"Greg Mayman" bravely wrote to "Mike Ross" (15 Sep 03  09:12:00)
 --- on the heady topic of "VEHICLE LED'S"

 -=> Mike Ross said to Greg Mayman
 -=> about "VEHICLE LED'S" on 09-11-03  23:16.....

 MR> What we're trying to achieve is to cancel the effect of the dynamo
 MR> internal reactance on the load we have. We need an ac power transfer.

 GM> Exactly.

 GM> The best way to cancel the series inducive reactance is by adding
 GM> _series_ capacitive reactance. When XL=XC, the output impedance
 GM> of the dynamo will be equal to the resistance of the windings,
 GM> plus other effects that appear as resistance.

 GM> But this will only occur at one particular frequency and speed.
 GM> That wouldn't be a lot of use, would it?

No it isn't of use because that isn't how to achieve a maximum AC power
transfer. To get this condition we must offer a load that is a
"conjugate" of the AC source impedance. Thus if the source is inductive
and resistive in series we must supply a load that is resistive and
capacitive in parallel.


 GM> No, it is 100% right for ALL cases, whether reactive components
 GM> are present or not.

 GM> Check your textbooks on the methods of matching a radio

Check your own books! Read up on Maximum AC Power Transfer.


 MR>  My real world dynamo has an inductance in it!

 GM> As I said before, the series inductance can be cancelled at one
 GM> particular frequency by adding _series_ capacitance.

Series capacitance won't work because it doesn't result in the required
"conjugate" load for a maximum AC power transfer". When you
use a series
capacitance it will only be possible to have maximum power transfer at a
single frequency.

The source impedance will be purely resistive at that frequency (since
inductive and capacitive reactances are equal and opposite thus cancel)
but at a higher and lower frequencies it then becomes respectively
inductive or capacitive. The load resistance doesn't change and thus it
will never be a match when not at resonance.

With a conjugate load, the reactances allow the load to receive the
maximum AC power possible and nearly so in a much broader range of
frequencies around resonance.

 Asimov
 ******

... Reactance: your imaginary friend.
--- Blue Wave/DOS v2.30