Testing car battery / alternator questions

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quentinmacdougall@gmail.com - 17 Sep 2008 00:48 GMT

My 2001 Nissan Sentra suddenly out of no-where will not start anymore.
I am trying to diagnose and learn how to solve this problem myself for
educational purposes. Here are the details I have diagnosed:

-The car will not turn over (no chug-chug-chug noise). When I turn the
key, I hear just a click.
-If I connect my dead batter to working car's battery with jumper
cables, my car starts fine
-I unhooked my bad battery, plugged it into a trickle charger
overnight and put it back in the car. I checked the voltage reading 24
hours after charging and it reads 12.5-12.6v (which at first I thought
meant my battery was okay?). However, when I put the battery back in
the car, it still wont start.
-If I boost the car with jumper cables, and check the voltage of the
car while its running, I get around 15v with nothing on, and if I turn
my headlights, heater, and turn up my stereo loud, it goes down to
about 14.8-14.9v.

Questions:
1) Does my voltage test while the car is running verify my alternator
is okay? Ive been told to check the batter voltage while the car is
running and if its above 14.7v while the car is running ,then my
alternator/charging system is functioning properly. Anyone confirm or
deny this for me?

2) My motomaster car battery charger has a 2A/12A/75A settings. The
75A setting even says "car boost" or something to that effect. When I
hook up the car battery charger up to my battery and set it to 75A,
the car will NOT start this way (It did a little chug-chug once, but
usually just makes the click sound). Is my motomaster car battery
charger just not powerfull enough to boost my car? Or is there
something else going on here I am not aware of?

Is the problem just my battery is dead? I want to make sure Ive done
all the tests to verify that it is my battery that needs replacement
before I go out and buy one.

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Ernest - 17 Sep 2008 01:38 GMT

> My 2001 Nissan Sentra suddenly out of no-where will not start anymore.
> I am trying to diagnose and learn how to solve this problem myself for
[quoted text clipped - 9 lines]
> meant my battery was okay?). However, when I put the battery back in
> the car, it still wont start.

A dead battery will show voltage. But! Not enough amperages to start the
car.

> -If I boost the car with jumper cables, and check the voltage of the
> car while its running, I get around 15v with nothing on, and if I turn
> my headlights, heater, and turn up my stereo loud, it goes down to
> about 14.8-14.9v.

Did you check the voltage with the jumper cables on?
Make sure you are only checking your voltage with your own battery connected
and engine idling.

I recently replaced my alternator on my 2001 Sentra. The battery light in
the dash never came on to tell me the alternator wasn't charging.
I got an alternator at a scrap yard for 110$. Now the charging light is on
when the car is not running as it should and disappear with the engine
running.
At idle. It's charging close to 14.7v. The Nissan book says between 14.1 to
14.7 is good.
There are also fuses you can check just beside the battery. The cover will
tell you which one.

Also maybe! Something is defective in your car and draining the battery when
it's not running.

> Questions:
> 1) Does my voltage test while the car is running verify my alternator
> is okay? Ive been told to check the batter voltage while the car is
> running and if its above 14.7v while the car is running ,then my
> alternator/charging system is functioning properly. Anyone confirm or
> deny this for me?

Correct!

> 2) My motomaster car battery charger has a 2A/12A/75A settings. The
> 75A setting even says "car boost" or something to that effect. When I
[quoted text clipped - 3 lines]
> charger just not powerfull enough to boost my car? Or is there
> something else going on here I am not aware of?

A very dead battery will take a while to start a car while been boosted. At
first It seem it just suck the power for itself.

> Is the problem just my battery is dead? I want to make sure Ive done
> all the tests to verify that it is my battery that needs replacement
> before I go out and buy one.

Check all your connections first. Battery, Alternator, Starter and ground.
No greenies...

I have the service manual in PDF, would you be interested? It's not that
big.

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nucleus - 17 Sep 2008 12:10 GMT

based on your description, the easiest and first thing to check is to
clean the
battery terminals. if your battery is a "top post" model, the
terminals can
optimally be cleaned with a tool that uses a wire brush design; clean
the
inside of the cable connections and clean the battery terminals. IF
your
battery is good, this should provide adequate amperage to run the
starter.

if your battery is NOT a maintenance free battery, i assume you
maintain
the electrolyte levels. if it is a maintenance free battery, is it
within the
warranty?

On Sep 16, 6:48 pm, quentinmacdoug...@gmail.com wrote:

> My 2001 Nissan Sentra suddenly out of no-where will not start anymore.
> I am trying to diagnose and learn how to solve this problem myself for
[quoted text clipped - 32 lines]
> all the tests to verify that it is my battery that needs replacement
> before I go out and buy one.

Reply to this Message

AS - 18 Sep 2008 03:10 GMT

From your description:

- With the engine running, no jumper cables, electric loads, the
voltage reading indicates that the system is charging and probably too
much. 15V is on the high side. My car, with full load, puts out 14.1.
The battery I just replaced was 7 years old.

- A battery after being charged for 24 hours even on trickle charge,
should be able to start the car.

- The 75A booster setting in your charger is just that... a help for
the battery to start the engine. If the battery is defective, the 75A
setting may not be enough.

- I would just replace the battery. I recently replaced mine and after
investigating about batteries, I decided to go with the batteries sold
at walmart, made by Johnson Controls who makes the DieHard batteries for
Sears and many others.

Good luck!

> based on your description, the easiest and first thing to check is to
> clean the
[quoted text clipped - 51 lines]
>>all the tests to verify that it is my battery that needs replacement
>>before I go out and buy one.

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