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Son of Samurai's Blog

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Pop Quiz: Can You Solve this Series Circuit Puzzle?

Son of Samurai


Think you know your circuits? How about we put that to the test!

In this excerpt from one of our many illuminating webinar recordings, the Samurai traces out the circuit for a refrigerator evaporator fan. Interestingly, the neutral side of the fan's power supply goes through both the defrost terminator and the defrost heater. How can this be?

Watch this excerpt and ponder the mystery for yourself. When you think you have the answer, click here to view the full webinar and see if you got it right. Along the way, you'll also learn a metric buttload about the difference between voltage and voltage drop, identifying loads vs. switches, and much more.

The full version of this webinar recording -- and the 45+ hours of other webinar recordings -- is available only to our premium members. Click here to become one today.


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Rt=r1 +r2 so on

It=i1 =i2  so on

So resistance R increase current I decrease  so current  I is so low  it will not  effect on df heater in this case  heater is just a wire so if heater or df terminator  is open  evap fan won't run

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If you think of it as a voltage divider between the defrost heater and the defrost fan, the defrost fan is a much higher impedance than the defrost heater so very little to virtually no voltage will be dropped across the defrost heater when only the defrost fan circuit is its source of voltage. 


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Samurai Appliance Repair Man


@Chashb is correct. You can also think of in terms of the Ohms Law equation for voltage drop: E=I*R. E is the voltage drop across the load; I is circuit current- the stream of electrons being pushed by voltage; and R is the resistance of the load. (impedance would include any capacitive or inductive components which are negligible in a defrost heater; the evaporator fan motor, on the other hand, has a huge inductive reactance compared to its resistance so impedance is the functional parameter).  

Since the resistance of the defrost heater is two orders of magnitude less than the impedance of the evaporator fan motor, we see from E=I*R that the voltage dropped across the defrost heater will be two orders of magnitude less than the voltage dropped across the evaporator fan motor.

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I would say yes its running, i cant say how much ?as you said in video series circuit there was only two devices on  N. side heater and def. therm. but i do see were you showed the formula E=I*R  thank you.

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