Pulsating Alternator Gauge

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Ag1753

'69 Cuda Fastback
Joined
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When I use my turn signals, the alternator gauge pulsates. It moves about an 1/8 of an inch. (It looks like a heart beat.) It stops when I stop using the signal. What gives?
 
The gage Chrysler labeled 'alternator' is a two directional ammeter.
It shows current flowing to or from the battery.
See where it is located in the circuit?
upload_2020-7-12_7-54-8.png

C = Charge, D = Discharge.
The range is 40 amps to 40 amps. Centered is zero amps.
If you notice the car is running on battery all the time, then the alternator isn't working. So in a roundabout way it is an alternator gage.

As the turn signals draw current from the battery, the needle moves.

Now here's the tricky part. We commonly call these 12 Volt systems and we commonly describe the power source as the battery.
In reality, there are two power sources:
The Battery which when fully charged is around 12.8 Volts
An Alternator which when running is regulated to supply power around 14 Volts.
When a circuit is turned on, Electricity flows from the highest voltage power source.

At idle speed the maximum an alternator can output is significantly less than at higher rpms. So sometimes at idle power has to come from the battery.

So what you are seeing could be normal, say at idle with headlights on, or
it may indicate an alternator with weak output or a poor connection in the output line.
 
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The gage Chrysler labeled 'alternator' is a two directional ammeter.
It shows current flowing to or from the battery.
See where it is located in the circuit?
View attachment 1715559994
C = Charge, D = Discharge.
The range is 40 amps to 40 amps. Centered is zero amps.
If you notice the car is running on battery all the time, then the alternator isn't working. So in a roundabout way it is an alternator gage.

As the turn signals draw current from the battery, the needle moves.

Now here's the tricky part. We commonly call these 12 Volt systems and we commonly describe the power source as the battery.
In reality, there are two power sources:
The Battery which when fully charged is around 12.8 Volts
An Alternator which when running is regulated to supply power around 14 Volts.
When a circuit is turned on, Electricity flows from the highest voltage power source.

At idle speed the maximum an alternator can output is significantly less than at higher rpms. So sometimes at idle power has to come from the battery.

So what you are seeing could be normal, say at idle with headlights on, or
it may indicate an alternator with weak output or a poor connection in the output line.
Wow! Clear, precise, and polite explanation. THANKS, definitely bookmarking this so my son can read and understand his car a little better! Sometimes kid's need to hear it from someone other than their old man !
 
What mattax said.

I can tell you it is totally normal for my 67 dart.

Might even be more pronounced if you have a mechanical voltage regulator vs a replacement electronic one.
 
I had that issue. After I replaced my front lighting and engine harness, and replaced the female connectors on the dash side for the Fusible link and alternator, it stopped. Switched to all LED front and rear bulbs later.
 
I had that issue. After I replaced my front lighting and engine harness, and replaced the female connectors on the dash side for the Fusible link and alternator, it stopped.
ya, could be the alternator is barely enough at idle or a dodgy connector anywhere in line. you can use a meter and start taking volt reads to look for a voltage drop
 
Sooner or later that gauge, or that circuit, is gonna make trouble. The best solution I have found is to bypass it completely. Out of sight is peace of mind.
If your system dies, you will know it only slightly later than if the gauge was still working;
It's kindof like when you lose oil pressure at WOT, The gauge doesn't tell you the oil pressure is gone; rather the chit going on under the hood does. Then you look at the gauge and see what you already know.
Or like when you blow a coolant hose; the steam tells you something is wrong. Then you look to the gauge to verify what you already know.
So it is with the Amp gauge. You look there to verify what you already know.

If the amp gauge does this only in one direction, then you may have a short in that circuit.
If it does it in both directions, then your charging system may need a look-see.
If your car has an electro-mechanical regulator it could be completely normal.
If you have a post 1971 Mopar with an electronic regulator, the gauge could be telling you that the charge-circuit needs attention.
Happy HotRodding.
 
When I use my turn signals, the alternator gauge pulsates. It moves about an 1/8 of an inch. (It looks like a heart beat.) It stops when I stop using the signal. What gives?
And this is abby normal, because, why?

853c68146ac447ba62fb4e1f7c68d9e7.jpg
 
I feel that the pulsating ammeter is normal, here is why...
My setup:
Stock 67 dart 273, reman round back, single field wire alt with ~2.5" pulley, aftermarket voltage regulator (electronic).

There is a lag for the voltage regulator(VR) to change the control of the alt to respond to a load.

When I step on the brake there is a momentary movement to the left on the needle then it settles back to center. At idle it is more pronounced then at speed. But it is there at both.

The turn signal draws then stops drawing, the VR responds but too slowly so it bounces. Again more pronounced at idle.

Note when the brakes are on and the headlights are on the needle is slightly to the left till the rpm come up then it is centered, but even with all the load the needle still bounces when the blinker is on.

I agree that clean contacts, heavier guage wires and even a MAD bypass are all good things but if the only issue is that the ammeter bouncing when the turn signal is on I don't feel it is an issue.

https://photos.app.goo.gl/y6riekMu5r1kn7ay5
Let me know if the link doesn't work
 
There well may be a lag, but its probably not the voltage regulator.
The regulator operates on its own frequency and when there is pulsing seen on the ammeter, its in step with the frequency of the turn signals.
The regulator points move as rapidly or as slowly as needed. And while it could be in response to the power demand of the turn signals, two factors make it unlikely. One is that especially with headlights on, brakes on, at slow idle the regulator points are probably at the full flow position.
The other is the magnetic field's strength decays rather than drops instantly in response to decreasing current through the rotor.

My guess is the pulsing may relate more to the nature of the flasher unit itself. It's a bimetal that heats up and then opens, cools and closes.

As far as the MAD bypass goes, there's some good points but also some bad points. So I can't agree that's a good thing.

Anyway for @Ag1753's '69 fastback, once he reads this, and then observes what the ammeter indicates under other conditions, it will become easier to decide if there is a problem. For example, checking what the meter shows with turn signal on while driving at 35 mph.

When I mentioned a poor connection it was in mostly in reference to the alternator power.
For example if there was a lot of resistance in the bulkhead connector where wire R6 goes through.
upload_2020-7-12_16-31-39.png


That could choke the amount of current that could get through from the alternator.
As a result then the battery becomes higher voltage power source for the turn signals.
 
Boy Matt I'm glad you posted. Made me go back out to my car and found I left the lights on!



And while it could be in response to the power demand of the turn signals, two factors make it unlikely. One is that especially with headlights on, brakes on, at slow idle the regulator points are probably at the full flow position

In my case I have electric VR no points but I get what you are saying effectively it is at full charging

Not arguing here. Just noting what I see.

With engine running If you press the brake pedal the needle momentarily moves left then centers if you let off the pedal the needle has a slight bounce to the right. Apply , release, apply, release at the right frequency and you get the same bounce.
 
Boy Matt I'm glad you posted. Made me go back out to my car and found I left the lights on!
Its nice to be useful! LOL
Not arguing here. Just noting what I see.
Not taken in a negative way at all. We're all just trying to figure out what best explains what we see.
There's a guy on moparts with the screen name Sniper. He's posted that his cars never show the dimming of the lights at idle, etc. But IIRC his are original v-8 B-bodies with the original alternators. Interesting though.
 
My previous reman alt had a almost 3" dia alt pulley. At idle with brake on the ammeter would be to the left.

Changed to a different reman with smaller but not as small as the parts book says it should be pulley and now at idle with brakes on it sits at center (after a slight blip to the left)
 
This old dodge did the same thing. I updated it to the dual field alternator. Easy Peasy. They even make a bracket so you don't have to drill new holes. Add one wire. Lights are now bright at idle and ampmeter is steady. The owner was happy.

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What's normal? Weak connections in a 50 yr old harness with so many connectors is common.
I can't believe the amp gauge twitched hard with the load of 2 1157 bulbs when the car was new. Buyers will comment/complain about every little thing. That's whats normal.
 
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Funny you bring that up because today I paid closer atention to when and when not the ammeter movement was noticible on my '85 Grand Wagoneer.
It has similar wiring strategy (single fusible link, power distributed from a mains splice, etc). Mine is equiped with a "94 amp" 12 SI alternator that can run most everything at idle except maybe when the rear defrost grid is added to the loads of wipers, etc etc.
Its uses 1157 bulbs front and rear, plus the front sidemarker also blinks with the turn signals.
Immediatly after cold startup ( cranked briefly three times) the ammeter showed the turn signals taking power away from battery recharging.
After the battery charging decreased there was hardly any ammeter movement caused by the turn signals.

When I got to the garage, I video recorded the starting and turning on the turn signal. No movement noticable.
At slow idle just the slightest movement. Another small movement toward discharge when stepping on the brake pedal.
Engine off, key in run, ammeter moved noticbly in sequence with the turn signals. Maybe 5 amps.



So what is the turn signal current draw?
Let's see. An old Wagner lighting catalog lists
1034 bulbs rated to draw 1.8 amps at 12.8 Volts for turn signal and braking.
1157 bulbs rated to draw 2.1 amps at 12.8 Volts for turn signal and braking.
158 bulb draws .24 amps at 14 Volts. Somewhat less at 12.8 Volts

Therefore a 67 A-body with 1034 bulbs and 158 dash indcator bulb would have originally drawn 3.8 amps with the system running at 12.8 Volts.
My '85 Wagoneer with 1157 bulbs the turn circuit draws at least 4.2 amps plus the current for the 158 bulb and 194 bulbs. Lets call it 4.5 amps at the same 12.8 Volts.

I don't know what the flasher adds to the currents. It must take some power to heat the bimetal. I just have no idea how much.

It does seem safe to say that under normal running conditions a turn signal circuit will draw at least 4 amps and perhaps closer to 5.
 
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it will have 2 field wire connections, so 3 wires all together
 
Wow! Clear, precise, and polite explanation. THANKS, definitely bookmarking this so my son can read and understand his car a little better! Sometimes kid's need to hear it from someone other than their old man !
What do you mean sometimes!
 
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