Pathfinder won't charge battery - Nissan Forum

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#1 Old Aug 19th, 2006, 07:20 PM
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Pathfinder won't charge battery

I've got a tough problem here. My 1995 pathfinder has stopped charging the battery.

The alternator tests good in repeated tests and is ~ 1 year old. Previous alternator had bad voltage regulator (after 7 years good) and was replaced. Problem started occurring 3 months ago with first symptom being rare (1-2 per hour) bursts of static in the radio.

Battery is new and tests good. It can be charged outside of this truck to where the Pathfinder will run for 20 hours or more.

When in the Pathfinder the battery discharges over a period of 20 to 50 hours of driving and the Pathfinder will not start. After jump start the battery will not charge and truck will stop after less than a minute. When running with headlights on the headlights and console lights brighten and dim every minute or two.

Tests shows that (a) alternator output is turning on and off with 13.7 or more volts showing at the battery when it running and 12.6 volts when it is not running, (b) SUV will not run solely on alternator for more than 3 minutes, (c) SUV will run for extended periods (many hours) with slow battery drain proportional to the electrical load. When the battery finally reaches dead state, the truck will run on alternator for less than 5 mintes then quit.

I've checked for parasitic drains and can't find any. I've not been able to find any shorts to ground within the charging system. I've adjusted belt tension from normal to very tight to with no effect on this problem.

Anyone have any ideas at all how to proceed with diagnosis or what this problem might be?
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#2 Old Aug 20th, 2006, 09:08 PM
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It's probably one of two things:

1 Are the cables in good condition ?

2 The alternator is faulty - was this a rebuilt unit ? A static test may show it's ok but a dynamic test might show a problem
#3 Old Aug 21st, 2006, 02:03 PM
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yeah, i know

Quote:
Originally Posted by golfer
It's probably one of two things:

1 Are the cables in good condition ?

2 The alternator is faulty - was this a rebuilt unit ? A static test may show it's ok but a dynamic test might show a problem
The thick double wire between the alternator and the battery is in good shape. All the wires at the triple splitter at the battery seem good. I replaced one wire at the 1x4 battery wire splitter that had bad contact from me shorting it. The heavy split from the alternator that goes off and vanishes into limbo is ??? since I can't find the other end. The heavy wire that goes from battery to the alternator plug is in good shape. The tiny thin wire that goes to the plug also goes off into limbo so I can't measure that one either.

If the new alternator is faulty, how can I prove it? It's passing the load tests at two retailers.
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#4 Old Aug 21st, 2006, 05:17 PM
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When the static appears on the radio and / or when the lights are dimming does the battery light come on??

The alternator is not getting any excitation voltage for the field coils that's probably why it stops running in about 3 minutes. This is usually a wire from the battery through a fusible link to the " S " terminal on the alternator.
#5 Old Aug 23rd, 2006, 04:44 PM
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Quote:
Originally Posted by Thrasher1995
The thick double wire between the alternator and the battery is in good shape. All the wires at the triple splitter at the battery seem good. I replaced one wire at the 1x4 battery wire splitter that had bad contact from me shorting it. The heavy split from the alternator that goes off and vanishes into limbo is ??? since I can't find the other end. The heavy wire that goes from battery to the alternator plug is in good shape. The tiny thin wire that goes to the plug also goes off into limbo so I can't measure that one either.

If the new alternator is faulty, how can I prove it? It's passing the load tests at two retailers.

When you say it passes load tests at two retailers , is this done at one of those bench testers ( static test ) in the store ?

If it's being tested in the vehicle while running ( dynamic test ) that's a different story.

#6 Old Aug 23rd, 2006, 11:41 PM
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thanks for helping out

Quote:
Originally Posted by golfer
When the static appears on the radio and / or when the lights are dimming does the battery light come on??

The alternator is not getting any excitation voltage for the field coils that's probably why it stops running in about 3 minutes. This is usually a wire from the battery through a fusible link to the " S " terminal on the alternator.
Battery light has never come on during the noise problem or light flicker. Never at all when the engine was running, for that matter.

The excitation voltage theory makes sense, but the wire from the battery to this terminal tests out as sound using ohmmeter and continuity light. I've no fusible links anywhere that I can find, only Fisher Price sized plugs between wire harnesses.

Quote:
Originally Posted by golfer
If it's being tested in the vehicle while running ( dynamic test ) that's a different story
When the alternator is in the vehicle and it's ON, it outputs 13.7 Volts. When the alternator is OFF, I get battery voltage of 12.1 to 12.6 volts depending on charge state. I can tell the operation state by the sound the alternator makes. It switches off and on periodically while idling. That's expected as far as I can tell. When the battery reaches some high level of charge (I've no idea how the alternator knows) the alternator should kick off. So I am at a loss to design a proper dynamic test that gives me a pass or fail. The alternator seems to be alternating. Yet the battery will drain down under 12 volts output.
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#7 Old Aug 24th, 2006, 07:50 AM
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Was this a rebuilt alternator ??

Interesting, when you say by the sound it makes you can tell if it's on or off , is this a noticeable load on the engine or a sound similar to the A/C compressor cycling ??


The alternator is basically an electric motor ; instead of electrical energy in to turn and mechanical energy output it uses mechanical energy in to turn and electrical energy output. The electricity produced is Alternating Current ( approx. 29vAC not good for automotive electrics ).

The diodes inside convert this to Direct Current ( approx. 14.5vDC ) used for automotive electrics. The regulator , now contained inside the alternator , is used to control ( regulates ) the electricity flow ( when and how long ) to maintain the battery.

The Diodes and the Regulator are electronic components and won't make noise unlike a relay. So when you say sound that perplexes me.
#8 Old Aug 25th, 2006, 08:01 AM
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If the alternator voltage is ok as tested, have you checked for amps? How many amps does your alternator gives? The amount of ampherage being produced by your alternator is the one which charges your batteries. If it does not produce sufficient ampherage, then that might be your problem.

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#9 Old Aug 25th, 2006, 09:13 AM
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The alternator is rated at 70 amps maximum but will vary depending on things like rpm , load on charging system.

Here are the specs. on your alternator :

70 amps rated output

approx. 22a / 1300 rpm

50a / 2500 rpm

67a / 5000 rpm

minimum rpm - 950

I doubt the average person would have a test meter rated for these D. C. amp ratings.

There is two options to consider :

1 - replace the alternator The economical priced rebuilds are hit and miss , I've gone through this before , the premium rebuilds are usually better . I usually rebuild my own when possible.

2 - take the vehicle to a shop where they can do a dynamic test on the charging system. The equipment they have will check the alternator output , while in the vehicle , at different loads and different rpm. This will definitely tell you what's wrong.
#10 Old Aug 25th, 2006, 04:49 PM
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Just normal mechanical noise

Quote:
Originally Posted by golfer
Was this a rebuilt alternator ??
I can't tell if the alternator is rebuilt, but it is likely given the age of the truck. The alternator is in warranty. I can have it replaced if I can prove that it is bad. Finding the last one was quite an affair. My truck is a transition model and everyone's computer has the wrong alternator listed. So I had parts guys digging though boxes for hours until we finally found the one that physically and electrically matched.

That makes me want to be diligent on things I can fix myself before going through the whole 'No, this ISN'T the right part, no matter what that computer says' routine at half a dozen parts shops again.

Quote:
Originally Posted by golfer
[B]Interesting, when you say by the sound it makes you can tell if it's on or off , is this a noticeable load on the engine or a sound similar to the A/C compressor cycling ??
The sound is belt rustle and mechanical hum as load is added to the engine. It's not bad bearings or fried brushes. I've checked the alternator spindle turn and it is free and smooth.

Quote:
Originally Posted by Terrano R3m
If the alternator voltage is ok as tested, have you checked for amps?
I don't have the tools for anything that high amperage. The bench test report says amp output is sufficient under a static load. My observation is that the derned thing isn't always running when it should be. To me that says the regulator is shot, or that whatever triggers the regulator isn't connected. Dunno how to prove if either of those things are the case, when it works sometimes and the wires show continuity all through.

Thanks again for the help, folks.
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#11 Old Aug 25th, 2006, 05:03 PM
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Do you still have the old alternator or did you have to turn it in for core exchange ??
#12 Old Aug 27th, 2006, 10:06 AM
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Turned in for core exchange ;(
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#13 Old Aug 28th, 2006, 07:59 PM
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I fail to see what your dilemma is. The alternator is not working, why don't you just replace it?

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#14 Old Sep 4th, 2006, 08:32 PM
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Alternator Won't Charge

I have a similar problem w/ 94 Sentra.
I connected a Vmeter inside and can see it charge than all of sudden drop to 12.5v.
It will start charging again.
I too can tell by the load on the engine when the Alt is charging and when it is not. Sound is similar to AC kicking in and out.

I think the problem is with the Trigger wire... this goes from L terminal on Alt to Batt but thru the Bat light dash and 10a fuse. This wire is how the Alt knows when to charge the battery.

If the wire is broken or intermittent or fuse gone, or even if Batt light is out the circuit is NOT complete. The Alt will NOT charge and you will NOT get a Batt light.

I have not fixed mine yet but I think i'm close.

Holler if i got it wrong.

mike
#15 Old Sep 4th, 2006, 09:32 PM
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Quote:
Originally Posted by vesposit
I have a similar problem w/ 94 Sentra.
I connected a Vmeter inside and can see it charge than all of sudden drop to 12.5v.
It will start charging again.
I too can tell by the load on the engine when the Alt is charging and when it is not. Sound is similar to AC kicking in and out.mike

Quote:
I think the problem is with the Trigger wire... this goes from L terminal on Alt to Batt but thru the Bat light dash and 10a fuse. This wire is how the Alt knows when to charge the battery.
That's not quite correct.

The " L " terminal is usually for the charge lamp circuit it doesn't tell the alternator to charge the battery.

This has voltage from the alternator and goes to one side of the charge lamp relay , the other side of this relay has power from the ignition ( battery ). This is compared so if the voltage from the alternator side is missing that's when the lamp is supposed to turn on.

The regulator is what determines the alternator to turn on and charge depending on the voltage drop of the battery.


Quote:
If the wire is broken or intermittent or fuse gone, or even if Batt light is out the circuit is NOT complete. The Alt will NOT charge and you will NOT get a Batt light.
You won't get a light because the wire is broken , intermittent or fuse is for light is gone.

This should not affect the alternator to charge.

The only other thing would be the excitation line which goes to the brushes to magnetize the rotor spinning inside the stator , that is controlled by the regulator.
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