John,
In your analysis, I think you might be mixing the functions of automotive
ammeters and voltmeters. In almost all automotive applications, the
ammeter MUST reside in the charging circuit/line as you suggest if you are
to get a true picture of charge/discharge (and you are correct in that the
starting current by-passes the circuit - but it is the only cct to do so in
most vehicles). Therefore, the headlights, and other loads are IN the cct.
I am not sufficiently familiar with modern alternator charging patterns,
and battery charge rates to know if your thesis of load leveling is true or
not. I do know that my Chrylser Concorde will happily get my AVO to FSD on
the 50A range quite easily (but whether that would occur on a TR, I just
don't know).
However, I would suggest that you DO need to match the alternator output to
the ammeter range, if you want to avoid blowing the std. 30A unit by
installing a higher output alternator. You may have noticed that later
LBC's equipped with ammeters had the +-60A Lucas units for just that
reason. The cheaper, and maybe less satisfactory solution used by some
budget conscious folks in the autoindustry (B-L?) led to the use of
voltmeters rather ammeters - the following might help explain why.
Once alternator amperage rose to significant levels, the current flowing
thro' the ammeter would have proved very expensive to cable adequately
(since current flow is a function of the area of the wire that the power is
flowing through - so you need fatter and more expensive cable for higher
outputs), and BIG cables add BIG costs!. Manufacturers that still
supported a "gauge" approach rather than idiot lights moved, therefore, to
voltmeters which indicated "condition" of the circuit rather than
charge-balance, and these needed very light wires compared with the ammeter.
The voltmeter is a less "direct" indicator since you need to recognize that
12V or less is not good, but it does a better job than idiot lights since
you can observe "deterioration" over time.
Tony
>
>Hi,
>
>Hope this does not prove to contentious but I would like to make this
>suggestion about ammeters.
>
>IMHO the principle function of an ammeter is to show wether the
>dynamo/alternator is functioning, if it is meeting the electrical
>load requirements, and if the battery is accepting charge.
>
>To satisfy the above the ammeter should be in the battery line
>(but not including the starter motor) which will allow the ammeter to
>indicate battery charge/discharge. All loads other than the battery
>such as head lamps do not feed through the ammeter but you
>still know if the alternator/dynamo is working by the ammeter indication.
>
>Therefor if you provide a higher current supply by changing a dynamo for
>an alternator then there is no reason to change the ammeter range. If you
>have a good battery it will still only take as much charge as it needs which
>will probably be around 10A (very variable number) so the standard 30A meter
>range is what is required. Even if the needle is on the stop no damage
will be
>done as it should only be there for a short time and then drop back to a
>reasonable charge rate.
>
>Hope the above makes sense, it was just a thought.
>
>John Dowson
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