I have a popcorn maker that I would like to be able to adjust the temperature on with a rheostat/pot--from about 50ish% to 100ish% of what it does now. I assume it is sufficient to control the power to the heating element(s) rather than include a thermometer as part of the control, since what the temperature is doesn't matter to me--only that I can adjust it in the approximate range I mentioned. I attempted to create a schematic based on what I observed inside the popper (see below). I assumed the components I have marked as diodes are actually diodes--I can tell they are polarized, but their markings are otherwise illegible. Since I see nothing the size of a transformer, I suspect the motor is AC.

What I need help with is identifying the specs for a pot. I guessed that a pot with specs like the shown resistor would be OK, but I see that such pots are $45 and up each. This leads me to believe that I have made an erroneous assumption, since the popper was probably around $20. I've assumed the pot would go where I have marked "Thick red wire." There's a slew of electronics things here I don't understand, so this is more an experiment than a project that must be completed successfully. Can anyone provide insight into my thinking and specifically, identifying a reasonably priced, appropriate rheostat?

 

the best way to control the temperature is with an ordinary light dimmer feeding the heater, a rheostat will get too hot.

 

Ditto, just make sure the dimmer is rated to the wattage of the corn popper. The fan will be only a fraction of the total, so you can just assume the dimmer needs to be rated for the total wattage.

 

Out of curiosity Greg, what would change if you make it to work at say 80%? Takes longer to pop all corns or what?

 

+1
I don't see the point of reducing the power. The kernels will take longer to pop or not pop at all.

 

Sometimes popcorn poppers are used to roast coffee beans.

 

Don't know what temperature you want for popcorn but I use about 455 oF to roast coffee beans in a modified air popcorn popper.

 

I did a simple mod on a poppery II for roasting coffee. There is a thermostat switch which causes it to cycle. I just bypassed it so it stays on all of the time. Roasts coffee perfectly even 10 batches in a row. It has at least 8 years working like that. Just be sure to clean debris from the inley screen regularly. Ill diagram it on mon if you'd like.

 

I have a popcorn maker that I would like to be able to adjust the temperature on with a rheostat/pot--from about 50ish% to 100ish% of what it does now. I assume it is sufficient to control the power to the heating element(s) rather than include a thermometer as part of the control, since what the temperature is doesn't matter to me--only that I can adjust it in the approximate range I mentioned. I attempted to create a schematic based on what I observed inside the popper (see below). I assumed the components I have marked as diodes are actually diodes--I can tell they are polarized, but their markings are otherwise illegible. Since I see nothing the size of a transformer, I suspect the motor is AC.

What I need help with is identifying the specs for a pot. I guessed that a pot with specs like the shown resistor would be OK, but I see that such pots are $45 and up each. This leads me to believe that I have made an erroneous assumption, since the popper was probably around $20. I've assumed the pot would go where I have marked "Thick red wire." There's a slew of electronics things here I don't understand, so this is more an experiment than a project that must be completed successfully. Can anyone provide insight into my thinking and specifically, identifying a reasonably priced, appropriate rheostat?View attachment 85411

In your diagram, the fan motor is supplied pulsed DC from the rectifier bridge made of four diodes. The switch in parallel with the power resistor appears to have the purpose of allowing the fan and warmer heater to run when open and to enable the main heater in addition when closed. If you insert a control for the main heater, do it on it's leg of the circuit so your control doesn't affect the fan and warmer.

 

Aha! Thanks for the lesson, KJ6EAD. I now remember my learning about that diode configuration. Thanks all for the suggestions for control. By the way, the popper is 1440 watts. As mentioned, I am using it to roast coffee beans. With "real" home roasters being rather pricey, air poppers are the commonly used economic alternative for giving home roasting a try. While the pattern of heating and cooling is overly simplified compared to what is ideal, it is made up by the fresh flavor. Beans are arguably at their best 1/2 a day after roasting and then for a few days. Right now it is a little too hot and while it makes a palatable French Roast, it loses its flavor nuances. It doesn't work for lighter roasts at all because too much of the bean is left unroasted-ish. This all assumes you are (perhaps overly) picky about your coffee.

 

I'd also recommend experimenting with different batch sizes (how much coffee you try to roast at once.) Coffee roasters behave very differently with different batch sizes, regardless of whether they're commercial or home sized and drum or fluid bed. Commercial roasters have better heat control and provide at least some adjustment of airflow as well, which allows for some flexibility, but there are still limits (many, if not most, Diedrich roasters only work well up to about 70-80% of their rated batch size!)

All of my experience was on commercial drum roasters, and I've been out of it for 6 years now, so my instincts could be off, but I'd try half or three-quarters your current batch size as a starting point and see if your lighter roasts are more consistent that way. That said, I definitely agree with your desire for some control over the heat, and agree with the earlier comment that you want to only adjust the heat, not the fan, cause I'd bet that the fan is already underpowered for coffee.

Sounds like Russel has lots of experience on a small home roaster like yours and might have good insights into ideal batch sizes for you. Good luck and have fun!

 

I did notice that a 1/2 cup of beans got to the burned stage more quickly. Something like 8 minutes instead of 11. Since then I've only been doing 1/4 cup at a time. I would probably find amounts too much less than that rather inconvenient. wmodavis' statement about 455 degrees F is helpful, since my thermometer will show that temperature, but the temperature of the air is quite a bit more at the moment.