Re: nighthawk 550 electrical problem


R. Pierce Butler wrote:

> If you can, feel the stator of the alternator after running the bike at
> about 3000 rpm for a minute. If the rectifier is bad that stator will
> generally be really hot! He careful as I have seen car alternators get so
> hot as to cause water drops on the cover to sizzle and dance.

I'm not sure what you can tell about a charging system from the fact
that the parts get hot, except that it's not a good idea to touch hot
parts.

There is always some heating in the metal cores because of molecular
friction as the electric currents try to align all the iron molecules
to a north-south axis. That's what engineers call "iron loss".

There is always *some* heating in the copper windings, if current is
flowing at all. Electrical engineers call it I-squared R loss, or
"copper loss".

If you are carrying a 300 watt load on the alternator at 12 volts,
Power/Volts = Amps, so 300/12 = 25 and since the internal resistance of
the stator may be as high as 1 ohm, 25 X 25 X 1 = 125 watts. You know
you can't put your hand on a lit 125 watt light bulb, so a stator with
125 watts
I-squared R loss is going to be noticeably hot to the touch...

This particular Honda's alternator does have a cooling fan, but the
internal temperature rise might be as much as 180 degrees Celsius.
Since the windings have nothing for insulation except some special
enamel, the solvents in that enamel will begin to boil out and that
distinctive odor of a hot electrical transformer will be noticed.

And, some of the heating you may have noticed in a car alternator may
be due to at least two other sources. One of those sources is the six
diodes that are built into the case. A diode is a semiconductor with
gawd only knows exactly what low resistance in the forward direction
and (hopefully) quite a bit more in the reverse direction.

Since current flows through the diode, the I-squared R effect makes it
get hot.

If the diode is conducting equally in both directions, it just gets
hot, and doesn't rectify AC into DC. I couldn't tell you what the
forward and reverse resistances are of any particular diode, because
the battery in an analog ohmmeter biases the diode and changes the
reading. If a shop manual specifies a resistance reading for a diode
test, it probably also specifies what model of ohmmeter to use.

The other potential source of heat in a car type excited field
alternator would be the rotor. If the diodes are bad, or the battery is
low, or there's a heavy electrical load the car's voltage regulator
will send full current to the rotor and the I-squared R effect will
cause massive heating of the rotor.

In a motorbike's permanent magnet alternator system, the diodes are in
the rectifier regulator, so the heat sink of the RR gets hot, whether
the diodes are working right or not. And, the voltage regulating
components inside also get hot, the zener diode and the silicon control
rectifier both have internal resistance and the SCR is expected to get
hot, it's a semiconductor and I-squared R effect is busily making it
hotter than hell.
>
> Given that it is trying to charge, I would say that one or more rectifier
> diodes are bad. Just keep in mind that a diode is nothing more than an
> electrical "check valve". It is supposed to allow current to flow one way
> only. If it doesn't it is NFG.

Ah, yes. NFG means "not functionally good" of course...

.

Relevant Pages

  • Re: nighthawk 550 electrical problem
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    (rec.motorcycles.tech)
  • Re: Dead alternator?
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    (uk.rec.cars.maintenance)
  • Re: External regulators (was NB Virgo)
    ... our boat uses a diode to split the charge between domestic batteries and a bow thruster battery. ... The diode causes a voltage drop between the alternator and batteries and the batteries never charged properly. ... Now whilst this *will* fully charge a deep cycle battery it will take a ridiculously long time. ...
    (uk.rec.waterways)
  • continuing saga was:bad diode stator means?
    ... tightening the belt long time ago and made no difference. ... serrated on the pulley side, but no glazing or obvious wear. ... under "Alternator Output: ... stator" which I guess legibly written means: Bad Diode Stator? ...
    (rec.autos.tech)
  • Re: Headset Noise
    ... while the alternator is spun-up is ... Every aircraft I have seen is wired such that turning off the battery ... (50mv of ripple) ... BadDiode.jpg = same as Normal, ...
    (rec.aviation.owning)