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Minimum practical voltage of AA battery

Dan Miller , Mar 12, 1998; 09:56 p.m.

During my last vacation I shot quite a few rolls, and went through my share of batteries for cameras, flashes, and motordrives. In all the excitement, I inadvertently mixed the "fresh" AA batteries with the "spent" ones. I'd like to determine which ones are good by measuring each of their voltages with a voltmeter. I'd like to know the minimum voltage below which a AA (Duracell, Energizer) battery is of little practical use. This will be my criterion for getting rid of those cells. I realize that cameras, motor drives and flahes will have different voltage requirements, so the answer is likely to be in some sort of a "gray area". However, all i'm looking for is a general guideline.

Thanks, Dan P. Miller

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Sean Hester , Mar 12, 1998; 10:32 p.m.

the easiest way to determine the fresh ones would be to buy some fresh ones, measure them, then compare them to the other ones. any that are not exactly the same voltage as the new ones are suspect.

the problem you have is that the voltage of a dry cell battery varies wildly with the load being put ont he battery. meaning that a new battery might measure 1.7 on a volt meter. (a volt meter (by design) doesn't put a load on the thing it's measuring) but when you put it in a flashlight, turn the flashlight on, and measure the voltage then, you'd only get 1.5 volts. say you then put a used battery to the same test. it may measure 1.6 (or even 1.7) on a voltmeter. but in the flashlight (when it's actually being asked to supply power) it may only measure 0.9 volts.

if you want a short answer, i'd say no less than 1.5 volts on a voltmeter. that may sound silly, but it's probably true.

Brad Hutcheson , Mar 13, 1998; 06:20 a.m.

I tested a few batteries to see. The Enegizers I bought a couple of weeks ago read about 1.6V. The ones I have had in storage for about a year read about 1.55V. The ones out of my flash (used a little) read about 1.45V. I didn't have any that were nearly dead so I can't advise on that. As stated above, the load will make a big difference, but a volt meter sould at least keep you from mixing old and new batteries at the same time.

Zack Lau , Mar 13, 1998; 09:29 a.m.

0.8 to 1.0 volts is a typical end of service voltage according to most manufacturer's data sheets. I'd say this is the "dead" range.

Complicated electronics, such as microprocessor controlled cameras, can be pretty conservative, since you always want the electronics and mechanics to start up in a known state. Thus, batteries may have lots of life left for other uses, but the camera won't work. I have a 2.92 volt lithium that doesn't start my P & S (3 volt battery).

1.2 to 1.4 volts may still offer lots of life in micro-power electronics. Beware of devices that depend on voltage for maintaining calibration (light meters?)

Those test strips that Duracell used to include worked on heating liquid crystals--you could also time the heating process to get a better estimate of how much life was left.

Glen Johnson , Mar 13, 1998; 10:18 a.m.

Radio Shack used to sell a Micronta battery tester. It can handle virtually all battery styles that are in common use, and many odd styles as well. I bought one around 1975, and I am still using it. I also have an old Micronta analog multi-meter that's still going.

For battery testing, you can't beat a dedicated battery tester. They typically offer a clear indication of good, marginal, or dead by swinging a needle into a green, yellow, or red region.

I am under the impression that the battery tester applies a load to the battery that is in the expected service range. A multi-meter is going to just load the battery with some incredibly high impedance that doesn't simulate any reasonable load at all.

I've got two boys at home, one in high school, and the other in college. They go through batteries, and they are notorious for leaving dead batteries behind in the fresh battery storage box. Because of this, I almost always test any battery that I get out of the box before I install it.

Zack Lau , Mar 13, 1998; 12:03 p.m.

True, modern meters often have impedances of 10 megohms or higher. OTOH, digital meters have enough precision to sort out which batteries were used together (three around 1.21 volts, four around 1.35 volts... though the odd cell will not match the pack). Thus, with ordinary alkaline cells and a precision meter, a load isn't needed to differentiate between used and unused cells. I'd use a load with an analog meter, unless it had an expanded scale.

Ted -- , Mar 13, 1998; 06:20 p.m.

There is an article in March/April issue of Photo Techniques about batteries. I read it earlier to-day and if I remember correctly the author stated that a new Duracell AA alkaline should read at least 1.6 when new and is dead at 1.4 mV. Ted.

Glen Johnson , Mar 14, 1998; 12:38 p.m.

I've never bothered to check batteries out with a volt meter, but any volt meter, whether modern or old, will be a very high impedance device, and will not present any kind of realistic load to the battery.

When you take a device that has stopped working that is normally powered by 4 AA batteries, and then check the 4 batteries, you will often find that one of the batteries tests "dead" on a battery tester, and the others may test "marginal" or "good." If I'm using the batteries to power a flash, I just replace all four of them at once, even if one of them might test good. I recycle the bad ones and the marginal ones, and I put the good ones back in the battery box for the kids to use in one of their devices.

My point in this I guess is that all of the batteries in a set of batteries don't "age" exactly the same way. Some must start out more powerful than others. The energy stored for a given battery voltage must be stochastic, rather than deterministic, and this makes sense just because of the fact that the battery is a geometric entity with tolerances.

I really think that if you want to actually test a bettery, it would be smart to get a battery tester. The battery tester is going to give an indication of the voltage under a load condition. A volt meter is not going to do this.

Zack Lau , Mar 15, 1998; 09:01 a.m.

I've been using a digital meter for over decade to check batteries--works just fine for alkalines under most conditions, so I don't bother adding a load.

A purist might want to test their cells under different loads to match them--this is the reason Nicad battery packs fail prematurely--the weak cell is actually charged backwards by the strong cells when the pack is discharged deeply. This is why satellite designers monitor each cell...

Instead of using resistors to buiild such a tester, you might consider using a power transistor as a load for more flexibility.

Sean Hester , Mar 15, 1998; 02:18 p.m.

i suppose with a precise enough meter (analog or digital) you could tell the difference between new batteries and ones that had been used a bit. if that's all the original poster wants to do he could follow my advice at the top of the thread.

but the real question (to me at least) is this: i find an AA battery lying around. i break out by digital volt meter and it measures 1.48 volts. is this battery worth keeping? my current answer is "i don't know". i know it's not new, but how "used" is it? without a battery tester (or building some sort of resistance network or other current drawing device (which is what a battery tester is)) i don't know if the battery is still useful.


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