp as the beans are roasting. I need help assembling the correct components and maybe some help wiring it all up.
Thanks!
 

ebeowulf17

Joined Aug 12, 2014
3,275
My first thought would be a standard TRIAC or SCR "dimmer" circuit.

IMG_4602.GIF
https://www.electronics-tutorials.ws/power/triac.html

IMG_4600.PNG
http://www.bristolwatch.com/ele/triacs.htm

IMG_4601.JPG
http://www.electroschematics.com/8411/scr-phase-control-dimmer/

Full disclosure: I haven't built or tested any of the circuits above - they're just examples of the concept I'd expect to see in this application.

Max knows his stuff far better than I, so if there's a reason to use a microcontroller instead of something like the circuits above, I trust his judgement and defer to him. I only mention these circuits cause they seem simpler to me, and don't require any programming.
 
Last edited by a moderator:

Reloadron

Joined Jan 15, 2015
5,781
Whats wrong with the very common method of using a temperature controller similar to this?
https://www.ebay.com/itm/100-240V-D...hash=item489bdcc080:m:mKBSCjRNRmldPUuBHkjdtiQ

Then heat is controlled based on an actual temperature value known from an actual sensor and allows a repeatable process.. You can simply adjust heat with up/down buttons..
That is what I would try. Controller plus a 40 Amp SSR for about $20 USD. Place the sensor (Type K Thermocouple) in the airflow and control the heat. I have no idea as to the quality of the linked products but for the cost well worth a try.

Ron
 

Reloadron

Joined Jan 15, 2015
5,781
My particular project uses electrical heating elements that use 220v AC and each running at 6k I will be working off of a 40 amp dedicated breaker.
I do have a question as to this part. When you mention the elements being 220 volts no problem but then you mention two elements and 6K. Would the 6K be a 6KW (6,000 Watt) element for a total of 12 KW when the elements are fully on? That gives me 12,000 Watts / 220 Volts = 54.5 Amps or close to twice the 30 Amp 220 Volt service you mentioned. That being based on heating elements being a resistive load. A pair of 6 KW elements would require well over 220 Volt 30 Amp service including the need for running AWG 6 (or equivalent) wire gauge between source and load. You could pair some 40 Amp SSRs but still need 60 Amp service at 220 Volts. Each element would require AWG 10.

Unless I am missing something?

Ron
 

ebeowulf17

Joined Aug 12, 2014
3,275
Temperature controllers and coffee roasting are a tricky combination. The target temperature changes more or less constantly throughout the process. Not at all like an oven, hot water bath, etc. It's also tricky, if not impossible, to effectively pre-program a series of ramps to do what you need, because subtle changes in the batch size, moisture content of the raw beans, etc. all change how much heat you need at what times in order to get the desired result.

You either need VERY sophisticated roast profiling control with full, continuously variable set point adjustment, or you need an experienced roaster driving "analog" controls. In this sense I don't mean analog in the sense that there couldn't be a microcontroller driving the TRIAC gate, but I just mean that the human behind the controls should be able to dual in any amount of heat input at any time, quickly and easily (like a trim pot, etc. as opposed to clunky buttons on a PID controller.)

Personally I still strongly prefer the hands-on "analog" approach. I'm fairly confident that with enough input data, really effective roast profiling could be achieved, but 90% of the automatic profiled roasts I've tasted paled in comparison to their "hand roasted" counterparts. Just like with LTspice, if you build an effective enough model of the coffee roasting process, you should be able to simulate it, predict it, control it digitally, etc. However, essentially no-one understands the process well enough to do that, so the old school approach still wins in my book... for now... when discussing small batch roasting of varying types and quantities of beans. Naturally the whole process becomes more predictable and manageable if you're a Folgers sized operation blending everything into a consistent, homogenous mass. Large scale commercial roasting is a different beast all together, but small scale craft roasting is hard to do right without a human touch.

Sorry, long rant. I miss roasting. Short version of the comments above: the thread starter is probably better off with a "wattage" knob than a temperature controller.
 

BR-549

Joined Sep 22, 2013
4,938
Twenty years ago.....a PID controller like mcgyvr exampled, would cost 150-200 dollars.

I use to repair them for 50 bucks flat rate. A 90 day warranty and free shipping.

Now..... China can stamp them out at 18 bucks.
 

Reloadron

Joined Jan 15, 2015
5,781
Temperature controllers and coffee roasting are a tricky combination. The target temperature changes more or less constantly throughout the process. Not at all like an oven, hot water bath, etc. It's also tricky, if not impossible, to effectively pre-program a series of ramps to do what you need, because subtle changes in the batch size, moisture content of the raw beans, etc. all change how much heat you need at what times in order to get the desired result.

You either need VERY sophisticated roast profiling control with full, continuously variable set point adjustment, or you need an experienced roaster driving "analog" controls. In this sense I don't mean analog in the sense that there couldn't be a microcontroller driving the TRIAC gate, but I just mean that the human behind the controls should be able to dual in any amount of heat input at any time, quickly and easily (like a trim pot, etc. as opposed to clunky buttons on a PID controller.)

Personally I still strongly prefer the hands-on "analog" approach. I'm fairly confident that with enough input data, really effective roast profiling could be achieved, but 90% of the automatic profiled roasts I've tasted paled in comparison to their "hand roasted" counterparts. Just like with LTspice, if you build an effective enough model of the coffee roasting process, you should be able to simulate it, predict it, control it digitally, etc. However, essentially no-one understands the process well enough to do that, so the old school approach still wins in my book... for now... when discussing small batch roasting of varying types and quantities of beans. Naturally the whole process becomes more predictable and manageable if you're a Folgers sized operation blending everything into a consistent, homogenous mass. Large scale commercial roasting is a different beast all together, but small scale craft roasting is hard to do right without a human touch.

Sorry, long rant. I miss roasting. Short version of the comments above: the thread starter is probably better off with a "wattage" knob than a temperature controller.
Wow, want to thank you for a very, very informative post. While I have dragged coffee beans, already roasted, from all corners of the world home with me I never knew what was involved in roasting the little suckers. I just wrongly assumed you put them in an oven, roasted them and done. Two things I acquired a taste for are 18 year aged single malt scotch and really good dark roasted coffee. Last year I dragged back 10 Kilos of beans from Costa Rica. Good stuff. Thank you again for sharing all of that information. Armed with that knowledge I can appreciate the need to use a manual control and to have a roaster (person) with the skills to roast the beans. Wow! :)

Ron
 

Reloadron

Joined Jan 15, 2015
5,781
I've never really thought it through, but I have roasted pine nuts in a toaster-oven, and it is exactly the same problem.

ak
Another of my expensive taste treats. I saw a TV special on them and how they are harvested which explains the cost. I like them in stuffing and other things but when you grow up NYC Italian pine nuts are a way of life. :)

Ron
 

Thread Starter

Glide Consulting

Joined Feb 27, 2018
7
I do have a question as to this part. When you mention the elements being 220 volts no problem but then you mention two elements and 6K. Would the 6K be a 6KW (6,000 Watt) element for a total of 12 KW when the elements are fully on? That gives me 12,000 Watts / 220 Volts = 54.5 Amps or close to twice the 30 Amp 220 Volt service you mentioned. That being based on heating elements being a resistive load. A pair of 6 KW elements would require well over 220 Volt 30 Amp service including the need for running AWG 6 (or equivalent) wire gauge between source and load. You could pair some 40 Amp SSRs but still need 60 Amp service at 220 Volts. Each element would require AWG 10.

Unless I am missing something?

Ron
Ron thanks so much for your attention to detail and trouble shooting. Yes the elements are 6,000 watts each. Awesome! You just saved me a LOT of hunting and pecking. I am learning as I move along and with input like I am getting here it wont take long. Thanks a lot!
 

Thread Starter

Glide Consulting

Joined Feb 27, 2018
7
Temperature controllers and coffee roasting are a tricky combination. The target temperature changes more or less constantly throughout the process. Not at all like an oven, hot water bath, etc. It's also tricky, if not impossible, to effectively pre-program a series of ramps to do what you need, because subtle changes in the batch size, moisture content of the raw beans, etc. all change how much heat you need at what times in order to get the desired result.

You either need VERY sophisticated roast profiling control with full, continuously variable set point adjustment, or you need an experienced roaster driving "analog" controls. In this sense I don't mean analog in the sense that there couldn't be a microcontroller driving the TRIAC gate, but I just mean that the human behind the controls should be able to dual in any amount of heat input at any time, quickly and easily (like a trim pot, etc. as opposed to clunky buttons on a PID controller.)

Personally I still strongly prefer the hands-on "analog" approach. I'm fairly confident that with enough input data, really effective roast profiling could be achieved, but 90% of the automatic profiled roasts I've tasted paled in comparison to their "hand roasted" counterparts. Just like with LTspice, if you build an effective enough model of the coffee roasting process, you should be able to simulate it, predict it, control it digitally, etc. However, essentially no-one understands the process well enough to do that, so the old school approach still wins in my book... for now... when discussing small batch roasting of varying types and quantities of beans. Naturally the whole process becomes more predictable and manageable if you're a Folgers sized operation blending everything into a consistent, homogenous mass. Large scale commercial roasting is a different beast all together, but small scale craft roasting is hard to do right without a human touch.

Sorry, long rant. I miss roasting. Short version of the comments above: the thread starter is probably better off with a "wattage" knob than a temperature controller.
Great post man! You express perfectly the reason I want analog simple up and down controls for roasting as its best done on the fly and by the seat of your pants reading the beans as you roast. I can control the roast by the amount of air and heat applied at any given time. Im going to use a variac on the blower motor to give me control there. Thanks
 

ebeowulf17

Joined Aug 12, 2014
3,275
Wow, want to thank you for a very, very informative post. While I have dragged coffee beans, already roasted, from all corners of the world home with me I never knew what was involved in roasting the little suckers. I just wrongly assumed you put them in an oven, roasted them and done. Two things I acquired a taste for are 18 year aged single malt scotch and really good dark roasted coffee. Last year I dragged back 10 Kilos of beans from Costa Rica. Good stuff. Thank you again for sharing all of that information. Armed with that knowledge I can appreciate the need to use a manual control and to have a roaster (person) with the skills to roast the beans. Wow! :)

Ron
I'm always happy to share my love of coffee! It's been almost 6 years since I roasted coffee, and 3 more than that since it was my main job. I sometimes miss it, but now I'm working on designing and building espresso machines, and that's an awful lot of fun too!
 

ebeowulf17

Joined Aug 12, 2014
3,275
Great post man! You express perfectly the reason I want analog simple up and down controls for roasting as its best done on the fly and by the seat of your pants reading the beans as you roast. I can control the roast by the amount of air and heat applied at any given time. Im going to use a variac on the blower motor to give me control there. Thanks
Yeah, I'm glad we're on the same page. I would've felt bad if you really liked the automation idea and I totally derailed your thread!

As for the circuit and controls you need for this project, I understand the basic concepts involved, but I have almost no experience with high power, variable power applications like this one. I won't be able to help with any details, but you're definitely in good hands with the crew on this thread. Remarkable collection of great minds that have chimed in on this one. People must love coffee!
 

Thread Starter

Glide Consulting

Joined Feb 27, 2018
7
Wow, want to thank you for a very, very informative post. While I have dragged coffee beans, already roasted, from all corners of the world home with me I never knew what was involved in roasting the little suckers. I just wrongly assumed you put them in an oven, roasted them and done. Two things I acquired a taste for are 18 year aged single malt scotch and really good dark roasted coffee. Last year I dragged back 10 Kilos of beans from Costa Rica. Good stuff. Thank you again for sharing all of that information. Armed with that knowledge I can appreciate the need to use a manual control and to have a roaster (person) with the skills to roast the beans. Wow! :)

Ron
Ron message me your address and I will bless you with some fresh roasted deliciousness. Hey! Its the least I can do for your help brother. Im very thankful to be able to access some knowledgeable folks here to help me along. I have a drum roaster that I use now the air roaster is an adventurous project I have wanted to undertake for a while. I enjoy all the equipment and tinkering (poor boy inventing) as much as the coffee (well kinda lol). Dark roast you say?? Ahhh I have some crazy good ethiopian on tap right now and freshly roasted its very very good. Of course I have the standards too... columbian, peruvian, mexico, panama... and a few other treats. Maybe a lil mix bag is in order.
 
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