battery tester

V=IR, Voltage = Current X Resitance W=IV, Wattage = Current X Voltage

If you have an ohmmeter you can determine aproximately what the current consumption of your camera is by measuring resistance at the battery leads. Invert the positive and negative test cables of your meter and take a second measurement, also take two measurements with the diode/ semiconductor option on your ohmmeter. Sometimes the battery feeds a protection diode and taking straight ohm measurements gives you a bogus reading. Once you know the aproximate resistance of your camera, use a resistor about that size and of a wattage 2X the dissipation of the camera.

cheers T.Alan

And your fist error!

Also about posting on-topic?

No.

Nick

This won't work... The load presented by electronic equipment simply cannot be measured with an ohm meter. The reason is that the equipment contains many transistor junctions that don't turn on unless sufficient voltage is applied. And the quiescent current is a tiny fraction of the dynamic (cycle) current. What you need to do is to hook a current meter between the battery and the camera with jumper wires. The easy way to do this is to get an extra pair or two of hands involved to hold the kludge together while you take the measurement. An old analog meter will work better than a digital because it will respond more quickly, and you will need a quick response to get an idea of the peak current when the camera is operated. Then, calculate the value of a resistor that will draw somewhat (maybe about 1.5x) more current than the camera needs.

But, a better approach would be to get the engineering data on the battery in question (should be available on the manufacturer's web site...). It is a safe assumption that the engineers knew what they were doing and chose a battery adequate to run the camera... What you want is a voltage vs. current or discharge curve so that you can determine the condition of the battery (never mind the camera...).

There is, of course, one big bug in the whole idea of battery testing. In many types of batteries, the voltage drops fairly quickly during the initial usage, then drops very slowly over most of the battery's useful live, then drops precipitously at the end. So, it may be very difficult to determine the difference between a battery with 90 percent of its life left and one with only 20 percent.

In short, a battery that is "mostly" used up may well be able to put out enough current at sufficient voltage to run the camera, but will fail in very short order.

Jerry

Hi Sam

What kind of chemicals are used in your "123" batteries. The CR 123 batteries are commonly Lithium. The voltage across the terminals of a Lithium CR 123 is fairly constant till the final few percent of the battery life. So, it is very difficult (impractical) to judge the life remaining life in a Lithium cell when only its terminal voltage is known. If you have rechargable 123 cells, you probably wouldnt be asking this question.

The "resistor load" will be usefull for determining which batteries are

A 50 ohm across the two CR 123 cells in series wil draw about 120 mills. I'd guess that current is close to what your camera needs for some functions. A 1 watt resistor wil serve your needs if you choose to use a

Jerry

I'd test with 3 ohms. Some digicams draw more than an amp, some less, but 3 ohms would work fine for testing. You'd want a 3 or 5 watt resistor. Some discharge curves for 123 cells can be seen here:

Hi Don

I sure need to laern to read better. I read the original post as Batteries in series. He had written that the battery is in series with a resistor, not two batteries in series. But, I guess he really wants to load the battery with a resistor across it and read the voltage across the resistor. I should have read more carefully. But, is it really practical to evaluate a Lithium CR123 cell by measuring the voltage across it while it is loaded to draw an amp?

Jerry

That's how I interpret Energizer's curves, but I could be wrong. Easy to check by experiment with a known new cell and then one that is known to have been used a while.

You might try simply putting the cells in question into the camera and see what the built in battery meter says. It already knows what the load situation is.

Pete Stanaitis

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snipped-for-privacy@veriz> Hi guys

sci.electronics.basics

That's right, most digital cameras probably have some sort of DC to DC converter as a power supply. I foolishly was thinking of an analog camera where the battery was only driving the light meter.

cheers T,Alan

What's that Lassie? You say that snipped-for-privacy@verizon.net fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by 5 Mar 2007 09:12:18 -0800:

Sorry I'm a little late. If it helps, you can get CR123 cells from batterystation.com for about $1.25 ea. Beats the hell out of $7.00+ at retail stores.