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Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » Building a Coffee Roaster

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1500W Poppers vs. 1200W'ers
joemud	#1 Posted on 03/27/2006 8:19 AM
Newbie Posts: 7 Joined: March 21, 2006	Never had a 1500W popper (like the Poppery I). Do they have a bigger chamber and a bigger fan to give the same results in roasting coffee as a 1200W popper, but able to just roast a bit more beans? About what is the max bean load of each, above which the fan hasn't got the air velocity to swirl the beans from start up? And, is there a device to up the voltage on the fan of either to give it more air velocity (I understand that rigging the fan with a transformer is to reduce the fan rpm, but can a transformer increase the rpm, also?). TIA, jm.


peterz	#2 Posted on 03/27/2006 1:13 PM
1/4 Pounder Posts: 88 Joined: December 27, 2005	I have used both for roasting, and finally settled with a 1500W West Bend P1 until I wanted really larger roasts. You can easily do a half pound roast with a P1. Mine was modified with dual Variacs. The Fan can be oversped and then backed off with this Variac, because most Variacs will boost the voltage, and the fan will easily take 130V. s:2 The heater is infinitely controllable also, although I usually ran it at less than max to avoid scorching the beans. s:3 It is fun, and a challenge to roast this way.. modifying heat and fan to keep the beans from flying out of the roaster s:8 while experimenting with different profilesB) Mike has done quite a bit of experimenting with P1's and has documented thoroughly. s:1 Overall I would say that 1500W is better than 1200W because you can control profiles better with larger amounts roasted. Hope this helps, PeterZ c:3


Mike	#3 Posted on 03/27/2006 2:53 PM
1/2 Pounder Posts: 283 Joined: October 24, 2005	JM, PeterZ has pretty well covered it. Yes, the Poppery 1 and the early Pumper both have larger chambers and can hold about half again more beans than the smaller poppers. And yes, transformers can be used to manipulate the voltage to the fan and the heater element both - a Variac is just a variable transformer. Most variacs, if wired for it, can push 120V power from the wall up to around 138 Volts. One of the things that is really attractive about these larger machines is that they use 120 Volt motors, so wiring a small variac into the circuit to adjust their speed is a pretty straight forward opeation. The smaller poppers use low voltage (20 to 24 volt) motors, they use a tap off of a heating element (wich is just a large resistor) to obtain the power for the fan at that voltage. A method of controlling fan speed with these smaller machines is to power the fan through a small transformer such as is used for door bells etc., you can then supply the small transformer from a light dimmer to get a variable voltage out of the transformer. Mike B)


PaulM	#4 Posted on 03/27/2006 3:14 PM
Newbie Posts: 38 Joined: January 02, 2006	Hi folks, How high do you think you can go with the voltage on the PII type fans? Mine run on a transformer that is delivering 24vac under load (27 with no load - there is obviously a drop somewhere and I can't get rid of it). I have a 2.25 amp variac that will boost 120 to 132 - 10% If I understand variacs correctly I should be able to have the transformer feed the variac and the variac feed the fan (or the other way around if my transformer will be ok accepting 132vac), which would then allow me to get up to 26.4vac under load (29.7 with no load, I suppose). I once gave one of those little fans 88 volts by mistake and let the smoke out. 88 is ridiculously high, but what about 30 or so? Thanks, Paul


Mike	#5 Posted on 03/27/2006 3:35 PM
1/2 Pounder Posts: 283 Joined: October 24, 2005	PaulM, Seems like I've heard of folks running these small fans up to 32 volts. I have no experience with this, so take that into consideration. Another avenue for experimentation is; putting AC through a bridge rectifier produces DC at an increased voltage. Putting some capacitance across the resulting DC smooths it a bit and is generally added. This is the way that quick and dirty, less than absolutely accurate DC power supplies are produced. The resulting DC is usually at a 15% or so increased Voltage. 5 Amp bridge rectifiers are available at Radio Shack for a couple bucks, or in old crapped out computer power supplies (with capacitors) for free. The small motors in these machines are "universal" motors that can be driven by AC or DC. The roatation of most of these motors can be reversed by changing the polarity of the DC provided (the fan is less efficient if run in reverse). So, if a guy controlled the voltage into or out of (either will work) your transformer, and then fed that current through a bridge rectifier you should end up with a voltage that would allow a lot of experimentation. I think I'd try the motor at whatever voltages I wanted to experiment with while the popper was apart - so I could feel the motor for overheating. Food for thought. Mike B) Edited by Mike on 03/27/2006 3:40 PM


PaulM	#6 Posted on 03/27/2006 3:46 PM
Newbie Posts: 38 Joined: January 02, 2006	Thanks Mike, I didn't realize those motors were universal. So I guess the real purpose of the factory diode bridge is not to provide dc but rather to provide a voltage boost and polarity? Paul


Mike	#7 Posted on 03/27/2006 4:01 PM
1/2 Pounder Posts: 283 Joined: October 24, 2005	Paul, Provide DC, voltage boost and polarity all go together. It seems like I've seen small cheap 120 / 28 volt transformers, can't remember exactly where right now. For testing purposes you could just meter the output of the small variac driven from 120 Volt, probably wouldn't be a good long term method. Sooner or later, if it were me, I'd screw up and hit the motor with more than I wanted - - and let the magic smoke out. Although - I've seen some industrial uses of variacs for voltage adjustment that have a mechanical stop which won't allow the variac to be adjusted to a voltage above a pre-determined maximum. Mike B) Edited by Mike on 03/27/2006 4:05 PM


PaulM	#8 Posted on 03/27/2006 4:19 PM
Newbie Posts: 38 Joined: January 02, 2006	Thanks Mike. Quote Mike wrote: For testing purposes you could just meter the output of the small variac driven from 120 Volt, probably wouldn't be a good long term method. Sooner or later, if it were me, I'd screw up and hit the motor with more than I wanted - - and let the magic smoke out. Although - I've seen some industrial uses of variacs for voltage adjustment that have a mechanical stop which won't allow the variac to be adjusted to a voltage above a pre-determined maximum. B) LOL, I am the same way or worse. Last weekend while looking at what kind of noise an SCR controlling my popper heater was adding to the AC to my temp controller, I managed to clamp the oscilloscope ground strap to the variac output, and let not only the smoke but also the light out. Vaporized around 10 windings. If I tried to set up a mechanical stop (on my NEW variac...) I would probably manage to build it out of a conductor, install it so it that contacted both the windings and the grounded aluminum box... ...and let the smoke out.


Mike	#9 Posted on 03/27/2006 4:46 PM
1/2 Pounder Posts: 283 Joined: October 24, 2005	Paul, It seems like keeping the magic smoke in, becomes my major consideration periodically. The following pictures are of a variac that was originally used to power a timing circuit in an X-Ray machine - - important circuit in a biological centered fashion. It employs a mechanical stop to disallow turning the knob to far. The picture doesn't show it to well but the red arrow is pointing at a plastic screw and nut that physically doesn't allow the brush holder to rotate past a given position: The coil taps of the variac (any variac) is the key to how a given amount of knob turning produces the variable voltage. Basically the output is a ratio of the difference between the # of coils between the output wires and the # of coils between the input coils. You want to have one of the two wires from both the input and output circuits hooked to a single tap. If you don't do this the resulting circuits will have the common wire at different potentials and trying to ground the circuits will result in the loss of magic smoke, tripped breakers and general mayhem. And here is an unusual way of providing a variable tap into the coils: Mike B) Edited by Mike on 03/27/2006 4:59 PM


PaulM	#10 Posted on 03/27/2006 5:22 PM
Newbie Posts: 38 Joined: January 02, 2006	Thanks for all the info, Mike. Mine was/is again a Superior 10-C. Looking at your first picture that brush stopper seems to be mounted to a nonconductive plate protecting the windings and the brush from damage. My variac doesn't have anything like that, just windings all the way around and the brush arm exposed at the back mounted only to the knob spindle afaict. I think I would either have to glue something directly to the windings (which seems to me like a bad idea but maybe that would be fine?) or mount something to the box in such a way that a stopping device could project into the brush path without touching the windings. Paul


peterz	#11 Posted on 03/27/2006 6:02 PM
1/4 Pounder Posts: 88 Joined: December 27, 2005	When I set up my Poppery II I used a regular light dimmer to feed a 120V AC to a 27 Volt transformer which fed the motor. B) It worked fine but had no real boost.s:7 If I did it again, I would probably feed the light dimmer to a 35V transformer. :@ The AC is converted to DC on the diode bridge built onto the motor. s:6 The motor runs on DC, but not sure how much it will handle before it blows. s:4s:3 Poppery II's are relatively common and inexpensive in yard sales and thrift stores. Please do not try this on your ONLY roaster.s:3


PaulM	#12 Posted on 03/27/2006 7:24 PM
Newbie Posts: 38 Joined: January 02, 2006	Thanks for the info Peter. Fortunately (?) I have a number of PIIs and PII clones in the garage, I buy them whenever I find them because I tend to kill them due to both overstressing them and doing stupid things. I keep looking for a PI or original pumper and will probably pack the PIIs away when I find one, but for now I refuse to pay ebay prices. Probably irrational, but I just know that as soon as I buy one for $40 I will find 3 of them locally for 5 bucks each... Paul


Mike	#13 Posted on 03/27/2006 7:40 PM
1/2 Pounder Posts: 283 Joined: October 24, 2005	Paul, The Variac is upside down in the picture and the metal plate that has the plastic screw in it is the rotating piece that the brush assembly is attached to - - better view of the plastic screw is in the last picture. >mount something to the box in such a way that a stopping device could project into the brush path without touching the windings< The small variacs such as yours (same as I use for fan control on my P1) don't have all the extra structural components. If I were going to persue this course of action, I would think in terms of a slotted dial on the front of the box with a screw into the box to disallow twisting it past a certain point, or something similar. Don't take chances with the small variac - when you find a P1, You'll need it for fan control - works great. I had to buy an EBay P1 recently to build a roaster for a friend. It's disgusting to pay $30 + S&H. Someone scored one the following day for $15 (my normal run of luck). Mike B) Edited by Mike on 03/27/2006 8:35 PM


peterz	#14 Posted on 03/27/2006 8:31 PM
1/4 Pounder Posts: 88 Joined: December 27, 2005	"I buy them whenever I find them because I tend to kill them due to both overstressing them and doing stupid things." Yup, I found it was easy to plug that little motor into 120V AC:( Talk about letting the smoke out!!s:6 s:8s:8 c:3 PeterZ


PaulM	#15 Posted on 03/27/2006 8:35 PM
Newbie Posts: 38 Joined: January 02, 2006	Hi Mike, Oh, I see, thanks for explaining that. I like your idea of working from the dial side very much. Can't remember if the dial spindle has a registration flat or if it is round, but either way I can imagine fashioning something that should work. Bigger variac would be nice, but my roaster box already contains a 1/4 din controller, that transformer, a big honkin' phase angle fired SCR/heatsink assembly, and various fuseholders, switches and connectors. Chose the variac in part based on weight, size and ease of panel mounting. Don't want a 20 pound roaster control box... Thanks again, Paul


PaulM	#16 Posted on 03/27/2006 8:39 PM
Newbie Posts: 38 Joined: January 02, 2006	Quote peterz wrote: I found it was easy to plug that little motor into 120V AC:( Talk about letting the smoke out!!s:6 s:8s:8 c:3 And even if you can catch the smoke in time and get it back in there, the "magic light" is gone forever. Had never heard of the magic light before, but now I know! ;-) Paul


Mike	#17 Posted on 03/28/2006 1:46 AM
1/2 Pounder Posts: 283 Joined: October 24, 2005	Paul, If you did some judicious designing with the small variac. It would do away with the need for the transformer. It'd free up a little room in the control box. Even the considerably large P1 fan only draws about 1 Amp when driven by 138 Volts, so the little variac is the bees knees for the fan application. A bigger one would just be weight. Mike B) Edited by Mike on 03/28/2006 2:03 AM


PaulM	#18 Posted on 03/28/2006 11:45 AM
Newbie Posts: 38 Joined: January 02, 2006	I'll try to accomplish that, thanks. Unfortunately I still need 24vac for the scr circuitry, but could use a much smaller transformer just for that. Paul


Mike	#19 Posted on 03/28/2006 1:48 PM
1/2 Pounder Posts: 283 Joined: October 24, 2005	Your SCR setup is intrigueing. Explanation? Schematic? Mike B)


PaulM	#20 Posted on 03/28/2006 4:25 PM
Newbie Posts: 38 Joined: January 02, 2006	Hi Mike, Let me say right up front that what I'm doing may turn out to be a complete waste of time. I was roasting with a small omega controller (cn4220 I think) with my pII and clones and was getting pretty good results. But I was surprised at some of the variations I was getting from roast to roast using same profile, same amounts of same beans, etc. I started to wonder whether the 1 second duty cycle on my SSR was too slow. Jim Schulman and others have said that they don't think switching faster than 1 second would have any effect because the changes would get lost in the "heat capacitance" of the PI. But my PIIs don't have the ceramic disc or overall thermal mass of the PI. And since many attribute the PI's superiority as a roaster to its ability to "smooth" roasts, it seemed to me that the PIIs must not be as smooth, and maybe faster switching would help them. Again, I don't know if this is true, I am just trying to see if faster switching would give me more repeatability. I lucked into a more advanced controller on ebay for $45, the CN3000: http://www.omega....CN3000.pdf It has an astonishing amount of functionality including dual universal inputs, ability to store up to 8 different pid sets and 99 profiles of 99 steps each, ability to call up different pid sets at different places in the profiles, onscreen datalogging and graphing (has a dot matrix display). Also mine came with a scalable analog output capable of outputting 4-20ma or 0-10vdc, or any range in between, user selectable. But I didn't have a device to accept the analog output. My brother is an EE and designed a simple circuit using timer and comparator ICs and some misc. caps and resistors that would convert an analog signal into a user-definable duty cycle. I assembled it on perfboard with the idea that I would set it for a 12hz duty cycle, as that is the sample rate of the controller. Seemed efficient to me. Well, to make a long story short the circuit oscillated at any rate I wanted (using a 15 turn 10k pot) between 9 and 15hz,and drove the SSR perfectly, but switching the SSR at those speeds created so much noise on the circuit that it caused my controller to periodically reset itself. At first I had assumed that the problem was a noticeable voltage drop, which is why I bought that first variac, but that didn't help. Oscilloscope then confirmed significant noise. I may try to fix that someday, but in the meantime I replaced the homebrew circuit and the SSR with this phase angle fired SCR: http://www.ccipow.../details/7 Could not believe I picked one up for $20 on ebay. Mine is 40 amp and I am drawing 10 or so, so the heatsink may not be necessary - dissipates 12 watts - but I'll leave it as is. Wiring is simple: 0-10vdc signal from controller to SCR, 24vac source (the transformer) to provide power for SCR circuitry, heater power to output. Just like an SSR except for the transformer. So does it work? I don't know yet. Latest obstacle has been fine tuning PID settings, but I'm honing in on what I want. It's been great fun though! Paul Edited by PaulM on 03/28/2006 4:36 PM


Mike	#21 Posted on 03/28/2006 6:42 PM
1/2 Pounder Posts: 283 Joined: October 24, 2005	Paul, I've got a series EP1 Phasetronics SCR unit that looks to have a similar feature set. I agree with your appraisal of the advantages of the SCR for the P1, after all the measuring and manipulation (hot air side and bean side) that I could throw at it with both an SSR and the SCR - - I didn't see a benefit, especially considering the 7 times multiple in cost. The SCR units are a neat machine - other projects will arise. ;) With the P2 and clones that have considerably less heat sink and resultant smoothing engineered into the machines - - there may, indeed, be a benefit. I'll be interested in following your analysis. Mike B)


PaulM	#22 Posted on 03/28/2006 7:08 PM
Newbie Posts: 38 Joined: January 02, 2006	Sorry if this posts twice, had some problems posting. Quote Mike wrote: The SCR units are a neat machine - other projects will arise. ;) If nothing else I could add a $3 potentiometer and have a 0-97% 40 amp variac, for $23. Agree they are really neat devices! One nice thing about this arrangement is that it frees up my SSR for service powering the heating coils in my espresso machine. Quote Mike wrote: With the P2 and clones that have considerably less heat sink and resultant smoothing engineered into the machines - - there may, indeed, be a benefit. I'll be interested in following your analysis. If I get any useful results I'll certainly post them here!


joemud	#23 Posted on 03/29/2006 10:30 AM
Newbie Posts: 7 Joined: March 21, 2006	Thanks, doods. I got my answer and lots more that I enjoyed and perhaps might get into should I ever hook up with a P1. Right now, I got sugarplums of a jerryrigged killer controlled heatgun, barrel plumbed, via. PVC or tin pipe to a bottom screened tin can roast chamber, all dancin' in mah head! Gonna temp. sample the beans with an ILT. Even rethinking the bottom screened tin can roast chamber with a swap to a fabricated louver swirled roast chamber in the poppery fashion. Any light bulbs lighting above anybody's head?

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