While on the topic, an unknown VU meter (and/or any galvanometer-based meter in general) can be scoped using a source of steady low voltage dc and a suitable potentiometer in series. Which household battery tester has best features MOTOPOWER Battery Tester for home use has the best features so it should be your top priority. The exact value of the resistors is probably not critical as the dial is relative and small errors are unlikely to be noticed by most end users (naturally, the movement is not exactly linear with respect to voltage, and it’s probably related to spring tension difference across the dial). Of course, this do-it-yourself battery tester too is basically a d’Arsonval meter with an appropriate voltage divider, and a load resistor to allow for the bleeding of surface voltage from the battery to see the voltage under load. ![]() And then carefully remove the dial to replace it with a piece of paper with a custom-made battery level scale on it (the dial drawing needs some serious homework). Now see, you can take apart the VU meter by removing two pieces of adhesive tape used to secure its casing. The 10Ω/0.5W load resistor is enough to bleed off surface charge and provide a more accurate indication of remaining battery power compared to reading the open state voltage. Note, the tester draws about 150mA (excluding the display part) because of its 10Ω load resistor (R2) on the 1.5V input. To ensure that you go with the right battery tester, all of these battery testers have been listed along with their major features and options. This will give you a range of 470-1470Ω, so plug in a dc source with known output voltage and adjust the trimpot until you get the needle where you want it. Using Ohm’s law, you can calculate that to get voltage of 2V (for 1.5V test) to deflect the needle to the maximum range of the milliammeter (2mA) you need a 1KΩ resistor in series with the meter (2.0V/0.002A =1000Ω).ĭepending on what resistors you might have handy, you can select something like a 470Ω fixed resistor (R1) and a 1KΩ multiturn trimpot (RP1). ![]() Simply, it all depends on what kind of meter you use to show the battery level.įor example, let say you’ve a VU meter (milliammeter) with a sensitivity of 2mA. Probably the only thing that may need explanation is the values of the resistors R1 & RP1 on this schematic.
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