Heating elements in series

[mbrooke]

What is the total power rating when heating elements of different sizes are connected in series?


For example:


Element one is 3410 watts at 240 volts.

Element two is 2585 watts at 240 volts.


Ohms law says element one is 16.8915 ohms.

Similarly element two would be 22.2824 ohms.


22.2824 ohms + 16.8915 ohms = 39.1739 ohms.

At 240 volt 39 ohms gives 1470 watts.


However when one thinks about it the voltage drop is not even. Element two would have more volts and element one would have less volts meaning the current draw would in theory change based on the voltage. What does it stabilize to and why? What would be the wattage dissipated by each element.

 

[K8MHZ]

In a series circuit, the current is the reference and only the voltage changes.

 

[infinity]

I agree K8HMZ the current is the same in the entire circuit based on the total circuit resistance found by adding the series resistances together.

 

[K8MHZ]

So roughly the 16.9 ohm element will be 639 watts and the 22.3 ohm will be 843 watts.

 

[winnie]

I think that the answer to 'why does the current stabilize' is kirchoff's current law. If you were to somehow have more current flowing in one resistor than the other, then there would be an imbalance of current at the node connecting the two resistors. Charge would build up at that node, and that would quickly block the unbalanced current.

Your answer for the total power output is correct. What is interesting is that the nominally higher wattage element will have a lower share of this total power output.

Lets take a similar example with simplified numbers.

Element 1 is 960W at 240V, for a resistance of 60 Ohms
Element 2 is 320W at 240V, for a resistance of 180 Ohms

In series the resistance is 240 Ohms, for a power of 240W and a current of 1A

In series, element 1 is dissipating 60W and element 2 is dissipating 180W.

-Jon

 

[LarryFine]

What is interesting is that the nominally higher wattage element will have a lower share of this total power output.

That's why it's usually the small loads that suffer when a neutral is broken.