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Charging/ammeter issue

Richard Cranium

Richard Cranium

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What causes an ammeter to read like this with the needle bouncing around about 1/8"? New NOS Chrysler voltage regulator, 1 year old battery, alternator & ammeter connections are tight. Good ground on the regulator & the bulkhead connectors are fine.

Thoughts?




IMG_0401.jpg
 
does it go back to normal after you drive a little bit? Draw from starting the car?
 
What is the battery voltage? Sounds like new regulator may be overcharging.
 
After my vr points stuck one day, I went with a solid state vr that allowed me to use the original cover. No problems since.
 
Thanks for all the replies. To answer questions.....

FitzyB5 said:
What is the battery voltage? Sounds like new regulator may be overcharging.
Click to expand...

I haven't checked the battery voltage.


davek said:
does it go back to normal after you drive a little bit? Draw from starting the car?
Click to expand...

No, at idle it's fine & as soon as you increase speed it goes +20 and the needle bounces.



70bigblockdodge said:
Pulsing is usually a bad diode (round back )or rectifier if your using a square back alternator.
Click to expand...

This is the original alternator on my 68 survivor Charger R/T.



turbine68rt said:
After my vr points stuck one day, I went with a solid state vr that allowed me to use the original cover. No problems since.
Click to expand...


Tried several voltage regulators, including the solid state. Same thing.
 
In my case I had a melted wire from the alternator and a couple burned terminal bays in the bulkhead connector. Someone once wrote that each one of those needle jumps on the alternator gage represents a short across wires or bulkhead connectors. That got me to thinking and looking and I found all the melted wire insulation and burned out bulkhead terminal bays.
 
70bigblockdodge said:
It has the 6 separate diodes in that round back alternator. Do the head lights pulse? If so, almost definitely a bad diode.
Click to expand...

Either the Mopar round back or the square back alternator has 3 positive and 3 negative diodes arranged in a three phase full wave bridge rectifier circuit. BTW...diodes, either positive or negative polarity or configuration are open or shorted, and once open, do not heal themselves. If open or shorted, they do not cause a pulsing output....if open the alternator is in a single phase condition, where the output (current) is reduced by half but under light loads, the output voltage can approach nominal. A shorted diode will cause a discharge of the battery, usually overnite, when the engine is off, thru the stator winding resistance to ground. Pulsing lights can be traced to an intermittent regulator or poor brush to slip ring connections causing fluctuating rotor field voltages and fluctuating output. Just my opinion of course.....
BOB RENTON
 
The voltage "ignition signal" may have a drop. This is the voltage the regulator uses for charging reference. Some fixes are a relay that sends battery voltage directly to the regulator while the key is in the run position. Cheap to remove the ignition switch from the cylinder and spray flush it with DeOxIt.
Try measuring the drop between the battery positive post and the regulator input with a DMM. Then you can trace around to see the drop.
 
RJRENTON said:
Either the Mopar round back or the square back alternator has 3 positive and 3 negative diodes arranged in a three phase full wave bridge rectifier circuit. BTW...diodes, either positive or negative polarity or configuration are open or shorted, and once open, do not heal themselves. If open or shorted, they do not cause a pulsing output....if open the alternator is in a single phase condition, where the output (current) is reduced by half but under light loads, the output voltage can approach nominal. A shorted diode will cause a discharge of the battery, usually overnite, when the engine is off, thru the stator winding resistance to ground. Pulsing lights can be traced to an intermittent regulator or poor brush to slip ring connections causing fluctuating rotor field voltages and fluctuating output. Just my opinion of course.....
BOB RENTON
Click to expand...
I'm no expert..... But, a good friend of mine who at one time when you could make a living at rebuilding alt, starters, etc. had a shop doing that, that was his answer about pulsing question. I never questioned it. It made sense since the diode arrangement is to make pulsing DC current from AC current. If you put one negative sine wave in there, would that not cause a repeating drop in voltage in a pulsing DC current?
Dirty, corroded, poor connection slip rings usually cause low output, which if his battery is being drained at idle can cause the +20 surge, but not a bounce in the needle.
Like I said I'm not a expert just from my experiences.
I'm also going to guess that like most of us he disconnects the battery when put up in the garage for overnight, days, weeks, so there drain issue would not be a issue.
 
Last edited:
I put on my spare alternator & the needle jumping has gone away, so I just dropped off the original alternator to my local repair shop.

I thank everyone for their input & advice.


terminator-thumbs-up-meme-arnold-schwarzenegger-i-ll-be-back-b5990cabddbc225a3cc40c638b175b3f.jpg
 
When you dropped it off did you tell the guy:
"I'll be back"?
 
70bigblockdodge said:
I'm no expert..... But, a good friend of mine who at one time when you could make a living at rebuilding alt, starters, etc. had a shop doing that, that was his answer about pulsing question. I never questioned it. It made sense since the diode arrangement is to make pulsing DC current from AC current. If you put one negative sine wave in there, would that not cause a repeating drop in voltage in a pulsing DC current?
Dirty, corroded, poor connection slip rings usually cause low output, which if his battery is being drained at idle can cause the +20 surge, but not a bounce in the needle.
Like I said I'm not a expert just from my experiences.
I'm also going to guess that like most of us he disconnects the battery when put up in the garage for overnight, days, weeks, so there drain issue would not be a issue.
Click to expand...

An alternator produces a sine wave AC output, which is RPM dependant and the actual numbers of poles in the stator windings, according to the this formula:
N = Speed of rotor in rpm
f = Frequency of generated emf
P = Number of Poles.
Using these values, one may easily figure out the frequency of an alternator. Then this generated AC is rectified to DC. With typical cruising speeds and engine RPM, approximating 3000, and an 8 pole alternator, the resulting frequency is approximately 400 hz, b4 rectification. The higher the RPM, the frequency will also be higher. The 3 phase full wave bridge rectifier circuit will typically provide a higher peak voltage, closer to the peak value of the sine wave generated (voltage), minimizing any ripple or voltage fluctuations or "flickering" of the connected loads (lights). If a diode fails, typically it opens, the resulting sine wave is distorted, causing a more pronounced output voltage fluctuation....but the battery supplies a more steady state output, minimizing the "fluctuations" in generated output. To troubleshoot a suspected alternator output issue, the individual diodes must be tested for shorts or opens, along with the stator windings and rotor windings, slip rings and brushes.
Just my opinion of course.
BOB RENTON
 
I know this thread is a couple months old but may I jump in here?
I have a similar, but different issue.
Ammeter jumps around at idle, 700 RPM, but steadies out upon slight RPM increase. Lights flicker as well at idle but flicker goes away upon RPM increase.
Just installed a square back 55 amp alt from Rockauto. VR is the original that's been on the car since '66. Battery is about 5 years old but has been kept in decent shape.
Gauge cluster has been restored and contacts are tight at ammeter. Never checked the voltage 'limiter' on the back of the cluster - my bad.
Other information is this. I just installed a Rick Erhenberg electronic ignition with the blue Hirev 7500 box and distributor. The car will not start upon cranking with just the battery installed. When I jump the battery from my other car it starts right up.
The battery shows 12 volts, but again it's an older battery.
I've read all the tech info here but it's way over my head.
Is it possible the older battery and old VR are causing my issues?
Thanks
 
VFilms said:
When I jump the battery from my other car it starts right up.
The battery shows 12 volts, but again it's an older battery.
Click to expand...
The battery is not fully charged, or it is bad. Load test and replace as necessary. I would also verify you have the “square-back” isolated field alternator field connections correctly configured for use in in what appears to be a pre-1970 Chrysler product.
 
72RoadrunnerGTX said:
The battery is not fully charged, or it is bad. Load test and replace as necessary. I would also verify you have the “square-back” isolated field alternator field connections correctly configured for use in in what appears to be a pre-1970 Chrysler product.
Click to expand...
Thanks. I had planned to replace the battery and reinstall the original alt in an effort to trouble shoot the problem. Would you suggest replacing the VR with a solid state unit?
 
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