Alternator fluctuations

I have a new delco alternator and new battery and I am getting strange fluctuations at the battery. It will read up to 13.6 volts and jumps rapidly all over the place down to about 3 volts and everything in between.

I have double checked the wiring a hundred times, and everything is correct.

I can only thing that it is a bad ground(the battery is grounded to the body), but I actually grounded the - batt to my other vehicles - terminal using jumper cables, and still got the fluctuations.

I have read about the plug wires being the problem, but they are newer wires from kaiser willys and are 7.5 mm.

This is actually the second alternator and battery from napa that have given me the same results(I replaced both after they both tested bad at napa the first time).

What is killing my charging system, and giving me these strange readings.

 

How is the alternator grounded? If your battery (-) is connected to the body, you could have an inadequate ground at the alternator. It would be better to have the battery (-) cable connected to the engine block, then run a ground cable from that point to the body.

Also, it would be a good idea to run a heavy ground wire from that ground point to the alternator. There should be a threaded hole in the back of the alternator's case for this purpose.

Where is the alternator's terminal #2 connected? This is the sense input wire to the regulator.

Where is the alternator's terminal #1 connected?

Where are you measuring the voltage? From your first sentence, it sounds like you're measuring across the battery. There's no way a (non-defective) new battery will fluctuate that much. If you are measuring between the battery terminal clamps, try measuring between the battery posts. If there's any difference, maybe your terminals need cleaning.

 

How is the alternator grounded? If your battery (-) is connected to the body, you could have an inadequate ground at the alternator. It would be better to have the battery (-) cable connected to the engine block, then run a ground cable from that point to the body.

the alternator is grounded directly to the battery -
the battery - is grounded to the rod that goes from the firewall to the front grill
Also, it would be a good idea to run a heavy ground wire from that ground point to the alternator. There should be a threaded hole in the back of the alternator's case for this purpose.

Where is the alternator's terminal #2 connected? This is the sense input wire to the regulator.

the #2 is connected and #1 are connected to each other through a purchased resistor and then to the positive on the alternator

Where is the alternator's terminal #1 connected?

Where are you measuring the voltage? From your first sentence, it sounds like you're measuring across the battery. There's no way a (non-defective) new battery will fluctuate that much. If you are measuring between the battery terminal clamps, try measuring between the battery posts. If there's any difference, maybe your terminals need cleaning.

the new battery measures just fine before connection and when car is not running...when alternator running and hooked to battery is when I get strange reading...

 

It would be better to have the battery (-) connect to the engine block. The heaviest load is the starter, which is grounded to the block. From there, you could run a ground to the body.

This is not clear to me. The #2 terminal could be connected to the alternator's output ("BAT") terminal, but the resistor should connect terminal #1 to a switched 12-volt source. If it's connected to the alternator output (which is also connected to the battery), it will drain your battery fairly quickly (maybe overnight).

Does the starter crank OK? If you turn on the headlights with the engine off, do the lights seem bright? If both answers are "yes", it would seem your battery connections and grounding are OK.

When your measurements are fluctuating, exactly where are your probes? On the battery terminals, or on the battery posts?

What do you get when you connect the probes directly to the alternator? That is, connect the (-) to the alternator case, and the (+) to the "BAT" terminal.

If you turn on the headlights with the engine running, do you see any fluctuation in the light output?

 

could be the alternator itself. If it is internally regulated, the regulator could be bad. Take it to a shop (electrical place) and have it bench tested. new regulators only cost about $20.

 

This is not clear to me. The #2 terminal could be connected to the alternator's output ("BAT") terminal, but the resistor should connect terminal #1 to a switched 12-volt source. If it's connected to the alternator output (which is also connected to the battery), it will drain your battery fairly quickly (maybe overnight).

I did not connect the #1 to a switched source, but I bought a plug that goes into the two terminals that creates the same effect withough a warning light and then goes to the bat terminal of the alternator...

The starter works fine when there is a charge in the battery which is most of the time, but over time, I feel that the alternator is not keeping up with the load of the lights...The lights also work fine with no fluctuations until the alternator seems like it is not keeping up. It is a 63 amp alternator...

The reading on the volt meter are taken on the terminals not the posts...

On the bat terminal of the alternator to the ground of the alternator I get readings of about 3 ot 6 volts...

 

I have a video on my YouTube channel of how to wire it up correctly. YouTube is doing site maintenance right now, and I can't retrieve the link, will post it tomorrow.

 

examined wireing multiple times and thing that everything is wired okay...

very confused however on this fluctuation of volt reading...when car not running, i get consistent readings. Starter works fine, headlights work fine when car not running also...

alternator is posessed(although the same thing was happening to other alternator)

 

OK, I assume this warning light is the "AMP" light in the speedometer. Does this light come on when the key is in the "ON" position and the motor is not running?

About how long does it run before the battery runs down? If the alternator is not charging, the battery should run the engine and the lights for a few hours.

This is the puzzling part to me, as well. If you were seeing this voltage at the alternator but not at the battery, it would suggest a bad connection between them. But if I follow correctly, you are saying the battery is strong enough to start the engine and run the headlights, but when the engine is running the alternator drags the battery down to 3-6 volts.

This would mean that the alternator would have to somehow be pulling more current than the starter. If this were happening, there would be smoke coming from somewhere.

How is the alternator's BAT terminal connected to the battery? It should be a heavy (10 gauge or so) wire running either to the starter solenoid or to the battery. This wire should have a fusible link in it.

Did both alternators seem to work correctly for awhile?

 

A direct connect is required from the Positive post of the battery to the BAT terminal on the Alt to determine the problem. The connection wire (10 gauge min) should not spark when making this connection with engine not running.

 

Are you still running the MSD-6?

 

Just for grins, with the engine running try measuring between each post and its terminal. That is, put one probe on the (+) terminal and the other on the (+) post, then do the same with the (-) terminal.

Ideally, there should be no measurable voltage across these connections, and the fact that the starter and lights work OK indicates there is not, but you're losing 6-9 volts somewhere . . .

Also, try measuring between the battery posts.

Is the fluctuation random, or is there a pattern to it?

 

Fair enough, but it might help sort out where the wiring is wrong. Just trying to make sense out of something that doesn't . . . yet.

I'm also assuming something is wired incorrectly, but I'm not yet sure what.

Re-reading, I may have misinterpreted this:

For some reason, I read this as "through a warning light", but maybe it is "without a warning light"? This actually makes more sense, and in that case, this is wired incorrectly.

Ben, can you take pictures of your alternator and battery wiring so we can see what we're talking about?

 

HERE IS THE VIDEO: Make sure its wired like this.

http://www.youtube.com/watch?v=ODYcBkmHtoE

 

You're right, these two wires should not be connected together.

Actually, the light is something of a side-effect. The primary purpose of terminal #1 is to provide a 12V source to "jump-start" the alternator. If it is connected to a lamp, and the other end of the lamp is connected to a switched 12V source, turning on that switch will apply current-limited 12 volts to the field coil of the alternator. This provides the magnetic field which enables the alternator to generate electricity.

Without this #1 connection, the only magnetic field is the relatively weak residual magnetism of the rotor. You can usually get by with this, but it requires much higher RPM's to get the alternator "started". The terminal #1 connection provides more reliable operation and at lower RPM's.

Once the alternator is generating, it produces the necessary current to maintain its field. At this point, this terminal is actually a source, putting out nominally 12 volts. Since the lamp then has 12 volts on both sides, it goes out. So, the lamp will be lighted when the alternator is not generating, and will go out when it is.

I know this is a source of some controversy, but this is my story, and I'm stickin' to it.

Terminal #2 is the voltage regulator's "sense" wire. The regulator will adjust the output voltage to attempt to maintain the set point voltage (nominally 12V, but actually something like 13.6V or 14.2V -- I forget the exact number) on this terminal. The simplest place to connect it is the "BAT" terminal on the alternator, but you can wire it further "downstream" to compensate for losses.

It sounds to me like the OP has terminal #2 connected correctly, but not terminal #1.

Yup.