real time dyno?

[Bruce Bowling]

> 
> 200HP = 149kW. On a 12 volt alternator, that's 12,417 amps! With a 
> 120 volt alternator, it's only 1,242 amps.
> 
> ---
> David Parrish
> So. How many homes you want to light?
> 
A few points:

1) A car alternator puts out more than 12 volts - it is regulated
down to the 12 volts.  If I recall, something like 60 volts open
circuit.

2) You do not want to suck away 200 HP, only enough to cause an
RPM drop.  Yes, at higher torque, you need to suck away more torque
to get a reliable RPM drop. 

3) Still, the RPMs drop down at idle when I put on the lights,
somewhere like 25 RPM (total guess).  What is the current draw
of headlights, something like 15 amps (total guess again)?

So, right now, I could probably perform the following test:
1) Fix the idle to something like 700 RPM steady. Headlights off
2) Turn on headlights. See and record the RPM drop.
3) Turn off the headlights.
4) Screw up the engine somehow, like disabling a cylinder (via.
spark or something). 
5) Do steps 1, 2, and 3.  The relative change in RPM drop between the
two tests should scale, something like:

  scale = (number_of_cylinders - 1)/(number_of_cylinders) + Other_losses

Will this work? I do not know, and I do not have the time to test this.
But this test is similar to the old "eliminate-the-cylinder" test
that a lot of the engine analyzers used to have, which simply
shorted the coil primary when a particular plug was firing, and
determined relative cylinder-to-cylinder performance by watching the
amount of RPM drop.

- Bruce
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                 Bruce A. Bowling
                     Mad Cow
   Thomas National Facility Accelerator Jefferson
    12000 Jefferson Ave - Newport News, VA 23602
                 (804) 249-7240
bowling at cebaf.gov  http://devserve.cebaf.gov/~bowling
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