More charging fun

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x_atlas0

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Heya, everybody.

Once again, my coupe is not charging properly. In an attempt to isolate the problem, I have run a 10 gauge wire from the positive output of the alt to the positive battery terminal. It doesn't seem to be charging, however, as the battery terminal voltage is ~12.8-13. However, when I look at the voltage of the "idiot light" on the dash, where the voltage regulator output is read, it is 14V!

Any suggestions?
 
Yep, it is attached at the alternator housing to the engine block. I also verified that the chassic ground and the engine block have the same voltage, 0.
 
If you are getting 14 volts, either the alternator isn't putting out enough current, or the battery isn't making use of it.

Disconnect the battery and test the voltage. Let it sit overnight and re-test, or take it to Sears and get it load tested (better approach). Try disconnecting the battery ground while the car is running. If it keeps running, then the alternator is at least putting out enough juice to power the ignition and fuel pump.

10 bucks says it's your battery

S
 
ScottAndrews said:
If you are getting 14 volts, either the alternator isn't putting out enough current, or the battery isn't making use of it.

Disconnect the battery and test the voltage. Let it sit overnight and re-test, or take it to Sears and get it load tested (better approach). Try disconnecting the battery ground while the car is running. If it keeps running, then the alternator is at least putting out enough juice to power the ignition and fuel pump.

10 bucks says it's your battery

S
Click to expand...

I've got a deep-cycle battery charger. It was pretty dead earlier in the week, but now it is fully charged. It is an Optima Red Top. The car has no trouble starting. I have checked several times to make sure the battery is still mostly charged. Oddly enough, every time I have checked it lately, after re-routing the alt, it is still at 100% charge, which makes me think it is actually working. Does anybody know the correct voltage between the positive and negative battery terminals when the car is running? I'm currently using a 65A internally-regulated alt from a later car. I've got the regulator already jumped, so the idiot light still works.
 
Correct or not, here are my readings with an 80amp internal regulator and a very new Optima yellow top:

Sitting cold (overnight): 12.85v
Started, fast idle,cold: 13.8-9
Started, warm: 13.95-14.1

My car is working fine - just made the round trip to Vintage at Vineyards with no issues (other than a rainy morning).
 
I re-read your first post.

It sounds like the alternator output is going to the idiot light, but not to the battery; since you have 12.8 volts at the battery and 14 at the light. The alternator is supposed to put out 14 volts +/-.


I don't have my wiring diagram with me, but usually there is a wire that runs more or less directly from the alternator output to the battery. It probably takes a somewhat scenic route through the fuse box. On later cars there is usually a fusable link, or giant fuse to prevent the alternator from catching fire if there is a major short (a good precaution for those of you who don't relish the idea of your coupe going up in smoke). I'd check tast wire for breakage, high resistance, corrosion, poor connector contact, etc.

S
 
It would be pretty hard to get the alternator output mixed up with the idiot light since the main outline uses a large bolt and the idiot light is a simple 18 guage (blue) spade connector. Based on the description, I suspect a ground path problem. My money says the battery is good.

12.8v on the battery and 14v at the idiot light with ground referenced to the alternator would indicate that the ground path to the battery is resistive but to the idiot light it is fine. This could happen even with a good positive connect if the ground path is bad. When you are measuring the idiot light where are you picking up ground? Ditto on the battery voltage (assuming across the terminals).

There are several ground path problem areas. I would do a simple test of measuring voltage between the negative battery terminal and the case of the alternator. If there is more than 0.2volts you have a problem. You can also try a jumper cable from the engine block to the negative battery terminal and see if the voltage changes. The ground path (and problem points are):

1. Alternator internal to alternator shell (bolts) - could be defective inside alternator
2. Alternator to engine block. You say you have a big new cable
3. Engine block to body (my money is here). There is sometimes are strap from the back of the engine to the firewall; if not you need to find and check the connection. Mae sure the metal is clean on all sides of the connection points.
4. Body to battery. The braid connector needs to have good metal-metal contact to the body and the battery terminals need to be clean.

I hope this helps.
 
Grounding results-

1. How would I check that without disassembling the alternator and bolting it up to a rotating assembly of some sort? I'm not sure what you mean.

2. Alt to block is good, as I have a 10g wire going from the housing bolts to the block.

3. I checked the negative battery terminal versus the engine block and I got a very, very small voltage. (<.002 V) I would say that is zero.

4. The gounding strap is in place, but I don't have any exposed body to check the voltage. Everything is painted.
 
In reverse order:

4. You can measure voltage on any bolt/nut on the body. However, because of your 0.002v reading from block to negative terminal you have pretty much ruled out a ground path issue.
3. "
2. "
1. Since you have a 14v reading on the idiot light and lower voltage at the battery we are narrowing this problem down. This leaves only the 12 path for inspection (without taking apart the alternator).

A. You should measure voltage across the 10 gauge wire you installed. It should be almost 0v. If it is, I suspect you have a problem in the alternator. It would be likely that there is a poor internal connection to the output terminal or the ground. Is the unit a rebuilt?
B. You may have a bad diode (or two). You can do a crude test by putting your meter in AC mode and measuring across the battery terminals and also across the alternation output and its case. You should expect to see a small amount of AC (perhaps 0.3v-0.5v). If you see more, especially at the alternator, it would point to a diode issue.
 
jhjacobs said:
In reverse order:

4. You can measure voltage on any bolt/nut on the body. However, because of your 0.002v reading from block to negative terminal you have pretty much ruled out a ground path issue.
3. "
2. "
1. Since you have a 14v reading on the idiot light and lower voltage at the battery we are narrowing this problem down. This leaves only the 12 path for inspection (without taking apart the alternator).

A. You should measure voltage across the 10 gauge wire you installed. It should be almost 0v. If it is, I suspect you have a problem in the alternator. It would be likely that there is a poor internal connection to the output terminal or the ground. Is the unit a rebuilt?
B. You may have a bad diode (or two). You can do a crude test by putting your meter in AC mode and measuring across the battery terminals and also across the alternation output and its case. You should expect to see a small amount of AC (perhaps 0.3v-0.5v). If you see more, especially at the alternator, it would point to a diode issue.
Click to expand...

Man, I hope it isn't the alt, as this is the 3rd one I've gone through trying to fix this problem.
 
Ok, new results:

Very, very low AC across battery. (<.02V) I started the car after checking the battery's current charge level, which was 85%, with a voltage of ~12.5. After starting the car, and running it for a few min, the voltage held steady at ~13V (between pos and neg terminals on battery) and after turning the car off and removing the positive lead, the battery charge was checked again and this time it read 100%.

I also noticed a ~1V difference between the radio's power cord and the negative terminal. It doesn't make sense, as the amp and radio were completely disconnected from the power supply, aside from the heater control switch, where I have it temporarily connected for the "car on" signal.

So, it looks like it is working, just not terribly well.
 
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