"Greg Mayman" bravely wrote to "Mike Ross" (11 Sep 03  07:55:00)
 --- on the heady topic of "VEHICLE LED'S"

 -=> Mike Ross said to Greg Mayman
 -=> about "VEHICLE LED'S" on 09-08-03  23:43.....
 MR> That's true but if it is a load critical value (i.e. XL=XC=RL) then
 MR> there is no resonant frequency and the effect of the capacitance is

 MR> Of course, it is resonant any time XL=XC,

 GM> So don't say "there is no resonant frequency." Let's try to avoid
 GM> such sloppy terminology.

You're manipulating what I wrote to mean something else since the first
case was a real case and the other an ideal case. Peaches and pears!
Let me clarify the first quote then. In that case when the load is a
conjugate of the internal impedance of the ac source then there will be
a maximum power transfer. Obviously we have to add capacitance to create
the mirror image reactance and this creates a resonant pole. If we chose
that pole such that the resistive component is equal the inductive
component then the rise of voltage will be sqr(2) at the pole.


 MR> maximum power will be transferred from the generator to the load
 MR> when XL=XC=RL.

 GM> I understand nothing of the kind!
 GM> The maximum power is transferred when the effective OUTPUT
 GM> RESISTANCE of the generator is equal to the resistance of the
 GM> load. The effective output resistance of a resonant generator
 GM> usually is NOT equal to Xc or Xl.

The lamp is obviously not equal to the dynamo's internal resistance.
What we're trying to achieve is to cancel the effect of the dynamo
internal reactance on the load we have. We need an ac power transfer.

If we look at the reactive power and the true power we find that the
ratio is 1/2 when the above conjugate load condition is met. Further
when Q=1/2 there is no resonance and the voltage rise broadens to cover
a wider range of frequencies.

Thus we have a maximized power transfer from "a reactive source" to the
load. We couldn't use a 0.2 ohm load because the winding inductance is
part of the impedance of the dynamo. However, you are right in your
objection to maximum power transfer but your above statement is only
partly right because it would only apply when no reactive components are
present in the circuit. My real world dynamo has an inductance in it!


 GM> Forget your simulator, and go back to basic theory.

 GM> 1. If the waveshape of the current is sinusoidal without the
 GM> capacitor, it will still be sinusoidal after the capacitor is
 GM> added. The current will NOT flow through the lamp for a greater
 GM> part of the cycle.

Doesn't the capacitor supply current back to the circuit when the dynamo
voltage drops to zero? Doesn't the inductive reactance of the windings
maintain that current flow? Is the lamp lit?


 GM> 2. The only way you can make the current effectively flow for a
 GM> greater part of the cycle is to change the waveshape towards a
 GM> square wave, which implies a greater amplitude of harmonics.

No harmonics are added. It's the load voltage amplitude which rises.


 GM> That is a lot different from saying that "the capacitor can
 GM> supply current to the lamp when the dynamo output goes through
 GM> zero and hence the current will flow for a greater part of the
 GM> output cycle."

And if the amplitude of the voltage is greater doesn't more current flow
over part of the output cycle?


 MR> That's a possibility but however improbable what remains is the truth.

 GM> "When you have eliminated the impossible, whatever remains,
 GM> however imprable, must be the truth."
 GM> A. Conan-Doyle, "The Sign Of Four".

 GM> If you must use quotations, you could at least get them right,
 GM> AND pick those that are appropriate.

I'm not debating Sherlock with a connoisseur!   What is
"imprable"?


 GM> In this case, since you admit that your simulator model of the
 GM> dynamo may not be accurate, a more appropriate quote would be
 GM> "GIGO - garbage in, garbage out." (origin unknown).

It is accurate for a portion of the frequency region of interest with
respect to reactive effects. I wrote it was obviously wrong for very low
frequencies down to DC. This doesn't mean its results are garbage. One
needs to asses what is being simulated in the knowledge that no
simulation is ever perfect. Are you just a contrarian, man?! 

 Mike
 ****

... I said, E.T., call OHM; but he resisted.
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