ray lunder wrote in
:

Anyone have any experience with
this type of thing?
Also, the fan is sucking air from the front of the pulley and blowing
it through the body and out the rectifier end towards the stern. Is
this correct? The cowling is pretty close to the front of the engine
so I don't see how it's going to get much ventilation. Thanks as
always.


Any charging system must have a series resistance to limit charging
current on initial charge. This resistance drops the excess voltage
between the battery's voltage at whatever state of charge it's in, what
the voltmeter in the dash reads, and the charger's natural design
voltage, which is around 18 volts for 12V alternators to make the
charging stable up to 15VDC, giving the regulator something to control.
(Your solar panel chargers run 18V loaded to spec and up to 28V sitting
in the sun totally unloaded. Their internal resistor is the silicon
cells, themselves, which get really hot at full load current.) In an
alternator, it's the resistance of the windings in the stator, in series
with the load current as they are the source of that current, that are
designed to be the series resistance of the charger. (The transformer
windings of an AC battery charger is the resistor in them as well as the
selenium rectifiers in old chargers.)

All this designed-in series resistance gets HOT (P=IxE) when there's lots
of I, the charging current. So, to cool this resistance, the alternator
has an open case with a cooling fan, in your car. In sealed boat
alternators, the cooling comes from conduction from the core to the case
and it gets lots hotter than your car's alternator, but is designed to do
that. In a large truck alternator on trucks and busses, the alternator
is gear driven directly on the engine block and crankcase oil is poured
through the alternator windings to cool it. They put out hundreds of
amps at 12 or 24 or 32 volts DC.

Now, alternator manufacturers know you are not going to be pulling 70
amps out of a 70 amp alternator for long. (Notice how the current drops,
substantially, after the first 10 minutes of charging caused by the slow
chemical reaction going on in the battery case.) So, the alternators are
not designed to be continuous duty at 70A for days on end like the big
truck alternators are. Economics rears its ugly head. The consumers are
not going to pay for a continuous duty alternator at $500 and the
accountants are not going to let the company produce an alternator that
never fails and makes little profit for the supply chain, so they build
it as cheaply as possible with a little built-in MTBF so you'll buy
another one in a few years. (Notice how many auto electric places are
located in your area.) We could easily build an alternator that would
last a lifetime. Some alternators at power plants are over 80 years old,
having been installed by Mr Tesla, himself. Westinghouse designed them
to run forever. In your alternator, the engineers are depending on
thermal lag to keep the temperature of the alternator below the
temperature it destroys itself, prematurely below the planned
obsolescence target. Simply, we have to keep it below that temperature
until the battery eases the load on it....or else.

Hmm....18V minus 11V for the discharged battery leaves 7V dropped across
the windings. 7V x 70A = 490 watts of waste heat the alternator must
dissipate (damn, I can never remember how to spell that word) through the
case or by the cooling fan. Yep, that case is gonna get HOT! There's
half the power coming out of a bathroom heater made inside there! Now,
as the battery charges, its voltage rises so our 7V alternator drop
drops. The charging current drops rapidly to, say, 20A to complete the
charge in a few minutes, too.
18V-13.5V=4.5V x 20A = 90 watts so the case gets lots cooler after that
initial blast that melted the label off it...(c; Ah, that's better.

Before I get blasted that the voltage regulator makes the alternator
output a flat 14.2V all the time and this is all wrong, look at where
this 14V is measured....at the terminals to the BATTERY. It senses
BATTEYR voltage, not the natural turns ratio voltage of the alternator.
The resistance is BETWEEN the natural voltage of the windings and the
voltage regulator's sensing. The regulator runs it wide open against the
resistance of the windings until the battery voltage trips it. Field
current is reduced to limit battery voltage by making the alternator
weaker. It's natural voltage drops because the magnetic field drops as
the regulator reduces armature field current.

--
There's amazing intelligence in the Universe.
You can tell because none of them ever called Earth.

"Larry" wrote in message
...

Any charging system must have a series resistance to limit charging
current on initial charge. This resistance drops the excess voltage
between the battery's voltage at whatever state of charge it's in, what
the voltmeter in the dash reads, and the charger's natural design
voltage, which is around 18 volts for 12V alternators to make the
charging stable up to 15VDC, giving the regulator something to control.
(Your solar panel chargers run 18V loaded to spec and up to 28V sitting
in the sun totally unloaded. Their internal resistor is the silicon...
(major snippage)

Wow! That was a great post, Larry. Thanks!

Ummm..."MTBF"? Something do do with planned failure from context, but could
you elucidate?

"KLC Lewis" wrote in
et:

Ummm..."MTBF"? Something do do with planned failure from context, but
could you elucidate?





Mean Time Between Failures. It's the tolerance set in the specifications
as to how long it should run, in the mean, between failure modes....

MTBF for the Chinese hard drives in your computer is hundreds of thousands
of hours for $99.

MTBF for a $35,000 American car is one hour past the end of the warranty
period, but they're not really good at making them last that long....

MTBF for a cored boat deck depends on whether it rains or not.

--
There's amazing intelligence in the Universe.
You can tell because none of them ever called Earth.

"Larry" wrote in message
...
"KLC Lewis" wrote in
et:

Ummm..."MTBF"? Something do do with planned failure from context, but
could you elucidate?





Mean Time Between Failures. It's the tolerance set in the specifications
as to how long it should run, in the mean, between failure modes....

MTBF for the Chinese hard drives in your computer is hundreds of thousands
of hours for $99.

MTBF for a $35,000 American car is one hour past the end of the warranty
period, but they're not really good at making them last that long....

MTBF for a cored boat deck depends on whether it rains or not.

--
There's amazing intelligence in the Universe.
You can tell because none of them ever called Earth.

Gotcha! thanks again. :-)