## Re: Hotplate questions

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• Answers interspersed... ... provide constant temperature to the still or will it work as-is with it s own thermocouple temp control? ... disrupts the reflux.
Message 1 of 3 , Jan 18, 2004

--- In new_distillers@yahoogroups.com, schwarzenduder
<schwarzenduder@y...> wrote:
> 1) For a reflux still, do you need to modify the hotplate to
provide "constant temperature" to the still or will it work as-is
with it's own thermocouple temp control?

>>>>>>> Yes. Modify it. A thermocouple switches on-off-on-off and
disrupts the reflux.

>
> 2) A 1000 watt hotplate operates at 1000 watts for intermittant
periods of time depending on the maximum temperature reached at the
hotplate thermocouple, at which time the thermocouple opens until
the plate cools below maximum temp. What is the maximum constant
wattage that can be applied to a 1000 watt hotplate without doing
damage to the coil?

>>>>>>>> You don't apply wattage. You apply voltage. Wattage is a
measure of the amount of work an element is capable of doing. In
comparison to horsepower, 746 watts = 1 hp. Voltage is a measure of
the pressure applied to a circuit. Amperage (amps) is a measure of
the current, or the amount of electricity flowing past any given
point in the circuit. Ohms is a measure of the circuit's resistance
to the current flow.
If you apply more pressure (voltage) you increase the current
(amps), without increasing the resistance (ohms). Therefore you can
overstep the coil's work rating (watts) and burst it. Think of it
all as water flowing in a garden hose. Too much pressure and you
blow the hose and/or connections.

>
> I have a big 15 amp variac (variable output transformer) which can
control AC output from 0 to 120 volts. In experiments with a 5
gallon pot of water, the thermocouple on the hotplate still will
open even with the AC input as low as 90 volts. At this time the
coil is only drawing 5 amps, this equals only 450 watts. This seems
to be too low of a setting to maintain temperature. I am reluctant
to disable the thermocouple. Should I?

Yes. For the reasons I said above. The variac will give you fine