# Pop goes the green bean - Another popcorn popper thread



## christos_geo (Feb 9, 2016)

I finally found a bag of RAVE Colombia Suarez green beans I thought I'd lost (3 years ago 🙄) I bought back then just to mess around with a popcorn popper, but assuming they were long gone the project was abandoned. To my surprise, I found them the other day and what with lock down and sunny weather I through I'd give it a bash 😁

Never done this before but I had read up a fair bit on it. Managed 4 consecutive roasts trying to work out optimal green bean amount which I think may be 100g. I was logging temp using IR thermometer every 30s while constantly mixing beans with chopstick at the early stages but I was getting up to temp way too fast and first crack by 1:30s! Was ending roast around 4:00 - 5:00. Colour wise and roast evenness wise I was fairly content, I was expecting half singed half green to be honest (picture of bean comparison was actually next to some Horsham Rwanda natural beans). Rested them over night, one of the roasts showed oil on surface so went directly in the bin and one was only with 10g so didn't even bother keeping. Cupped the other two though. One was vile, the other one was passable but pretty poor on cooling. Now, besides the amateur lightning fast roasting, these were ancient greens so wasn't expecting miracles.

100g green beans. Ambient temp 25.6°C

00:30 - 105°C

01:00 - 150°C

01:30 - 184 °C (1st crack starts)

02:00 - 212°C

02:30 - 198°C (1st crack ends)

03:00 - 216°C

03:30 - 202°C

04:00 - 220°C

04:30 - 209°C

05:00 - 216°C

05:15 - 86.2g roasted (may have lost a bean or two)

Not sure if the fluctuation in temp is the thermostat kicking in or the bean surface temp the IR happened to hone on. .


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## christos_geo (Feb 9, 2016)

Next step, popcorn popper modification. I know it's been done multiple times but I wanted to play around and maybe learn a thing or two along the way. Bought myself 1kg of Foundry greens to ensure I don't blame the greens + some of the same ones roasted by Foundry for comparison. Opted for Dambi Udo, Guji - Ethiopia natural.

As my electric circuit knowledge is limited, at which point you may be thinking why the heck I'm even considering messing about, I really want to educate myself as I know a lot of you here are gifted in this area.

I must have read every mod blog online but still have questions. I intend to add switch and dimmer control to the primary and secondary coils (no need to have separate) and independent dimmer control of the fan motor.

I understand that AC voltage powers the primary coil which is reduced by the higher resistance of the smaller coil before being converted to DC by the bridge rectifier on the 30V DC motor.

And now some questions.. On element schematic I drew from what I can tell, AC live wire goes via thermal cut-off to point A. Heats up large coil from A-B. From B it goes either through 10A thermal fuse to C connected only to neutral wire, or through small coil to D and in turn to bridge rectifier.

To achieve element control I have purchased a 220 VAC 5000W SCR unit. As I want to have both primary and secondary coils controlled together would I have to add a wire to close the loop? Would you connect D to A or perhaps D to B?

As for the power going to primary coil assuming a coil resistance of 13ohms (value from other blog), what is there in its current configuration to regulate power going through coil? I thought it only draws circa 1100 watts. Waiting on a kill-a-watt any day now to see what the amperage is as the numbers don't stack up..

To achieve fan motor control, I bought a AC 240v - DC 24V 2A switching transformer which I will hook up to a split portion of the mains wires. In series I was going to add a DC 6V 12V 24V reversible motor speed controller regulator and then link to motor. This part I'm finding trickier to get my head around.

Question 1: In unmodified config, the live wire seems to go via on/off switch to thermal cut-off where it splits going either to element or to bridge rectifier. Where does the voltage reduction occur through that path? I don't see any resistors along the way. When fan is on separate circuit is there any need for it to pass through thermal cut-off?

Question 2: Seeing I ordered AC-DC transformer instead of AC-AC step down, is there now any need for the bridge rectifier to be in place? Do I connect straight to the motor +/- poles or still solder to diode bridge? Advantages/Disadvantages?

Question 3: Besides connecting earth wire to metal enclosed transformer and metal chassis, is there any need for earth to be connected anywhere else on fan? There doesn't appear to be any additional earthing in its unmodified state seeing it's all plastic besides to metal chassis by element and on thermal cut-off.

Sorry for the long post and forgive my ignorance but any pointers would be helpful.


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## BlackCatCoffee (Apr 11, 2017)

Ahh that takes me back!

This is how I got interested in coffee roasting stood on my balcony of a flat in Manchester....

I eventually ended up doing a little bit of work on my popcorn machine so I could control the heater and the fan.

I also did a super important mod.......cut up an empty soup tin and stuck it in the top of the popcorn machine to provide a funnel to stop the beans flying out all over the place!

Have fun with it


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## Batian (Oct 23, 2017)

@Hasi


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## christos_geo (Feb 9, 2016)

BlackCatCoffee said:


> Ahh that takes me back!
> This is how I got interested in coffee roasting stood on my balcony of a flat in Manchester....
> I eventually ended up doing a little bit of work on my popcorn machine so I could control the heater and the fan.
> I also did a super important mod.......cut up an empty soup tin and stuck it in the top of the popcorn machine to provide a funnel to stop the beans flying out all over the place!
> Have fun with it


It's just that one more coffee related bug I was hoping not (read, desperately keen) to get bitten by.

Sent from my SM-G960F using Tapatalk


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## christos_geo (Feb 9, 2016)

Had to wait a bit for some of the components but managed to get everything though the post a couple of days ago and made a start. 
Drilled all the holes and dremelled the ports for the on/off switched and dimmers on the project box and started the control box assembly. Made sure every metal surface was grounded and started on popper wiring. 
I decided to remove thermostat as it would cut out and drop temp significantly in its unmoded state. As for motor, I removed the board containing the diode bridge rectifier and power from AC heater and instead connected to a step down AC-DC 24V transformer and voltage regulator. Hooked up directly to poles and it works a treat.

Heating coils are controlled independently through an SCR voltage regulator but here's my conundrum. I can't seem to get both coils to heat up at once. I thought I might have to link the point from where white wire (small coil terminal and black and red coloured wire on diagram) is and was previously sending power to motor to the large coil. Depending on how I link them I either get heat in outer coil or inner coil. 
Question is, is it even possible to get them both to heat up considering the huge difference in their resistance? I measured 60ohms for large and 230ohms for small. Maybe the small one never actually heated up much in its unmoded state and was only in place to accomplish the necessary voltage drop for the motor. 
So, what would be the safest way of finishing off the circuit? Should I just cut off the white wire and only use large heating coil or do you propose an alternative?












































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## christos_geo (Feb 9, 2016)

Unmoded wiring
Clockwise A, B, C, D. 
Only thermal fuse connected to C, no coils.
Black/Red wire is white wire on popper which goes to motor.









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## christos_geo (Feb 9, 2016)

Ok, so here's an update. Messed around trying to get both coils to heat up, turns out it's probably not possible using the same regulator. I toyed with it to the point where I blew it up .... Who needs the small coil anyway.

Put it all together after testing all connections and plugged it into an RCD and wattage meter and off we go. 
Super happy with the level of regulation achieved. Took note of watts which will make it much easier to replicate roasts. 
Roasted 85g of Dambi Udo Guji, Ethiopia natural from foundry and while it took longer it ended up light medium. 
Cupped it 24hrs later and I was shocked that it actually tasted of blaming blueberries! Obviously there were underlying baked notes but actually hitting the intended notes was so rewarding. 
I roasted two more batches today trying alternative heating regimes to prevent stalling, which I'd say were less optimal. I ended up going through 1st crack without the audible cue. I read this could be due to 'baking' the beans in the drying phase which eliminates moisture to the point where there is no momentum for crack. I'll up tomorrow though and compare. I think I need to regulate element to ramp up a bit slower in the first 2 min and then push it a bit harder.

Just waiting for my Mastech to arrive to connect to artisan.

Anyway, this has been an incredibly fun experience that I'd recommend everyone should try. 



















































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## wan (Oct 19, 2016)

christos_geo said:


> View attachment 38380


 @christos_geo do you have ebay item number for this part? can i used this modification for my severin pop corn maker? Thanks.


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## christos_geo (Feb 9, 2016)

wan said:


> @christos_geo do you have ebay item number for this part? can i used this modification for my severin pop corn maker? Thanks.


 Hi @wan

Here you go:

AC-DC transformer. I went for the 24V 2A one which should work fine for your Severin too. However I think your motor is an 18V one vs mine which is 30V, but there is a little screw on the transformer where you can adjust output voltage.

https://www.ebay.co.uk/itm/Power-Supply-AC-DC-24V-Switching-Converters-Lighting-Transformers-General-indoor/392334321381?ssPageName=STRK%3AMEBIDX%3AIT&var=661412179143&_trksid=p2057872.m2749.l2649

This is the regulator and switch I installed in series to the DC transformer. If I was doing the project again I think I would find an AC-DC transformer with regulator inbuilt.

https://www.ebay.co.uk/itm/DC-6V-12V-24V-Reversible-Motor-Speed-Controller-Regulator-Car-Truck-Boat-Drivers/392753305241?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

This is the AC SCR regulator for heater element control

https://www.amazon.co.uk/gp/product/B01LXLU3SD/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

Here is the project box

https://www.amazon.co.uk/gp/product/B00IFEX9U6/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

Here is the RCD

https://www.amazon.co.uk/gp/product/B01JUNR8AW/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

Here is the voltage meter

https://www.amazon.co.uk/gp/product/B07FZZ17ZY/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Here is the AC rocker switch with LED I used as the main power switch

https://www.amazon.co.uk/gp/product/B07438Q5ZZ/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Here is the Mastech MS6514 temp logger with type K thermocouple

https://www.ebay.co.uk/itm/MASTECH-MS6514-Digital-Thermometer-Dual-channel-Temperature-Sensor-USB-Interface/324102303733?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

And some 3 core cabling

https://www.ebay.co.uk/itm/3183Y-13-AMP-Electrical-Cable-Black-Round-Mains-Wire-Flex-1-5mm-3-Core-Per-Metre/283774742659?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649


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## wan (Oct 19, 2016)

@christos_geo Thank very much. I will study this.


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