[DeTomaso] Amp gauge

[MikeLDrew at aol.com]

In a message dated 5/18/12 9 41 35, kirby.schrader at gmail.com writes:


> 
> I disagree and can not at all see how this approach is valuable...
> That's the way my GT40 came 'incorrectly' wired.
> As you turned things on (fans came on, A/C compressor, etc. etc.),
> the ammeter kept climbing as it measured all the loads. Do you really
> care?
> I suppose for bragging rights. Look at me!!!! 83 amps!!! Woohoo!
> 

That's not how an ammeter is designed to work, and as you said, your car 
was wired *incorrectly*.   

If the car is shut off and you start adding loads (turning on lights, fans 
etc.) then the ammeter registers in the negative, not positive.   When the 
car is turned on and the alternator is charging, ideally the charge should be 
slightly higher than the load, so that the gauge indicates slightly 
positive.   When you first start the car, if your battery is weak, it will be 
drained quite a bit, so the ammeter will reflect a high state of charge for a 
minute or two as the charging system rapidly returns the battery to a fully 
charged state, and then it will come down to show a slight charge (ideally).   
If your idle speed is too low, you might show a slight discharge at idle 
with all your components (lights/fans etc.) running.

Sounds like your car had both the supply AND the loads wired on the same 
side of the ammeter?   That would deliver crazy readings for sure.

My point is that it's senseless to take high-load components and wire them 
outside of the ammeter so that the ammeter never registers their draw when 
running.   It's like partitioning your fuel tank so that the fuel gauge only 
registers part of the fuel you have on board.   Doing so guarantees that 
you'd never know exactly how much fuel you have.   What would the point of that 
be?

An ammeter will instantly indicate a charging system failure because the 
needle will displace into the negative side, which is easily apparent.   A 
voltmeter is much more subtle; it will show 12.5 or 13 volts when all is good, 
and will ALSO show 12.5 or 13 volts if your alternator fell out of the car, 
because it's just showing the state of charge of the battery. 

The common fallacy is that the voltmeter tells you about your alternator.   
It doesn't tell you JACK about your alternator, it only tells you about the 
state of your battery.   An AMMETER is the only gauge that tells you about 
your alternator, because it instantly informs you as to whether it is 
charging the battery, or if the battery is being discharged.

Over time, if your alternator clatters onto the roadway, your voltmeter 
will drift imperceptibly lower as the battery drains, but at a glance it will 
still look healthy.   When it gets to 11.5 volts or whatever, you'll sputter 
to a stop with a 'dead' battery.

It would be ideal to have both a voltmeter and an ammeter, but given the 
choice I'd take an ammeter any time.

Mike