Re: [Amc-list] Oh generator, thou doth suck.

[Tom Jennings <tomj@xxxxxxx>]

Frank Swygert wrote:
> The main reason ammeters are rather rare nowadays (is that a word??) is that the average Joe hasn't got a clue as to how to read it! They do know the battery is 12V and the meter should read a little higher when the car is running, and that if they have less than 12V there might be a problem. That's about it! I've got a general idea about how to read an ammeter, but wouldn't want to bet anything on it... 

Yeah, it's best left to a computer :-) Seriously -- if you pay attention 
(!) you can glean battery and charging state from EITHER. But neither 
tells the whole story.

Battery at 11.5V yet taking 20 amps is NORMAL -- if you 2 minutes ago 
you were cranking it started in -10F weather after it sat for a weekend. 
In Los Angeles it would mean something severely wrong. That's just one 
example...

A 2-D table of terminal voltage vs. charging current, there's points on 
that map you could mark red-yellow-green for bad to good, but even then 
you'd have to account for the cold-cranking and other factors. So 
another dimension is needed -- time. If that hypothetical cold battery 
above persisted at 11.5V @20amps for 10? 20? minutes, there's a problem. 
If it rises to 12.5V after 5 minutes and current drops to 5A, normal. Etc.

That's where the meat computer staring at the gauge comes in.
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