maxine in ri > wrote:

>OK all you home-handypersons, mechanical geniuses and electrical
>wiring experts, have i got a question for you!
>
>I got a new yogurt maker at a yard sale (lady had a failed
>kitchen store business, it was brand new in the box sealed
>etc.) First batch came out grainy (probably my fault)
>so I made the second batch under closer observation.
>
>Finished product was just over 130 degrees, which is
>the high end for yogurt cultures.
>
>Is there some way i can build a temperature control into
>the electric wire to reduce the temperature, or do I need
>to count this up to the usual yard sale failure?
>
>maxine in ri, soldering iron at the ready

Sure. Although the classy way would be to use a rheostat or variable
autotransformer, but can guesstimate the value (in ohms) of
a fixed resistor to wire in series with the unit as follows:

R = ((130 - T)/(T - 70)) * (14400 / W)

where W is the actual wattage of the unit (which is probably a value
somewhat lower than its rated wattage), 130 is the observed
temperature now, 70 is the ambient temperature, T is the desired
temperature, and 14400 is the square of the line voltage.

So for example, let's say the unit is rated at 100 watts. Probably,
it consumes 90 watts, and you want the temperature to be 120
instead. In this case you need a 32 ohm series resistor. It better
be rated at 15 watts or more (in this example).

(Of course don't do this unless you're confident you can do
a safe job of wiring it up and insulating it and protecting
it from any mechanical trauma. Having a second person check your
work is always a good idea. Etc.)

Steve