Honda Car Forum

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
"Tibur Waltson" <Toush@hi.com> wrote in message
news:3c6ef977c6e834d280c29ce6a4a2aa8b@news.bubbane ws.com...
> 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
>
>
>
>
>
>

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.







"Tibur Waltson" <Toush@hi.com> wrote in message
news:3c6ef977c6e834d280c29ce6a4a2aa8b@news.bubbane ws.com...
> 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
>
>
>
>
>
>


---

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Tibur Waltson wrote:
>
> 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
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:

> 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?

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.


--
Fan of the dumbest team in America.

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

>"L0nD0t.$t0we11"
> Roughly 12/27/03 21:47, Tibur Waltson's monkeys randomly typed:
>
> > 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?
>
> 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.
>
>
> --
> Fan of the dumbest team in America.
>

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).

Tibur Waltson wrote:
> 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?

"w_tom" <w_tom1@hotmail.com> wrote in message
news:3FF0D3B0.A06D4A73@hotmail.com...
> 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.

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.

Bob wrote:
> 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

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

w_tom wrote:
>
> 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.
>
> Bob wrote:
> > 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