McFadyean wrote:
>
> Hear hear!
>
> The voltmeter requires the user to be a little bit more knowledgeable to be
> able to get the best from it.
>
> It will tell the state of charge of the battery (i.e. in percentage terms
> prior to start-up) and a failed or shorted cell will be immediately
> apparent.
> It tells whether the battery is being charged, overcharged or not charged
> at all.
>
> It won't tell accurately the remaining storage capacity of a batter
> which is normally done at annual-time by means of draining down through a
> fixed load.
Exactly...and not just 'more knowledgeable' but psychic. If you've
ever attempted to charge good and bad little batteries using a
regulated bench power supply, you won't be able to see how volts
relates to a good or bad battery, unless really bad. Higher volts
means more current either way. But in 10 minutes, the current drops
to zero. Turn voltage up for the next 10. Using a series power
resistor crudely fixes that, so it dissipates excess heat, not the
battery, resistor cooling down as battery comes up.
The regulator thus doesn't really send current to the battery; the
battery draws from it. When a regulator sees the volts drop to the
magic 13.75V, the bartender tells the battery it's had enough; go home
and sleep it off. A defective battery doesn't know it's defective, so
it's happy. Until the next time you hit the starter. This is also
why an external charge is often needed for a discharged, but
reasonably good battery.
The most significant voltage is that where a good battery is fully
charged. Especially RG's. A little bit high, and the battery's life
is being slowly shortened, not noticeable on the ammeter either. Thus
I agree also that these can and should be just periodic maintenance
matters.
Best,
Fred F.
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