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Air Popper Heater
Hi everyone, I'm working on my first roaster and think the Air popper will make a nice little tester to learn on.
I have a Betty Crocker popper 110v 1200 watts.

I have done a fair bit of reading and know I've seen some of the heaters in parallel and I'm sure I read hook the coils in series as well but can't find that? So I tried my hand at some calculations and think I have two options and would like to ask what you think is the best one. Will be splitting the fan motor and heater into two circuits.

So two coils in the heater 9.3 ohms and 3.6 ohms. In parallel it looks bad at about 4500 watts, not an option.
Series is 12.9 ohms at 940 watts
Single large coil 9.3 ohms at 1300 watts. Would this heat evenly enough?

If I never made any mistakes in the calculations the Series connection might be the best?
Is it ok to run the coils like this and is that hot enough?

Thanks for your time, I hate to burn it up on the first try.
Welcome to HRO!
Not sure if I've ever heard of any popper heating element with a 3.6 ohm resistance. There is normally the primary which you measured at 9.3 ohms but the other is usually way higher and is the one used to drop voltage to the blower but that's assuming it's one with a permanent magnet dc motor. Please shoot us some photos of the two elements.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
Hello Alenb, I never took any pictures but I measured it with everything out of the circuit. The heater looks almost identical to many other on the site, fuse on the heater but thermostat on the outside of the chamber and two coils. It is brand new I have only run to test that it works and now worked on the blower, strange about the resistance, what is it normally?

I have started testing the fan and have put High temp silicone on the outside edge to seal it up, lots of lost air out around the wires and base. Might have enough air to roast 100 grams which would be nice. If I take it apart again will take pictures.

I triple checked the the resistance of everything they should be correct and it is the one to the motor (Small diameter coil in the middle and hard to see any of it).

Do you think the 940 watts is too low to roast or should I go with just the primary at 1300 watts and see if it survives and roasts ok?

The rest of my parts have arrived and will be testing the heater tonight after work.

Thanks for your reply.
My assumption is that the 3.6 ohm coil was used as a dropping resistor in series with your motor and the combination of that was in parallel with the primary 9.3 ohm heating coil. This is only a guess. Either way, you'll need to use the 9.3 ohm primary element by itself and disregard the 3.5 ohm coil if you have another means of powering and controlling your fan motor. Since it's nameplate states 1200 watts, there would be no way of achieving that wattage if you were to use the two elements in series and would not provide enough heat in my estimation.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
I have never roasted coffee so I was wondering if the 940 watts would not be enough. I can switch easily from using the two coils in series or the primary coil.
I will be running the fan separately.

I don't know how much the middle coil even does?

Think I will test the heat from both coils in series and then the primary by itself and see how it goes.

My thermocouples have not arrived but I have some BBQ/meat thermometers should give me an idea.
Some testing results:
Series Coils at 90% of my SCR is only 201C
Single Primary Coil at 90% of my SCR is 271C

Room temp was at 23C and full 100% fan setting.
Medium to Medium dark roasts it should get by right?

By the way anyone wondering if those 10000w 220v SCR digital regulators work on 110v, it looks to control the current to the coil well.
Comments on the site went back and forth saying they won't/will work for 110v? Working for me.

Going to try my first roast today, outside so think I will wrap the popper in some exhaust wrap to stabilize the heat.
Just going to dangle a probe in the beans for now as it's a little long to go into the side of the heating chamber.
A SCR is not voltage dependent, they have same build for any voltage, works even as low as 12/24V, but A/C, not DC !
The limiting factor is the current, not the voltage. Maximum voltage of switching elements usually covers even the 400V of three-phasic EU networks.
Rating a SCR using Watts is misleading, same unit can control double watts in EU than in US.
Those 10.000 is not real, gross overrated, comes from the 40Amps limit of the triac used, multiplied by average 230V of the EU mains, thus 9200 Watts, rounded to 10.000. Numbers sells...
But... no EU home is allowed for more than 25 Amps cabling, and the heatsink used in that SCR will boil water at 25 Amp, and surely exceed 120 C degrees maximum allowed for an industry semiconductor, if pushing it at the 40 Amps limit.
The conclusion of the above is that in US, using 115V mains, you can control maximum something in the 2000-2500 Watts ballpark.
Edited by renatoa on 07/24/2022 1:11 PM
HarryDog, you mentioned 100 grams which is an extremely small batch size. If that's really the amount you're looking to roast each time, you'll be fine as long as whatever is used to lift the beans can do so. 900 watts is plenty even if you only have 110 - 120v unless your roaster's design is terribly inefficient.
Thanks for the feed back Renatoa and Progen, I just did 3 batches and the first was a screamer and got it a bit dark, the next two look much closer to what I was looking for. Will give it a few days before tasting.

First I don't recommend anyone use that exhaust wrap as its made of fiberglass and when I cut it I was getting some fiberglass bits. I covered it in aluminum tape to make sure it does not fly around.

Best to look for that ceramic tape Renatoa suggests.

Progen, it's a small air popper and was glad to get 100g in it but now that I sealed leaks it might do 120g?

I can't say I like the roast smell, hope that's not from the fiberglass tape.
Couple of pictures of the setup.
HarryDog attached the following images:
roasts1.jpg airpopper1.jpg
The greatest availability of an insulator material is wool. Pure wool, no synthetics combo.
The melting/burn point is way over 500C, that's why is safe for this job.
No to any cotton combination, it melts at 230C, which is too close to the maximum roasting temperatures.
The plastics are even worse, under 150 C.
Edited by renatoa on 07/25/2022 2:33 PM
I will look for some wool.

This Exhaust stuff works well as insulation rated at 1400F sustained.
Don't like the glass particle issue and the smell is a deal breaker.
It only stinks near the end of the roast, it's not pleasant.

I read that it should stop but on this little roaster that could be a long time before it's burnt off.
After two days Rest the beans start to develop some nice coffee aroma.
First Taste:
Guji was under developed and was a bit veg-ital with a bitterness that is intense already not sure how this is going to be as a darker roast?

Abyssinia Mocha I mistakenly roasted this to a Full City plus and I like it, would be proud to serve this to a dark coffee lover.

Guatemala was a medium roast and surprised me it was great, a well balanced cup with a wonderful aroma kind of a fruity fermented coffee scent. This would fit well with with lighter coffee drinkers but still give them some solid coffee flavor.

Looking forward to day four and see if anything improves.
HarryDog, is that aluminium foil on the outside? Were you using it as an insulator or to extend the roasting chamber? With such a compact unit and virtually negligible distance between the blower, heater and beans, I don't think an insulator is needed. If you can find one which fits, and considering that you most likely have more power than needed for 100 grams, perhaps a taller borosilicate tube can be used to give you slightly more capacity but bear in mind that everything comes at a cost. With all other factors being equal, a taller roasting chamber of the same diameter means more work for the blower since the bean bed will be deeper.
I extended the tube using a can. I then wrapped the chamber with exhaust wrap that has fiberglass in it. When I cut it glass particles dropped all around the chamber so I used aluminum tape to keep them from getting sucked into the chamber if anymore fall off. The stock scoop is only 30ml, so using 100g of beans goes over the stock chamber. I have good movement on 100g but I might be able to get a bit more out of it once I sealed the leaks, I was thinking the insulation would help so I could roast in the winter outside as I live in Canada.

I would like to use glass on a popper, are there any examples on this site with glass on a popper?
Some French Press glass in the 4-600 grams ballpark fit pretty tight on the popper, you should measure exactly to know.
And also, you should have the know how and skills to cut glass.
For me did the job a Dremel with 30 mm diamond disk, under water flow.

Much simpler could be a Coleman lantern glass, check here the sizes chart:
I'm looking at a different popper with vents like the side vents on the one I have now but on the bottom. It feels like it has twice the air flow of my other popper and instructions say to use about double the corn. Just wondering how this one will move the beans as the old side vents roast very evenly?

Was thinking of trying a glass candle chimney inside this popper, any tape like product that might take the heat for a seal?

Like that pipe wrap to seal leaks, just don't know if it will take the heat?
Kapton tape is called what you want, a model with at least 260 C maximum temperature.
Even the lowest models, with 230 C maximum works, but need replacement every some months.

You should look also to Ikawa vent slots pattern, they are in the very bottom (floor), not on the lateral walls of the roast chamber.
This pattern is more effective for uniformity than a popper, imo, because the main issue of a popper RC is the lack of a vigorous ascending movement.
In a popper RC the beans are layered, the bottom beans travel to the surface is very slow, or even non-existent for an overloaded roast chamber => tall narrow column.
You can have yellow beans at bottom and green beans at surface, not good.
Among others, will led to a great dispersion in time of first crack, thus difficult to judge development time.

A very simple solution to the above, confirmed by several forum users, is to create a discontinuity/un-balance of the movement in the roast chamber, that led to "channeling" to surface for some beans, along the shortest resistance path.
Sounds a complicate solution, but you can do this as simple as leaning the roast chamber from vertical by some degrees. Just try and see how beans start bubbling Grin
Edited by renatoa on 07/29/2022 6:05 AM
What do you think of Sharkbite silicone wrap? Good to over 500F and used on water lines with the fittings. I could not find where it exactly said food safe but used on water lines would it be safe? Would want the wrap to give a little as the glass expands, so less chance of breaking.

On the first popper I did use a lift of about 3/4 of an inch to assist in moving the beans. I think the roast evenness was very good.

I have been watching videos on fluid roasters and some were poor to terrible for roast evenness. I just watched a video of a fluid roaster that looked amazing but the roast was the worst I ever saw? I did see one commercial roaster that was very good.

Will look at the Ikawa as I did see videos on youtube.
Looks much like the Ikawa vents.
HarryDog attached the following image:
No experience with that tape, sorry.
The European equivalent seems to be Tesa 4600:
Will give it a try the next build, is cheaper than Kapton.
Working on a different popper, the motor is Jmy mode 365
that's all I can read, what is the voltage of this motor?

Looks to be a rage of different motors out there, 6v to 36v.
I didn't want to pull the fan off in case I broke it but maybe I need to.
Measure working voltage of the motor, in the popper, as it comes from the factory.
If about 19V, as are those I encountered so far, then it is good for a DC power source rated 24V maximum.
Edited by renatoa on 08/01/2022 3:15 AM
Looks like my PSU is having issues.

Do you have a replacement DC motor you like to use?
Been looking at trying a 380 motor?
Thank you, we are probably on different continents, so shipping cost for such motor don't worth.

380 motors are VERY high RPM, probably more than 40K, compared to 20-25k the 365.
For this reason the 380 power consumption is bigger, even without load, because the friction in bushing/brushes is proportional with the square of RPM.
So be prepared with a PSU rated more than 4 Amps for 380, while 365 is happy with under 1 Amp, maybe two...
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