12 volt battery meter9/20/2023 ![]() ![]() voltmeter used to show the battery condition and state of charge on most late model testers is a special design known as an "expanded range" or "suppressed scale" D.C. A battery tester puts a resistance load across the battery being tested, and shows the voltage under load conditions as well as at no load, before and after charging. The voltmeter leads go directly from voltmeter to the battery charger clips by separate leads to avoid erroneous readings due to the voltage drop in the heavy cables. voltmeters are used in battery load testers, either as a separate test unit, or built into a combination battery charger and battery tester. The cover will go on only one way correctly without using force.ĭ.C. Observe the position of the tabs on the cover and be sure they line up with the proper notches in the meter case. The cover can be pulled off with the fingers, and snapped back into position. In cleaning plastic meter covers, use only soap or detergent and water. ![]() The snap-on type of plastic meter covers are easy to replace, and often do need replacement. Usually, the left terminal, while facing the terminals on the back of the meter, is the positive connection on most voltmeters and ammeters. For a negative output charger, the negative output connects to the meter negative terminal, and the meter positive terminal connects to the negative cable clamp. The negative meter terminal would then go to the positive cable clamp. However, an ammeter is series connected so that the positive output of the charger goes to the positive meter terminal. voltmeters must be connected in parallel to the circuit, that is, positive terminal to positive terminal, and negative terminal to negative terminal. Two separate small leads go to the battery charger clips directly, to read the voltage at the battery terminals, avoiding error due to the voltage drop in the charging cable.ĭ.C. When the voltage reaches approximately 13.8 volts for a 12 volt battery, it is considered to be fully charged without gassing at normal room temperatures. voltmeters connected across the battery charger output are used as charge indicators. In Figures 18-1b and 18-1c, moving the shunt connection in the direction of I is for an increased meter reading, and D for a decreased meter reading. The shunt is usually mounted on a heavy stud, such as provided by the circuit breaker, solenoid, or rectifier. Only a very small wire is needed between the shunt and the meter. The external shunt type avoids running heavy cables to and from the meter. The meter is a millivoltmeter, but it is calibrated in amperes for a particular shunt. This voltage drop is only a few thousandths of a volt, or millivolts MV. The meter operates from the voltage drop across the shunt. In both cases, the main charger current goes through the shunt SH. The less metal between the meter terminals, the lower the reading with the same current through the shunt. Both shunt types work on the same principle, and are adjustable by loosening the screw, and moving the connection to change the position of the meter on the shunt. The external shunt type is shown in Figure 18-1c. The meter mounted shunt type is shown in Figure 18-lb. The dial shows the amperes either in numbers on any of the three types, or by a scale marked in color to show the limits of maximum charge for each battery voltage. There is no adjustment on this type of ammeter, except a "zero" adjustment in some cases. The full current goes through the meter to register the amperes. ammeter, as shown in Figure 18-la, which has one or more turns of heavy wire in the meter, or the cable on the outside, indicating by induction. ammeter, the meter mounted shunt type, and the external shunt type. Three types of ammeters are used on battery chargers: the direct connected D.C. In combination battery chargers and battery testers, there may be an additional calibrated battery testing voltmeter. ammeters) either with or without an external shunt, and "bulb indicators," which are zero center D.C. The most common electric meters used in battery chargers are "charge rate" indicators (D.C. ![]()
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