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funny poppery behavior
Hi folks,

I'm roasting with a Poppery I with the heat controlled by PID and the fan controlled by variac.

Without futzing with the variac I have plenty of heat to get to second crack and beyond. I have not modified the thermostat.

My thermocouple is located in the "Uber Popper" position. During a couple of roasts recently I find I get up to about 434F and the heat starts cycling on and off. Frustrating because it is within 2-4 degrees of when I like to stop the roast. Usually by this point I have cut the fan voltage by about 10% to keep the bean agitation relatively low and, so I thought, to ease the burden on the heater.

But now I'm wondering if by lowering the fan speed I am actually causing the poppery internals to heat up to the point where the thermostat starts to cycle. I see logic in this but haven't seen it discussed (sorry if I missed it).

Does this make sense? If so, if the heater can maintain the profile even with a really wild bean agitation near the end of the roast, is there any reason to reduce fan speed?

Any advice appreciated.

Hi Paul,
My first long endeavor into home roasting was when I got a P1 (Finally). I wrung that beast to its limits and beyond, but then I wanted to roast MORE :@s:6
Back then my setup included a 25 Amp Variac for the blower and a smaller Variac for the heater. I would work the blower so the beans would agitate well and not fly out of the chamber.s:3

And the heater so the temperature would climb as slow as I wanted it to. s:2s:2

Heat was never a problem. B)
The heater was more than adequate and I seldom ran it at full power.Shock
The Variac was used to throttle it back after the initial startup.s:1

IMHO you must bypass the thermostat. B)
This is the culprit causing you grief.s:8s:8
Even though it looks solidly made, it has been my experience that they are never adjusted the same from unit to unit, they cut out too quickly.....
and they really are annoying s:6
Run a wire around it s:2B)

With my feeble efforts I could not make the P1 roast a pound evenly.
When I finally found what I thought was a large enough chamber to hold a roasted pound, the blower was not strong enough to circulate that amount. :(:(

I bet Mike will make it happen though B)s:2s:2s:2s:1s:1
Edited by peterz on 06/16/2006 9:59 PM
Peter, ....Was that a challenge? ;)


From personal experience and from information supplied by several other roasters. Thermostat - - wire around it or remove it. There are a couple of suggestions in one of the Poppery modification threads. I think what happens is: the thermostate never gets exercised as a popcorn popper, but as a roaster you are right near the set point and the temp it cycles at drifts lower as it is used.

If everything else...SSR is OK and the PID is showing that it isn't cycling the heater for you, then - thermostat.

You either have one whose set point is:
way high and you never have a problem,
too low - has to be fixed immediately,
or - the set point drifts lower with use...which is the problem I had.

If you find that it is something else - - be sure to let me know so I can add your discovery to one of the articles.

Peter and Mike,

Thanks! I was reluctant to break the darned thing open again but will do as you suggest.

One question: what kind of solder would you use? I have bypassed the thermostat on PIIs and had the solder fail due to the heat. Once I had pieces of solder actually fall back into the fan after it melted. Disaster.

Do you use anything special? Is lead-based solder a problem?

Thanks again,

check this thread--- http://homeroaste...ead_id=269


If you will look at picture P1 2-14 you will see the little white nub on the right hand side being pushed up by the bi-metal strip. On some of the thermostats this is ceramic and can just be pulverized with a pair of needle nosed pliers - - or removed with a little more difficulty if it is a different thermostat. Without this nub the bi-metal strip can move all it wants and will not change the position of the points.

What I do is to completely remove the thermostat. A little later in that same article you can check out pictures P1 2-20,21 and 22. If you decide to do it this way you don't have to do any soldering Grin . I've tried to give pretty good directions on how to do this modification in the article. If you need any further clarification, send me a PM as well as posting here (the PM generates an email - which may get my attention a little quicker).

Edited by Mike on 06/16/2006 11:47 PM
Thanks again Mike,

But keep in mind that my popper maintains temp over the whole roasting range UNTIL I start cutting the air supply via variac, then it starts to fail

Particularly curious about whether Variac produces any difference in the cup in the case where heater can keep up with profile without the need to reduce airflow, even through second crack.

Another thing I noticed about roasting with a P1 was the large temperature diffeneces in different spots within the bean mass. s:4s:4

My TC was in a thin copper tube, and I could move it to different areas easily by hand during roasting. B)

Perhaps slowing down the air flow changes the position of these hot spots in relation to the TC so that the PID thinks it is overall hotter than it is. :|

I am not sure where your TC is placed, but I finally positioned mine so it gave me a reading that looked like what the beans were at. B)s:2
Really, I knew they were not at 800F,s:8s:8s:8

also I knew they were not at 300 when first crack was happening.s:7

It is just a reference anyway so you can get an idea of a profile to repeat. :)

I suspect the only way you will ever get an even input air temperature is to provide some sort of mixing chamber for the hot air afer it leaves the red hot heater coil, and before it gets into the roasting chamber.

Otherwise you will always have severe gradients.c:1s:8

Some of the air passes right by a glowing piece of heater and goes right to a bean, s:3

other pieces of air hit the wall and bounce around before going through the slot into the bean mass.Shock

No Mike, not a challenge..
A vote of confidence s:1s:1s:2s:2

PeterZ c:3

Having the problem with the thermostat when you slow the air flow is to be expected. Have you noticed that you get a short term temperature increase (bounce) when you cut the fan speed? Less air flow + the same heat input from the heater and thermal mass of the roaster = hotter air (especially in the area of the thermostat - well before the TC). Remember that little hole in the ceramic heater assembly relieves hot air (before it reaches the roast chamber) directly at the bi-metal leaf of the thermostat.


With a longer glass chimney, I have roasted up to 400 gms in the Ubber Popper. The limitation ends up being not enough heat to keep up with my profile in the 300? to 400? range. If I slow the fan enough to keep up with the heat up rate in that range, I start to get tipping because the beans aren't moving fast enough through the hot part of the roast chamber.


My feel for the difference in the cup from changes in air flow is that more air makes the cup a bit 'brighter' less air makes the cup more like a drum roast. The problem with my appraisal is: it could just be between my ears! ;)

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