Sunday, January 2, 2011

Completing Hiro's journey - Poppery II mod

Modifying Poppery II for coffee roasting

Full props go out to Hiroyuki Okamoto for his original site: Modifying Poppery II for coffee roasting

I recently won a West Bend Poppery II Air popcorn popper on eBay.  This is known as a DIY Hot Air coffee roaster.  The Poppery II can roast coffee straight away  without any modification. But if you have a bit of skills to modify it, it's relatively easy to make a few mods that allows you to control the temperature and roast speed. has a nice article How-To: Make a popcorn popper coffee roaster which has lots of pics.  The site has a very informative thread called Help with PII wiring .
Garybt3's blog site has an excellent article 7 steps to hot rodding a Popcorn Pumper . The Pumper is another model made by West Bend that has virtually the same innards as our PopperyII.  
There's a good instructable listed at, too.

The hot air popper that makes such good popcorn also works extremely well for small batch roasting of your favorite coffee beans.  The chamber is like this.

Bought all these tools at Ace Hardware and at Radio Shack.

Parts List:

  • Hot air popcorn popper (West Bend Poppery, Poppery II, Pumper or recent clones )
  • Four gang plastic electrical box
  • Two hole switch cover
  • One gang blank cover (no openings in it)
  • A Continuously Variable wall dimmer  (Lutron or Levitron brands found at Home Depot)
  • Light switch
  • Two computer power cables, or one fifteen foot extension cord. Recommend 16 gauge wire.
  • Radio Shack  Model: 273-1512 Transformer or similar (25.2V Center tap 2.0A.) 
  • Electrical tape or heat shrink tubing
  • Soldering iron or twist on wiring nuts.
  • Green coffee beans

Detach black lid by removing 3 screws, also squeeze restainer and pry it out.

The bottom of the chanber. There is a motor attached on it.

Take a look at the top of the motor briefly.  Notice the four diodes in a rectifier bridge on top of that connect to the motor contacts.  This rectifier bridge converts the AC power to the DC power required by the DC powered motor installed in this unit.  This in the second major difference in the Poppery II model from the original Poppery.

The motor. The label says "MODEL HR 355OU 20.5 VOC 1.78 A MAX"

Remove the 3 screws.

Open the lid with the motor.

Remove 2 rings.  HINT:  Make special note of where these rings go and connect.
There is a quiz coming in an hour or so after when you ready to put this all back together!!

the heater section.

The primary heater coil is stretched around the outer circumference of the sandwhich of two fireproof disks and connects from point A to point B.

The secondary heater coil is stretched around the INNER circumference of the sandwhich  and connects from point C to point D.
The thermal protection switch connects point B to point D.
And the thermal fuse is connected between point D and point E.

the whole deassembled popper now looks like this.

This side view shows the heat coil in the head section. If you look closely you can see the primary on the outer edge and the thin secondary coil inside through the slots.

The bottom of the aluminum chamber. The hot air enters from the sides, allowing the beans to heat evenly and rotate.

The top of the aluminum chamber.

Remove the wire connector.  In my PopperyII there were three sets of wires crimped together.

Remove the tiny metal from the thermostat to disable the thermostat. Take a small precision flat head screwdriver and lift the left end of the center copper strip and remove the shiny silver disk inside (it's the small football shaped metal piece on the tablecloth).

NOTE: The following is for INFORMATIONAL PURPOSES ONLY, it is not a recommended mod to your popper as it defeats both thermal safety mechanisms.
This popcorn popper is designed to operate at approximately 300 degrees F to pop popcorn.
Coffee is roasted when the beans' temperature rises to 435-450 degrees F.  The roaster may not roast properly with these safety mechanisms in-place.

 On my popper, I used a small precision flathead screwdriver to uncoil the leads of the thermal fuse from both rivets.  I them added the GREEN wire shown in the picture above and soldered the wire after wrapping the twisted strands around and under the rivet.
There is no need to remove the thermal safety switch once the bimetallic strip is removed (as shown in the previous picture).  The remaining black wire is no longer used and should be clipped once you get all the wires joined.

This is a simplified schematic of the stock PopperyII.   Most poppers are built with two heating coils. One  is used to reduce the voltage powering the fan motor. Sometimes one of the coils has failed, so test the popper to make sure it gets hot enough to pop popcorn. If the test resulted in a nice snack, it's probably in full working order.    Updated 8/9/2013 thanks to a catch by Dale.


Here's a new schematic and a wiring diagram for this mod to separate the control of the heater coils and fan.
When the project is done, the popper will have two separate circuits. The dimmer will be used to control  the fan, while the switch will turn the heating coils on and off. 

Radio shack sells a couple of 25.2 volt center tap transformers. Make sure to get the 2.0 Amp version. If you pick up the 450ma version, the fan on the popper won't go fast enough (and the transformer will get pretty warm). Get an four gang plastic electrical box to mount the switch, dimmer, and transformer in.

I included an optional Router Speed Controller in the electrical schematic.  I'm told they can sometimes be found on-sale at Harbor Freight.  I notice them listed on EBAY for ~$30.00 with free shipping.  The Router Speed Controller is a low cost way to get some control over the power to the heating coils - perhaps better control than turning the power switch on and off.

With the green wire added to the heating coil as described above, you're ready to reassemble the motor and heating coil assembly onto the aluminum housing.  I missed a couple picture opportunities but here's where the TEST comes in to play.

Once assembled, connect the white (primary coil) and red (secondary) together with one of the original cord's leads. The green return wire is connected to the other black lead from the original power cord.   (NOTE: I used green only because it was handy -- this is NOT a green ground wire.)

In this picture you can see the white extension cord wiring coming up out of the popper's plastic shell (threaded through the same hole as the black power cord..  This wire will power the fan motor in our new circuit.  The two wires on the top of the fan motor are connected in twist caps to the new white power cord.

There are a couple of wire to wire connections. You can twist these together  and use wiring nuts, or solder them and insulate them with electrical tape or quality heat shrink tubing.
You may notice a knot in the new white power cord which should act as a strain relief.

Mount the switch, dimmer, and transformer into your four gang box.

You need four total or two pair of wires from the popper to the control box, and a pair of wires leading to a power plug. The 16 gauge extension cord I used had a three prong plug - meaning it included a ground wire. Keep in mind that green is used for a safety ground in AC wiring. If you're using a cord with a three prong plug on it as I did, the other two will be the 'hot' wires.

NOTE TO SELF: correct your wiring diagram as you used green for the power wire, dummy.

One of the hot leads will connect to one pole of the switch and the dimmer. The other will connect to one lead from the heating coil in the popper and a primary wire to the transformer. The other pole of the switch connects to the second lead to the popper's heating element. The other wire of the dimmer will connect to the other primary lead of the transformer. Finally, the two outer yellow leads are connected to the other pair of wires to the popper. Those two will be connected to the fan motor.

Switch of the left control the heating coils. The center switch is a continuously variable dimmer with an on-off switch. I mounted the transformer on the right; there's no magic to this order so feel free to be creative if you're so moved.

Here's the completed wired project. I attach a one (1) two gang light switch cover and one (1) blank cover to finish it off.

I plan to check a couple nearby thrift stores to search for glass oil lamp thingies to act as the chimney for this roaster. The chimney prevents the roasting beans from being blown out of the roaster as the original popcorn design encouraged.  Right now I have a Hormel chili can duct-taped on top of the black top plastic piece.

Here's an additional mod recommended by Garybt3 on his site 7 steps to hot rodding a Popcorn Pumper.
Gary's idea is to enlarge the hot air slits you see in the bottom of the aluminum chamber.  His technique doesn't work easily on the PopperyII as the aluminum shroud comes down more and you cannot enlarge the "scoops" from the underside.

So here you'll see two indentations made by the edge of a long screwdriver as I pushed the soft aluminum at the top and bottom to achieve the desired enlargement of the scoop.  Do it all the way around for every opening.

It's a bit hard to see in this picture from underneath as the flash didn't catch it, but you can make out the bumps of the new "air scoops" and you can see light through at least one of them.

I have not seen anyone else discuss this "air scoop" mod so I believe credit goes exclusively to Garybt3.

I'll add a picture when I find and install a glass chimney.

If you care to send thanks, please consider sending green KONA coffee beans.

Key words: coffee roasting guide how-to West Bend Poppery PopperyII Poppery2 West bend Pumper hot air popcorn popper continuously variable dimmer 25.2v transformer


  1. So what is the main advantage of adding the transformer and separate fan control / dimmer switch?

    It seems others are having success without this mod, i am just wondering if it is really worth it?

    1. Adrian:
      The transformer reduces 120v house current to 25v to run the motor element.

    2. The dimmer switch is to provide variable control of how strong the motor runs/ fan blows. It’s not absolutely n3cessary as you state , just makes things more controllable.

  2. You can do more beans with more cfm, and you can control the temps very effectively by controlling how much air flows how quickly over the heating coils. More air per minute equals cooler air. Slow it it down, it's hotter. As beans roast they become less dense, requiring slower flow. Handy -- since you need higher temp air later in the roast anyway. Tilt the roaster to get nice fluidization.

    In a Wearever 1400W model I can start with 10 oz. of greens, ensuring a half pound roast. Try that in a unit with no boost to the fan! ;-)

    1. Do you find that the Wearever is better than the Poppery 2? it looks I can get a decent deal around $40 on a Wearever 1400 watt on ebay or get a local Poppery 2 for $20. What would you do? The wearever can do more beans?

  3. Adrian: RASQUAL answered your question very completely before I could. I hope it makes sense.

  4. I love this mod! I went one step further and wired the two heating elements on different switches. I can individually control the heating power. I was finding once I reached first crack the popcorn popper was to hot and second crack came to fast.

    I have been told the heating elements can be controlled by a continuously variable dimmer too.

    Thanks for the mod!!

    1. I know it's been years, but do you have a sketch of how you wired everything to separate the 2 heating elements? I'm having the exact same problem. Thanks!

  5. It appears that the initial schematic has an error in it. You said that your "point D" connected to the "secondary heater", but "point D" is between the "Fuse" and the "Thermostat". In the schematic, there is no connection from the point between the fuse and thermostat to the secondary heater!
    Please advise.

    1. I see your point referring to the "simplified stock PopperyII schematic. I'll update it.

  6. Transformers can also be purchased at thrift stores for $1-5 ea. Look for printer, laptop, or battery charger adapters with the correct Voltage and Amperage.

  7. Tip: If you join Harbor Freight's email newsletter you'll receive discount coupons monthly. I used the Christmas Holiday "50% off single item" coupon to buy a Router Speed Controller for about $15.00.

  8. Jim,

    I roasted coffee on my poppery for like 3-4 years before completing this mod. After I finished, I attempted to roast 2/3 cup, and the beans aren't even beginning to turn color.

    I tried roasting with very little fan power, a lot of fan power, etc... (I tried a lot of different things) and I can't seem to get the damn thing hot enough :)

    Any ideas? The wires from the outlet are probably 4 feet or so (longer than the original model). I'm just not sure what the issue could be, and am hoping for some ideas.


  9. why is nichrome used in heating coils?

    1. Heats repeatedly without melting.
      "The important factors are its high electrical resistivity, its high temperature corrosion resistance and high melting temperature of 1400 degrees c."

  10. You got a really useful blog I have been here reading for about half an hour. I am a newbie and your post is valuable for me.
    e nail dabber

    1. dabber: Check out the forums over at on popcorn poppers. There's a wealth of information and the knowledgeable users there will gladly answer questions and offer tips.

  11. What a fantastic mod. I just completed it yesterday but I am wondering what I should do with the green ground wire on the light switch and dimmer as well as the other wire on the transformer. The electrical cords I used don't have a grounding prong. Should I just terminate these wires?

  12. Sweet Maria's offer a great selection. Be careful, a little goes a long way, surprisingly.

  13. Great mod. Works like a champ, but, I can already see the need to change the on/off switch on the heater to a variable control. Continuously turning the switch off and on to control the heat is a bit of a pain, but it's a great start. Looking forward to playing with different profiles. Thanks for the guide.

  14. Thank you for illustrating this modification so well. I'm wondering if a similar mod could be done on a 1250 watt Wearever Popcorn Pumper. However, instead of using a transformer, could a 24V / 2A AC adapter connected to a PWM speed controller be used to power the fan? Thanks.

  15. J: I’m not an electrician so know that. The 24v/2A AC adapter might work as they have internal transformer circuitry, right, they take 120v IN, and provide 24v out. And that’s close to my transformer voltage. I don’t know how to evaluate the 2A rating. I guess the worse you’d do is smoke it/melt it down! I feel confident the PWM would work, I use one in another hobby to control voltage for heater element. $12 buys a robust Chinese one on eBAY.

    1. Thanks for such a quick response Jim. I am not an electrician either, but believe your description of the adapter is correct. I'm considering the use of an adapter because it is more readily accessible to me than a transformer. Also, thanks for the recommendation on the PWM. I may give this a try.

  16. The first hurdle with my poppery II is getting the 3 small nuts off. Seems like the manufacturer purposely made it difficult to access the heads of the nuts. I could not get any of my small sockets to grab. any suggestions? Just looking to disable the thermostat as far as mods go. Thanks for posting

  17. They are not nuts, they are rivets. I used the smallest screwdriver I couldFind to on pry the leads of the thermal fuse from under the rivets. I then installed the Green bypass wire back to the same rivet post.
    You could easily simply snip the leads of the thermal fuse but I thought it was neater To simply install the green wire to the same rivet head.
    Does that make sense?

    Also be sure to re-read the text and make sure that you’ve taken the little fusabke link piece called a silver disc out from between the leads of the thermal switch in the diagram.

  18. Thanks for the response. I have not figured out how to get inside the unit yet. I am referring to the three screws that hold the top and bottom of the outer shell together. I can't get a socket on them. The screws are in a concaved recession, which makes it a challenge. I don't remember how to post a picture, but I will email you one just to be clear.

  19. Hi.
    My pop corn popper is not working.
    I have noticed it heats but the noise and air flow has decreased a lot. Any idea what´s going on?

  20. How did you connect the coils to the 240VAC? From your wiring it appears that the inner coil is in fact not connected. If you connect them in parallel, the small one will snap as it cannot take that much voltage. I done that.

    So, you are saying that you connected the green at one end of 240VAC, and white and red together at the other end of 240VAC?

    1. This mod uses standard 110v house current to power the heating coils. The 110v is reduced to 25.2v by the transformer to power the diode bridge for the DC fan motor.

      There is no 240v anywhere in this project.

  21. My WestBend Poppery II acquired many years ago and modified with a thermometer via instructions at, has worked wonderfully without further mods, except: the overheat thermostat began kicking off at around 425º F. as measured by the thermometer. Solution: dismantled the popper until thermostat was exposed and bent the bimetallic strips to tighten the connection. This has worked fine so far. However, the fuse in the circuit finally gave out yesterday. Thanks to the circuit layout Jim has provided here, I was able to take an ohmmeter and narrow down the culprit to the burnt out fuse. Once cut out and replaced with a piece of insulated copper heavy gauge wire, all running good again. Thanks, Jim! Oh yeah, because I’ve not modified control of heat and fan, my 2/3 cup of green beans, depending on sieve size, might have a tendency to roast quite unevenly. It takes only 6 minutes to roast without the mods to control roasting rate. However, shaking the popper up and down during the roasting period has circumvented that problem.

    1. Thanks Steve. Your real-world usage experience is very helpful to new roasters.