Charging System testing

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  #1  
Old 06-07-04, 01:51 AM
doingitmyself
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Charging System testing

From the "Read This Note Before Posting" Forum Sticky Note:

6) Charging system basics. A digital meter is very handy here. In short, a fully charged modern battery should have 12 to 12.5 volts to start. 14.2 when the engine is running with no acessories. Slowly add accessories (lights, blower, A/C, radio, wipers, etc). Watch the meter. With full load, if you get below 13.5 on the meter, the alternator is likely worn out.


1989 Honda Accord LXI 2.0 FI 4 cyl.

The battery (charging system?) warning light came on tonight. It is intermittent: sometimes it will go out, but then come back on. Am trying to determine if I have a bad battery, alternator or just a faulty connection. It's late at night as I write this, and I don't have my voltmeter with me right now so I need some advance troubleshooting advise, if possible.

I've recently replaced the water pump, and the serpentine belt for the pump also drives the alternator. The water pump pulley seemed to be warped when I put it back together, but I didn't bother to replace it and now, at times, I hear the squeal of the belt. I'll probably have to replace the pump again soon, and if so, will also get a new pulley.

I said all that to ask the following questions:

1). Is it possible that an improperly adjusted/worn alternator belt will cause the voltage differences as listed in the sticky note that I posted above? That is, if I get less than 13.5V, as listed above, do I automatically assume the alternator itself is bad, or might it be the belt?

2). Also, as a quick "go/no-go" test, could I test the condition of the alternator by disconnecting the negative lead from the battery with the engine running? If the alternator is good, the engine should still run, correct? And if the alternator is bad, the engine might die? Again, I don't have my voltmeter with me at the moment.

Thanks for reading, and if I left out any additional info you need, please let me know.

-Terry
 
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  #2  
Old 06-07-04, 03:31 AM
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Originally Posted by doingitmyself
[b]
2). Also, as a quick "go/no-go" test, could I test the condition of the alternator by disconnecting the negative lead from the battery with the engine running? If the alternator is good, the engine should still run, correct? And if the alternator is bad, the engine might die? Again, I don't have my voltmeter with me at the moment.
DEFINATELY NOT! That's one of the fastest ways to destroy an alternator.
Obviously you need to repair your belt problem first. I suspect you do have an alternator problem though. If the light is only intermittantly coming on, then using a voltmeter when it's off is futile. Check it over for loose plugs or damaged wires but probably a bad alternator.
 
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Old 07-04-04, 03:48 AM
doingitmyself
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OK, light has been steady now for a couple days. Tonight, I had to jump start the car. I put in a different battery (not new). Pre-start, the battery voltage is 12.2. It drops to below 12V with the car running, with very insignificant further drop in voltage with the lights on.

Guess my questions are:
1). how certain can I be that I have a bad alt.? The cost of a new one for this car is significant for me.

2). with just a digital voltmeter, can I check the output voltage from the alternator, and draw any conclusions? where are the terminals located, and would they be marked, such as: BATT, START, etc?

Basic troubleshooting with voltage and charging tests is what I'm after.

Thanks for the help.

BTW: The belts are okay.
 
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Old 07-04-04, 05:18 AM
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Well, with the voltage readings you have, you can be sure the alternator is NOT charging. Now the question is, "is the alternator itself to blame"? If you have access to the large terminal on the alternator, see if you have 12 with engine off. Another way I quicky test this is to run a jumper wire from that terminal to the battery with the engine running to see if it suddenly starts charging. That would indicate a bad alternator fuse. Other than the fuse, (or the belt) I would blame the alternator.
 
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