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Urgent-ish low pass filter question..  Can I use a capacitor in parallel with a resistive heating element as a LPF to reduce power to the element?

farrpro

Hi,

 

Our vendor shipped us heating elements that are out of spec and I need to find a way to safely use them in our product. 

 

Right now we have a triac fired through an optocoupler from a micro controlling the power output.  The element, however, is 600W / 115 / 22.3Ohms when it should be 350W.  Will the circuit breaker trip if all the triacs fire at the same time even though the integrated power output vs. time is 350W? 

 

If so, can I simply make a low pass fiter at fc = 60Hz with a capacitor in parallel with the element? 

 

Are there any (other) ways to make this work?  Getting desperate -- the vendor was late and now we have no time to re-order.

 

Any help is appreciated.

 

 

-Amos

  • 0

    Hi Amos,

     

    If your circuit is designed for 350 Watts you should get the correct value elements. The idea of using a capacitor will not solve this problem. If your micro controller can Pulse Width Modulate the output down to the effective wattage that is needed you might be able to get away with the change but the higher wattage heating element will have a lower resistance and so the instantaneous current will be twice what is drawn by the correct element. This will stress components like the triac and circuit traces that feed the heater element. You may also find that the micro controller is not designed to compensate for this much difference in element resistance. If the duty cycle is 50% with the correct element the duty cycle will need to go to about 25% with the 600 W elements. Not knowing more about your circuit and equipment design all of this is just guessing. If there is an electrical engineer available to you it will be worth your while to run some of your questions and concerns past him or her. I would be inclined to send back the wrong elements and get the correct ones sent express. The trouble you may create trying to use an out of design component might cause you a lot more headache that the initial delay will cause.

     

    John

  • 0

    As John points out, a capacitor in parallel won't help.

    A capacitor in series might, but it would need to be gigantic to get enough power through it.

    You could simply put 2 resistive loads in series. Doubling the resistance would cut the total power in half.