Low voltage and alternator charging issues....my voltmeter remains at 12 volts even when car is started.?

Question

I've been having an issue with my 1969 chevy impala and its voltage not being adequate on my voltmeter gauge. These are the items installed: voltmeter model #SUN-CP7955 alternator model #PWM-37294 and a Optima Red Top battery. Voltage of a car when it is not turned on should be at or around 12 or so, then when the car is started and the engine is running, voltage should jump and remain between 14 and 14.7 volts. My alternator is pretty much brand new and has a built in regulator thats rated at 14.7 output. I have tried multiple configurations of my alternator setup, which can be used as a 1-wire or 3-wire setup. My alternator does not seem to be charging my battery as the voltage remains at 12 volts when running, when driving the car the voltage slowly drops to the point where the battery begins to die. Alternator failed a test at Kragen, but worker didnt seem like he knew what he was doing, performed self test at home by starting car and removing + post of battery, car stayed on!

Someone please help me...I had the suspected faulty alternator tested at Kragen and they said it probably have a bad diode and a faulty rectifier. I will be sending this high-ouput alternator back to get a new one. Here is my new issue, I have installed my backup alternator that I bought from Kragen before upgrading to my high-ouput one, however I am still having the same problem with low voltage. I ffully charged my red-top optima battery with my battery charger before installing this alternator. Voltage at my custom dash mounted voltmeter never went anywhere close to 14 volts or even over 12 for that matter. What is going on, someone please help. How can I figure this low voltage and battery not charging issue out?

Answer 1

"Alternator" can fail and still be putting out like a welding machine

Alternators make AC current,,,
there's some electronics in it which convert that to DC Current.

Your Battery will Crank the car.....
and
A partially performing Alternator will RUN the car

But it will be running on an A/C wave leaking thru the Alternator's rectifier

The effect of AC on a Battery is exactly the same thing as REVERSING the Polarity of a Battery Charger connected to it.

Ever see anbody hook up Jumper Cables Backwards,,Wrong Polarity?

Hot to Ground,,and Vice Versa?


That does LOTS of Exciting things.....
But Charging a Battery AIN'T one of them.

A faulty Diode in an alternator "FLIPS" the Polarity several times per second.

It's NOT merely a Short to Ground,,,it's NEGATIVE VOLTAGE.

It's Not just Draining the battery,,,it's actually trying to make the Battery Flow Electricity BACKWARDS


Its a Weird Property of Electricity to be able to have ONE WIRE carrying a wide range of Frequencies and waveforms,,and Polarity.

The "Hot & Ground" in your house is 60 Cycle AC( in the USA)
It FLIPS 60 times per second..

Stick a DC meter in a Wall Socket,,and it usually wont read ANY Voltage.
It Might Twitch,,but will then sit dead on Zero.
With 110 Volts in it,,,but AC Volts.

But put the DC Meter to EITHER wire,,,,and a pipe stuck in the ground,,,and You'll see some DC voltage

On a DC Power Supply,,,that wont work that way.

You should NEVER get an AC current on a DC line.

And on a BATTERY,,,you never will,,it's impossible.

So if you take an AC Meter and check a Car's Battery Cables,,
You should NEVER see ANY AC whatsoever.

On OLD cars with GENERATORS,,,there Never Could be any AC.
They can Only ever produce DC.

But Alternators produce Alternating Current.
Their NATURE is PURELY AC.
That's ALL they can produce.

The RECTIFIER Circuitry is what converts it to DC.
In Car Alternators,,,it's commonly called "Diode Plate".

It's several semi-conductor devices in an arrangement.

1/2 of them Block the Positive Side of the AC Wave,,,
so the Line OUT is ( -) Ground/Negative.

Other Half of the Diode Array blocks Negative side of the AC Wave,,,so only (+) comes thru.
That creates the Hot Wire,Red,,Positive Cable

If one of the Diodes fails,,,,BOTH Sides of the AC wave comes thru that side.

It doesnt matter whether it fails on Hot or Ground Side,,
Because HALF the Time,,,Half the Wave is OPPOSITE Polarity

You get a Pulse of Opposite Polarity from the AC,,,same as Tapping a Cross-Wired Battery Cable to "wrong battery post" several times a second.

The Ignition system WILL run on AC,,Lights will shine,,etc

But it WONT charge the Battery.

Actually,,it slowly Destroys the Battery,,,not simply drains it.
AC will Ruin it beyond being rechargeable.

Diodes can fail in a variety of ways.
They are simply "Electrical One-Way Check Valves"

They can fail OPEN,,and not conduct anything,,either way.
Just like a Broken Wire or blown fuse.
This makes for a NO Charge or LOW Charge output.

They can fail CLOSED,,,and conduct BOTH Directions.
No Longer BLOCK the current in opposite direction.
This admits AC to the Battery,,
and it also will DRAIN a Battery when car is shut off---it creates a "leak to Ground",,,it's a electrical Draw on the battery.
It'll run fine for a 100 years,,,battery will start the car all day long--if ya run it long enough to add back what ya drained.

But let it sit 8~10~12 Hrs,,,Boom,,it's DEAD BATTERY.
Everything "Back flowed " OUT to ground.

Diodes can also LEAK,,,,,they can have only very SLIGHT leakage Backwards.
Which only puts Faint Amperage of AC into the Batt.
Or is only a FAINT short to ground.
Or yields on a Slight Reduction is Alternator's Output.

That can be TRICKY---because the Voltage Regulator can Compensate for the Drop in Voltage to some degree.
The V-R doesn't ADD any voltage,,,it just senses Low Voltage,,,so it allows More than it would normally be clipping off.

Makes "All SEEM fine",,,,,while it really AINT.

If You got a lil' Multimeter which reads AC Voltage,,,
Try it on Each Battery cable,,to ground.
Keep turning the scale down till you get to lowest voltage.

It Can be as low as a FRACTION of a Volt AC,,or 1 or 2 V AC.

Should be ZERO AC.

AC is Poison to a Battery.

Sorry to bore ya with the BS.

Easier to just say,,"Bad Alternator".

But as in your case,,,,it just doesn't Seem BAD.

It's Bad ,,,it's about the HOW's and WHY's that make it Bad.

There's Lots more than simply putting out voltage to run the car.

We CALL it the "Alternator",,,it's actually the RECTIFIER circuit which is an "accessory" built into the Alternator which is bad.

They're 2 entirely different worlds ELECTRICALLY.
But in Automotive Alternators,,,they're 2 different devices assembled as a Unit,,,,and we seldom refer to them or think of them as anything but "Alternator".

Reason why your gauge slowly drops is because the Batt builds up while it sits.
Then when you run it,,,the Alternator begins pulsing it with reverse polarity.
It eventually overwhelms the battery's charge,,,and Voltage starts dropping.

Car will RUN on that,,,it's AC though that it's running on.
To SOME of the stuff in a car ,,,"Electricity is Electricity",,it dont care whether AC or DC.

But the Battery Does,,it's Gotta have Pure DC Only.

Typical of a "Bad Alternator",,,
which is Actually a BAD Rectifier aka "Diode Plate".

Plenty Electricity,,,but wont charge even a flashlite battery.

Simply,,,Wrong Flavor of Juice.

Whatever it is,,,get that '69 RIGHT & Rollin'.
That's a Heckuva nice ride.

Answer 2

alternator is fine. check the two wires from the battery to the frame, the ground wire, and the starter, the hot wire. if they have a corrosion build up inside the wire they wont allow sufficient voltage to charge the battery at 13-14.7volts. next, take a voltmeter and check the dc voltage at the battery posts and then the post connectors with the car running and the positive post off the battery. car will keep running, but you will get a better voltage check of the alternator output when the car is running but the battery cable is off. if under 13 volts, replace the regulator if alternator is good, you may have a near-dead cell or bad terminal on the battery. if any corrosion is around a terminal replace the battery. also, check the water level in the battery itself. it may say maintenance free, but yoiu can still remove the caps and refill the water. low water prevents the battery keeping a charge and needs to be checked periodically. refill with distilled water, rather than tap water. the only reason they say a battery is maintenance free is to keep people from getting the full battery life because they go bad if they run out of water in the cells and the manufacturers don't want you to keep a battery as long as you are willing to buy another before you really need to.

Answer 3

I had a similar problem once before and it threw me for a little while. I had voltage from the alternator, but it was right at battery voltage. If the alternator is running at battery voltage it won't charge the battery even when the battery falls way below normal voltage. However the alternator does produce enough to give the ignition system juice when you try that test. You have a bad alternator. Maybe it came from the factory bad, I don't know - I do know it is bad.

Answer 4

Battery should read 14.5 with alternator running. Bad ground or something isn't hooked up correctly. Test the Alternator Output, check it against any Manual or Specs that are on the paperwork. Then check each Wire Lead to the battery from the Alternator then at the Battery. Sounds like either a bad connection or a fusible link somewhere went pop!

Answer 5

Car Voltage Meter

Answer 6

Seeing as the engine continued to run with the cable off (sure don,t recommend that one) It tells you the alternator is putting out something. I would expect to find a diode problem. There are six of them in there. If one goes out you loose 1/3 of the maximum charge rate. If two go out you loose 2/3 of your max. output. Sounds to me like you are running at 1/3 output max. and that will not keep the battery charged up.

Answer 7

Low Volts

Answer 8

The problem that you are having is that you r voltage regulator is not charging at low rpm you need to replace the voltage regulator onr of the diods ar bad

Answer 9

Sounds like to me you got a bad voltage regulator in your alternator? I would suggest replacing the alternator.

Answer 10

1st of all never dissconect the battery while your cars running,it can cause a voltage spike,blowing the diodes in the alt. 2nd check the batt. wire on the back of alt. should have batt. voltage the alt. must have batt voltage before it will charge although you may have already fried it!!!if you still have prob. contact me @ my e-mail address