Battery tester. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells

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The author of the published article works at the Taganrog Metallurgical Plant in a workshop for the repair of portable radio stations. These radio stations are powered by a battery of ten disk nickel-cadmium batteries D-0,55. To check the condition of the battery and individual batteries, the author uses a simple home-made device, the description of which we offer to the attention of our readers.

The main problem is that during the operation of radios powered by a battery of nickel-cadmium batteries, due to dust and oxidation of the contacts, the resistance between the batteries increases. A voltmeter connected to the battery in this case will show normal voltage, but the radio station may fail at the most inopportune moment. When checking such batteries, for example, using a low-voltage load lamp, they are sometimes mistaken for discharged and charging is continued, which often ends in failure and even destruction of individual batteries. During charging, some batteries are recharged, and some, on the contrary, are undercharged and when they are discharged, they change polarity. This, as practice shows, is the main reason for the failure of batteries, even if all charging and discharging standards are observed.

The purpose of the proposed device is to check the degree of charge and distinguish discharged batteries from faulty ones. The device allows you to measure the voltage on the battery and individual batteries at maximum and minimum load. The greater the difference in readings, the greater the internal resistance of the battery. Based on this information, we can conclude about its serviceability and the degree of charge. For freshly charged batteries, the voltage, as a rule, can be slightly higher, and then within about an hour it decreases and the degree of charge can be judged from the steady value.

The device is very simple, can be used to test any batteries and batteries. Even a novice radio amateur can assemble it. The diagram of the device is shown in the figure. To improve the measurement accuracy, the device uses a voltmeter with a "stretched" scale from 10 to 15 V. The measurement limits depend on the stabilization voltage of the zener diode VD3 and the resistance of resistors R2 and R3. Resistor R1 sets the rated stabilization current of the zener diode. The resistances of the resistors R2 and R3 indicated in the diagram are selected for the M4256 microammeter with a total deviation current of 50 μA. You can use other micro- and milliammeters for current up to 15 mA. In this case, you will have to choose the resistance of the resistors R2 and R3, and the resistor R1 can be excluded. The SB2 button is used to connect the load - the HL2 lamp and the R4-R6 resistors - the assembled battery, and the SB1 button - to connect the load - the HL2 lamp and the R4 resistor - when checking individual batteries.

The design of the battery case does not exclude its incorrect assembly and connection, which is dangerous for the radio station. Therefore, it will not be superfluous to have a circuit of the VD6 diode and the HL3 lamp, which will light up when the battery is connected in reverse polarity. In this case, the VD4 diode will protect the microammeter from overload. Similarly, the HL2 lamp will also turn on through the VD1 diode, signaling the wrong polarity of connecting individual batteries. In this case, the microammeter will protect the VD1 diode from overload.

To check the battery, a device is connected to its contacts and the voltage is measured without load. Then, pressing the button SB2, measure the voltage under load. Testing individual batteries is even easier. The disk battery is inserted between the contact plates fixed on the housing (+1,5 V-Common). The voltmeter of the device will show the voltage without load at the limit of 1,5 V. If the battery is pushed further to the stop, the contacts SF1 will close, which will connect the load - the HL2 lamp and the resistor R4. If the difference in readings is large, you should clean the contacts of the battery and the device and then repeat the measurement. Failed, as well as elements with a significantly increased internal resistance, are rejected. It is important that batteries of similar parameters are assembled in the battery.

The device uses N5819 Schottky diodes (VD1, VD2, VD4, VD5) with a low forward voltage drop. Lamps - MH1,25-0,26 (HL1, HL2) and MH13.5-0.16 (HL3), buttons SB1, SB2 - KM 1-1, switch SF - MPZ-1.

According to the above scheme, you can also make a device for testing, for example, car batteries. It is only necessary to replace the load with a more powerful one and use a button whose contacts are designed for the corresponding load current. If you need a device to measure voltage at other limits, you should replace the zener diode.

To test power supplies of different sizes, such as galvanic cells or car batteries, three sockets must be provided on the instrument case for connecting flexible wires. Opposite the +15 V socket is the SB2 load connection button, and opposite the 1,5 V socket is the SB1 load connection button.

In any case, the adjustment of the device consists in the selection of additional resistors R2, R3 and the graduation of the scale according to an exemplary voltmeter. For ease of adjustment, resistors R2 and R3 can be replaced with trimmers and graduation can be started from the limit of 1,5 V.

Author: S.Gorenko, Taganrog, Rostov region.

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