[Homeroast] variable transformers

miKe mcKoffee mckona at comcast.net
Tue Feb 28 20:51:19 CST 2012

Balderdash! Using the proper tool for the job controlling electric heated
roaster works quite well. However, trying to skimp and use the wrong tool
for the job indeed can result in meltdown. Variable transformer works quite
well "combined" with variable air-flow control, especially with boosted
voltage capability. Used dual variable voltage boosted voltage control split
wired Rosto Roasting for years. Just controlling one or the other is
extremely limiting in what you can do with your roaster.

Another method that works well IF you don't need or want additional power
from boosted voltage is PID (or other method) of pulsing the heater on time.
Or combined with fixed boosted transformer :) Air-flow fan however needs
linear control rather than pulsed.

Slave to the Bean miKe mcKoffee
URL to Rosto mods, FrankenFormer, some recipes etc:

Ultimately the quest for Koffee Nirvana is a solitary path. To know I must
first not know. And in knowing know I know not. Each Personal enlightenment
found exploring the many divergent foot steps of Those who have gone before.

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-----Original Message-----
From: homeroast-bounces at lists.sweetmariascoffee.com
[mailto:homeroast-bounces at lists.sweetmariascoffee.com] On Behalf Of
raymanowen at gmail.com
Sent: Tuesday, February 28, 2012 5:24 PM
To: A list to discuss home coffee roasting. There are rules for this
list,available at http://www.sweetmarias.com/maillistinfo.html
Subject: Re: [Homeroast] variable transformers

KISS- Do Not, rpt, NOT control temperature of a heat process by varying the
power applied to the electric heater. Skipping all the details, just run the
heating device at Full Power- 100%, or whatever you can get with the
available power.

Instead of trying to control temperature by varying the line potential and
heater current, just control the low power drawn by the air mover.(fan
motor)  Low air flow through a heating device or Corvair engine causes the
air stream to get hotter and the engine to cook a couple dozen O-ring oil
seals after the fan belt flips.

SCR, Triac/ diac dimmers are extremely non-linear devices and resistive
heaters respond exponentially to applied potential changes. Kiss temperature
control goodbye.
Persist in old ways; expect new results - suborn Insanity...
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