Replies to post #3803 on Cars, etc. (GEARHEAD)

[Phil(Hot Rod Chevy)]

Good Morning PW.

A fully charged "12 volt" battery should be storing around 13.5 volts.

So yours in great shape.

I'm surprised the commander's will even start his car.

It could be on the verge of dieing and might leave you guys stranded when you least expect it.

On the other hand, it might be a loose alternator belt.

Not likely if it's a late model car with a serpentine belt though.

If it were me I would have it checked out by a mechanic

Phil

[Bob Zumbrunnen]

The Commander's car likely has a dead cell in the battery and it should be replaced in the near future. Full charge is 13.8 volts or 2.6 volts per cell. Remove a cell from the equation and you get 11.2 volts.

At the very least, he should make sure the electrolyte level is good on all cells. If one is pretty low, add distilled level to take the level up enough to cover the plates and then some (like 1/2" over the plates). If you do find and take care of a low one, you're likely to get a better reading on the voltmeter without even driving the car.

There are a number of reasons you could be getting 13.33 volts instead of 13.8. As the battery approaches full charge, the alternator should start to taper off, so it can take quite a while to get that last half volt. Also, if a door was open (interior lights) or there's an under-hood light, that'll cause a small voltage drop. Or if the car's new enough, the computer is constantly drawing juice.

I've got a BMW motorcycle that's so under-batteried and over-computerized that if I let it sit for 2 weeks, the battery is completely drained. I really need to get a couple dozen trickle-chargers for these darned things that sit for such long periods of time. Might save hundreds on the Spring ritual of replacing batteries at my place.

Edit: 11+ volts is more than enough for a car to start well. It's all a matter of how much power is stored in the remaining good cells. You can have as many as 2 completely out-of-the-loop cells (10.4 volts) and as long as the 4 good ones are really good, the only difference will be the starter not spinning quite as fast, and it'd be such a subtle difference that it likely wouldn't be noticed. Especially with an engine that lights right up.

[Id_Jit]

Hi gals and guys.

I agree with Phil and Bob about the Commander’s battery having low Voltage.
The cause could be a shorted cell, loose alternator belt, bad alternator or an alternator’s bad Voltage regulator. There is a very slight chance that the culprit is “Surface Charge”.
The (internal to the alternator) Voltage regulator in my ’76 Capri partially failed while driving through the mountains one Winter. In checking it later, instead of putting out the nominal 13.8 Volts, it was charging the battery at around 12.7 or so Volts. That was enough Voltage to keep the battery fully charged, so I never did get around to replacing the regulator. I really should have though. That extra Volt or so would have helped spin the heater fan juuussst a little bit faster. The heater was under capacity for Alberta Winters.

Places that specialize in selling replacement vehicle batteries have test equipment that will quickly test the charging system and battery to determine what is at fault. A good garage should have one too. Sometimes they charge for the diagnostic test.
Semi OT: The place that I usually buy vehicle batteries from has a ritual of doing the test first at no charge. I took my dual battery Surburban there (Edit: more than) one time. (Edit: That time) I told the ‘young’guy that I needed a new battery. He told me to drive it in and pop the hood. I did. He pulled out the test cart and was about to hook it up for the test. I advised him that one of the two batteries was 10 years old and had a shorted cell... Replace it. He stopped short with that deer in the headlights: “Something’s wrong here … Now what do I do?” After replacing the battery, I let him do the test. All was now well… Employee and battery wise. <g>


Let me introduce a new lead-acid battery sub-topic: “Surface Charge”

From:
http://www.uuhome.de/william.darden/carfaq4.htm#remove

4.3. Remove Surface Charge

Surface charge (or "counter voltage") is the uneven mixture of sulfuric acid and water along the surface of the plates as a result of charging or discharging as the electrolyte has an opportunity to diffuse in the pores of the plates. It will make a weak battery appear good or a good battery appear bad. Larger wet lead-acid batteries (especially over 100 amp hours) could also have electrolyte stratification where the concentration of acid is greater at the bottom of the cell than near the surface. Open Circuit Voltages (OCV) will read higher than they actually are. Stratification can be eliminated by an equalizing charge, stirring or shaking the battery to mix the electrolyte.

The surface charge can be eliminated by one of the following methods after recharging a lead-acid car battery:

Allow the battery to sit (or rest) without discharge or charge for between six to twelve hours at room temperature, if possible, to allow for the surface charge to dissipate. (Recommended method.)

Turn the headlights on high beam for five minutes, turn them off, and wait ten minutes.

With a battery load tester, apply a load at one-half the battery's CCA rating for 15 seconds and then wait ten minutes.

Disable the ignition, turn the engine over for 15 seconds with the starter motor, and wait ten minutes.

Apply a load that is 33% of the ampere-hour capacity for five minutes and wait ten minutes.

With a battery load tester, apply a load is one third the battery's amp-hour rating for five minutes and wait five minutes.


This is a segment of an excellent lead-acid battery information site:
http://www.uuhome.de/william.darden/index.htm


My translation:
A lead-acid cell has a nominal Voltage of 2.1 Volts. A 12 Volt lead-acid battery composed of 6 cells will have a nominal Voltage of 6 x 2.1 Volts = 12.6 Volts.
When the vehicle is running and the properly operational charging system has had sufficient time to recharge a good battery, the Voltage across the battery will be the output Voltage of the alternator. Typically this is the nominal 13.8 Volts or so. (It could be up to 14.2 Volts or so.) When the engine is shut off, the Voltage immediately will be the charging Voltage from the alternator. Soon it will slowly drop to around 13.2 Volts, and many hours (overnight) later will settle around the nominal 12.6 Volt level.
This “temporarily increased Voltage level” is the Surface Charge Effect.
Think of it as a little extra transient Voltage temporarily stored in the battery


From:
http://en.wikipedia.org/wiki/Lead-acid_batteries

The following are general voltage ranges for six-cell lead-acid batteries:

Open-circuit (quiescent) at full charge: 12.6 - 12.8 V
Open-circuit at full discharge: 11.8 - 12.0 V
Loaded at full discharge: 10.5 V
Continuous-preservation (float) charging: 13 - 13.2 V
Typical (daily) charging: 13.2 - 14.4 V
Equalization charging (for flooded lead acids): 15 - 16 V
Gassing threshold: 14.4 V
After full charge the terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V.

Id