Voltage and power dropping.

[seabeelt]

Last night while on a small sunset drive, the dash lights started getting more and more dim, the the directionals wouldn't work. Pulled into a small convenience store to get milk on the way home and the battery is too low to start the car. Had to get a jump. Small ding to the pride but OK. Put the charger on the car over night. She fires right up. Battery voltage with car off 12.53 volts. Battery with the car running 15.4 volts. As the car warms and the engine cycles the cooling fan a few times, I'm checking the directionals, lights and so forth. Initially they work fine, but as the car warms the directionals start going slower and slower, lights start to get dim and the battery voltage is now down to just over 13 volts. Is my new 95 amp alternator starting to fail after only 1000 miles, or is the battery on the fritz . Hard to believe it is either one, since the battery seemed charged from the overnight charging........... Shouldn't the alternator charger or continue to put out its normal voltage/current even if the battery is possibly going dead.....

I'm at a loss. HELP!

[So Cal Mark]

if the alternator is putting out 15.4v then I'd say it's working. Have you checked voltage when the lights are dim?

[azruss]

If you are at 15.4v with a full battery, you are probably cooking the battery.

[focodave]

13.8 to 14.5 volts charging voltage is more reasonable for a 12-volt battery.
15.4 is slightly high.
More is not always better in this case.

[So Cal Mark]

the battery may be sulfated, causing high charging voltage. The 95a alternator should put out higher amperage, not voltage

[seabeelt]

Voltage starts out fine, but after the car warms, it drops to just over 13 volts. Almost like its running on the battery only, but with not much juice in the battery.
R/

[So Cal Mark]

after starting, charging voltage is high until the battery is returned to full voltage. Then the voltage should drop some

[seabeelt]

Decided to go ahead and replace the battery. Sticker on the top was unclear and had a range of years from 2005 to 2010. I'm guessing purchase was somewhere in the middle by the PO. New battery voltage out of the box is 14.38 without any load. I will keep,an eye on it and see if I end up with a dead battery after a while or not. Running voltage is 17.86. I'm guessing my meter calibration is off a couple of volts, but it reads the same on all three scales

As an additional thought, if the alternator is supposed to be outputting amps, .......then would not all of the things like directionals, lights etcetera still work even if the battery were low because of the amperage output???????

R

[Piccola]

17.86 volt is really HIGH voltage and I guess your multimeter is not properly working. Can you imagine the bulb works at this voltage ? no way......
below some ( helpfully info )

Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell)
Open-circuit at full discharge: 11.8 V to 12.0 V
Loaded at full discharge: 10.5 V.
Continuous-preservation (float) charging:
- 13.4 V for gelled electrolyte;
- 13.5 V for AGM (absorbed glass mat)
- 13.8 V for flooded cells
All voltages are normally considered at 20 °C (68 °F), and the adjustment should be -0.022V/°C for temperature changes.
Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation)
Gassing threshold: 14.4 V
After full charge, terminal voltage drops quickly to 13.2 V and then slowly to 12.8 V.

Then different multimeters show different number according with the quality.

[majicwrench]

SB,
IF your TS, dash etc are going dim, you are correct,your alternator is not putting out enough current. Once running, the battery plays a very small part. Even something as simple as a loose belt can cause this.

I would bet you meter is correct!! WHy doubt it?? Go to some other car and verify. 15.4 vots is high but somewhat acceptable, 17+ volts is not.

After starting car, voltage will be low, output amperage will be high as alternator produces current to replace that used by cranking engine. As battery get closer to full charge, amperage output will go down, voltage will go up.
Keith

[spider2081]

A simple way to check your volt meter is to measure a known good carbon zinc 9 volt battery. Your meter should read very close to 9 volts.
Digital meter's accuracy goes crazy when their internal battery gets weak.
With 15-17 volts at the battery your lights would be super bright

[seabeelt]

Boy do I feel foolish Kieth, I checked all of my cars. They all read high. So I go hmmmmmmm, Then after reading the post about the multimeter, I check that.... Sure enough the LOBAT is in the display. Thing is, there is a big scratch right over it and you have to tilt the meter to see it. I replaced the battery in the meter and I now have "normal" readings. 12.34 at rest and 13.91 after starting and letting it run for a couple of min. I sure do feel better about the readings......

I am still curious as to why the dash lights would go dim and the turn signals would not work. Could the old battery have been that much of a draw on the alternator??????
R/

[majicwrench]

No. Battery is almost not a player once car is running. Like I said above, if dash/ts etc going dim when driving, alternator is not putting out enough current. Could be as simple as a loose belt, or alternator could have a problem.
Good news about meter/voltage.
Keith

[seabeelt]

I will take it out for a drive tonight and see what happens
R/

[seabeelt]

Took the car out for an evening spin. All electricals seem to be working fine. I did notice however, that if I wind the engine out to 6500 rpm, the alternator light at the bottom of the tach comes on . Car has new 95 amp alt and new electronic ignition. Is that a tach warning light of sorts, or is something wrong still in the charging system???