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Charging System Issues

Rustee

Rustee

New member
Joined
Sep 12, 2009
Location
Ontario, Canada
Ok, long story short I'm getting a mad voltage drop under accel, sometimes the dash lights come on dimly for a few seconds. It did it way worse before I put a new voltage regulator on.

<embed width="600" height="361" type="application/x-shockwave-flash" allowFullscreen="true" allowNetworking="all" wmode="transparent" src="http://static.photobucket.com/player.swf?file=http://vid116.photobucket.com/albums/o15/Tyler-K/240/101_0655.flv">

You can see the headlights dim in the video.

I just put a new regulator on the other day. Today I did a bunch of tests with the multimeter and found the small ground wire was causing a big voltage drop. So I put a second ground cable off the alternator to the head. Also cleaned all connections and used dielectric grease on everything. This raised idle voltage up to a solid 14v.

What could cause this? Whats sucking that much power under acceleration? I can turn the e fan on at idle and it goes back up to just under 14v.
 
Sounds like the rectifier is bad on the alternator, and possibly a diode or two if the lights dim as well as voltage drop.
Get a rebuilt/new alternator. Pull it off and test at a shop, bet they find the prob easily.

I just went through this and put a rebuilt alt in my 245 yesterday. A j/y alt worked fine, but above 3800 rpm's the dash lights came on. After driving for about 12k miles keeping it under 3500 rpm mostly, noticed teh battery loose water due to boil over. The voltage was fine on a test from idle to 5000 rpm, showed 14.1 volts, and full load 13.8 volts. Changed the voltage regulator and brushes and still did the same thing.

The rebuilt alt fixed everything.
 
Hmm, that's not what I wanted to hear :-(

I went back out and took the main wire off the alternator and tested voltage while revving it up and it dropped as expected. I can't afford a rebuild so I'm going to tear it down and clean everything as best as I can and hope that helps.
 
Same as above.

Seems like an alternator or related to it and mostly it looks like it is just cutting out and the voltage is dropping to the loaded battery voltage. Look closely at the voltage after dropping and then with the lights on and dropping, my guess it will be a half volt even more.

You may compare the voltage to the engine off state and see if it is close to that same voltage when dropped as well.

Why is it dropping could be anything but you may want to check the alt. dash light wiring too. It could be an external short but this would have to be quite large. You would see the voltage drop across the supply and ground wiring go up if that is the case.

To properly test an alternator you need to have a variable speed motor to turn it and load tester and a means of looking at the diodes such as a scope.
 
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I took the alternator out (only takes a few mins now that I've done it so many times) and I'm going to bring it in to where I used to work and test it on a alternator/starter testing machine and see what happens. Even though I'm fairly certain its not working right.
 
I will post my charging post below, try that. Take accurate measurements at different points as listed and also at the alt. light control wire. Do this at various rpm's and in the fail mode. Write them down and then post, this data will zero in on the target problem. :nod:
 
Voltage test first:

Measure the voltage at the alternator output post and case with heavy electrical loads on (lights, fan, etc.) after five minutes at idle, note.

Measure the voltage right at the battery posts not the connections at the same time, note.

The difference between the two should be less than .3 volts. If the voltage difference is greater then check the charging circuit wiring and connections, you might need to upgrade wire size if that is the problem. Getting the voltage close to zero is the goal here.

The older alternators will have a output voltage around 13.8 volts, the newer alternators greater than 14 volts. The newer lower maintenance batteries of the last twenty years require the higher 14+ volts to insure their long life.

The above test will tell you more in ten minutes than anything else you can do. It is better to test first then attack the problem to prevent wasted time and parts. Once you touch anything with wiring you do not know if you fixed the problem or made it worse.

This test will tell you if the alternator is producing the correct output voltage or if the wiring is at fault for poor connections in the charging circuit. This is very quick to do and should always be the first test when having electrical charging issues with voltage problems on any system. Much more likely for wiring problems are the terminations as the very short runs of wire used can carry very large amounts of current with minimal voltage drop.

If the voltage is low in the entire charging system check these:

alternator/regulator
alternator light/gauge and wiring
belt slipping
shorted battery

To test for current drain with the key off a test light or current meter inserted in series with the battery at the battery connection. Just remember some devices use current all the time, a clock for example. Pull one fuse at a time to find the circuit leaking.
 
The voltage drop test is one of the first things I did. Its 14.2v at the alternator post/case and 14.0v at the battery posts. Mind you, I only had the headlights/parking lights on (DRLs, always on).

Where should I test the alt. light wire? And what do you mean by fail mode?
 
Now that I think about it - I have a feeling that the aftermarket voltage regulator is at fault here, I'm going to check the brushes tomorrow to see if they are making full contact.
 
Fail mode; when the system is not functioning as in the condition of high rpm's that relate to the low voltage or when she gets up at the table on the first date and says something just came up I must go.

To verify the power flow direction is positive measure the voltage drop from the positive post of the alternator compared the positive post of the battery with the negative lead referenced to the negative post of the battery. When the alternator is suppling power the voltage will be higher at the alternator post then the battery post, if the alternator has a problem it may use power and the voltages will reverse, higher at the battery. No voltage difference just means no transfer of power.

If you short the dash light control wire to ground after removing it from the alt. does it light in the cluster brightly with the other warning lights with the key on?
 
If/when you eliminate the wiring issues and believe you need another alternator. I have a spare 80amp that you can have, just pay shipping. It's a little greasy from a valve cover leak, but it works.
 
When you are measuring the voltage is that at the alt. itself when it drops out?

What is the voltage on the dash light control terminal on the alt. when running ok and when failing?
 
doeboy said:
make sure your belt is also solid and new and not slipping. easy thing to overlook.
Click to expand...

Yes, they do slip silently on glazed pulleys and belts. Also, if this is the 90 in your sig, the harmonic balancer may be slipping. Sure you expect the screech, but it does not always happen that way, especially around oil leaks. It slips under load when you try to rev up.

If you need proof, that meter you show looks fancy enough to measure frequency. The W terminal on the alternator has AC proportional to the engine RPM (for use as a tach generator in Diesels). Look at the frequency to be commensurate with the tach reading as you rev it up and lose charging.
 
Voltage @ Alt.: 14.25
Voltage @ Batt.: 14.1
Voltage @ D+ terminal: 14.4
Voltage in fail mode @ Alt.: jumps to about 12.40 and goes down to 12 and probably lower
Voltage in fail mode @ Batt.: same as above
Voltage in fail mode @ D+ terminal: drops down to 11.9 and probably lower

Nothing is slipping at all.
 
The circuit is fine, so you probably need another alternator, at least it is the easiest way, and those things cost like 30$ so not worth struggling for very long.
 
My first guess at this point would be the slipping that cleanflametrap mentions. If you are sure it is not slipping then it is the alternator. If it is the alternator the only thing that would do that is the regulator so you might want to just change that.
 
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