ltc

Anyone we know
Besides, the presence of a total lighting failure is merely a way to extend the life of your battery

Interesting to note that everytime my Ford's go in for routine service, they always load test the battery (or batteries in the case of the diesels). Not sure if PCNA does a load test as part of routine service.

IIRC, PAG batteries are OEM from Douglas Battery....at least in the 911 days.

wingless

Load testing has generally gone the way of the dinosaur. It has been replaced, thank goodness, with measuring the AC conductance, as with the Midtronics Battery Tester.

The best thing to do is to observe the voltmeter, using the instrument cluster gauge, to ensure that the charging system is operating properly. All properly equiped tow vehicles include this as standard fare.

When a fully-charged battery has sat for several hours the voltage should be about 12.5 VDC. A dead battery is about 10.5 VDC. When the engine is running, charging the battery, it should quickly rise to about 13.8 to 14.0 VDC.

A multimeter may be used, if the dash voltmeter is missing or defective. It may be connected to any "unswitched" 12 volt source, or better yet, directly to the battery. The mulitmeter has high impedance, so leaving it connected will not affect the drain.

If the vehicle does not bring and maintain the battery at 13.8 VDC while running, then the alternator may be bad.

If the battery "quickly" drops from 12.5 to 10.5 VDC, then the battery may be bad. It is also possible, but not likely, that the vehicle has abnormal "dark current" draw killing the battery. It is possible to park the vehicle with the meter display visible from the exterior, to see what happens after several days. I would log voltage versus time parked, (but that would be the highlight of the excitement in my life).

It is likely that if the alternator has been bad, then the battery has not been fully charged causing the battery to become defective.

MadFox

Good post.. and no elephants either!?

Thus, can we engineer types but don't use our degree conclude if the voltmeter in the dash with the engine running pegs exactly at 14. volts (which mine does) that the battery and alternator are both in good working order? The only time that I had to jump my car I noticed that the voltmeter in the dash was under 12 and with the key turned it dropped significantly (the car had sat for a few days.. a light was on and apparently the timer didn't kick it off -- software??).

wingless

Yes, 14 volts on the voltmeter is a very good indication of alternator health. It should hold steady at that reading.

The battery is another story. It should level at 12.5 several hours after the vehicle rests and hold there. The battery capacity is 95 Ah, ampere-hours. So, at a slow rate of discharge, it should provide about that much energy. If there were ½ ampere of "dark current", then the battery should last for 190 hours before it dies.

The Midtronics Battery Tester measures and quantifies the battery capacity, taking away the mystery.

BTW, the turbo has a boost gauge instead of the voltmeter.

ltc

Somehow I don't think the math is quite that simple...but it matters not for this discussion.

356driver

...and it is quite a bit more entertaining.

wingless

Right, the battery Ah capacity is typically specified at a 20 hour discharge rate. So, the 95 Ah battery would last for 20 hours, when discharged at a rate of 4.75 amperes, to be considered to have 100% capacity. If it died sooner, then it would have a lower percentage capacity.

It is very helpful to now be able to make a quick measurement, just like using a voltmeter, to quantify the Ah capacity of the battery, using the AC conductance measurement.

wingless

Except that the times that it would be cool to see it in action, my attention is drawn to inputs occurring outside the vehicle.

356driver

True. But I was comparing it to a voltmeter.

ltc

http://physics.about.com/od/physicsg...onductance.htm
Definition: The ratio of a current in the conductor to the potential difference between its ends. Reciprocal of resistance. SI unit is siemens, abbrev: S

Wingless,
Your fancy AC conductance meter is nothing more than a battery load tester.

tkerrmd

Thanks for all the above info and help again!! I 'll just buy a new battery and see what happens!! Oh yea, I was a chemical engineering student also!!!!! Then I realized I wasnt smart enough so I went to med school instead!!

tom

wingless

Nope. It draws almost no current. It stimulates with AC voltage and measures AC current to calculate AC conductance. The meter is setup with selecting the battery chemistry and capacity. It monitors ambient temperature. All this information is used with standardized tables to arrive at a result.

A load tester, on the other hand, uses load resistors, or a transistor load, or some other means of drawing a very large current out of the battery. The current is drawn for a specific amount of time, 20 or 30 seconds, while measuring the voltage. The end voltage is compared to a standardized table to arrive at a pass / fail result.

IMO, the most accurate means is to use a transistor load, set at the 20 hour rate and characterize the battery to fully discharged. Of course, this is after floating the battery at 13.8 VDC for 24 hours, to ensure it is fully charged. (No look-up tables involved.)

But, the AC conductance meter does provide useful, easy, repeatable, safe and reasonably accurate results.

MadFox

Even us here Bubbas can see that... but let me tell ya... if'n you follow that there logic.. then a battery load tester is nothing more than a FANCY eggspensive way to see if yo' battery done discharged... let's see you wet yo' index finger and thumb on one hand and squeeze the + pole (it be "red" ... er, no pun intended) and then you put yo' palm on da metal part of that thar pepper and if yo' heart skips two beats and yo' hair stands up your battery it'd be good. Ain't that right Forrest? Pass me a-nutter Beer.

MadFox

well if you say so doc.. the killer at Vandy was all the pre-meds in my organic and chem classes screwing up the curves because they studied all the time.. the chem e's were still sobering up from mixing chemicals late at night.. man, engineering science was such a breeze after thermo and ee courses too.. engineering mgt. vs. pre-med.... ahhhhh you be smarter!