Winston writes:

?Short? I do agree that current limiting will be a major issue.

228 A through a 50 A alternator. Until a real short shows up,
this will do nicely.

So your portable one-lung generator will source 228 amps? At 120V that
means 27 KW. The small portable gas generator in my garage is a lowly
0.75 KW; I'm jealous..

A friend has a 7.6KW model for his house; when his 5KW well pump starts,
it audibly stumbles for a few seconds and recovers; even when it is the
sole load. If he has other loads on it, it sometimes just stops.

In short, the model involves some non-linear components; pretending
they are linear won't do justice. (No rotating generator can be modeled
as a pure voltage source.) For example, if the battery is quite dead,
its resistance will be quite high & it will not take a charge at
first. Patience shall be required.

If he can get the generator to idle; that will be a big help.

The only weakness in Pete and Paul's otherwise brilliant solution is
that Clack implied that we cannot change the voltage coming from the
generator:

"(...)power from the generator which is making 110 volts
AC(...)"

Based on 20 years of listening to Click & Clack; I'd say their Puzzler
limits are not THAT cast in stone. (But then, I just watched Kirk beat
the Kobayashi Maru exercise.) After all, it is described as an "electric
drill" he has, not an "electric motor with chuck that can drill holes OR
spin the alternator.."

You can try using the drill, but the trigger speed control may object.

I suspect that the drill will run happily (at significantly reduced RPM).
It has a source of DC that pulses from 0 to ~150 V to 0 every 16.66 mS.
We only need it to run for a few minutes so cooling shouldn't be an issue.
Lock the trigger down full and try the headlights in a few minutes.

One issue on the drill is while its nominal reactance is well suited for
our needs; it will draw a lot more in locked rotor mode. If it does not
quickly get out of that mode and to a reasonable RPM, will it still
be a suitable current limit....?

If he has a plastic bucket, water, and some salt [including that
morning's used beer]; he can use a salt water bath resistor scheme. I
know of a supersonic 10'x10' wind tunnel that uses that approach.

Drill is *much* safer and much faster to implement. And *way* more
pleasant to be around.

Salt water resistors are used in some interesting places. For example,
for the 87,000 HP drive motor system on a NASA wind tunnel.

I suspect the salt in new beer is sufficient...but agree it would be
a sin to waste beer..


With no DVM, you could use a headlamp as a current indicator; dim
will be several amps; full brightness is ~10A.

Or one could look at the drill motor nameplate and subtract ~60%.

Lamp is at least resistive, and linear over the DCish waveform.
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