Elle replied:




Notice that Elle omits this very revealing information,

The "10 V" that cause sucking eggs are in disagreement
with a battery test, so the important question is,
"Where exactly was the voltage measured?" The inquirer,
we can tell, is ignorant about matters electricity. He
needs help.

Add to this the the other information the inquirer had
provided, like both the battery and the alternator
tested fine, and the proper diagnosis is "weak
connection." The probability is very high that cleaning
the terminal and the clamp (this involves taking off
the clamp and, if necessary, removing corrosion from
the contact surfaces) would have solved the problem,
and that a new battery was unneeded.

It is disturbing that experts find it easier to suggest
replacing parts instead of using their brains to find
the causes of the problems.

To make connection problems less likely, particularly
at the battery terminals, apply vaseline liberally. And
make sure that the clamp grips the terminal tightly -
if it is too large thin wires from a multistrand cable
can be inserted between terminal and clamp.


..

karl wrote:
Elle's right.

You jump because the battery is dead, right? No point jumping a full
battery. It wouldn't do anything anyway, as the jumper and jumpee are
at same voltage potential. If they are at a different potential, it is
called charging.
The jumping is not so much the problem, but the fact that the battery
was allowed to discharge to near dead and I am sure that's what Elle
meant.

A deep discharge causes the internal resistance of a a regular lead
acid battery to creep up. Do this a couple of times and you'll loose
serious capability. That is inherent of the cells used.
After one deep discharge one might permanently loose as much as 5-10
percent of capacity on some cells.(Capacity, as in the amount of
current it can deliver, both peak and constant)

Just using simple high school physics:
Since your internal resistance crept up, yet your output voltage
remains pretty much the same, the capacity goes down.
(E=IR -> E(constant) = I(high) * R(pretty low) = I(lower than high) *
R (crept up)
This is also why a battery like this will not 'take' a charge. You
might put a charger on a totally dead battery to find that the charger
indicates 100 percent charged in less than 10 minutes. Same reason.

If you need a battery to run til near empty, one should get a battery
tolerant to deep discharges. Commonly used on boats, etc.

Remco

karl wrote:
Eehhhh... Not sure where this second guessing way after the fact is
coming from because Elle was right: The guy went to autozone and they
found the battery bad...
His battery was replaced a while ago with another old battery. They
don't last forever.

Also he checked the battery terminal but let's analyze what you said:

the car was not running. Nothing was on and he measured 10V.
Draw yourself a schematic with a battery and a resistor attached to the
positive of the battery, equivalent of having a bad contact.
The other side of the resistor is not connected to anything --
remember: nothing is running.

You say that it totally depends on where you hook your meter up to see
the right voltage. That is simply not true in a static circuit (as in
no current running):

Envision hooking a voltmeter across the battery terminal. You'll
measure the potential of the battery.
Now think what you'll measure if you hook that very same voltmeter
across that open resistor and ground. You'll still measure very close
to the potential of the battery. This is because that bad contact
resistance is relatively small by comparison of the resistance of the
meter (which is ideally infinite, I'll grant you that it usually
something in the order of a 100K or more, even on a cheap meter).

So to drop 2V across the bad contact, the resistance of that contact
would need to be about 20K. Sorry, but NFW that you'll ever see 20K
there!

So first think, check your facts, then type (And critique after the
fact is just not useful)

Remco

"Remco" <whybcuz (AT) yahoo (DOT) com> wrote
That was implied, but I wasn't particularly thinking that
it's really the fact that the battery has gone to 'deep
discharge' that causes its life to shorten. So you're "on
the money" here, Remco.

I thought you were right with this assertion (and you are),
but I must say I had a heckuva time confirming it. There's
plenty of chatter about how battery plates/grids corrode
over time. But finding a site that says, 'This corrosion
increases the battery internal resistance' (something
somewhat intuitive but not spot on definite to me) took
awhile. I finally found this:

"The internal resistance of Lead-acid batteries is very low.
The battery responds well to short current bursts but has
difficulty providing a sustained high load. Over time, the
internal resistance increases through sulfation and grid
corrosion."
http://www.epn-online.com/page/10082...es-batteries-t
o-fail--increasing-internal-resistance.html

I also saw at one of the battery sites to which Tegger's
site links that keeping a battery below about 90% full
charge on a regular basis will reduce its life
exponentially. This implies that doing anything that results
in a run-down car battery often, and so requiring frequent
jumps by anyone mortal, will way reduce the battery's life.

I agree with the essence of the rest of your analysis,
Remco.

Elle wrote:
I did some research on a battery related problem we were having at a
time, actually something totally unrelated to cars. (do R&D in real
life - the car thing is just a hobby).

I'd have to look through my notes to be absolutely accurate, but do
remember that the exponential nature of the damage done was true in my
case.
The stuff I was tinkering with at that time was better than off the
shelf commercial junk and found about a 5-10 percent drop in capacity
in some cells after the first deep discharge. Being just commercial
stuff, car batteries may be a lot worse but are certainly not much
better.
Combine that, a cold morning and your car stands a snowballs chance in
hell to start in the morning.

If you have jump started your battery a bunch of times, start thinking
about a new battery.

"Remco" <whybcuz (AT) yahoo (DOT) com> wrote
Do tell.

Well, it sure shows. Touch-of-bona-fide-class in writing and
thinking...

I think my last line above, about agreeing with just "the
essence" of what you said, is misleading. Let me clarify and
just say all you presented makes sense to me.

You (and I guess Karl) are certainly right about checking
connections, terminals, etc. Probably should have mentioned
this to the OP, though there was a lot in his post that
suggested he was alert to this and had cleaned and
tightened, yada, when he got that 10 volt reading. Just
seemed obvious to me that when he went from around 15 volts
with the car running (which is high but maybe not
unreasonable) to 10 volts with the car off, that that
battery wasn't holding charge no way no how.

'course, speaking as an amateur, but I hope a studied one, I
still wouldn't rule out further problems just yet, like I
posted to his last post.

snip but comments all noted

Elle wrote:
I think your assesment was totally correct and complete from jump.
You don't have to clarify anything as it was spot on: If you see 15V
with the car running and 10V with the car off, it most likely is the
battery.
Just like when you drive the car and hear "whompa-whompa" it is most
likely a flat tire. Can it be something else? Sure but to first assume
it isn't is just silly

Good call.

As Remco details, Elle got it right.

Any battery that is charging at 15 volts and after charging reads 10 volts
under load is bad... poor connections or not. As Remco pointed out in an
earlier post, the caveat is that there really could be a significant load,
and that slim possibility had to be ruled out to be iron-clad certain.

Mike

"karl" <ottokarl (AT) cognisurf (DOT) com> wrote

get weaker the battery voltage deteriorates, from failure to hold a charge
and sometimes from shorted cells. Either way, failing batteries (or dead
batteries) cause the alternator to put out maximum current for progressively
longer times in order to bring the voltage up to the regulator level.

Alternators are odd things - by design, they will only put out so much
current for a given field excitation. The ratings you see on alternators are
those maximum ratings for about 14 volts on the field. The way that works is
that the voltage they produce is proportional to rpm, and the frequency at
which they operate internally is proportional to rpm. Since the stator
windings are inductors, their reactance is proportional to the frequency (in
turn proportional to rpm) so the maximum current the alternator will put
out, even into a short circuit, is limited.

In the '60s, the alternator could put out the full rating (usually 35 amps)
indefinitely. They were big, Tim Allen devices that scarcely ran warm at
full output. Those days are long gone. Modern alternators are much smaller
and are called on to put out much more current - often 60 to 100 amps. With
a good battery, the electrical systems are carefully designed not to burn up
and still keep up with demand. With a bad battery, the alternator runs too
hot and cooks the insulation and the diodes. Eventually too much damage is
done and the alternator fails.

Mike

"Michael Pardee" <michaeltnull (AT) cybertrails (DOT) com> wrote in
news:1-mdnaKB-sX9-VnenZ2dnUVZ_tudnZ2d (AT) sedona (DOT) net:


<snip>




Nice writeup. It's going into the FAQ.


--
TeGGeR®

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/