Hi, I've been using a hot air popcorn popper to roast coffee. I started over a year ago and it's been great -- best coffee ever! I bought a PID controller and wired it to switch the heating element, that is working great. But I would still like to be able to adjust the fan speed and I have no idea how to do that. Coffee beans get significantly less dense as they roast so the perfect fan speed at the start of the roast is far too fast by the end of the roast. The result is coffee beans flying all over, getting broken or chipped etc.

I'm a complete amateur when it comes to electronics so I'm here seeking advice on my options. I believe it would be a mistake to attempt using a potentiometer to change the fan speed, my understanding is that the electromagnetic motor is built to run on a specific current and that using a potentiometer to alter the current will likely damage the motor in the long run. I know that Home Depot sells fan speed controllers for ceiling fans -- is that an option or is that a completely absurd idea? Any suggestions?

Thanks for your help.

-Dave.

 

Need motor information, AC -DC, 120 V, 50 or 60 Hz??

 

In addition to what Bernard as asked for, how do you want to control the fan speed, by temperature? Timer? Manual?

 

Hi, I've been using a hot air popcorn popper to roast coffee.

If you have a minute, I would be interested in knowing to what extent the caffeine that is extracted from the beans during roasting accumulates in the popper, how do you remove it, and what do you do with it?

 

Seems as though you want some kind of thermal sensing element (thermocouple) that controls the fan in a scaled analogue fashion that gradually reduces the fan speed as the temp rises?
Max.

 

If you have a minute, I would be interested in knowing to what extent the caffeine that is extracted from the beans during roasting accumulates in the popper, how do you remove it, and what do you do with it?

The roaster is hot enough to sublime and fan powered, so the caffeine will not accumulate in the popcorn popper. He should only lose a gram per kilogram of finish roasted coffee. Most poppers are only 100 grams or less so 100 mg or less of caffeine will hardly be noticed. It will show up as dust in his home or haze on his windows over time.

 

Need motor information, AC -DC, 120 V, 50 or 60 Hz??

I believe the motor is AC 120V. It's a regular home use hot air popcorn popper, you just plug it into an outlet and turn it on. I maybe be able to find specs for the motor if I take it apart but not sure.

 

In addition to what Bernard as asked for, how do you want to control the fan speed, by temperature? Timer? Manual?

I would just like to control the fan manually to turn it down towards the end of the roast. I don't think I need anything more elaborate than that.

 

Its usually a universal motor. Most likely its a small dc motor with a bridge rectifier on the back and then hooked across a small portion of the heating element as in a hairdryer.

Yes these poppers are more or less just a hairdryer with a popper attachment.

 

You might just consider obstructing the airflow path, either the inlet or the outlet. The fan may speed up - like when you plug a vacuum cleaner - but (and because) less air will be flowing.

 

The one problem with restricting air flow on a Universal motor when overdone is cooling, many rely on the air flow, preventing it too much can burn out the motor that is not designed to take it, not to mention the over-speeding that can take place.
Max.

 

All true.

 

Need motor information, AC -DC, 120 V, 50 or 60 Hz??

I took the popper apart and there is a label on the motor. It says:

120V 60HZ 0.84A

 

I took the popper apart and there is a label on the motor. It says:

120V 60HZ 0.84A

Does it appear to have brushes?
That is a very small motor, current wise.
Or a picture?
Max.

 

Does it appear to have brushes?
That is a very small motor, current wise.
Or a picture?
Max.

Yes, I surprised that the amperage was so low. I wondered if I had misread it.

It does appear to have brushes. I've attached a photo (I may be able to get a more high-res one if needed).

 

Yes it is a Universal (AC/DC) motor, you can obtain simple Triac controllers for these type of motors, for that current you may be able to get away with a light dimmer? (triac also)!.
Max.

 

Yes it is a Universal (AC/DC) motor, you can obtain simple Triac controllers for these type of motors, for that current you may be able to get away with a light dimmer? (triac also)!.
Max.

How would I know if a fan controller uses a triac? Is it safe to assume that any basic one I might buy at Home Depot would be that type? Like this one:

http://www.homedepot.ca/product/rotary-variable-fan-speed-control/971401


Thanks for your help with this!

 

It is pretty much a given that the device usually used is a triac controller, all the ones I have opened up anyway.
If you can look inside it without destroying it, the marking on the S.S. component should be on it, then Google it and it should confirm it.
Max.

 

That is a very small motor, current wise.

What's so small about a 100W fan? That's more than a typical ceiling fan.

 

What's so small about a 100W fan? That's more than a typical ceiling fan.

Wow, I'm surprised that it's more than a typical ceiling fan! The popper is a West Bend Poppery I, built in the 80s. They're built like a tank, unlike today's disposable appliances, and they have a 1500 W heating element so they're perfect for roasting coffee. The only problem is that they're hard to find so that's why I want to be pretty careful that I don't burn out the motor trying to control the fan speed.

I thought about using a variac but even second-hand that option is going to run me close to $100 I think. So if there's no real risk to the motor in using a triac controller then I'll definitely go that route.