Lower heating coil temp in dehydrator

Discussion in 'The Projects Forum' started by Brewtrooper, May 28, 2015.

  1. Brewtrooper

    Thread Starter New Member

    May 28, 2015
    1
    0
    I have a food dehydrator...just a fan blowing over a nichrome wire. I want to be able to reduce the heat of the wire. Either with a switch or variably. It's all 120 AC on home 15 amp circuit.

    What should I use to lower the temp (current/voltage)? I will keep the fan speed at the present speed so only looking to add something into the heating element circuit.
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,651
    632
    An incandescent lamp dimmer would be a good solution. Just make sure it is rated for the number of watts that your dehydrator draws.
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Adding a big diode in series with the heater will cut the power in half.

    Ken
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,112
    3,039
    My dehydrator has this capability built in. I may have the schematic - I'll look. Basically it's a triac (as in a light dimmer) under control of a thermistor.

    [update] I found my hand-drawn sketch but it's too crude to be much use to you. My food dehydrator contains a very simple circuit for controlling an AC powered heating element. The circuit is based on Motorola's CA3059 IC, which unfortunately is obsolete but has been replaced by the Atmel T2117 which is very similar to the U217b. Check the data sheets of those ICs for application examples.

    It's designed for direct (through a 10KΩ resistor) connection to the mains and controls a triac (rated 10A, 400V) based on detecting zero-voltage crossings. It makes its own DC supply. A thermistor senses temp and turns the heater on or off via the triac. All of this is handled by the IC, so the PCB is quite simple. There's a 98°C thermal fuse that will trigger if the temp rises to about 20°F above normal range.
     
    Last edited: May 28, 2015
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
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