Battery Charging Voltage

An amp meter isn't needed for an alternator equipped vehicle??? Where do you get this crap? Ammeters were used for many years after alternators replaced generators. They are just two different ways of determining the "health" of the charging/starting system. In fact, testing the system includes using BOTH.

While a volt meter will tell you what system voltage is, an ammeter is the only way to KNOW whether your battery is being charged or discharged, and at what rate. The switch to voltmeters from ammeters probably has more to do with trying to avoid confusing or alarming those who are easily confused. Like you seem to be.

Ammeters constantly fluctuate with electrical system loads, while voltmeters stay steady unless something is seriously wrong. People don't like seeing their gauges fluctuate.

Gee, that's funny, my volt meters must be psychic or something.

I can always tell the state of my charging system by knowing where my voltage gauge sits during 'normal' operations. When it starts fluctuating out of the normal, according to how, I know what to check. It seems pretty easy. If the gauge didn't reflect the operation, then the gauge is useless and you may as well have one idiot light only.

I find the volts reflect the charge state really well.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

bllsht wrote:

Dave, Sounds to me like a normal reading. That's what my TJ"s voltmeter reads. And, it's always a good idea to clean the terminals every year (before winter sets in). I use a foam battery cleaner in a can and a battery terminal sealer, also in a spray can. After I use the cleaner I use a battery post/cable wire brush then reconnect the battery cables and spray with the sealer....Works for me ! Tom T

An easy way to check battery health is with a voltage load test. If you find that your battery voltage goes from high to low (relative term) then odds are it's not handling a charge very well and is bleeding off quite well.

If you throw a battery on a charger and then measure the voltage you'll measure a 'skin' charge (or surface charge) that will be equivalent to the charging voltage. You need to load the battery to bleed this off. I use an automotive lightbulb (12V/40W) for 1 minute and then I measure the voltage again. Being that the charging voltage is around 14.5Volts, if I measure after bleeding and find a voltage less than 13V then I get worried.

A battery with only 12.1 volts is considered to only have 50% charge left in it (this is amp capacity it's referring to).

I may have gotten my terms back to front...(and am not entirely sure of the bulb wattage) but this is a good rough method to determine your battery health.

Using a voltmeter, wether on the dash or independant of the vehicle, can be an 'iffy' situation. A person who pays close attention to their dash voltmeter behavior would certainly know the 'history' of what is going on (as in Dave's case)and could be useful. Using a dash voltmeter, or any voltmeter independant of the car, I personally would not use. A charge indicator on a battery charging unit measures AMPs as in Cranking Power, wether by a meter or lamp, is a better indicator.

When you buy a battery you do not ask if it is 12 volts - you look for the correct size & Cranking Power for your vehicle. The old and still effective way to measure your battery to determine if it will turn over your engine (and not just turn on the lights) is by using a hydrometer which measures the batteries (or it's electrolytes) specific gravity which will indicate it's ability to crank your engine. (Gosh, I hope I remembered all that the right way, but I think it's close.) FYI - Volts are measured in parrallel, amps are measured in series. Steve

OOP's, I mean the way Mike watches his dash voltmeter. Steve

I'll type slower for ya this time, and maybe you'll get it...

I didn't say a volt meter wasn't useful. I said they are just two different ways of determining the "health" of the charging system. I'd actually like to have both. However, if I had to choose one or the other, I'd prefer an ammeter because a volt meter doesn't tell you DIRECTION or AMOUNT of current flow.

If you really like your volt meter, you have my permission to keep it.

May be that. Or it may be in response to it.

I always figured that the switch from ammeters to voltmeters had more to do with saving money on a dozen feet of heavy gage copper wire.

While proper instruments are nice to have, it isn't rocket science. If my Cherokee volt meter is reading 12 volts instead of 14 then I know that the belt is slipping and the alternator isn't charging the battery.

Of course, I'll probably notice that the signal flasher has slowed, too.

-- "I defer to your plainly more vivid memories of topless women with whips....r" R. H. Draney recalls AFU in the Good Old Days.

I was more implying my volt meter is really swingy when things 'start' to go wrong so I find it pretty useful. I don't find it waits until 'something is seriously wrong'.

Mike

bllsht wrote:

Since generators, that are no longer installed in passenger vehicles, would allow the battery to be drained at slow engine rpms, it was useful to have an amp meter. I grew up with amp meters and know what they do and how they work. How would an ammeter be useful in an engine whose alternator doesn't have the generator's drawback of allowing battery discharge at idle? The ONLY time you'd see a negative flow is during starting, winching or something else that draws more than what the alternator is capable of generating.

bllsht wrote:

I wach mine - that's why I know that +0.3v difference is unusual :-)