I'm new to roasting and someone introduced me to roasting with a popper. Apparently, there are poppers which are easy to split the heater/fan circuits and others that are tied in together and can't be separated. Well, I found one of the latter types in a thrift store for $3, so I decided to give it a try.

Opening it up revealed a small DC motor connected to a 4 diode bridge, which converts AC to DC. The motor is rated at 18v and is wired in series with the heater elements (there are two of them for some reason--a small one and a large one). I presume the heater elements lower the voltage to the motor from 115 to 18. The only way to get the circuits separated was to simply do away with the rectifier circuit (diode bridge) and connect the DC motor directly to a 19v laptop power adapter which I had kicking around. The polarity needs to be correct or the fan won't blow very well.

I had a 3 way resistor pulled from an automobile heater fan circuit which steps down a vehicle blower to speeds 3-1 kicking around, so connected that to a 4 way switch (pulled from an old stereo--the mode selector switch) which steps down the voltage to the fan using the resistor, allowing 3 fan speeds. This allows some control over heat, especially when roasting outside in cold weather. This is potentially a cheaper way to control fan speed than a variac, if you can find a heater resistor at a junk yard cheap.

I connected the heater elements to the power switch to give more control over the temp, wrapped up the wiring with some elec. tape and connected a plug to it all.

I find with the fan on low speed, it heats up way too quickly, achieving first crack in 40 degree weather with 1/2 cup of beans within 2 minutes. On low speed, I can see the heating element overheating protector kick in as the ambient lights dim and brighten, so it's about as hot as it an get, even in cold weather.

On high speed, first crack is around 5 minutes in 40 degree weather, which is still too fast.

So I'm waiting for my digital thermometer with dual probes so I can control the temp better with the power switch.

If anyone is interested in circuit diagrams, etc. I can do them up and post them. I've since secured a couple more generic poppers and both of them are wired the same, with a 4 diode bridge in series with the elements, so if the popper elements go, it won't be hard to transfer the mod to another popper. I imagine these poppers are much more common than the specific models with which the circuits can be separated easily. In fact, of the three different generic poppers I have, they all use the same heating element: a set of two elements with an overheating protector sandwiched between two pieces of cardboard like material (but definitely not cardboard!), so the element can be dropped in as a replacement should it fail from overheating. And all use an 18v DC motor...

Sounds like someone needs a Variac...
(Not that cheap, though...)