The photo shows an inexpensive (often free) multimeter from Harbor Freight. I added a white dot to the indicator. Notice that the white dot points to a battery test function for 1.5 volt and 9 volt batteries. Batteries should normally be tested under a load because a no load voltage test could read normal, but drop considerably when the battery is under load. This
multimeter's manual indicates that the battery test circuit adds 360 ohms of resistance as a load. According to the label on the meter, a 1.5 volt battery in good condition should show a current draw of 4 milliamps or more and a good 9 volt battery should show a current draw of 25 milliamps or more. There is nothing mysterious about this. It is a simple application of Ohm's Law, which says that voltage (E) in a direct current circuit is equal to resistance (R) multiplied by current (I), or E =
IR. Factored, that is current (I) equals voltage (E) divided by resistance (R). This is not my better meter, but one I needed in a second location. It does not have a battery test function, but I decided it would be handy to add one. I can use the 200 m function. But, I will need to add about 360 ohms in resistance when in use. (My better meter also does not have a
battery test function, and I made one of these resistor probes for it, too.) It would be ideal if I could have gone to Radio Shack to buy a pack of 360 ohm resistors, but they are not available. I rummaged through my junk box and found a 270 ohm resistor and a 100 ohm resistor. Soldering these two end-to-end (series) gave me one resistance of about 370 ohms. (Resistors are usually not exactly
their stated value, but vary just a little. Check the actual resistance with the Ohms function on your multimeter. My chain of resistors is actually 367 ohms. Also, resistors use a color coding system to indicate their value. The colors shown on the resistors in the illustration are accurate for the values indicated.) See the second photo. I soldered a small alligator clip to one end of the resistors. I slipped a soda straw over them and added some hot glue at each end to provide some
physical strength. I scraped the resistor lead opposite the alligator clip to remove any hot glue that might act as insulation. I could have brought the 367 ohms down to exactly 360 ohms by soldering another resistor of 19000 ohms in parallel to the two resistors. Resistances in parallel function differently than resistances in series. (Adding 19,000 ohms, if such a resistor were to be available, is more of a hypothetical example than a serious suggestion.) Here is an on-line calculator for parallel resistances. To use, just attach the alligator clip to one of the test leads. Set the multimeter to the 200 milliamp scale. Use the bare resistor lead as the probe. Touch the probes to the battery under test. Step 3: Make a LabelIt is easy to forget what the thresh hold figures are for testing batteries. I made a label for the back of the meter. My figures are not quite accurate, but are close. It may well be that a battery considered depleted in one application would still function in a less demanding application. See the second photo. The battery that read 3.9 milliamps in the photo for the Introduction with 360 ohms added reads 3.8 milliamps with my 367 ohm resistance added to the circuit. You can easily make your own resistance load from resistors in your junk box for checking common batteries under load with a meter you already own, even though it may not have a battery test function. Step 4: One CautionThis meter contains a fuse. It is easy to blow the fuse if the selector was set to the wrong range for a test you performed recently. If the fuse is blown, the milliamp scales will read zero (0). At first you may wonder what is wrong. You simply need to install a new fuse. The fuses used by this particular meter are not easy to find locally. I ordered a package of five from Amazon. 1 Person Made This Project!RecommendationsWatch batteries are small round batteries used in electronics such as watches, desktop computer motherboards, PDAs, toys, calculators, remotes, and hearing aids. They come in different types and have varying diameters and heights. Two popular watch batteries are lithium and silver oxide. Batteries have positive and negative terminals. In watch batteries, the positive side is usually marked with a plus sign and the battery type. The negative side is normally less shiny and smoother than the other. The voltages of watch batteries are typically 1.5 or 3 volts, and may be checked using a multimeter. Instructions
Switch the multimeter on. Make sure that it is on a DC voltage setting, which may be indicated by the letters DC or a short line placed above three side-by-side smaller lines. Place the instrument on a setting of at least 3 volts. On a multimeter, the side of the dial used to do voltage measurements is usually indicated by a V. Hold the red probe of the multimeter against the positive terminal or side of the lithium battery. Hold the black probe against the negative terminal. One way to do this is to lay the battery flat against one probe, while placing the other probe on top. Another way is to hold the battery upright using an insulator such as plastic, rubber, cardboard, or wood, and then placing the probes on each side to do the measurement. Record the voltage. Fresh lithium watch batteries are typically around 3 volts. Repeat Step 3 but with the silver oxide battery. Fresh silver oxide batteries will be around 1.5 volts. Turn the multimeter off. Things You'll NeedTipsHow many volts should a CR2032 battery have?The ubiquitous CR2032 battery is a coin-shaped three-volt lithium-ion battery.
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