charging system 81 cb750f

ive been fighting with this charging system for months now. ive
replaced every part concerned so far with no sucsess. 1st from the
wiring harness to voltage regulator/rectifier, there is current, aprox
13v dc. ok. 2nd, from rr (black and white leads there seems to be no
current (? should there not be the same 13v there going to the
brushes?). 3rd, when bypassing the regulator and sending 13v dc
straight into the black and white leads off the stator, i get up to
aprox 50v ac out of the yellow leads. this i assume to be correct -
stator and rotor ok (?). leaving me to think that the
regulator/rectifier to be at fault. id believe this if i hadnt
already gone through two of em trying to correct my problem. what am i
over looking? am i somehow burning out regulators?

 

http://www.electrexusa.com/electrex_fault_finding.html

Download the pdf (and acrobat reader if needed)

If you're getting AC into the rectifier, sounds like the
regulator/rectifier. When you bypass the regulator and send
D.C. to the brushes, do you see a voltage increase at the
battery ?

 

when bypassing the two leads to the brushes, sending dc straight into
the stator with the three yellow attached to the rectifier, yes, there
is an increase at the battery. with everything pluged in right,
nothing...

 

It sounds like your *electrical* problem is with the regulator portion
of the rectifier regulator, the wiring from the RR to the brushes, or
maybe the RR case isn't properly *grounded* to the MC frame...

It's also possible that the positive wire from the RR to the battery
doesn't make good connection, is broken inside the insulation...

That positive wire is probably the wire that does the voltage sensing
for the RR...

But you also seem to be having a difficulty with terminology. It's
important to call a rotor a "rotor" and a stator a "stator" so you can
describe your problem accurately and, if necessary, buy the right parts
for replacement...

An alternator that has brushes and slip rings is called an "excited
field alternator". The voltage regulating part of the rectifier
regulator senses battery voltage, and, if the battery voltage is low,
it will send some *current* from the battery to one brush. That current
will cause an electromagnetic field in the *rotor*, which is being
turned by the engine, while the *stator* remains stationary....

As the rotor turns, the electromagnetic field turns with it. The
magnetic lines of force pass through the copper windings of the stator,
inducing *voltage* in the windings. This causes an AC *current* to flow
through the three yellow wires to the rectifier regulator where a three
phase full wave rectifier bridge will turn the AC in DC that will
charge the battery...

A rectifier bridge such as I describe, has a total of six power diodes.
The diodes are arrange in pairs, anode to cathode, and the three
resulting pairs are arranged in parallel...

AC current from each of the three yellow leads comes into a pair of
diodes between the anodes and cathodes and current will flow toward the
battery through one of the pair of diodes and be blocked by the other
diode...

If either one of a pair of diodes in the bridge is burned out, the
rectifier output will be decreased by half...

 

current, aprox 13v dc. ok. 2nd, from rr (black and white leads there
seems to be no current (? should there not be the same 13v there going
to the brushes?).

Voltage and current are not the same thing, they aren't
interchangeable. Lay persons can envision voltage as a force that
*pushes* current through a circuit, but the physicists will argue back
that current flowing through a circuit "uses up" the voltage...

That argument doesn't matter, but you need to call current "current"
and voltage "voltage". I suppose you are measuring *voltage* with your
voltmeter because you say "13v dc"...

You can have voltage at any point in your wiring, but current may not
be flowing because the *circuit* isn't complete. Troubleshooting with a
voltmeter consists of looking at a wiring diagram and probing the
system at all points where you think there should be voltage. The
component or wiring after the last point where you find voltage is
suspect...

Well, that takes a lot of *nerve*, or just total ignorance of
electrical theory. I would have used a *flash light battery* to keep
the current through the expen$ive rotor low...

The resistance through the brushes and the slip rings on the rotor
might be as low as 1 ohm, so you could be pushing up to 13 amperes
(current) through the rotor, and the power dissipated by the rotor
could be as much as the current *squared* times the resistance...

That power could be as high as 169 watts! You know that you can't touch
a 100 watt light bulb while it's lit. The rotor would be getting rather
*hot* while you are taking your voltage measurements...

So far as the 50 volts you're getting out of the three yellow leads is
concerned, I would expect *more* voltage than that, if the stator is
wound in the usual "wye" configuration, where all three neutral leads
are connected and neutral isn't connected to ground. I would expect to
see 70 to 100 volts from phase to phase to phase *open circuit* and NO
voltage from any phase to ground. If you have AC voltage from phase to
ground, that indicates a grounded stator winding...

But, you didn't say what RPM you were doing the voltage test at.
Usually 5000 RPM is specified for an open circuit test RPM...

And, if you're telling us that you get 50 volts across the phases with
all three wires *connected* to the RR, that shouldn't be possible,
unless you have blown out diodes in the RR. An AC voltage connected to
a battery through diodes is normally going to be pulled down to battery
voltage...

So, check out your wiring diagram and find out if the stator is "wye"
wound, the electrical symbol will look like a Mercedes Benz emblem with
curly arms...