lost.blue.istari@gmail.com

While I cannot argue with your equations I have to ask if they take
into account over-generation by the vehicles alternator? Do you know
if alternators do indeed only put out the minimum required power for
any given situation? I would think not as they need to over-generate
to recharge the battery. How much excess power is typically generated
and how much would that reduce the over-all fuel consumption due to
DRL use?

dan_thomas_nospam@yahoo.com

NO excess power is generated. The voltage is held constant at
about a volt or so above battery voltage to keep it charged, and this
difference is there whether or not any lights are on. If the battery
has a resting voltage of about 13 volts, the alternator will put out
14 volts or a little more, and that will be constant regardless of
load, until the load beomes so heavy that the field current is maxed
out and the alternator can't put out any more. Alternators are sized
to the auto's requirements and unless someone has installed huge
lights or winches or some other power-greedy machinery, the alternator
cannot be maxed out.
If there is no load, the regulator will reduce the field
current to the absolute minimum needed to produce the battery
maintenance current plus the bit needed for PCMs and ignition.
You need to study the alternator/regulator functions. They
make perfect sense once you know what's up. Even the old
electromechanical vibrator-type regulators were able to control the
full range of alternator output current, from zero to max.

Dan

steve

"Over-generation?" That makes no sense. The alternator puts out enough
current to maintain the bus voltage, no more.


Absolutely. That's the function of the voltage regulator. If the
alternator just put out its max power all the time, you'd have 60 volts
when driving at 70 mph with no lights or AC on, and 12 volts at idle
with the high-beams, wipers, AC, blower fan on max, brake lights, and stereo on.

Nope. The alternator restores the charge of the battery after the engine
is started, then throttles back so that it is providing all the power
for the electrical loads of the vehicle and nothing more.

dan_thomas_nospam@yahoo.com

With full battery voltage to the alternator field and the
engine RPM up around, say, 2000, the alternator will generate well
over 100 volts. You used to be able to buy a kit to install in your
vehicle that cut the regulator out of the circuit and disconnected the
alternator output from the battery, and with some means of keeping the
RPM fixed, you could run power tools (with series-wound motors only,
since it's 110V DC), lights, and so on until the battery got weak and
you had to switch back to recharge it. I had one of these things,
andbefore i installed it I opened it to see why it cost so much. A
DPDT toggle switch, a neon light with dropping resistor that fired at
110V so you knew when you were at the right RPM, and a household
electrical outlet. Total cost no more than five bucks back then, maybe
ten today. You could even weld with it, though the current rating of
the alternator had to be respected. And that's what limits the
alternator: current. Too much demand and we burn it out. It really
doesn't care about turning out 110 volts if we want it to.


The regulator holds the alternator's output voltage constant,
and with the battery run down a bit its voltage will be lower so it'll
allow more current through it. The current decreased as its voltage
rises and opposes the alternator voltage. All the regulator senses
(and controls via field current) is output voltage.

Dan

steve

The "output voltage" is the same as the voltage at the positive terminal
of the battery, neglecting wiring resistance. If the internal charge
state of the battery is low, the set-point voltage of the regulator will
result in a charging current flowing into the battery. If the battery is
fully charged, the voltage on the bus doesn't change, but the charging
current no longer flows into the battery so the regulator is able to
throttle back the field current and therefore the output current (not
voltage) of the alternator. The term "voltage regulator" seems to
confuse some people. Yes, the voltage is what is being regulated- but
"regulated" actually means "held constant" in this case. The current out
of the alternator is what varies in order to make the voltage stay constant.