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chasb(at)satx.rr.com
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 Posted: Sun Aug 02, 2009 8:26 am Post subject: Alternator charging battery |
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Bob, et. al.,
I am aware that the wrong battery charger will overcharge and
ultimately ruin a PC-680 type battery. My 60 amp B&C alternator puts
out a lot of amps right after engine start, and has that capability
indefinitely. Of course, the regulator maintains the voltage at a
reasonable level. But what determines the alternator amperage output
during battery charging and after the battery is fully charged. It
would seem to me that during a several hour flight, the battery could
be over charged and damaged by the alternator output. That apparently
does not happen, but I don't understand why not.
Charlie Brame
RV-6A N11CB
San Antonio
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Bob McC
Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON
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| Posted: Sun Aug 02, 2009 3:15 pm Post subject: Alternator charging battery |
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Charlie;
The wrong battery charger will eventually overcharge and ruin any battery. Your 60 amp B&C alternator puts out whatever current is required (up to approximately 60 amps or so) to recharge your battery and support system loads whether right after starting or any other time it’s turning quickly enough to do so. (Always assuming everything is operating correctly of course) Yes it has the ability to do that indefinitely. The voltage regulator regulates the output of the alternator to maintain the system voltage at the required level, approximately 14 volts. If the battery is charged, then no more current will flow into it and the alternator will just be supplying system loads. Should the loads exceed the alternators ability to supply current then the battery will take up the slack. When system loads are again reduced below the 60+ amps able to be supplied by the alternator alone, then the excess current will recharge the battery once again until it is fully charged at which point the alternator output will reduce to match the system requirements. The only way to overcharge the battery is for the regulator to fail and cause the system voltage to rise too high. Hence the desirability of over voltage protection. The alternator only generates whatever current is required not its full rated output. Just like your battery might be capable of supplying 1000 amps, but if all you have connected is a single 6 watt light bulb, it will only supply the ½ amp or so required by that light bulb, not the full 1000 amps it’s capable of.
Bob McC
> -----Original Message----
> -
> From: owner-
> aeroelectric-list-
> server(at)matronics.com
> [mailto:owner-
> aeroelectric-list-
> server(at)matronics.com]
> On Behalf Of Charles
> Brame
> Sent: Sunday, August
> 02, 2009 12:24 PM
> To: AeroElectric List
> Subject: AeroElectric-
> List: Alternator charging
> battery
>
> --> AeroElectric-List
> message posted by:
> Charles Brame
> <chasb(at)satx.rr.com>
>
> Bob, et. al.,
>
> I am aware that the
> wrong battery charger
> will overcharge and
> ultimately ruin a PC-680
> type battery. My 60 amp
> B&C alternator puts
> out a lot of amps right
> after engine start, and
> has that capability
> indefinitely. Of course,
> the regulator maintains
> the voltage at a
> reasonable level. But
> what determines the
> alternator amperage
> output
> during battery charging
> and after the battery is
> fully charged. It
> would seem to me that
> during a several hour
> flight, the battery could
> be over charged and
> damaged by the
> alternator output. That
> apparently
> does not happen, but I
> don't understand why
> not.
>
> Charlie Brame
> RV-6A N11CB
> San Antonio
>
>
>
>
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_________________
Bob McC
Falco #908
(just starting) |
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nuckolls.bob(at)aeroelect
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| Posted: Mon Aug 03, 2009 7:43 am Post subject: Alternator charging battery |
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From: "Bob McCallum" <robert.mccallum2(at)sympatico.ca>
To: <aeroelectric-list(at)matronics.com>
Subject: RE: Alternator charging battery
Date: Sun, 2 Aug 2009 19:13:25 -0400
Bob,
You've offered a great explanation of the physics of
battery charging as we understand it. I'll offer to
expand on your treatise as follows:
Charlie;
The wrong battery charger will eventually
overcharge and ruin any battery. Your 60 amp B&C
alternator puts out whatever current is required
(up to approximately 60 amps or so) to recharge
your battery and support system loads whether
right after starting or any other time it’s
turning quickly enough to do so. (Always assuming
everything is operating correctly of course) Yes
it has the ability to do that indefinitely. The
voltage regulator regulates the output of the
alternator to maintain the system voltage at the
required level, approximately 14 volts.
Exactly, battery charging behavior is very tightly
tied to system voltage. We know that the lead-acid
battery will EVENTUALLY assume 100% state of charge
if the system voltage is held at 13.8 volts. However,
a design goal for the use of batteries in vehicles is
to achieve a timely replacement of battery energy
used in pre-flight. The folks who have studied battery
physics in detail are in lockstep agreement. The
current "smart" chargers have a CONTROLLED recharge
protocol that looks like this:
http://www.aeroelectric.com/Pictures/Curves/Battery_Tender_Recharge.pdf
http://www.aeroelectric.com/Pictures/Curves/schumacher_3.jpg
If one wishes to MAXIMIZE battery life as a function
of charging protocols, then present thinking suggests
that you charge at best rate (what ever current your
charger is capable of) until the battery voltage
reaches a plateau in voltage that assures a timely
top-off for state of charge. This is generally on the
order of 14.5 volts.
Holding the battery at this charge level is mildly
abusive of the chemistry. In other words, once top-off
is achieved, holding the battery at this level whittles
away at the battery's chemistry in tiny chunks. It's
important to emphasize that this is only slightly
abusive of the battery. I had a GMC Safari with a
"bad" regulator that was ran 15.3 volts that didn't
kill the battery for the first two or three YEARS
that I owned the car. When I replaced the battery,
and discovered the too high voltage, I decided to
leave it and see how it goes.
The car ran another two years on the too-high voltage
before the alternator crapped . . . the new alternator
ran at 14.5 volts. But the battery did't get "cooked"
and was still in the car when I sold it a couple years
later.
However, the folks who have optimized battery CHARGING
and STORAGE protocols have told us that after top-off,
you can drop the system voltage to some value just
above the battery's open-circuit terminal voltage.
That number is just above 13.0 volts. Too low
to charge a battery, but high enough to keep the battery's
internal leakages from running the battery down
while stored.
If the battery is charged, then no more current
will flow into it and the alternator will just be
supplying system loads. Should the loads exceed
the alternators ability to supply current then
the battery will take up the slack. When system
loads are again reduced below the 60+ amps able
to be supplied by the alternator alone, then the
excess current will recharge the battery once
again until it is fully charged at which point
the alternator output will reduce to match the
system requirements. The only way to overcharge
the battery is for the regulator to fail and
cause the system voltage to rise too high.
Exactly. As I've described above, a system voltage
that is "too high" by perhaps a volt or more does
not stand your battery against the wall for execution.
It's not ideal but not automatically lethal.
Hence the desirability of over voltage
protection. The alternator only generates
whatever current is required not its full rated
output. Just like your battery might be capable
of supplying 1000 amps, but if all you have
connected is a single 6 watt light bulb, it will
only supply the ½ amp or so required by that
light bulb, not the full 1000 amps it’s capable of.
This emphasizes the importance of PREDICTABLE and
reasonably ACCURATE control of the alternator (or
battery charger's output voltage). Plug-in-the-wall
battery chargers of yesteryear had NO voltage regulation.
They ranged from BOOST or CRANKING current levels
of a dozen to hundreds of amps of output capability.
These devices had to be SUPERVISED. You came back in
a few hours to disconnect the thing after you were
convinced that a top-off event had occurred. The
larger machines had a timer built in to prevent
inadvertent destruction of your battery if you forgot
to come back and shut the thing off.
Modern chargers offer some form of the battery
RECHARGE and MAINTENANCE protocols described
above and are suited for continuous and unlimited
connection to the battery being serviced. Your
alternator behaves in the same manner EXCEPT that
its regulator doesn't offer a set-back feature for
reduction of bus voltage after top-off. Given that
the duration of operation in the top-off mode is
tiny compared to the service life of the battery,
the cost of adding a "set back" feature in the
voltage regulator has a poor if not zero return
on investment.
Bob . . .
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