Controlling coffee roasting using light dimmers: addendum
Controlling coffee roasting using light dimmers: addendum, by Simon Phillips
I have recently come across an alternative to modifying a domestic light dimmer. This circuit is probably an easier option for most people. The part is a ready made 1500W triac controlled motor speed controller, but it is also fine to use with a resistive heater, like a popcorn machine heater. The unit is made by a Spanish company Cebek, and is available from CPC (if I find other sources I will put them up) at approx £14 incl VAT.
The circuit board is nice and sturdy with a reasonable quality potentiometer for control (unlike most domestic dimmers which have poor quality ones). There are also nice screw-in terminals for wiring. All you need to do with one of these is put it in a box, wire it in, and off you go. The heatsink is quite large, and so requires a tall-ish box.
I have one running the heater in my Imex, and it seems excellent. The instruction mention using a vented metal box as the unit can get hot, but I found it stayed pretty cool running the Imex heater so it is mounted in a plastic box.
If you had doubts about modding a dimmer buy one of these and get your roasts where they should be, nicely profiled.
Footnote: If you are wondering why you don't see more information on the 'net about using dimmers instead of variacs for heater control, it is because most of the stuff you see on the net is from the US. The US uses 110V, and therefore for a 1300W heater you need a lot of current compared to European systems (roughly twice), so US dimmers of 1500W are expensive and not that common.
The circuit mentioned in this article can be ordered from here
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great tip! I would never have thought of looking for motor speed controllers.
I've just seen in Maplins an equivalent device. I can't find it in their online catalogue, but it's in the printed one in-store. It's good for 800W as-delivered, but up to 2600W suitably heat-sinked. You have to provide a 47KOhm pot. £11.99, from memory.
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