Richard Notton wrote:
>
> ----- Original Message -----
> From: <M35products@aol.com>
> To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
> Sent: Monday, November 19, 2001 9:15 PM
> Subject: Re: [MV] Wanted: Battery Guru's
>
> > Some random rules about charging lead-acid batteries:
> >
> > 3. All diodes, regardless of their voltage or current rating, have an
> > inherent voltage drop of 0.7 (zero-point-seven) volts. Whatever voltage
> > setting that is available at the input (anode) is reduced by 0.7 volts at
> the
> > output leg (cathode) of these isolators.
> >
> We usually regard the forward diode voltage drop of 0.6V for ordinary
> silicon devices, germanium devices show a lot lower drop but are virtually
> extinct and do not come in high current form. Shottky and other modern
> constructions may show a lot more. It is important to note that the forward
> volt drop of a diode P-N junction is totally independent of current flowing
> through it.
>
> > 4. A maintenance charge of 1 to 3 amps should be sufficient to keep good
> > batteries up to par, in temperate weather. 25 amps is way too much
> current.
> > You will cook your batteries. (You will never see a truck's ammeter at
> that
> > reading for more than a minute or two, if that long.) This current
> > recommendation assumes that all parasitic loads are removed. These are
> loads
> > that are caused by moisture and insulation breakdown in the vehicle, along
> > with devices such as alarms, clocks, etc. (Disconnect the positive cable,
> in
> > other words.)
> >
> We are missing the point here, the charge current is dependant on the
> voltage of the source supplying it.
>
> Both dynamos (DC generators) and alternators are controlled by voltage
> regulators, usually externally for dynamos and internally for alternators
> except very large ones purely for convenience.
>
> Either type senses the battery voltage and adjusts it field winding current
> (hence output voltage) to achieve its reference set, battery full charge
> voltage, for a dynamo this is electro-mechanical (a very voltage sensitive
> relay) and for the alternator an accurate electronic reference (zener diode
> or band-gap reference).
>
> For either type when it senses its terminal voltage (the battery) to be
> below the reference setting, it increases its excitation (field current) to
> compensate and this leads to charge current, the dynamo needs additional
> current sensing to restrict its power output (watts or V x I) to safe design
> limits. The alternator is current (hence power) limited by design, at full
> output the internal magnetic field is saturated and you get what you get.
>
> Increases in electrical load, turning on headlights for example, drop the
> battery voltage which is immediately sensed by either charging machine type
> which jacks its self up to compensate, thus supplying, or balancing, the
> extra load and maintaining whatever charge current the battery wanted
> previously.
>
> > 5. Commercial chargers have a circuit that will limit, and ultimately
> reduce
> > to almost zero, the current presented to the battery. The internal
> > resistance of a lead-acid battery increases with its charge condition,
> which
> > is a self-limiting feature. This is another reason not to try to use a
> 25-amp
> > supply.
> >
> This is achieved by designing the charger to inherently supply only a few
> hundred millivolts more than the maximum terminal volts of a float charging
> battery. Its a voltage thing again, no matter what the current capability
> of the "charger" at nearly full charge it will only deliver a few amps
> because its voltage and that of the battery are very close.
>
> To grossly overcharge, or supply 25A as is inferred above to a fully charged
> battery, the supply would have to be set very high indeed. The danger with
> heavy current capable chargers comes when using them on small batteries that
> are very discharged and cannot stand this level of current.
>
> An earlier posting suggested modern (low or no maintenance) batteries in
> domestic cars being taken to 15V, this is way too high and I suspect the
> meter used was seeing the ripple of the alternator or just reading high.
> Modern gas recombination batteries usually are labelled that 14.5V is the
> absolute maximum, at this level the battery is gassing to the maximum
> capability of the recombination arrangement.
>
> > 6. Automotive batteries lose half their potency at 32 degrees F. They
> lose
> > 3/4'ths their potency at 0 degrees F. While this fact has nothing to do
> with
> > charging, it is recommended to take the batteries indoors during extreme
> low
> > temps, to aid the charging process.
> >
> Important point.
>
> > 9. Put on your safety glasses, when connecting, disconnecting, or messing
> > around with, batteries, even if they do make you look like a nerd. Better
> to
> > be a seeing nerd than a blind tough guy.
> >
> Everyone should very aware that conventional lead acid batteries out gas at
> around 13.8V (for a 12V battery or 2.3V/cell), it is independent of size
> being a function of chemistry.
>
> The bubbles given off are in a perfect ratio down to the molecular level of
> 2 hydrogen atoms and one oxygen atom.
> It blew out all four sides (luckily) like a card house immediately followed
> by a lot of sulphuric acid which (also luckily) I was not in the way of.
>
> I would not like to repeat this experience ever again and suggest its more
> excitement than anyone would wish to handle.
>
So Richard,
Are you saying you touched off a HYDROGEN BOMB?
Where IS that flame shield when you really need it.......
Mel Miller
M725
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