Is it possible to reduce the heat generated by a strip heater by wiring them serially

Discussion in 'General Electronics Chat' started by varun sreenivas, Dec 26, 2014.

  1. varun sreenivas

    Thread Starter New Member

    Dec 26, 2014
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    I have two 500w (230V, 2.17A) strip heaters and each having max operating temp of 300 deg centigrade. If i wire them serially will i be able to reduce the heat generated to 50%?.. Some one plz advice.
     
  2. MrChips

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    Oct 2, 2009
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    Correct.
     
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  3. varun sreenivas

    Thread Starter New Member

    Dec 26, 2014
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    Thanks a lot friend :)
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    It will be close to 50%.
    I did the same with my two bar electric fire.
    E
     
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  5. varun sreenivas

    Thread Starter New Member

    Dec 26, 2014
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    Yes.I was thinking to use a PID temperature controller with a J-type Thermocouple for regulating temp and for switching i will use 230v,40A SSD. I was planning to make a heated table(Iron sheet of thickness 16 gauge) fixed with twelve 500W strip heaters wired serially and in parallel under its surface. 12 strip heaters will be divided to 6 group, each strip heater in a group will be connected serially and then 6 groups will be wired in parallel. The reason for reducing temperature is that the table's top surface is coated with a non-stick PTFE fabric and its max operating temp is 250 deg centigrade. When the system runs at 100% power a parallel type connection will generate closer to 300 deg centigrade damaging the PTFE fabric which comes directly above the heater. I hope with this setup i can reduce the temperature generated to 150 deg or closer. Can you please share your views. I have attached my table design.

    Table1.JPG
     
  6. MrChips

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    Oct 2, 2009
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    Power generated would be approximately 50%.
    But that does not mean that the temperature will be reduced by 50%.
    That is a bit more complicated. The temperature will depend on a lot of other things including thermal loss through conduction, convection, radiation and thermal mass of surrounding material.
     
    Last edited: Dec 26, 2014
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  7. varun sreenivas

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    Dec 26, 2014
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    I want to maintain the surface temperature of the table at 80 deg centigrade. so i hope with this design and the generated temp it will take more time to heat the table to 80 deg centigrade (considering the table's initial temperature is 25 deg) with the present wiring scheme.
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    No. 25% !
    If you wire two 500W heaters in series each will see half the voltage and they will consume a total of 250W instead of 1000W, since power is proportional to the square of the voltage.
     
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  9. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Err what? o_O

    250 + 250 = 500.
     
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  10. MrChips

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    Oct 2, 2009
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    Err what?;)

    The voltage supplied is still the same, let's say 250V to simplify the math.
    The current is cut in half from 2A to 1A.

    Power is V x I = 250V x 1A = 250W
     
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  11. varun sreenivas

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    Dec 26, 2014
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    Yes ! you are right!.... Is there any way by which temp can be reduced to 50%?.
     
  12. MrChips

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    Last edited: Dec 26, 2014
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  13. cmartinez

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    Jan 17, 2007
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    You may want to take a look at this circuit. I built it to control a heat element for a foam cutter and it works great... I later modified the NFET driver to make it a floating one, and now I'm able to continuously control power (and temperature, using an MCU) from virtually zero to all the way up to 100%
     
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  14. varun sreenivas

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    Dec 26, 2014
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    I have checked some capillary thermostats but the problem is that most of them comes with power rating of 10-15 amps. Here i think the total power rating of 12 strip heaters will come to at least 26 amps. Is it possible to drive a SSR with a Capillary Thermostat?..
     
  15. MrChips

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    What is the maximum current capacity of your AC mains supply lines?
     
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  16. varun sreenivas

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    Dec 26, 2014
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    I think its 32 Amps...
     
  17. ericgibbs

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    Jan 29, 2010
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    You can use the N/C contact of a capillary thermostat to control a higher power SSR, with a little extra circuitry.

    Have you considered distributing the heating elements over the surface area of the metal plate and switching groups as required to maintain an even distribution of the heat.?
     
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  18. tcmtech

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    Nov 4, 2013
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    I would go with using a PID controller myself.

    Once set up it will give you the best heat control and accuracy.
     
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  19. varun sreenivas

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    Dec 26, 2014
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    Hoping to get an even heating with this heater arrangement. I am bit skeptical on using PID since this system is a slow response one and considering the complexity of tuning a P,I and D parameters. The material which is to be heated is an iron sheet and it has low thermal conductivity so heating is going to be slower hence i believe tuning PID is going to be a difficult job. I believe the PID system initially runs at 100% power and reduces power as the system stabilizes here the heaters will generate 300 deg centigrade at 100% power and it may damage the PTFE fabric (Max Operating Temperature ~ 250 deg centigrade) by the time it stabilizes hence i need to reduce the temperature generated. Is it possible to reduce the temperature generated by strip heater to 50% by adjusting P,I and D parameters? and Is it possible to start the process at 50% power if it is a PID system?


    HeatingElement.jpg
     
  20. MrChips

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    Oct 2, 2009
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    You don't reduce the temperature generated. You reduce the power to the heaters and thus reduce the rate of temperature rise.

    Either PID or ON/OFF control will work in your situation. With heating systems, PID control is implemented with PWM which is essentially ON/OFF at higher frequencies.
     
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