Intermitted Alternator or something
Had problem earlier, I thought I fixed it.
New Battery (1 week old)
New Alternator. (1 week old)
Problem still here.

While driving the voltage meter in the car erratically jumps from 14.1 volt to 12.2 or lower.
Sometimes the alternator can handle full load (AC on, headlights on, etc.) with no problem and still supply car with 14.2 volts. On other occasions the alternator will be putting out 14.2 volts once I turn on something (AC, brake lights, head lights, or etc.) the voltage begins to jump around and drop back to a lower voltage around 12.2 or lower.

Can it be another bad alternator? I want to check other components within the car which might cause the problem. Keep in mind the battery is one day newer than the alternator. I measured 78 amps drawing from the alternator with the AC on, headlights on, hood lights, and radio. During this test the alternator was still putting out 14.2 volts. Tomorrow I try to get the car to repeat the failure of the voltage dropping to around 12.2 voltages. At that time I will re-measure the current draw at the alternator. This might help me find what the problem may be.

I purchased my alternator from "The Last Detail" in Atlanta GA. it's a AC Delco rebuilt. I paid $144.00. Do I need to spend more money fro a better one?


Any ideas

 

Are the symptoms exactly the same now as before replacement of the battery & Alternator? If so, it is probably not a bad rebuilt alternator, but something else, as it is unlikely two alternators would fail in the exact same way.

It sounds like the alternator is being turned off or not detecting the battery (12.2 vDC, which represents a 50% charged battery, would be the voltage if the alternator was not charging, yet the battery was being used to run the car).

It sounds like a connection between the battery and the alternator is loose, or an important ground connection is loose.

Have you checked the wiring between the alternator and battery for a broken or partially broken wire/cable?

have you checked the important ground wires -- e.g. the ones grouped together on the driver's side of the bell housing (at the middle bell-housing to engine bolt on the driver side)?

Hope this helps...

 

Measure the battery terminal voltage when the dash voltmeter starts jumping and see if the voltage at the battery does also. You might just have an intermittent connection to the dash. At 12.2 volts, the battery is supplying the car's electrical load and the alternator is not, so your red battery symbol light on the dash should be lit. If it isn't, you might have only a dash problem.
Also, 12.2 volts tells you that your battery is 20% charged up. 12.0 volts and below, discharged. 12.9 volts and above, fully charged and linear in between.

 

Upon the voltage dropping.
The dash showed 12.9
At battery 12.8v (+) (-)
At Alternator 12.9v (+) (frame of Alt)

New test (done later)
The dash showed (I forgot)
From battery (+) to Alternator (+) = 0.5v
From battery (-) to Alt frame (-) = NO Voltage drop.


In all cases of my testing the Alternator voltage has alway been very close to the battery voltage and dash voltage. Something is causing the alternator to put out lower voltages erratically. I can't determine what causes the tripping of this problem. It's Hard to repeat.

I tried to find the ground connection. VERY HARD TO FIND OR REACH.
I need ideas. I even try to find it by lifting up the car. How do I find this connection? I did find the jump start point located behind the battery.. It looked OK.

I will do more testing today before I replace the alternator.

 

It's possible that you have a faulty ground somewhere. One is beyond the battery towards the engine, one near bellhousing and another on the driver's side wall.

Also when you have it running check the AC voltage from the alternator I believe this will tell you if you have a diode leaking. Test from alt + to a known good ground.

Alt link

There are also some links in that post about alternator AC voltage which details more about it.

You'll have to pull the battery to get to the one that is just inboard of it. It is an exposable area where moisture may get and the connection can be rusty or corroded.

I believe you can detect shorts to ground and open circuits with a DVOM and the Ign to On, not running. I can't remember at the moment may someone can state how that is done.

Also you said a 'new' battery, did you look inside the boots around the terminal connector wires to see if there was any corrosion inside before re-connecting to new batt? Lots of times corrision begins inside there and you can open it up some and put baking soda to disolve the corrosion. Then rinse with water. The corrosion can cause an intermittent source of power.

 

Today..
Drove car...Car dash reads 14.1 to 14.2 constantly.
Load: AC, Radio.
Drive for about 20mins...Engine nice and hot.
Drive average 30 to 45 MPH.

PUNCH IT to 80 to 90 MPH for 10 to 15 seconds.
Problem back. Voltage drops..13v, 12.8, then 12.2.....
Drives back home about 3 miles @ 12.2 voltages.

AT Home...
Car dash reads 11.8 volts
Check current from battery (~20amps)
Check current from Alternator ( 0 amps)
Battery voltage read 11.9v (across battery post)
Alternator voltage reads 11.8v ( at alternator "+" and frame of alternator)

If I had a wiring problem the voltage across the battery would be ~12V and the alternator voltage would be ~14.2V. Since both devices are reading close to the same voltage indicates the wiring between the two are solid.
Something is causing the alternator to shut down (over-current, over-heat, or something) ALL I can think it to be is bad alternator or something in my car pulls a lot of current then shuts down the alternator.

Help....

 

Your alternator is intermittent and when it isn't charging the battery the red battery symbol light on the dash should be on. Replace the alternator, all your measurements show a normal charging circuit except that the alternator does not put out current intermittently.

 

I let car sit for 3 hours.
Re-started car.
Load: No AC, No radio,
Battery at 12.2v (42 amps measure )
Alternator at 12.2v ( 0 amps measure )

Drive around for about 10 mins.
45 to 60 mph.
Kept current meter on alternator.
Watched current 0amps, 1 amps, 4amps, 0amps
After 2 to 3 miles of driving, push it to higher speeds for about 3 seconds.
Instanteously dash voltages jumps to 13V then 14.2V
Now current is at 86 amps. Dash meter 14.2V
Drive home.
While car is sitting idle, I turn on AC, High beam, fog lights, radio, lower window. Current at alternator rise to ~110amps.
Next I raise the engine rpm and the current rises even higher.
THe alternator is rated at 124amps.
I think I am exceeding the rating of the alternator which causes it to shut down.
Is it a problem that my car is pulling this much current or is the alternator under-rated. Why is this a problem now?

Is there an internal circuit in the alternator that shuts down the alternator at over-current. What resets it?

 

The voltage regulator attempts to maintain 14.7 volts output which drops to 13.7 volts as the alternator warms up to it normal operating temperature. There is no shut down circuit in the alternator but the voltage regulator llimits the output current to its maximum current rating by dropping the output voltage to prevent output current from exceeding its rating. You have an intermittent inside the alternator, probably worn out brushes which you can make work for a short period by high rpm. You need to replace your alternator, the one you have is defective !!!

 

I have the exact problem with my 85. I pulled every fuse I could find and still have a dead battery in two days. When I get home I just disconnect the battery so that I can drive it when I need to. I went to the local Carquest store and they tested the charging system to see if the alternator was bad but it checked out ok. I thought maybe I wasn't grounded but I can't find the ends of the cables. I have disconnected the negative battery cable and put my voltmeter to it. One lead in the battery and one on the cable, with the key off I am getting 12.2V. I shouldn't be getting anything right? I am getting close to taking it in to a mechanic. I will sell it before I take it to the dealer. HELP.

 

I measured the current draw from the alternator on my Ford Expedition with AC on, High beam, radio, amps, wipers, fog light all equal to about 80amps with high rpms

The same items on my vette equals about 110 amps. Once I raised the rpm on my vette the current went up beyound 120 amps which tripped the alternator. The alternator is rated at 124amps

On my truck the current did not change as my rpms went up.

What can cause the current to go beyond 124amps at high RPM.

AC compressor? or Alternator itself? Starter relay? etc.

 

Alternators cannot generate their rated current at idle rpm and this is the reason why you see your alternator current rise with an increase in rpm. Also, the 124 amp rating doesn't mean EXACTLY 124.000000000 amps! Your ammeter is not EXACT either.

 

When you connect your multimeter in series with the battery cable to the battery terminal it has to be set on AMPS, not volts, that is why you see 12.2 volts. Your meter will then be able to measure the current drawn from the battery when everything is off. GM says leakage current should not exceed 50 milliamps. Myn 87 vette measures 27 milliamps. If your battery discharges in two days, you should see leakage current around 1 to 2 amps. All the circuits are not fused, some have a circuit breaker and some have a fusible link. Behind the battery is a bolt with 8 red wires on it. Remove the nut and disconnect one wire at a time and watch your ammeter for a dramatic drop in current, then identify that wire and check the circuit it supplies power to for leakage.

 

I am using a multimeter in the DC voltage mode.

I read the battery voltage by placing the (-) black lead on negative post of the battery and the (+) red lead on positive post of the battery.

I read the alternator voltage by placing the (-) black lead on the frame of the alternator and the (+) red lead on the ( thick red wire) positive screw of the alternator.


As for current, I have a current probe. I do not need to open the connection. I place the clip around the main red wire from the alternator and it reads postive numbers if the current is flowing from the alternator. It reads negative numbers from current is pulling from the battery bacxk into the alternator. Zero means no current flow.

The alternator should be at a higher voltage (14.2) than the battery (12.2) therefore current should always be flowing from the alternator to the battery trying to pull it to 14.2 voltages therefore keeping the battery fully charged. The alternator also support all the other current loads in the car during operation. The fact that it supplying 14.2 voltage is why everything pulls from it.

 

Do I need to ask this question as another thread within this forum?

1992 vette, LT1 engine.
How much current is normal to be draw from the Alternator while battery is 95% full charged, AC on max, fans on max, 35watt fog light on, high beams on, CD/radio playing, interior light on, and high rpm.

My car is drawing 115amps to 120amps.

I want to know if my car is requiring to much current for operation or this is normal.

My truck with the same conditions only draw 90amps.

 

I understand. I am sometimes too detail. I am an EE tech.
I guess you are saying my car is pulling a lot of current from my alternator and as the rpm increase the alternator tries to supply the needed current.

I keep reading about the 140amp alternators, mine is currently rated at 124 amps. The "The Last Detail" is going to modify a 1995 vette alternator (140amps) to fit my car by changing the pulley.

Why is the load of my car so close to the max load of 124amps? Is this normal and is this why so many other C4 owners upgraded to the 140amp.

 

Your question really belongs in C4 tech, but since it hasn't been moved by a moderator just stay with it here.
The current you measure is below the rating of the alternator so I wouldn't be concerned.
Some members have installed the 140 amp alternator because of the number of failures they have experienced with their OEM alternator. I have an 87 and drive it every day and I have had to replace the alternator 3 times in 16 years. Early C4's have the reputation of eating alternators and a higher current rated alternator will probably last longer. I don't think your current draw is unusual and if you no longer experience the alternator quitting, I would just drive your car.

 

I still have the problem. The current probably spiked up. I am going to close this thread and ask the question under the tech side.
I traded in my 92 Early, 124amp alternatior for a 92 late, 140amp alternator. I hope it fit.