Re: Voltage stability in old truck

From: Ol' Duffer (DontSend_at_MeSpam.com)
Date: 09/10/04 

Date: 10 Sep 2004 17:26:40 GMT

In article <r9f2k0ls3icodo9t6hnulo60g1a7s59vfm@4ax.com>,
Vampyres@nettaxi.com says...
<snip>
> (The main reason the industry switch to 12v systems, 6v batteries just
> could not hold up under constant use and the variable charge rates as
> well as being limited in the amount of loads from the ever increasing
> number of system accessories that were being added to cars.)

Actually, the underlying reason is that you need more
current to do the same amount of work at low voltage.
It was taking like 2 ga. wire for starter motors on
some of the larger engines, but at 12V you can do the
job with 4 or 6 ga. All the connectors had to be
beefier at 6V, corrosion and wire/connector resistance
were more problematic.

Copper wire being an expensive and [potentially] short
supply strategic material, the military bumped most of
their systems on up to 24/28 Volts.

And we may have not heard the last of it. There has
been talk of going to 42 Volts to power the increasing
demand of proliferating electronics in automotives.
It is unclear how this might be implemented, as this
is above what is normally considered "consumer safe"
low voltage. Check one of *those* with your tongue!

> There was a time when a solid state 6v regulator could be
> had, as well as a decent 6v altenator.

Check the rebuilders, like Jebco and Triodiode. You can
still get 6V regulators, reverse polarity diode packs, etc.

> BTW if you take a look at the electrical design of virtually any auto
> made in the past 30 years you'll see that the function of the
> altenator is not to run the entire electrical system of the
> engine/car, but to simply charge the battery.

Now here you are just dead wrong. Nearly all automotive
alternators since the early 70's are equipped with remote
sensing so that the alternator will maintain a nearly
constant voltage at some point other than the battery.
This is done both to reduce the amount of charge/discharge
cycling on the battery, thereby improving longevity, and
to minimize dimming of lights and similar problems that
would be associated with running from a battery in varying
states of charge. Turn something on, the alternator picks
it up right away. The only times significant current is
drawn from the battery is for starting, or at idle if you
have so much stuff turned on that the alternator won't
carry it all. Watch your ammeter if you don't believe me
(if you have one - ammeters are becoming extinct as modern
electronically regulated alternators do such a good job
you don't have to worry about it). The battery still acts
as a huge water dielectric capacitor to smooth alternator
ripple, but this is AC which has no net effect on charge
and is not hard on the battery.

There are one-wire alternators made for simpler electrical
systems, like tractors, where charging the starting battery
is about all it has to do. These are not well-suited for
automotive applications, but a lot of backyard mechanics
use them in error because they are easy to hook up without
having to understand how the electrical system works.
Performance varies from fair to poor. Don't even think
about using one of these with a high-power sound system,
you won't get good results. They are disappearing even
from agricultural use as more high-demand electronics
make inroads.

> Doubly so with those with computer systems/fuel injection etc....
> The regulator and/or the onboard electronics "traps" the charge coming
> from the altenator to prevent it use in the system.(this is to prevent
> damage to the electronics and engine from using fluctuating voltage.

Smoke and mirrors and fuzzy thinking. Nothing in those
sentences solid enough even to poke at.

> A real no-no when you have an onboard computer, fuel injection and
> variable valve controls. They must have smooth, clean constant voltage
> to perform properly.)

That's a bit misleading. Modern engine systems have
built-in filtering and regulation where needed. They
are well hardened against anything even a poor charging
system is likely to throw at them. They may perform a
little *better* with clean power, but it usually takes
some kind of major deficiency to bring them down, and
most of the time they don't even seem to care.

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