Popper Fan Speed – Thermal Switch Function

If you hear the fan speed increase slightly somewhere between first and second crack, the Popper might have hit it’s temperature limit. Here’s a video showing what it sounds like, and what to do…

The Popper coffee roaster has a thermal switch which prevents the roaster from getting too hot too fast. This can kick in some time after first crack, as the machine nears second crack. It’s annoying perhaps but required to have for UL certification.

Popper Fan Speed Acceleration and the Thermal Cutoff Switch

If it’s still an issue it is quite easy to modify the position of the switch a bit, pushing it up higher on the roast chamber. But opening up a roaster means voiding the warranty so consider that! Here is a video dedicated to explaining the thermal cut off switch and how to address the issue.

8 Responses

  1. First!

    I love my Popper for the most part. Notwithstanding the thermal switch issue and heating cutoff occurring at a progressively lower temperature on progressive roasts, its overall ability to easily create a roast that meets this DIY home roaster’s coffee taste preferences makes it a purchase that’s proven to be well worth the price. Having been a long time SM’s customer who for years was using a hot air popper with okay results, making the move up to the Popper’s added an ability to finesse a bit and ultimately achieve roasts that not only taste significantly better but are easier to produce than those using my simple, die hard (still alive after literally 100’s of roasts believe it or not) ‘Toastees’ hot air popcorn popper. With all that said, the Popper’s cutting out at exactly 128 degrees F now (measured with a thermal probe I’d purchased from SM’s) regardless of roast times. It previously was achieving at least 135° as I recall; now it’s not able to complete first crack regardless of type of bean or rate of temperature rise.

    Sounds like your thermal switch ‘tweak’ is the solution. I might even bypass the switch completely (with all cautions taken into account) should elevating the switch’s position outside the roast chamber not quite do the trick. Regardless, thanks for the workaround!

    1. Hi David – hmmm sorry to hear that the thermal cutoff is getting progressively lower in temperature. I had looked at a Popper that had a similar issue and saw that the silicone boots around the thermal switch contacts had been singed … they should stand up to that temperature but over time it seemed the wires had been exposed to a lot of heat. Another person who reported the same simply bypassed the switch by joining the 2 wires going into it. He reported not only solving the problem of low heat, but actually needing to rethink his roast settings because it resulted in a big boost in power to the heat coil. I actually have spare thermal switches I can send to replace any that aren’t working (free too) but it might end up serving your interests better just to bypass it, IMO

  2. Hi Tom. Got after it this morning. Took it apart, did this and that and in the end, managed to elevate the thermal switch’s position several inches. It’s now positioned a bit above the flat spot that’s inside the roast chamber with the switch’s terminals now positioned vertically which seems to allow for better contact. I’d also cut the cable tie that was securing the leads going to the thermal switch allowing for additional length (you’d mentioned that as a possible necessary step in your workaround video). It’s all good news, at least for now. Tossed in a batch of some SM’s Colombia Veradas Vecinas I’d ordered not too long ago. It passed the 128°F mark and made it all the way through first crack, yay! Went up to 145° before I’d cooled it, no doubt 2nd crack’s in the cards when that occasion’s called for. Oh yeah, I’d misspelled the hot air popcorn popper I’d been using for years, it’s a “Toastess”. It was discontinued years ago apparently and has now been relegated to backup.

    Thanks for everything you and your crew do at Sweet Maria’s, support included!

    1. Great – I am glad to hear it is working better! Yes the Toastess was a really powerful popper…

  3. Could not move the thermal switch to a point above the flat spot because the insulation hit the clamp that holds the thermal switch to the roast chamber. Instead, I desensitized the switch by mounting a stainless steel flat washer between the switch and roast chamber. This means there is no need to carve a notch out of the insulation or lengthen the wires to accommodate a raised switch.

    1. That’s a very good solution. I did the same with heat resistant mica material that is made for this purpose, because I had some laying around. But your approach is better since everyone has a washer somewhere. I imagine other items – a dime? would be great too. Thanks for sharing your solution!

    1. Hi Neal. I’m trying to picture what this led woukd do- can you explain? There are 3 leds on the front to indicate the function mode

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