[Homeroast] Roast not done?

Martin Maney maney at two14.net
Fri Feb 12 16:52:21 CST 2010

On Thu, Feb 11, 2010 at 09:08:38PM -0700, raymanowen at gmail.com wrote:
> Of course, they run differently. Different US homes have 110v-115v-120v-125v
> "standard" power. The heating power generated in the machine varies
> exponentially with the power supply voltage. The power and ultimate heat
> available vary wildly.

I'm sorry, I am compelled to pick this nit.  The power will vary as the
square of the voltage, not an exponential.  That would still be about a
30% change from 110 to 125, which is enough to make results vary

> With a more powerful heater and PID temperature control, the operational
> problems would diminish. So would the $300 price tag, and the tyranny of
> numbers [of components] could escalate problems.

It shouldn't cost much (in terms of per-unit costs) to implement the
PID logic in the microcontroller, but for that to work it needs both
more responsive sensors than it has (or maybe the problem is more one
of just what's being measured) as well as possibly a substantial change
in the high power control parts.  At that point it seems silly not to
be measuring the actual bean mass temperature, which means getting a
sensor inside the drum, which may mean a complete redesign.  Yeah, the
price would have to go... ;-)

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