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Severin popcorn dimmer etc..


PhilDawes
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(I'm pretty new here - sorry if people are getting bored of popcorn modding discussions).
I bought a severin a couple of weeks ago (recommended elsewhere in the forum!) for 25 quid to get back into roasting coffee. Unmodded it roasts ok, though very quick. E.g. First crack was somewhere between 3 and 4 mins. At this sort of rate it is pretty uneven and I had to roast to almost 2nd crack to get something that looked consistent.

I found this instructables piece which gives a lot of detail on controlling it with an arduino and TC4+ shield.  This is quite a lot of work, but I realised you can do this stuff in stages and get something usable / drinkable at each stage:

  1. Unmodified popcorn maker, stopwatch, watch for yellow, listen for cracks
  2. thermocouple in the chamber
  3. dimmer on the AC lead, simultaneously reduce fan+heat in tandem to slow roasting speed
  4. separate the DC motor and AC heating element, control manually
  5. hook up to TC4, artisan, record roasts
  6. PID control etc

To get to (3) I bought the following which worked out well:

Severin popcorn maker 25 quid

Thermocouple + reader 15 quid

Cheap shitty voltage dimmer 8 quid

The cheap voltage dimmer is pretty scary. I made sure the casing was grounded, but I'm still using rubber gloves to move the dial!
It was worth doing though, I was able to get a roast to stretch out to longer using the dimmer to vary the temperature climb.

Redber Colombia Excelso Huila, 100g green, 84g out
Yellowing was about 160c 2 mins in, first crack at 200c 9 mins 30, dumped at 210c 17.5 mins


'bean' temp curve:

curve.png.f4aaed985c34317597c6902d82178e0e.png

 

The beans looked quite a bit more even out of first crack than with the unmodded popper. Still a bit uneven in the early stages though.

Next step is to get control of the dc motor and heating element separately. I'm hoping that having the fan up high and the heat low in the early stages will allow for a more even roast.

Edited by PhilDawes
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Following on from the previous post, I've now made the changes to allow the Severin's dc motor (fan) to be controlled separately from the ac heater coil. (Basically you snip the circuit after the rectifier and connect your own dc supply to the pins). This means the heater piece and the motor+fan are completely separate.

Along the way I found out a few things about the Severin and thought I'd write it up.

IMPORTANT: There's a bunch of pictures of extremely dangerous live circuits with cheap equipment here. I have some safeties (RCD plug, rubber gloves, earthed casing on dimmer checked each time), and this is still very dangerous. Please don't copy anything I've done.

So I basically disconnected all the bits and put it together outside the casing. I did this for ease of fiddling and rustic appeal. I mounted it on a bean tin can full of stones for stability, with some holes drilled for airflow to the fan.

no_case_20200510_204504.thumb.jpg.0adb8d1bc545b06bbbb67d7ced6e6250.jpg

The DC fan motor on a Severin is an RS-385SA-2065R. I think this is rated 18v (see the production description tab on this page)

fan_20200510_140034.thumb.jpg.51ed70c59dd866985c85da83d76511bb.jpg

motor-IMG-20200429-WA0005.thumb.jpeg.5d88c882a118a2d59d4ae561ab61af99.jpeg

I found I could jack the motor up to 30v (as high as my cheap bench supply goes) where it draws around 3 amps. According to the spec the stall load at 18v is 5.52 amps, so I'm a bit under that. At this voltage it will easily agitate 100g of greens without assistance, and probably quite a bit more. I should do some experimenting to see how high I can take the bean mass.

I should note I don't have any experience with electric motors - I'm guessing that abusing the voltage like this will cause it to break at some point. Does anybody have opinions/experience of running cheap motors above their rated voltage?

I guess I also might be able to replace the motor with something more powerful.


The thermal fuse below the heating element in the Severin is rated for 240 degrees C (and is behind a card heat shield), so I guess that's why you can use a Severin popper for coffee roasting out of the box without modding it. From reading accounts of other popcorn makers it seems that most have fuses at lower temperatures and these need to be bypassed.

thermal_fuse_20200510_140212.thumb.jpg.f05ca4acffc2fec4193ae26a0f6502bf.jpg

I experimented with connecting the heater wires up to mains AC and found that black + brown cause both heating elements to glow so I snipped the grey wire.

Before:

element_before20200510_173742.thumb.jpg.5f6b8c55cd8018b31ad8c1abaec7182a.jpg

After snipping the grey wire:

element_after_20200510_173831.thumb.jpg.45dbdbc328abb1a352cd65fcd74aca9b.jpg

Heating element out of case:

heating_element_20200510_150359.thumb.jpg.893fff8bf01acefeeb346274cf3119c4.jpg

The elements heat up really fast and hot. I only dared to test this for a couple of seconds without the fan (here's a picture of it at 166v, with the dimmer module from the previous post controlling the ac voltage)

hot_element_20200510_174327.thumb.jpg.1bf1082ec29531ab4a895cb9d2233f55.jpg

After mounting it on the tin can and checking the grounding, I took the unit outside to roast 100g of Colombia Excelso Huila from Redber.

roaster_20200513_100601.thumb.jpg.ab573df23412376118f275e146b0684b.jpg

The outside temp was about 9c today and a bit windy. I started with the fan jacked up to 30v/3a for maximum agitation and the heater at 207v. I then increased the temp of the beans by increasing the heater voltage until it maxed out at 237v about 5 mins in. Unfortunately the roast started stalling so with no more heating power I had to reduce the fan motor to increase the bean mass temp.
I slowly reduced the fan motor in stages until the end of the roast (fan motor is yellow line/right axis in the chart below, bean mass temp is the blue line). I dumped the beans after reaching 214c at 20 mins.

913656303_roast-graph2020-05-13.png.d9748568c2c91632f74591c222c85844.png

The roast was much more even through all the stages than before, but I was suffering from a lack of heat. The popper in its original state was easily able to take the temp up really high with the fan strong even outside (through 2nd crack into burnt roast territory in ~8 mins), so this is a problem with my rig rather than the popper components. I think the main issue is not having the plastic housing to protect from ambient temperature and wind. I could put this back on, or maybe lag the heater and chamber.

The other option might be to increase the input bean mass. I might try this first since there's plenty of fan power to move the greens around.

Anyway, here's a picture of the beans at the end.

beans_20200513_134028.thumb.jpg.5b182796455c0d55fefd32154ddd3544.jpg


 

Edited by PhilDawes
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Hi Wan,

Project definitely not finished yet! 

I quite like it without the white plastic body, but may put it back on for 2 reasons:
 - heat insulation around the chamber
 - It pushes down on the chamber and reduces air leaking out the sides, which is important when I have the fan motor jacked up to 30v. I've currently got the chamber tied on with string to try and do this but it isn't as strong.

Ideally I'd like to increase the batch size - e.g. 200g of beans, so that might require a more powerful motor for the fan. Also once I have manual roasting working well I'm hoping to automate with software + arduino + tc4+.

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Question for the knowledgable:

I'm operating under the illusion that in terms of roast quality, a modified popcorn maker could roast coffee as well as any higher end fluid bed roaster. Assuming:

 - temp probes
 - sufficiently powerful controllable heater
 - sufficiently powerful controllable fan
 - software to control it

is there anything else?

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Excellent thread Phil, thanks for sharing. I am actually attempting pretty much exactly what you have done with a popper I happened to have. Started a thread but never got a chance to get it going. I finally received all the components the other day and spent the morning drilling holes in my project box to fit AC to DC transformer for motor and a SRC voltage regulator for the AC. 

I had a question for you, Did you come across any issues when connecting to the bridge rectifier on the motor from your transformer? I was unsure as to whether to keep the bridge rectifier in place or remove it entirely and connect straight to the + and - poles. Seeing they are designed to cheaply convert low voltage AC to DC how would it work if the input is already DC? 

And secondly, your heating element wiring is slightly different to mine in that my thermostat is on the side of the chamber in series with the live and the large coil. Not sure if I have to bridge the gap between the beginning of small coil and beginning of large coil. The ends of each are connected by the thermal fuse and what appears to be neutral whereas the beginning of the small one is what seems to power the fan motor. Do you get your current through your small coil or is it heating up purely as a result of heat from the large one? 

Thank you!!

 

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Hi Christos,

I bypassed the rectifier (cut the diodes out), but there were also some smoothing capacitors around the motor so I connected my dc supply before these. In the first picture of the fan in my post you can see where I connected the dc wires. Actually the picture after that one in the post shows the fan before I'd made the changes so you can see the rectifier before I snipped it out.

I *think* I'm getting current in the small coil because IIRC it was glowing orange like the larger coil.
(This surprised me to be honest - I was expecting to have to wire them together).

Hope that helps - I'm no expert here and I was mainly following the steps in the instructables post.

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Hi Christos,
I bypassed the rectifier (cut the diodes out), but there were also some smoothing capacitors around the motor so I connected my dc supply before these. In the first picture of the fan in my post you can see where I connected the dc wires. Actually the picture after that one in the post shows the fan before I'd made the changes so you can see the rectifier before I snipped it out.
I *think* I'm getting current in the small coil because IIRC it was glowing orange like the larger coil.
(This surprised me to be honest - I was expecting to have to wire them together).
Hope that helps - I'm no expert here and I was mainly following the steps in the instructables post.
Great! Thank you, and for the instructables link that I'd forgotten about!
The order of your motor photos did throw me off at first, now it makes sense. I finished all the wiring for mine this morning. As I didn't have any smoothing capacitors on my motor PCB I just removed it entirely. Only thing left is to hook up the elements to the SRC and work out which cable to snip and which to join :) I'll update the thread. Really keen to see you finish it off with the Arduino! I'm going to go with the handheld IR until my type K thermocouples arrive so I can connect to artisan

Sent from my SM-G960F using Tapatalk

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@PhilDawes 

" To get to (3) I bought the following which worked out well:

Severin popcorn maker 25 quid

Thermocouple + reader 15 quid

Cheap shitty voltage dimmer 8 quid  "

This is your quote above. 

Can you advise me how i can read my temp without doing heavy modified not like? Just need the probe temp like thermocouple you mentioned it.  I got problem to read the beans temp and can't see the color. All depend on timer and First crack and first crack end.  

Thanks.

 

 

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Hi Wan,

Yes you can measure temperature quite easily with a cheap thermocouple and reader, you can pick them up for under 20 quid with a reader from ebay or amazon.

I drilled a small hole just above the vents in the chamber and threaded the thermocouple in. e.g. like in the instructables post:

https://cdn.instructables.com/FPJ/028K/JW4TKCHR/FPJ028KJW4TKCHR.LARGE.jpg?auto=webp&frame=1&width=1024&height=1024&fit=bounds

If you don't want to do anything to your popcorn maker you could try dangling in a metal probe from a meat thermometer, that might be enough to give you good enough accuracy to predict the time of first crack

Edited by PhilDawes
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  • 3 weeks later...

@PhilDawes

thermometer is done. T1 for heating temp, and T2 for beans temp.

however, by mistake i don’t why blue wire so difficult to remove and suddenly snap off on/off button.  Now, i have to reposition outside till i get replacement. Any idea where i can get button on/off? For sure i will place out side make easy for me For next plan.

here is photo:

 

3497E9B8-0096-4BAD-91B5-02150081B9C5.jpeg

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  • 1 year later...
On 09/05/2020 at 20:56, PhilDawes said:

(I'm pretty new here - sorry if people are getting bored of popcorn modding discussions).
I bought a severin a couple of weeks ago (recommended elsewhere in the forum!) for 25 quid to get back into roasting coffee. Unmodded it roasts ok, though very quick. E.g. First crack was somewhere between 3 and 4 mins. At this sort of rate it is pretty uneven and I had to roast to almost 2nd crack to get something that looked consistent.

I found this instructables piece which gives a lot of detail on controlling it with an arduino and TC4+ shield.  This is quite a lot of work, but I realised you can do this stuff in stages and get something usable / drinkable at each stage:

  1. Unmodified popcorn maker, stopwatch, watch for yellow, listen for cracks
  2. thermocouple in the chamber
  3. dimmer on the AC lead, simultaneously reduce fan+heat in tandem to slow roasting speed
  4. separate the DC motor and AC heating element, control manually
  5. hook up to TC4, artisan, record roasts
  6. PID control etc

To get to (3) I bought the following which worked out well:

Severin popcorn maker 25 quid

Thermocouple + reader 15 quid

Cheap shitty voltage dimmer 8 quid

The cheap voltage dimmer is pretty scary. I made sure the casing was grounded, but I'm still using rubber gloves to move the dial!
It was worth doing though, I was able to get a roast to stretch out to longer using the dimmer to vary the temperature climb.

Redber Colombia Excelso Huila, 100g green, 84g out
Yellowing was about 160c 2 mins in, first crack at 200c 9 mins 30, dumped at 210c 17.5 mins


'bean' temp curve:

curve.png.f4aaed985c34317597c6902d82178e0e.png

 

The beans looked quite a bit more even out of first crack than with the unmodded popper. Still a bit uneven in the early stages though.

Next step is to get control of the dc motor and heating element separately. I'm hoping that having the fan up high and the heat low in the early stages will allow for a more even roast.

HI Phil. 

Awesome stuff, looking to trying this out. Any further updates? 

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