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Re: Hotplate questions

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  • Harry
    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
      Answers interspersed...

      --- 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
      control over your reflux.

      HTH

      Slainte!
      regards Harry
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