charging system blues

[Michael Siple]

1971 Duster V8 - have a 3 wire alt w/a electronic volt/reg. amp meter indicates normal chg/dischg condition. at idle it shows slight discharge then increase r's it shows on the chg side - but across batt only shows 12v on a voltmeter. amp meter indicates chg voltmeter across batt indicates none. going to look a little closer today. suggestions-direction appreciated. I've read FABO for 2 days getting ideas. thanks, mike.

 

[TrailBeast]

Find the two smaller wires on the back of your alternator that has power to it with the key on.
There better be one with power to it or there's your problem.
Leave the big one alone.(It has battery voltage all the time normally)
You will need to pull both of the smaller ones off and find the one with power when the key is on.

Now that you have identified the one with power plug that one back on and ground the other connection spade to the body of the alternator with the motor running.
If it charges now and your battery voltage goes up it tells you the alternator is ok and the problem is likely the regulator. (Which needs a good ground by the way)

You should hear the alternator load increase when you ground the one terminal to the case.
It'll spark a little when you ground it and that is ok.
What you are doing is verifying power to the alternator field and manually doing what the regulator does by completing the circuit for the field so it can produce voltage.

 

[67Dart273]

You may have a bad battery. First thing to do is charge the battery and have it tested.......with a load tester

Only problem with TB's suggestions above is that there might be a wiring problem causing "the problem."

I tend to divide these problems into "areas.........."

The field wiring
The output / charge side wiring
The components, alternator and regulator

To do the test above and eliminate the field wiring as a problem, get some alligator clip leads which you "should have" anyhow. Remove both field wires, ground one, of the alternator field terminals, and run the other to the battery

Now monitor battery and see if voltage "comes up" with throttle increase. With the engine running "fast" (simulate) low / medium cruise RPM, voltage might be over 16V. Turn on headlights, blower, etc, and see if it "keeps up."

Also compare the battery reading to the alternator output stud. Easiest way to do that is hook one lead of your multimeter to battery POS, and the other to the alternator output stud. Bring up RPM to what you judge to be no more than 16V in the first test, "a good fast idle" or little more. You should not read more than one volt, maybe 2 at the most, the less the better

Voltage regulator MUST be grounded. Remove it, scrape around rear of bolt holes, firewall and regulator, and remount using star lock washers. "Work" the VR connector in/ out several times to scrub it clean and also visually inspect it for loosness and corrosion

 

[Mattax]

Those are all good suggestions, but I'd switch the order of checks a little.
Based on the description, I'd start by measuring the voltage at the alternator output (the stud with the heavy wire) while the engine is running. Compare with the battery positive voltage.

Here's why I'm suggesting this.
Engine off, the battery normally should be 12.5 volts or a little higher.
Engine running, you see the ammeter indicating current flowing to the battery.
This is normal, and with most alternators, increasing rpm will increase current.
So the only thing possibly odd is that the battery voltage didn't come up at least a little bit.
Usually while its charging, the voltage on the positive terminal floats up close to the alternators voltage. That's why I suggest checking the alternator output voltage. If its also low (and doesn't come up rpm ) then its worth checking whether its the voltage regulator or the alternator at fault. (see above posts for that)

However if the alternator output voltage is normal (somewhere around 14 volts), and the battery positive is 12volts, then check the voltage at each exposed connection. Could be high resistance from a poor connection or damaged wire. If the wire is only 12 volts at the starter relay, then check the firewall connections.

It would not hurt to fully charge the battery on a slow charger. Then recheck the voltage again (engine not running) and then at both the alternator and the battery with the engine running.

 

[67Dart273]

You can do this either way but you don't want to get "led down a road." You want to put the output line under a lot of power so that it will show up poor connections. This is why I check it with the field "full fielded" so that IF the alternator is charging you have a LOT of current going through the output

The functional path is shown in the MAD article simplified diagram:

Notice I said "functional path" I don't want to get into arguments about the direction of electron flow LOL

From alternator output stud........the TERMINAL on the BLACK wire.......through the BLACK wire to the FIREWALL CONNECTOR...........THROUGH THE CONNECTOR........to the WELDED SPLICE (up under the dash)..........to the WIRE TERMINAL at the AMMETER..........through the AMMETER.....out the WIRE TERMINAL on the RED WIRE...........back out through the FIREWALL CONNECTOR.........to the FUSE LINK.........to the STARTER RELAY STUD............through the BATTERY CABLE to the BATTERY.........through the GROUND CABLE and back to the ENGINE BLOCK.......to the ALTERNATOR GROUND

Notice there is lots of CAPITALIZED words. Each of those capitalized items is a possible TROUBLE SPOT. There's about 4 of them or so right at / in the ammeter. The two wire terminals can fail. The stud nuts can be loose. The ammeter studs can be loose on the ammeter shunt assembly, the "guts" of the thing. Any and off of these things constitute resistance and voltage drop

Checking this under heavy current flow will show up potential "hot spots," pun intended

Catalog

 

[AJ/FormS]

I had this problem once and found that the amp gauge was a choke. The needle indicated correctly but the shunt inside was bad so actual power delivered to the battery was very low. My solution was to jump the studs on the gauge with a strap,effectively bypassing it. That brought everything back to normal. Having now solved the problem, it remains to either replace the gauge, or get rid of it in favor of a voltmeter.
In Del's diagram, you can see the gauge down on the bottom there.Normally all power for the car comes from the alternator, and whatever is extra goes to the battery,follow the path.
But if the alternator fails to meet the demand, then the battery goes to work.
The amp gauge tells you which one is supplying by the direction of the needle.And it tells you how well the regulator is balancing the supply and demand by the amount of deflection. But it cannot tell you if the shunt (bypass) inside it is adequate to pass the juice.
You don't have to pull the dash apart to get to it. You can bypass the ammeter anywhere in the circuit, between the #1 splice and the battery. The easiest place to test this is right at the bulkhead connector,lol

The fusible link can also be a problem. I have seen those corroded so bad that they pass just enough to energize the starter relay during starting,and no more. With the alternator disconnected, the engine would continue to run, but as soon as I turned on the heater or lights the engine stalled.

 

[TrailBeast]

I had this problem once and found that the amp gauge was a choke. The needle indicated correctly but the shunt inside was bad so actual power delivered to the battery was very low. My solution was to jump the studs on the gauge with a strap,effectively bypassing it. That brought everything back to normal. Having now solved the problem, it remains to either replace the gauge, or get rid of it in favor of a voltmeter.
In Del's diagram, you can see the gauge down on the bottom there.Normally all power for the car comes from the alternator, and whatever is extra goes to the battery,follow the path.
But if the alternator fails to meet the demand, then the battery goes to work.
The amp gauge tells you which one is supplying by the direction of the needle.And it tells you how well the regulator is balancing the supply and demand by the amount of deflection. But it cannot tell you if the shunt (bypass) inside it is adequate to pass the juice.
You don't have to pull the dash apart to get to it. You can bypass the ammeter anywhere in the circuit, between the #1 splice and the battery. The easiest place to test this is right at the bulkhead connector,lol

The fusible link can also be a problem. I have seen those corroded so bad that they pass just enough to energize the starter relay during starting,and no more. With the alternator disconnected, the engine would continue to run, but as soon as I turned on the heater or lights the engine stalled.

And to think, I would have pulled the blue wire off the alternator and stuck a screwdriver across the exposed terminal to ground and see what happens and then went on with the other possibilities if the alternator didn't start whining.
If it didn't I would lick my two index fingers and touch one to the battery negative and the other on the regulator casing.
You'd find out right now if the regulator had a ground or not.

I figured out why I do things the way I do.
Because when I was growing up and wrenching to make my cars run with almost no tools and zero money for equipment, I learned how to diagnose without them.

 

[AJ/FormS]

Ok TB,so are you burning me? Or ?

 

[Michael Siple]

batt new a week ago - batt good. checked wires at back of alt - none hot without key on. key on - black wire hot & the field with the two blue wires gets hot. single green on other field not hot. double blue wire at ballast hot with key on. bulkhead plug looks good outside & in - hot under the hood & inside things work. cranks & starts , lights... good ground at vr, checks were done w/a test light. went back with a meter & had batt volts at each check. i'm thinking "damn amp meters"

 

[RedFish]

Check again. The black wire at BATT post on alternator should be hot at all times, switch on or off.

 

[Super-Cuda]

Check again. The black wire at BATT post on alternator should be hot at all times, switch on or off.

batt new a week ago - batt good. checked wires at back of alt - none hot without key on. key on - black wire hot & the field with the two blue wires gets hot. single green on other field not hot. double blue wire at ballast hot with key on. bulkhead plug looks good outside & in - hot under the hood & inside things work. cranks & starts , lights... good ground at vr, checks were done w/a test light. went back with a meter & had batt volts at each check. i'm thinking "damn amp meters"

Hey MichaelSiple,
Electrical problems suck..going through some myself!! I would pay attention to the simple stuff first including 67 Dart273's suggestion to load test the battery. Just because its new doesn't mean anything. A battery can show 12 volts on a meter and still be bad. This will show up on a load test. Bring it back to the place you purchased it as most reputable auto supply stores can do this for you free of charge.

 

[AJ/FormS]

You can test your battery at home, in the vehicle.Start with a fully charged battery.
Put a voltmeter on it and crank it for 12 seconds with the coil wire pulled and near-grounded, so it can still spark, but the engine cannot start. A good battery will/may drop to about 10/10.5 volts and hold there. Under 9 is trouble,probably junk. 9 to 10,charge it again,check the specific gravity, and repeat the test.

 

[Mattax]

I've marked agree on the above two posts because a new battery will still get run down if its not getting recharged.

went back with a meter & had batt volts at each check. i'm thinking "damn amp meters"

Are you saying that everything in the system is showing 12 Volts????
The ammeter shows whether the battery is charging or discharging. If everything is at 12 Volts, especially with lights on etc, then battery voltage is getting everywhere with no loss.
The questions then are:
Why is your voltmeter showing just 12 Volts?
Is the Battery down to 12 Volts?
Is the Alternator putting out only 12 Volts?
Or is your voltmeter bad?

Except when starting, all of the power comes from the alternator, and the alternator should be putting out at least 13.7-14.7 volts.
Internally, a charged battery is 12.5-13.2 volts. So it does provides no current once the alternator is running. It draws power only while recharging.

Your car may or may not have a problem. The only thing you posted that suggests a problem is that you are measuring 12 volts at the battery terminal, and elsewhere too???
As far as the ammeter showing charging: That's normal after starting.
The ammeter showed higher current flow with increasing rpm from idle. That's also normal.
When the battery is charged, the ammeter should show no current in either direction.


The voltage will drop every time it hits resistance or is used to drive something (that something can be a motor, a chemical reaction in the battery, or a lamp). The test light doesn't show how much voltage.

It could be your voltmeter is bad or not getting good connections. Test it against a known voltage like a 9volt battery.

Then recheck the voltage at the Battery terminal and the voltage at the alternator output terminal. They should be very close to the same voltage.
You can do this when the engine is off just so you can see. if one is 12.8 the other should be about 12.8 Volts. If not either something is wrong, or the test probes didn't have good contact with clean surface.
With the engine running, observe the ammeter and measure voltage at the Battery and at the alternator output. The voltages should be within a few tenths of each other.
IF voltage is within a few tenths, then there may not be a problem in the wiring. Verify with some load tests. Move on to figuring out why the voltage out of the alternator is low.
IF there is a voltage drop of 0.5 or more, there is too much resistance somewhere and it is important to figure out where. In this case, measure the voltage at each connection you can have access to. The first easy one is the starter relay. Then the connectors.

Testing with load. AJ is correct that without any load, there will be no voltage drop. So, once the battery is charged, it will be harder to trace a problem if there is any. You can turn on the headlights, and look for voltage drops on the alternator out put wire and connections. Then turn off the motor and do the same for the battery wire.

Another way to look for resistance is disconnect the battery positive and the alternator output wire. Then measure resistance in the wire. Same deal, work back to the firewall if it shows a lot of resistance. Then remove the bulkhead connectors or go underneath the dash and measure resistance.
Do this methodically and write down every reading and what it is across. Then you'll know if it is the wire from the battery to the starter relay, or relay to bulkhead (includes the fusible link), under the dash, or in the alternator output line and its connection at the bulkead.

If the wiring route is getting confusing. draw yourself a diagram.
Feel free to download and modify Understanding Charging Systems with Ammeter

 

[TrailBeast]

OMG! disconnect the green wire from the alt and with the car running ground the terminal where that wire was to the alt case.
Does it charge now?
Then there is a wiring or regulator problem, and the alt is fine.

 

[TrailBeast]

Ok TB,so are you burning me? Or ?

No, just frustrating watching all this and wondering if he's going to spend 3 weekends finding out the regulator is bad.
I just happened to quote your post.

 

[Michael Siple]

Check again. The black wire at BATT post on alternator should be hot at all times, switch on or off.

I will double check black (charge) wire on back of alt again to see when it gets power-pretty sure it gets hot with key on - fellas don't get frustrated with me - I know a little about a lot & a lot about a little - going to full field alt & see what happens if it doesn't bump up batt volts and my wiring seems to check good it will get alt & reg - this all started at a cruise one eve when a few mopar bums told us headlights seemed dim, ammeter showed system was chg & dischg according to rpm, this indicated to me system was operating as it should, until I chkd batt volts while running & it only showed 12v - not being chgd. before I started checking I really expected to have a wiring problem but so far its looking like alt or reg. if its a bad alt it will getalt & reg if a reg cures it alt will stay. full field will tell the way I understand things

 

[Mattax]

Trail Beast - That's good advice IF the alternator is not charging.
But IF there is a problem with a poor conduction, going full field could cause more damage.
That's why I suggested verifying the voltage at the alternator output first.
If the voltmeter is giving bad information....
Note what Michael wrote about his voltage tests.
In post #1, the voltmeter appears to contradict the ammeter. If current is flowing to the battery side of the ammeter, then the voltage from the alternator side must be higher.
In post #11, it shows battery voltage everywhere. With no load, this means nothing. If the engine was running, the ammeter should have shown slight discharge, not charge, if it was real.
In post #11 Michael says there is no power at the alternator output (Black) wire. If true, this indicates a break in the wiring. That's why I sugguested rechecking after verifying the voltmeter is accurate.

 

[Mattax]

Michael - Here's MAD's diagram modified so it looks more like a 71 Duster.
Everything connected to the Battery's positive should have the same voltage.

 

[Tooljunkie]

Not one guy questioned the condition of the voltmeter.
Go test it on a known good charging car.
I always test my test light, and constantly verify my meter is correct.
Main reason i bought a good quality ohm/voltmeter.

Lots of good advice here, i dont need to add anything else.

 

[Michael Siple]

here now with car - pulled green field off alt , grounded spade on alt housing saw the little spark but no volt increase across battery listened for it to draw when field grounded & got none. black wire back of alt is hot with key off - good volt readings at key points - think its safe to say i have a bad alt - gets a reg too . how'd i do ? ammeter in dash fooled me- shows chg with a bad alt. thanks . mike

 

[Mattax]

Mike, I think you need a new voltmeter.

Not one guy questioned the condition of the voltmeter.

You must have got tired of reading. :LOL:

If the voltmeter is giving bad information....

The questions then are:
Why is your voltmeter showing just 12 Volts?
Is the Battery down to 12 Volts?
Is the Alternator putting out only 12 Volts?
Or is your voltmeter bad?

 

[Mattax]

Mike this post of yours was delayed on showing on my screen...

... this all started at a cruise one eve when a few mopar bums told us headlights seemed dim, ammeter showed system was chg & dischg according to rpm, this indicated to me system was operating as it should

Basically correct.
Here's the deal. The lights get dim because the alternator is not keeping up with demand at idle. So instead of running on the alternator, the car is running on battery.

Yes if you see the battery discharging at idle, then the alternator should charge it when the rpm go up. If you idle this car for long periods of time with the headlights on, its going to drain the battery. This is because the alternator is not getting enough power to all the circuits at idle rpm.

This is common on older vehicles for a combination of two reasons:
a. Oxidation, and sometimes loose or poor connections.
b. Base model alternators produced just enough power at idle to run the ignition and one or two accessories (wipers or lights). This wasn't a problem when the wiring was in brand new condition and the car wasn't idling for longer than a normal traffic light. As soon as the car was moving, the alternator recharged the battery.

Anyway, start with a good voltmeter and clean all of the connections. If the ammeter shows the car running on battery with no accessories on, that's not the way it should be.

 

[AJ/FormS]

You know the easy test for this is just to disconnect the battery NEGATIVE cable,with the engine idling. If it stalls, the charging system ain't putting out. If it didn't stall turn the headlights on. If it stalls now, turn off the key reconnect the battery, full field the alt and repeat the test.If no change get a replacement alternator. But; If now it takes both the ignition load and the headlight load, shut it off. Reconnect the battery, clean the grounds on the regulator,reconnect it,and repeat the test. If no change get a new regulator.But If now it takes both the loads, shut it off and reconnect the battery. Problem solved with No voltmeter required.The regulator cannot work unless it is well grounded.
If the battery cranks the engine, it is good.
If the charging system test above still does not charge the battery, then there is a poor connection between the alternator side of the bulkhead connector and the battery. And the most common areas to fail are: the bulkhead connectorS, the fusible link,the ignition sw and the ammeter. Look on Del's drawing or the updated one; those are the connecting points.
The wires very rarely fail.
Looking good does not mean are good.
Good looking doesn't mean anything when it comes to wiring,lol.
Now, some fellows might tell you that disconnecting the battery negative on a running engine spells disaster for the system. Well maybe it does I can't say. But I can say that in the 44 years that I've been doing it, on NON-EFI cars, nothing bad has ever happened.

 

[Tooljunkie]

How to boost a car with no jumpers,swap batteries. While running.
Then there was the real ugly redneck way,flip good battery upside down and touch posts. Bad idea, just throwing it in, people are crazy.

 

[Michael Siple]

a different question- hands are dirty while i type- on the back of the double pulley alt coming off it has a batt wir & 2 fields. on back of single pulley alt going on it has a batt, a field and a ground. ? the hot when key on double blue field would go to the field spade, batt wire to batt, green field go to the ground position ? hope i'm being clear. wanted to go to single pulley cause of a/c remove before us.