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Old 05-05-2011, 11:16   #1 (permalink)
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strange electrical problem

Hello, my 2001 ranger discharges the battery while I am driving.

Some charging is going on - I get a couple days of normal usage out of a freshly charged battery.

It is not a bad battery, the battery is new.

It is not the alternator, the alternator is new (this is the second new alternator because I thought the first one was a lemon).

The problem is intermittent - occasionally I notice the fan speed suddenly increase or the cab lights get brighter suddenly - I look down and the battery indicator looks normal.

Any ideas on what this could be? Otherwise, I've ordered a Haynes manual and I guess I'll just go through everything with a voltmeter...
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Old 05-05-2011, 12:08   #2 (permalink)
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Re: strange electrical problem

Sounds as if alternator regulator has an intermittent fault and is over charging .
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Old 05-05-2011, 13:35   #3 (permalink)
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Re: strange electrical problem

Check your grounds, also, just because the alt is new, doesn't mean it is good. check connections at the alt too.
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Old 05-18-2011, 12:48   #4 (permalink)
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Re: strange electrical problem

There is continuity in the entire charging circuit as diagrammed in the Haynes manual.

I performed the charging system check in the Haynes manual, which lead me down the "under voltage" check. All the tests passed except the last test, which I didn't do because the action to take after the last test is to replace the alternator regardless the result of the test.

There was 13 ohms between negative terminal and alternator housing, but I hooked a jumper wire from the negative battery terminal to the alternator housing and no effect.

None of the fuses are blown.

The positive battery terminal was heavily corroded. I replaced it, however it looks the the corrosion goes at least several inches into the wires.




Now here are more details of the problem:

- Turning on the lights/fan cause the battery indicator to drop.

- Coming to a stop causes the battery indicator to rise.

* pushing the clutch in while the vehicle is rolling does not cause the battery voltage to rise according to the battery indicator

- The voltage across the battery terminals drops when the engine is revved by about half a volt according to my DMM.

- There is 0.22 A being drawn while the vehicle is off (including all lights). That seems reasonable.

- The problem is still intermittent. It occasionally "clicks back in" and everything seems normal.

- When the problem is there, the oil and temperature gauges behave very unusually. The oil gauge will read slightly high and flutter occasionally, and the temperature gauge will read high - often it will climb high enough to turn on the warning light and then come down to normal in about 30 seconds.

- The vehicle will run with the positive lead disconnected from the battery (although its pretty rough and the battery indicator will read pretty low).

- The serpentine belt appears to be good (no cracks/splits/damaged ribbing).
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Old 05-18-2011, 16:23   #5 (permalink)
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Re: strange electrical problem

"The positive battery terminal was heavily corroded. I replaced it, however it looks the the corrosion goes at least several inches into the wires."
If you just changed the ends and not the cable, this is a likely suspect. Still sounds to me like a bad connection and likely a ground (lack of) problem.
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Old 05-18-2011, 19:08   #6 (permalink)
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Re: strange electrical problem

I sort of agree in that I would have more of a warm fuzzy feeling if I replaced the entire cable (actually there are two - battery<->alternator and battery<->starter relay).

However, like I said there is continuity... 0 ohms between positive lead and alternator output stud.

As for the ground, I even tried hooking jumper wire from negative battery terminal to alternator housing.

So the alternator is definitely in direct electrical contact with the battery. Maybe I really did just get two bad replacement alternators...

Otherwise there is some sort of short that is loading the system BUT
1) wouldn't this blow a fuse or circuit breaker or fused link?
2) how the hell would I ever find some obscure short somewhere in the electrical system????????
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Old 05-19-2011, 18:24   #7 (permalink)
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Re: strange electrical problem

OK - I don't think there is a short here is why:

- I put an ammeter between the negative battery terminal and the negative lead.

* Ammeter reads 0.25 A

- I turn ignition to "run" (without starting the vehicle) and turn off everything in the cab e.g. the radio

* Ammeter reads 4.85 A

4.85 A isn't very much - I am pretty confident 4.85 A is just the LEDs on the dash (they'd be .1 or so each) and all the electronics that are powered on when it is in run.

I'm basically counting on the idea that when the thing is in "run", all the circuits are hot and ANY short would show itself at this point.

So basically.... I need to buy a third alternator after I replace the serpentine belt (in case this one is somehow slipping) - because I mean really what else could it be?

1) alternator is in direct electrical contact with battery
2) there is no short in the system
3) there really isn't anything else to consider... it's freaking simple!

The alternator simply isn't producing enough power so it (or the integrated regulator) is damaged or it isn't being spun reliably by the belt.

I'll post again after I replace these things.

edit: Just to be TOTALLY sure there isn't a connection problem, tommorow when it gets light I will hook up jumper cables from the battery to the alternator housing and alternator output stud.
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Old 05-21-2011, 08:48   #8 (permalink)
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Re: strange electrical problem

Have you connected a jumper from the neg. term. of the battery to the body and fire
wall ? What is your stator voltage ? Did you jump the regulator at the back of the
alternator ? That should give you about 20 volts and full amperage so make sure nothing is
turned on.
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Old 05-22-2011, 16:00   #9 (permalink)
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Re: strange electrical problem

Solved.

The engine/alternator assembly was poorly grounded. There was a test in the Haynes manual that should have revealed this but I guess I was sloppy about it.

Basically, there is 1 wire that grounds the engine to the frame and it was making bad contact. Without the wire there is ~15 ohms resistance which is significant because of the low voltage/high current.

I have no idea why I didn't see this the first time I hooked up jumper wire from negative terminal to alternator housing - maybe it was because it was a small gauge wire and heated up too much (resistance increases with temperature) or maybe I just made bad contact.
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Old 05-22-2011, 19:09   #10 (permalink)
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Re: strange electrical problem

Glad you found the problem. I thought it would be a bad connection. They can be a pain to find sometimes.
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