Darrough, James wrote:
In fact, it is better for a lead acid based battery to be charged and
discharged than to let it sit. At least, when I went to school we spent
a lot of time talking about charge-discharge cycles. The real enemy of a
lead-acid battery is drawing the cell voltages too low, e.g., less than
about 11.5 volts total battery voltage.
The excide people and my auto-electric class at LCC disagree. :)
For a deep cycle battery, you can discharge/charge many times.
For an automotive battery, the plates are not as heavy, so they warp if
cycled too much.
But who knows. I'm not going to test it.
The reason the alternator has such high current capacity is so it can
recharge the battery after starting the car. Considering that some
automobile starters can draw up to 100 amps or so for a few seconds, and
some folks maintenance habits are poor, resulting in a lot of cranking
to get their vehicle started, it is necessary to really overdesign the
alternator.
And many of the vehicles today have 150 amp alternators to drive the
computer and other electronics required to run the vehicle. I realize
your 90 Metro doesn't have as much computer, but my 04 Cavalier has a
computer that would put my first 286 to shame. It's a base model, with
no bells and whistles. It has a 95 amp alternator. My 72 Ford had a 35
amp alternator and about 5 times the engine to turn. With no bigger of a
battery.
It is true that the battery is there to start the car, but it also
serves as a sort of filtering device for the output of the alternator.
If you knew that you would only start your car twice a day, and that it
would start immediately each time, you could reduce the size of the
alternator considerably. My guess is that full-load on a small car with
high beams, etc., is probably around 10 - 20 amps.
If you're only running the lights, yes. But on a modern car, the engine
and lights are the smallest part of the electrical needs of the car.
The part I love about the "hybrids"... They make them to run on
electric, and add more electric do-dads that suck more juice, which
kicks the motor on...
Why would you suggest running the alternator off the crankshaft? The rpm
is too low most of the time.
Overdrive it. The point is to only drive the alternator when the vehicle
is moving.
It's a trick I saw in Hot Rod once.
Great discussion. But I suspect people are growing tired of it, so
thanks for your comments.
Probably. I'll shut up now.
Russ
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