"Greg Mayman" bravely wrote to "Mike Ross" (05 Sep 03  08:31:00)
 --- on the heady topic of "VEHICLE LED'S"

 -=> Mike Ross said to Greg Mayman
 -=> about "VEHICLE LED'S" on 09-02-03  21:59.....

 MR> The impedance is pretty low, in fact I've thought about adding an AC

 GM> Somewhere I read that the inductance of the windings (and hence
 GM> the impedance) was relatively high.

I measured 4.2milliHenry. It's not high at all.


 GM> As the dynamo turned faster and generated more voltage, the
 GM> frequency would also go up, causing a greater voltage drop across
 GM> the internal inductance to give a more or less constant voltage
 GM> to the lamp.

The frequency cut off for 4.2milliHenry and a 12 ohm filament (hot) is
about 455 Hz or about 27,300 rpm. I don't think the dynamo would ever
turn that fast unless I was ripping along at 152 miles per hour!!!
I think that is close to the record bicycle downhill ride from the top
of Mt.Fuji. The guy blew both tires out but just kept on going. I don't
think he could have stopped if he wanted to. 


 MR> capacitor across the lamp to increase the power factor and thus extend
 MR> the power band somewhat. It's kind of like a resonant circuit where

 GM> It's _exactly_ like a resonant circuit, that will have maximum
 GM> effect at one particular frequency.

That's true but if it is a load critical value (i.e. XL=XC=RL) then
there is no resonnant frequency and the effect of the capacitance is
spread out over a much broader frequency range.


 MR> the capacitor supplies power when the generator goes through zero thus
 MR> keeping the filament more fully lit on average by increasing the

 GM> No it won't since the capacitor will take power from the
 GM> generator when the generator output is at a peak.

The capacitor current will be at an angle leading the voltage while the
inductor tends to make the current lag the voltage. When the internal
ideal generator voltage is zero the inductor is returning energy stored
by the capacitor while it's voltage is zero. The only loss is the
winding resistance and a little in the magnetizing inductance's
reluctance?.


 GM> If the waveform
 GM> that comes out of the dynamo is more or less a sine wave, adding
 GM> a capacitor will not change the waveform to any great extent,
 GM> apart from removing some of the harmonics.

There won't be many harmonics unless the pole steel behaves in a very
non-linear fashion and saturates.


 MR>  Or more simply by cancelling the
 MR> series inductive reactance as seen by the lamp. I haven't taken any

 GM> It will cancel only at one particular speed/frequency. If it
 GM> works, the light would brighten up at that speed, but be
 GM> noticeably dimmer at higher speeds due to the low pass filter
 GM> effect of the capacitor.

I've tested it on the circuit simulator and on the contrary the voltage
level stabilizes out to a much higher frequency. Then it drops at twice
the previous rate without capacitor. The bicycle ride experiment with
the capacitor installed replicated the same voltage leveling effect.
The difference being that the circuit simulator didn't have the proper
generator model and the low frequency effects couldn't be simulated.
In the field test the lamp got to full brightness sooner and stayed
there.


 MR> Not on the dynamo... ME!!!   Mr. Motive Source!!!

 GM> The load is first of all on the dynamo, since that is the only
 GM> thing that the circuit is drawing power from.

 GM> Then it would also be indirectly on you, unless you're coasting
 GM> downhill ;-)

Even for the sake of science, I'm *NOT* going down Mt.Fuji!!!

 Mike
 ****

... Is reactance then illusory?  No, it just appears that way...
--- Blue Wave/DOS v2.30