Crude alternator load test. 88-Honda Accord

Today I load test the alternator by an instruction in an aftermarket repair
manual. The instructions says to turn on headlights, defoggers, fan, radios,
cigarrete lighter, etc and measure the voltages. It reads 13.6V at 2000 rpm
or 11.2V at 750 rpm. It's within normal range according to the book. But the
headlight seems a bit weak unless rpm is above 1300 rpm or sometimes it just
too weak for the starter. We hardly drive in the highway. It has an alarm
system. Is the alternator fine?
TIA
Tibur

 

Alternator is fine, what you need is a new battery.
Bob

 

Attn: Tibur Waltson

Yes, you can use the car as a charging system load along with a dc
voltmeter, however it is only as good as the battery's percentage state of
charge (ie 70% or higher), temperature and being a good battery. If the
battery is discharged or bad or cold engine your test will be erroneous.

Remember, with a battery charger you are replenishing the expired portion of
the reserve capacity.

An alternator is not a battery charger and can limit its output if the
battery is discharged.

In order to get both the 2000 and the 750 rpm voltages to increase, you may
need to charge the battery with a battery charger to at least 70% state of
charge or a hydrometer test 1.245 specific gravity.

Also, when retesting with a voltmeter, a reasonably tight alternator drive
belt, and a good known battery, only turn on the headlights, AC, and radio
that would simulate about a 40 to 45 amp accessory load. You should observe
about 14.2 to 14.5 volts d.c. at a 2000 rpm fast idle.

Think of summer night driving whether you are driving at 60 mph (ie 2000
rpm) or stopped at curb idle (ie 750 rpm) and waiting for a traffic light to
change to green.

This really is not rocket science.

 

why not go to auto zone and get a free battery, alternator test and be
sure.. it sounds like the battery is low/bad..... but check it out..

 

Roughly 12/27/03 21:47, Tibur Waltson's monkeys randomly typed:

It looks like the alternator is OK, but the battery itself
may be on its way to failure.

You may want to try AutoZone or Sears for a quick check of
your charging system and the battery itself.

First make sure that all of the battery connections are
squeaky clean and tight. If the cable posts are loose
inside the battery might as well head to the battery store.

You can load check the battery itself with similar test as
above.

With nothing connected, the battery should read 12.4 volts. If
below that, it isn't charged fully or is defective. If you
have a battery charger, try it.... but replace any battery that
can't hold 12.4 volts or higher with no cables connected.

Then make sure the battery isn't just taking a surface charge
by giving it a load, then check the open circuit [no cables]
voltage again. Turn on your headlights [with battery connected]
for 15 minutes, then turn them off and wait 5 minutes. The
battery should still show at least 12.4 volts. If it can't,
it is getting old and is only taking a surface charge.

With no-load and the headlight 15 minute load test, rough battery
voltages for charge are:
12.0 volts = 25% charge
12.2 volts = 50% charge
12.4 volts = 75% charge
12.6 volts or more = 100% charge

If the battery is 5 years old, swap it anyway if it is a premium
model. If not a premium model, derate that to 4, 3, 2 years.

 

Attn: Everyone,

The 3-year old low-price, drained-several-times, weak-battery described
above is now replaced with a new 7-years warrantee battery. Let's see how
long this one will go. I have another similar alternator question for a
second car, if I may.

Recently my wife's '97 BMW 318ti's alternator was replaced and it shows
13.7V at any rpm with no loads. With loads it's 13.6V at 2000 rpm or 9-10V
at idle. Engine off it reads 12.6V. Alternator is Valeo, made in France.
Battery is two years-old. Is the alternator fine?
Attn: Battery experts! Thank you.
Tibur

 

I don't see anything suggesting the battery was bad.
However the volt meter makes testing a battery so simple.
Find a problem before trying to fix it - which is why that
voltmeter is a so important tool.

Run car even at idle without electrical loads. Battery
voltage should be above 13 volts. Turn car off. Battery
voltage should be somewhere in the neighborhood of 12.5 to 13
volts. Turn on high beams. Battery voltage should maintain
over 12 volts and over many minutes, never drop below 12
volts. That is a good battery.

Described previously is what I would expect from an
alternator problem. Alternators really are three separate
electrical generators. If one fails, then output voltage will
appear low during low RPMs. This is why smarter mechanics have
an oscilloscope). Alternator will charge battery under most
conditions but will slowly discharge battery during a full
load of electrical peripherals (headlights, read window
defogger, heater fan).

That idiot light can be a problem. An alternator that
outputs power will still discharge battery. Idiot light
properly reports that alternator is outputting electricity
(even if that is not enough electricity). Same problem can
also occur if fan belt to alternator is slipping. Great
profit to the local repair shop. They sell a new battery
since - as demonstrated here - knowledge of how alternators
can fail is so little understood.

A car battery that does not last at least seven years (never
even garaged) suggests a car problem - either in design or a
maintenance problem. Demonstrated are two reasons why an
alternator can suggest battery failure - slipping fan belt
that makes no indication OR loss of 1/3rd of the alternator
(usually a diode failure inside the alternator).

 

Wow, that's the biggest load of crap I've heard in quite some time. I doubt
if even 5% of batteries sold make it to seven years and I'm pretty damn sure
that doesn't mean that the other 95% all have car problems.
Bob

 

In over twenty years, never had a single car go less than
seven years on a battery. BTW, the lead acid batteries used
for battery backup (in serious systems) are expected to last
on the order of 20 years. But then they sit inside controlled
environments.

Back in the 70s, a battery had to last at least 3 years (and
yes, many did not). Better material purity and better
designed charging systems (temperature compensated controls,
et al) are some reasons for longer battery life expectancy.
My last two batteries went 8 and 9.5 years - exposed to all
temperatures.

 

I do not think your experience is typical. I have never had a battery
that lasted more than 4 - 5 years. (Northern California)

 

And you live in an area where batterys should live a long life due to
temperatures that don't get extremly high or low. On my own vehicles I load
test the battery every fall but pass or fail it's outta there after 5 years.
Batterys are cheaper than tow trucks.
Bob

 

I've heard bigger loads of crap, but that was pretty good. People's
personal experience always comes out in these posts. We don't know who
the experts are in most cases. Take everything with a grain of salt.
I went to jump start a lady's car two weeks ago who walked home
because it was dead. It was parked in a grocery store lot with cars
next to it. The battery read 8.69V on my digital meter and yet it
started. Go figure. The battery actually was serviceable while the
voltage regulation was gone. Weird things happen. A battery can last
15 years, barely. I've never kept one more than four years myself.

 

Roughly 12/29/03 18:10, w_tom's monkeys randomly typed:

And more importantly, are of an entirely different construction
and design, since they have an entirely different set of
design requirements than an auto battery, so this is pretty
much meaningless as far as an auto battery is concerned.

In addition to their design, UPS batteries are rarely subjected
to prolonged vibration, even in California.

As for batteries lasting 7 years, perhaps yours do, but careful
folks change them out much sooner, 4-5 years even for the
premium units.

Older lead acid batteries used brute force with lotsa lead
available. Current ones have considerably less lead and
rather different internal construction. At least in the
50's and 60's you would usually get a warning as the battery
begins failing more gradually compared to todays life cycle
that looks pretty much like Niagara Falls.

Both lucky and highly untypical.

 

The trouble is that most people are ignorant of how the battery works and
abuse them... and the auto mfrs keep adding features which encourage the
abuse. E.g. how many people with auto-off headlamps use it as a feature
rather than as a safety against forgetfulness?

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??

 

Therein lies 'battery stress' that can lead to premature
failure. If one completely discharges a battery, then
premature failure is probable. Just another reason why that
inexpensive 'headlights left on' warning device should be
standard equipment.

As car battery life expectancy increased, so did life
expectancy of lead acid batteries in controlled environments
such as communication buildings. Both increases due to better
battery construction and superior recharging methods.
Engineers note life expectancy in communication facilities has
increased substantially to something just under 20 years -
which is consistent with increased battery life expectancy in
cars. To be consistent, car batteries that once got 3 or 5
years in the 1970s are getting something less than 10 years
today.

For those who are suffering battery failure in 5 years -
what model car? Yes, battery life expectancy has increased,
in part, because some manufacturers have programmed superior
battery recharge systems. What model cars are not providing
more than 5 years from a battery (assuming owner has not left
the headlights on overnight)?

 

In my former life, I managed a battery specialist distributorship.

The statement: "To be consistent, car batteries that once got 3 or 5
years in the 1970s are getting something less than 10 years today."
is wrong.

The expected average life:

up to the late 1970's antimonial lead alloy - 26 to 29 months

hybrid antimonial lead and lead calcium - 36 to 39 months

calcium/calcium lead - 46 to 49 months as quoted by ACDelco.

 

Expected average life is a confidence index; not a
statistical average. It means a majority of batteries must
exceed those numbers. For example, 99.9% of antimonial lead
alloy batteries will exceed the 26 to 29 month life
expectancy. It does not mean that 99.9% of batteries will
fail in the 26 to 29 month period. It means that battery can
be warrantied for 26 to 29 months, and manufacturer should
have very few premature failures (and pro-rated warranty
claims).

If batteries lasted 26 to 29 months, then something
approaching 50% of the batteries would fail prematurely while
still under warranty.

I have a 2 liter bottle of coke. Does that mean the coke
contains 2 liters? No. Maybe 99.999% of those two liter
bottles contain 2 liters or greater. Again, 2 liters is not
the expected average quantity. Two liters is also a
confidence level. Battery is rated same way. Battery is
expected to last longer than 26 to 29 months - a confidence
level.

My 1976 GM Freedom battery (that 'no add water' battery, an
early calcium lead type?, became the 1970s standard) was still
working in 1981 when I sold the car. Ironic because in its
first year, during a -20 degree F day, it died and was
'thawed' out by a jumper cable charge. Failed under low
temperature one day and yet still worked 5 years later.
According to those numbers, I should have only gotten 4 years;
give or take a few months. But I got as the manufacturer
claimed. I got more than 4 years. I got five. Battery
conformed to the confidence level.

 

Just thought I'd throw in another alternator question in this thread. I've been
getting intermittent voltage fluctuations in my electrical system. The
fluctuations can be seen the in lighting system and by the in-dash volt meter.
An oscilloscope on the battery terminals with the car at idle shows +/- 0.2
volts at approximately 6Hz (higher Hz at higher RPMs). I had my charging system
tested at an auto parts store and it turned up ok, with the battery being a
little weak. About 8 months ago I had a voltage regulator go out and was
over-charging the battery for a little while. Since then the alternator was
replaced.

My question are:
- What is the acceptable +/- voltage that a properly functioning alternator
supposed to output, if any?

- Will the voltage fluctuations cause damage to other systems in my car?

- Is it possible that my slightly weak (and possibly damaged) battery isn't
"filtering" the voltage fluctuations?

I plan on pulling the alternator and having it bench tested, but I'm waiting
until the weather clears.

Thanks,
- Dave

 

One needs to remember the improvements in SLI secondary automotive lead acid
wet cell batteries from the 1970's to present.

1. Very few manufacturers offered more than a 36 month limited warranty
until the mid to late 70's.

2. The battery industry made a running change from Natural Hard Rubber Tar
Top Covers and Cases to Polypropylene covers and cases. This remarkably
reduced self discharge through the very porous rubber case and thus
increased service life.

3. ACDelco test marketed lead calcium batteries actually discovered by
accident by Prestolite in their laboratories seeking a substitute to the
free worlds supply of antimony.
The development of lead calcium alloy batteries opened the need for a whole
plethora of automotive electrical advancements such as a higher charging
voltage, battery overcharge resistance, solid state voltage regulators,
digital displays, electronic ignition, and improved alternators to name a
few.

 

Apparently "w_tom" <> likes to make something very simple
very complicated.

In my previous post, my quotation of "expected average life" is in reference
to aftermarket replacement of OE batteries and not confidence index as
"w_tom" <> suggests.

My purpose was not to imply any reference to warranty. Warranty in those
days (70's)was secondary to brand popularity.

He is the one that dreamed up the "confidence index"? and his accompanying
doctoral dissertation. The battery industry has used for statistical
purposes a 90 percent confidence level for published ratings.

Based upon the thousands of scrap batteries I have had to personally
prepared for proper disposal and shipment, I simply say rubbish to his
lecture. By simple observation, one learns to read manufacturer date codes
and deduce a scrap/spent battery's age. After palletizing about 20 per
layer and 3 layers banded or shrink wrapped on a 40" wide by 42" long pallet
loaded upon a semi trailer with about 19 others at least 2 to 3 times per
week was a lot of work 52 weeks per year for about 25 years.

Maybe "w_tom" <> sat in a office playing with his slide
rule and a chalk board dreaming of one day he would get a chance to lecture
about the battery industry.

No one cares about Coke bottles.

"Failed" can be interpreted from within a limited warranty statement
"failing to hold a charge based upon defects in materials or workmanship".

Accept the fact if widget lasts longer than its warranted life, it has
lasted longer what is average without a doctoral dissertation. You have
simply beat the averages.
So what about warranty! Maybe you would be glad to pay the manufacturer for
that extra time that you enjoyed the benefit of the longer life ACDelco
branded product.

As for his "1976 GM Freedom battery (that 'no add water' battery, an early
calcium lead type?, became the 1970s standard) was still working in 1981
when I sold the car." story.
A lead acid battery's performance based upon the temperature of the battery
is a fact of life.
Just because a vehicle fails to start due to a -20F degree temperature does
not mean the battery is defective. A lead acid storage battery performs
close to 100% efficiency at 80 degrees F and about 40% at 0 degrees F. So
depending upon Reserve Capacity, one may or may not get their car started in
sub 32 degree F weather!

snip