Charging System Troubleshooting on 72 - Chevy Nova Forum
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Old 29th-April-2007, 08:54 PM   #1
leejoy
 
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Charging System Troubleshooting on 72

what is the best quick method to see if my charging system is working on my 72? My alternator has a plug with 2 wires, and a post terminal with a 3rd wire (the output terminal). I have an external voltage regulator with a connector harness (I think it's 4 wires?) I have a voltmeter in the car and she used to read 13-14 volts when the car was running. Lately she is only reading 11-12 volts. The battery is new. The alternator is about 1 year old. Less than 500 miles on it. I think it's a 65 or 70 amp output?

If I disconnect the battery (positive) when the car is running, should I read about 12V on the positive battery cable to ground if the charging system is working? that would only take me a minute to do. Any other suggestions?

When I go to start the car a couple days later the battery is only at 11-12V and not enough voltage to turn over my BB 454 engine. when I charge the battery for a few hours, she holds a 13V charge and the car starts up fine.

Lee
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Old 29th-April-2007, 09:38 PM   #2
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The best quick method is to turn the key to the run position and see where the volts are at then start the car. With the engine running it should be one volt or higher than with the engine not running.
NEVER disconnect the battery out of the charging circuit. Doing so can cause damage.
Since after a couple of days later your battery is only at 11-12 volts then the battery could have a drain on it, be defective, or not getting enough from the alternator and it's related wiring.

Try this, charge the battery up and then get a reading with a volt meter after it's sat for about an hour with the charger off. Now disconnect one of the battery terminals and come back a few days later and see where the battery voltage is at. If it is down to 11 volts then the battery may not be holding a charge. If the battery is sitting around 12.5 volts or so, put an ammeter inline between the disconnected cable and the battery post it was on and take a reading. A number around 0.02A to about 0.04A is OK but larger numbers like 1.0A or higher then this will drain down a battery.

Old cars and old wiring can cause voltage drops or have it one day working good, another day not so good and a third day working again. Get the engine running and see what voltage you get at the back of the alternator and see where it might be dropping towards the battery and your interior gauge.

You might also have a problem with the voltage regulator and if so replace it with a solid state one.

Jim
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Old 29th-April-2007, 09:39 PM   #3
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Do not disconnect the battery while the engine is running. If the alt wasn,t blown before it is now. Replace the alt. And it wouldn't be a bad idea to throw the reg. away too.
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Old 29th-April-2007, 09:47 PM   #4
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Hi Lee,

Your voltmeter readings are a good indication that there's a problem.

The old trick of disconnecting a battery cable while the engine is running runs the risk of damaging things due to voltage spikes (more of a concern on newer cars but it's still not a good idea). And there's also the risk of a spark causing the battery to explode.

A better way to test the charging system is to use a voltmeter. With the engine off, connect it to the battery posts and you should get a reading of a little over 12V on a fully charged battery. Start the engine and measure the voltage again. If the charging system is working the voltage should be higher (like 13 to 14V). You've basically already done this test with the voltmeter you have in the car.

In order to see if the problem is in the alternator or the regulator, you can try "full fielding" the alternator. Do that by unplugging the 2-wire plug and connecting a temporary jumper wire from the "F" terminal to the "BAT" post on the back. With the jumper in place and the engine running you should get a higher than normal voltage if the alternator is okay. Obviously, you don't want to run it like this for long ... just a quick test. If the alternator is okay, the problem is likely a bad regulator or a bad connection in the wiring.
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Old 29th-April-2007, 10:34 PM   #5
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wow - thanks guys - I really appreciate it. Very good ideas. I have a Fluke VOM and will try the tests and suggestions you guys said in the next few days.

for what it's worth, the voltage regulator (external) is also new. So basically - everything (including lots of the wiring) is new. I'll do what you guys said and let you know

Lee
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Old 30th-April-2007, 12:55 AM   #6
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And for what its worth...

If you end up having to replace your alternator, upgrade to an internally regulated unit. The cost is about the same (maybe a few bucks more) but a WHOLE lot better.
Save yourself some headaches, and clean up all those extra wires from the external reg.
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Old 30th-April-2007, 08:40 AM   #7
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Quote:
Originally Posted by Bscman View Post
And for what its worth...

If you end up having to replace your alternator, upgrade to an internally regulated unit. The cost is about the same (maybe a few bucks more) but a WHOLE lot better.
Save yourself some headaches, and clean up all those extra wires from the external reg.
question: Do the 2 wires in the "plug connector" control the alternator "field" or "armature? I'm trying to understand how it works. I forget. What do those 2 wires do? I'm figuring that the voltage regulator (external) senses voltage and switches on/off either the alternator field or armature current to maintain about 13V. Is that right?
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Old 30th-April-2007, 10:01 AM   #8
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Here's a little info on alternators:

http://www.1stconnect.com/anozira/Si...alternator.htm

http://www.rv8.ch/article.php/20060523194935550

http://www.nationsautoelectric.com/function.html
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Old 30th-April-2007, 10:14 AM   #9
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thanks Mike

I have a good understanding of basic electricity (AC/DC) and am good at troubleshooting and using multi-meters. With the aid of those diagrams you sent me I should be able to to tackle my problem with the charging system. However should you decide to come to my house and help my I will not decline your offer (west chicago suburbs)

thanks

Lee
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Old 1st-May-2007, 08:21 PM   #10
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guys

I'm an idiot (but you already knew that right?)

I found a "loose connection"

thanks to the information you guys provided me, I was able to troubleshoot and locate the problem.

there was no voltage getting to the field terminal "F" on the alternator. I had rewired that about 3 years ago and covered the wiring with that plastic wiring duct. The connection I made was done with a "butt splice" I normally do those very well and test them by "pulling on them" after the splice is made. anyhow, after 3 years of that rumbling bumbling cam I put in there, the butt splice connection broke loose and I lost my field voltage to the alternator. Using a VOM I tested for continuity from the external regulator field terminal "F" to the alternator and there was "no continuity" after digging around tracing my new replacement "spliced wiring" I found the culprit.

thanks for all the help guys.

Lee
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