# Maximum power transfer question

Discussion in 'Homework Help' started by electroboc, Nov 24, 2011.

1. ### electroboc Thread Starter New Member

Nov 17, 2011
4
0
Any body able to give me a hand with this question?

A. The value of R and X that will result in maximum power to be transfered across terminals A and B?

B. The value of Maximum power?

can anyone give me any direction??

Many thanks

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2. ### jimkeith Active Member

Oct 26, 2011
539
99
My guess is that if you isolate the load and determine the thevenin Zequiv in rectangular form, you will have the max transfer of power when R and X are equal to these values as L and C will series resonate.

Happy Thanksgiving Day, if you live in the US

Last edited: Nov 24, 2011
3. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
782
Another perspective:

The load would need to be the complex conjugate of Zequiv.

So if Zequiv=A+jB then the required load for MPT would be Zload=A-jB.

4. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
507
I believe maximum power transfer always occurs when source impedance matches load impedance. That's why antennas use impedance matching transformers to match the 75 Ohm transmission line.

5. ### Yako New Member

Nov 24, 2011
245
2
^ Yeah that's right

XL = XC = resonance / max amplitude

Tuning for max amplitude.

6. ### Yako New Member

Nov 24, 2011
245
2
XC = 1 / 2 pi (fc)

I have forgotten XL equation.

7. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
782
That's true when the load and source impedances are purely resistive.

When there are complex reactive terms involved then the MPT occurs when you have complex conjugate matching between the source and load.

8. ### electroboc Thread Starter New Member

Nov 17, 2011
4
0
one question i have, i have removed the load and worked out the short circuit voltage and have 50 volts.

when you work out the impedance i am struggling on whether just product over sum

5x5 over 5+5 or do i need to incorporate the j10ohm as well due to the phase angle?