Power supply for a sick battery. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power supply for a sick battery. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Desktop computer motherboards often use nickel-cadmium batteries, which consist of three disk cells. When the computer is turned off, the battery powers the system clock and a CMOS chip that contains the computer's internal settings. Over time, the nickel-cadmium battery becomes unusable. When the computer is turned off for more than a few hours, the battery is discharged so much that the system clock starts to lag behind, the settings in the CMOS chip go astray.

Unfortunately, it can be very difficult to get a new battery - computer companies don't usually sell them. It is possible to adapt a cordless phone battery for the motherboard, but such a battery can cost more than a similar motherboard! It is not advisable to use domestic disk batteries D-0,06 and others to assemble a new battery, since their electrodes quickly oxidize and the contacts between the elements in the battery are broken.

The oldest battery can be "revived" with a simple mains power supply (see figure). Its assembly will take much less time than finding a new battery.

Power supply for a sick battery

The power supply works as follows. The mains voltage through the fuse FU1 is supplied to the primary winding of the transformer T1. The transformer lowers the voltage to 3,5 V. Then it is rectified by the diode bridge VD1 and fed to the simplest stabilizer, consisting of capacitors C1, C2 and a diode VD2. The output of the stabilizer is connected to the GV1 motherboard battery. There is no overcharging of the battery, since the voltage at the output of the stabilizer (about 3,5 V) is slightly lower than the nominal voltage of a fully charged battery. Thus, the power supply, constantly connected to the network, does not allow the voltage on the battery to drop below 3,5 V. When the mains voltage fails, the VD2 diode prevents the battery from discharging through the leaking capacitor C1. The power supply "gets along" very well with the internal charger of the computer.

Details. Diode bridge VD1 - any of the series KTs402, KTs405, etc., capacitor C1 - any electrolytic, for example K50-16. Diode VD2 - D220, D226, KD105, etc. Capacitor C2 - paper or metal film, for example K7317, etc. Any small-sized transformer with a mains winding of 220 V and a secondary winding of 3,5 V is suitable for the circuit. With a slight alteration, you can use " personnel "transformers from old tube TVs, for example TVK-110-LM-K or TVK-110-L1. In such a transformer, the resistances of all windings are measured. The winding with the highest resistance is carefully connected to the network. If the transformer does not hum and does not heat up, it is ready for work.

Measure the voltage on all secondary windings. If there is no winding with the required voltage, then a test winding containing 30 ... 40 turns is wound on the transformer frame with any insulated wire. Often this can be done even without disassembling the magnetic circuit. The voltage on the test winding is measured and the number of turns of the new secondary winding is calculated based on the fact that the voltage is proportional to the number of turns. The magnetic circuit is disassembled, unnecessary windings are removed and a new secondary winding is wound with a PEL wire with a diameter of about 0,2 mm. After assembling the power supply, measure the output voltage. If necessary, it can be slightly reduced by connecting another diode in series with the VD2 diode.

The details of the device are mounted inside the computer power supply (if space permits) or in a separate metal casing located inside the system unit. A metal casing is preferable to a plastic one from the point of view of fire safety, since the power supply is constantly connected to the network, without supervision.

Author: S. L. Dubovoy

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