Re: XS650 ROTOR

Rick Cortese wrote:

> IIRC the early DTs were 6V systems and I would guess the XS is a 12V.
>
> I saw a couple of adverts from people that rewind coils/stator but I
> thought the price was a little steep, around $70.

Well, since most street bikes are going to be battery and coil systems,
the
permanent magnet alternator coil usually used for the energy transfer
magneto can be used for battery charging and general electrical loads
instead. That would give 1/3rd more power.

When I first suggested using a permanent magnetor alternator what I had
in mind was a unit off of some older 1960's Honda street bike, and when
my machinist type buddy produced the dirtbike alternator, I figured we
were in trouble, either he'd have to return it to whoever he got if
from, or we'd have to convert it from 6 volts to 12 volts or run 6 volt
system on the race bike.

So I researched the subject and found that the output of permanent
magnet alternator would be a function of the RPM of the engine, the
number of coils in each winding and the flux density of the magnets. We
had no way of knowing what the flux density was, so my machinist buddy
suggested that we just wind as many turns of finer wire on the coils as
possible to get more voltage. He said that we could then measure the
voltage output at high RPM and remove as many coils as necessary to
reduce the voltage.

We didn't know about how small low-powered alternators' output voltage
was "clamped" to battery voltage or just a little more. We were amazed
that the little re-wound alternator was able to push 1 or 2 amps of
charging current into the battery.

But we wanted MORE current than that. It seemed that we also had an
electronics engineer on this blundering design committee and he had
suggested using a Chrysler multi-fire ignition system to fire all three
coils simultaneously three times per revolution! Believe it or not,
this system *worked*. The engine ran and put out a lot of power, enough
to be dominant over the 750cc 4-strokes---while it lasted.

But the Chrysler system drew a lot of amps. It drew about 30 amps when
the engine wasn't running and the current dropped off to about 7 or 8
amps at higher RPM. We wanted to get more current out of the alternator
to keep the battery charged, so I came up with the solution of using
TWO 3-phase full
wave rectifiers instead of one. That cut the resistance in half and
doubled the current available for charging. We had no voltage regulator
at all, since the alternator output voltage was so closely tied to
battery voltage.

Our entusiastic blundering engineer and our enthusiatic blundering
machinist was accompanied by a generally enthusiastic blundering madman
who was ripping all the existing wiring out of the wiring harness to
save a few ounces of weight, and I was the enthusiastic electrician
trying to wire up the electical system while the enthusiastic madman
was ripping wires out and turning the K-mart coils around backwards.

I had my doubts about whether the Chrysler ignition system and the
K-mart coils (and the Thunderbolt CDI that the enthusiastic engineer
had insisted needed to be on the bike) would last for the six hour
endurance race, so I wired up a spare stock ignition points plate, just
in case.

When I got to the race track on Saturday morning, the enthusiastic
blundering crew had everything all torn apart trying to figure out why
the engine kept cutting out on one cylinder. It seems that the special
8-gallon endurance racing gas tank was touching one of the ignition
coil terminals that the blundering madman had turned around backwards.

Everybody cheered when I arrived, because nobody had any idea of how to
wire up the points plate using the aircraft modular terminal blocks I'd
installed.

The bodged up permanent magnet alternator rotor was falling apart, so
we figured that the Chrysler ignition system would drain the battery
too fast and therefore we installed the points plate and ran a total
loss system for as long as the engine lasted.

That wasn't long, since the water pump couldn't circulate any water
through the cooling system. It was all plugged up with an excess of
Bars Leak. The center piston melted, there was a hole in it, it seized
and broke the connecting rod.

.

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