[Eug-lug] hardware query...

[Russell Johnson]

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