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Old Nov 29, 2004, 10:37 PM   #1
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Hi. I am hopeless at electrical things. If I can get hold of a multi-meter (at least that's what I think they are called, those meter with rotary dial and all that), how do I use it to check whether a rechargeable battery is fully or only partially charged? Say, where should i set the dial, what to measure, what's the expected reading figure for AA batteryetc. That way, I can now whether the charger I presently have is any good or not. Thanks in advance.
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Old Nov 29, 2004, 10:47 PM   #2
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Here is a recent thread on the subject of testing batteries if you want to see how to do it:

http://www.stevesforums.com/forums/v...mp;forum_id=51

You may also want to take a look at this section on batteries and chargers. You may find that it's easier just to buy a decent "smart" charger and some good batteries, and simply keep them topped off if in doubt of their charge level (versus trying to test them). The Maha chargers are highly recommended, and you'll find links to reviews of popular models here:

http://www.steves-digicams.com/nimh_batteries.html


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Old Nov 30, 2004, 5:05 AM   #3
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tourist wrote:
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If I can get hold of a multi-meter (at least that's what I think they are called, those meter with rotary dial and all that), how do I use it to check whether a rechargeable battery is fully or only partially charged? Say, where should i set the dial, what to measure, what's the expected reading figure for AA batteryetc. That way, I can now whether the charger I presently have is any good or not.
1. There is no easy way to check the state of charge, other than by discharging it under standard conditions, and seeing how long it takes (but don't discharge it fully or you'll kill it). You can measure the open-circuit voltage, or the voltage on load (see below), but these will give only a rough guide, and will depend on the cell's history, both long-term and recent. You'd need to know the current-voltage curves on discharge, and they'll be a bit different every time. A smart charger will probably have an intelligent discharge facility, and you can make a guess at initial state of charge from how long that discharge step takes.

2. A good way to measure of the health of a cell and the charger that charged it is to buy a multimeter which has a built-in battery tester. These are common in electronics stores like Radio Shack etc., and just a tiny bit more expensive than the same make without the battery test facility. The meter will havea pair of separate ranges on its selector dial, labelled, typically, "1.5V" and "9V". These do the same thing as the home-made add-ons featured in other threads about this topic.You can then compare any cell with a known good one, by seeing how it performs under a standard load.

The cell on test is connected to astandard resistor (hidden inside the meter),and the current passed is measured, by measuring the voltage across that standard resistor. What is displayed on the meter's display depends on the meter, and its instruction book. In my case the "1.5V" range uses a 37-ohm resistor and the "working fine" current displayshows 40mA. In practiceI get well over 40mA from a fresh throwaway AA Mn-alkaline cell, and about 38-39mA for a fully-charged AA Ni-MH rechargeable. If you battery-test a set of cells (individually) after the camera has given its "low battery" warning, or shut itself down, you'll get typical figures for discharged cells.

Then you can guess what intermediate figures mean for partially discharged cells, but it'll be a bit hit & miss.

Good luck!




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Old Nov 30, 2004, 7:50 AM   #4
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Hi. Thanks for all the replies. Much appreciated. I will take some time going thro' all of these.
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