Alternator not charging battery

[OC66]

I have had my alternator and battery both checked and they are both good but for some reason my alternator is not charging my battery or atleast charging it too slow. When my battery is fully charged it is only at 12V as I drive especially when using the lights or heater it drops to 10V and will completely die whether I am moving or not. The wiring seems to look good and the belt is tight. Any idea why the alternator is failing to charge my battery?

 

[Stroppe-Envy-77]

Voltage regulator?

 

[Cortez]

voltage

I had the same issue and likely had a short somewhere but I couldn't track it down for the life of me. My solution was to go with a one-wire alternator that has the integrated voltage regulator...problem solved. Got mine from Summit for $89.

 

[Steve83]

Battery terminals & engine ground are the most likely places to start. Remove all the heavy battery & alternator wire terminals, clean, repair/replace, & tighten them. For long life, apply MotorCraft Electrical Grease (NOT silicone/dielectric grease) shown at the bottom of the caption of the 2nd pic below.

.

 

[oleguy74]

check or replace regulator.

 

[rwill]

I had a similar issue and it was bad connection at the regulator

 

[bmc69]

. When my battery is fully charged it is only at 12V ...?

Clue for ya: A fully charged battery will show close to 14V on a voltmeter when the engine is running and the batter really is fully charged. Right after you shut off the engine, a fully charged battery will briefly read over 13V..but will settle down shortly to around 12.6 or so.

Your description means your alternator is not charging even the tiniest little bit; i.e as others have suggested, a voltage regulator or possibly a wiring problem (corroded harness plug terminals..things like that)

 

[DirtDonk]

Hey OC66, what alternator/regulator setup do you have? Stock, or something else?

And how long does it take to die when you turn on those other things? How long does it take to fall down to 10 volts or so?
Reason I ask is that, with a good battery, just turning on the heater motor should not draw the battery down that far. In battery terms, 10 volts is just plain dead. So if it's going to 10 immediately, have someone else check that battery.

Also, wouldn't hurt at all to verify your voltmeter on a known good system. Couple of the guys here recently have found their meters to be mis-reading.
If yours checks out ok, then pull the plug on the body-mounted regulator and check voltage at the Yellow wire(s) and the Red w/green wire. With the engine off, and the key off, only the Yellow wire should have power. With the key on, both the Yellow and the Red w/green wires should have power.
With the engine off, both wires should have exactly the same voltage as the battery does. So if the battery currently reads, for example, 11.8 volts, then the wires at the regulator should read exactly that amount. If not, then there is a bad connection or corroded wire somewhere in between that needs to be fixed.

Good luck.

Paul

 

[OC66]

As soon as I turn the lights on it immediately drops from 12V to 11V.

 

[Viperwolf1]

As soon as I turn the lights on it immediately drops from 12V to 11V.

That indicates the alternator is not charging. If it was tested GOOD then your problem is likely the regulator or wiring going to it. When you put the new regulator on make sure you mount it before you attach the connector. Better yet, disconnect the battery before replacing it.

 

[markperry]

If I remember correctly if you pull the positive battery cable off while the engine is running and it dies, the alternator is bad, if it stays running it's good and your problem is somewhere else!

 

[DirtDonk]

As soon as I turn the lights on it immediately drops from 12V to 11V.

This is with the engine running, or off?

So that full volt drop to 11 volts sounds normal to you then Viper? Sounds like quite a steep drop to me, but I haven't tested that theory lately so might not have noticed such a preciptious drop when putting a slight load (less than 10 amps) on a battery. Maybe after using the starter too, it would do this?
If just turning on the lights, and nothing else, I would think it would stay above 11 volts for a little bit longer at least? If it does that with just the lights, what would it be doing with the starter or heater motor?
Unless the battery is still partially drained that is. If that's the case, then I guess that drop would be expected.

I'm wondering mostly because we've been able to start and run EFI engines on battery only for at least half-an-hour before it starts acting funny. Sometimes longer. Don't know what that voltage reading was when it started acting funny, but I would expect somewhere between 10.8 and 11.5 perhaps.
Running a new EFI conversion with no alternator just a few weeks ago, the voltage stayed near 12 for 15 minutes of run time, including starting, and testing the lights and signals.
Never saw it drop by a full volt.

Granted, fixing your charging system will get things back up to full charge and staying there OC, but if just turning on the lights drops your battery a full volt, then it still seems to me like you've got a weak battery.
How well does it start the engine? I guess that's always the real acid test. If it can make the starter turn your engine over for a few moments, then I guess it's not suffering any malaise.

Paul

 

[DirtDonk]

If I remember correctly if you pull the positive battery cable off while the engine is running and it dies, the alternator is bad, if it stays running it's good and your problem is somewhere else!

Yes, but it's also really bad for alternators sometimes.

Paul

 

[Viperwolf1]

This is with the engine running, or off?

So that full volt drop to 11 volts sounds normal to you then Viper? Sounds like quite a steep drop to me, but I haven't tested that theory lately so might not have noticed such a preciptious drop when putting a slight load (less than 10 amps) on a battery. Maybe after using the starter too, it would do this?
If just turning on the lights, and nothing else, I would think it would stay above 11 volts for a little bit longer at least? If it does that with just the lights, what would it be doing with the starter or heater motor?
Unless the battery is still partially drained that is. If that's the case, then I guess that drop would be expected.

I'm wondering mostly because we've been able to start and run EFI engines on battery only for at least half-an-hour before it starts acting funny. Sometimes longer. Don't know what that voltage reading was when it started acting funny, but I would expect somewhere between 10.8 and 11.5 perhaps.
Running a new EFI conversion with no alternator just a few weeks ago, the voltage stayed near 12 for 15 minutes of run time, including starting, and testing the lights and signals.
Never saw it drop by a full volt.

Granted, fixing your charging system will get things back up to full charge and staying there OC, but if just turning on the lights drops your battery a full volt, then it still seems to me like you've got a weak battery.
How well does it start the engine? I guess that's always the real acid test. If it can make the starter turn your engine over for a few moments, then I guess it's not suffering any malaise.

Paul

It's impossible to make any accurate judgements on the batteries condition if it's been being discharged for days. That's why you need to fully charge a battery before doing a load test on it.

 

[Steve83]

x2 %)

It's critical to fully recharge the battery any time you repair/replace the alternator BEFORE starting the engine.