Strange Beeeeeeeeeep

[Brett Dikeman]

At 12:14 AM -0400 4/11/04, TM wrote:
>Greg-
>Sounds like the alarm went off. This usually happens when the battery
>is very low and the electrical system starts going nuts.

The alarm horn isn't under the dash...

>I've BTDT the last several months with my battery discharging from
>sitting too long.

Ok, more than you ever wanted to know about lead-acid batteries, and 
didn't ask:

Unless the battery in question is a spiral-wound like an Optima, or a 
sealed gel(like a VRLA, Valve Regulated Lead Acid)- this is very, 
very bad for the battery, almost "fatal".  If it continues, you'll be 
replacing it soon.  Batteries sulfate as they are left discharged, 
and the sulfation is essentially a crystallization of sulfur on the 
plates, reducing surface area and hence the capacity of the battery. 
It is the #1 cause of battery death.  In fact, you should pop the 
cover on the battery and check with a flashlight what the plates look 
like and the levels are.

Any time a battery will be left for more than two weeks(longer if 
disconnected- almost a month for a fully charged, excellent condition 
battery), it should be placed on a maintenance charger, such as a 
BatteryTender.  Past that, sulfation occurs...especially in warmer 
conditions.  I have a nice Yuasa unit that we use to charge a number 
of lead acid's around the place and which I put the car on if it will 
not be driven for a long time.  There are also a number of solar 
panel based units; you don't need(or even want) large units; 100mA is 
plenty to counter self-discharge and radio/ECU/seat memory drain on 
our cars.  The small wall-wart units are about 500mA, and fully 
regulated for float(so they only put in what's needed).  They're 
perfect for motorcycle batteries but will take a week to charge an 
automotive battery.  The next step up is generally the 1.5A(1500mA) 
units which are more useful as 5-stage chargers, and can bring an 
automotive battery to full charge from a heavy discharge within 24-48 
hours or so.  Every few weeks I put one of the family cars on it, and 
it generally goes for a few hours tops and then switches to 
maintenance mode(13.26v or so), and I leave it on float overnight.

   If left over time to fully discharge(won't start the car, or 
struggles to start the car), budget a new battery as yours will be so 
sulfated it will have lost significant useable capacity.  This 
problem will get worse and worse as the normal parasitic drain from 
the car discharges the battery faster and faster(since it has less 
and less capacity as sulfation builds up), until the capacity of the 
battery(and hence the max rate of charge it can take) is too low for 
the alternator and your battery cooks (you'll notice this when the 
severe gassing breaks apart the grid in one cell and the cell shorts 
itself out).

Also, a battery that has been left to discharge slowly until it has 
lost significant capacity should be recharged slowly(with one of 
those said maintenance chargers; it can take days, but it's the 
proper way to do it).  NOT by starting it up and running it around 
the block(or even worse, idling), which probably won't be enough for 
a full charge anyway.  If your battery is 65AHr and has been drained 
to half, it is going to take at least 30 minutes assuming your 90 or 
110A alternator has 60 amps to spare.  Why no idling?  First, because 
Audi tells you not to leave your car idling, especially unattended. 
Second, because at idle speeds, the alternator barely spins fast 
enough to match load from systems in the car, and further- alternator 
output drops substantially as the temperature of the alternator 
rises(the regulator does this to keep the alternator from exceeding 
the temperature rating of the insulation on the coils) and under 
heavy load, airflow from the alternator's fan won't be enough to keep 
it cool enough to sustain maximum output unless it's pretty brisk 
outside.

   Rate of charge should match rate of discharge except when 
performing an equalization charge(which should only be done to a 
mostly-charged battery anyway), which has to be based on the capacity 
of the battery.  Part of the purpose for an equalization charge is to 
get the battery to gas a little and stir up the electrolyte, 
especially after topping off levels with distilled water.  Less of an 
issue with batteries in cars though, as they get pretty well shaken 
up.

Speaking of Optimas, I'm quite happy with mine- I once left the main 
interior light on for about 12 hours, and the car started like 
nothing happened.  It also started the car with 10w30 oil in -30 
degree F temperatures one morning at the club's winter driving 
school.  However, I did have to block the battery all the way towards 
the passenger side(it is not as wide as most), and build up a 
significant + terminal shield arrangement to make sure it wouldn't 
contact one of the support bars in the seat if it did accidentally 
slide back.  Letting it slide all the way to the driver's side would 
put the + terminal very close to one of the aforementioned bars. 
Speaking of which, I need to check up on the arrangement when the car 
comes out of the shop...

Brett
(the lead-acid battery know it all :-)
-- 
"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin
http://www.users.cloud9.net/~brett/