Little secrets of a rechargeable flashlight. Encyclopedia of radio electronics and electrical engineering

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

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At present, power outages have become very frequent, therefore, in amateur radio literature, a lot of attention is paid to local power sources. Not very energy-intensive, but very useful in emergency shutdowns, is a compact rechargeable flashlight (AKF), in the battery (battery) of which three sealed disk nickel-cadmium batteries D 0,25 are used. The failure of the ACF for one reason or another causes considerable grief. However, if you apply a little ingenuity, understand the design of the flashlight itself and know elementary electrical engineering, then it can be repaired, and your little friend will serve you for a long time and reliably.

Circuitry. Design

Let's start, as expected, with a study of the instruction manual 2.424.005 R3 Battery lamp "Electronics V6-05". Inconsistencies begin immediately after a careful comparison of the electrical circuit diagram (Fig. 1) and the design of the flashlight. In the circuit, the plus is from the battery, and the minus is connected to the HL1 light bulb.

In reality, the coaxial output HL1 is constantly connected to the plus of the battery, and the minus is connected through S1 to the threaded base. Having carefully examined the mounting connections, we immediately notice that HL1 is not connected according to the scheme, the capacitor C1 is connected not to VD1 and VD2, as shown in Fig. 1, but to the elastic contact of the structure, which presses the battery minus, which is structurally and technologically convenient, since C1, as the most overall element, it is rather rigidly mounted with structural elements - one of the pins of the mains plug, structurally integrated with the ACF case and the battery spring contact; resistor R2 is not connected in series with capacitor C1, but is soldered at one end to the second pin of the mains plug, and at the other end to the .U1 holder. This is also not taken into account in the ACF scheme in [1]. The remaining connections correspond to the diagram shown in Fig.2.

But if you do not take into account the design and technological advantages, which are quite obvious, then in principle it does not matter how C1 is connected, according to Fig. 1 or Fig. 2. By the way, with a good idea to refine the circuit of the charger (charger) of the ACF, it was not possible to avoid the use of "extra" elements.

The memory scheme [1], while maintaining the general algorithm, can be significantly simplified by assembling it according to Fig.3.

The difference lies in the fact that the elements VD1 and VD2 in the diagram in Fig. 3 perform two functions each, which made it possible to reduce the number of elements. The zener diode VD1 for the negative half-wave of the supply voltage to VD1, VD2 serves as a rectifier diode, it is also a source of positive reference voltage for the comparison circuit (CC), the (second) function of which is also performed by VD2. CC works as follows: when the value of the EMF at the VD2 cathode is less than the voltage at its anode, the battery is being charged normally. As the charge increases, the EMF value on the battery increases, and when it reaches the anode voltage, VD2 will close and the charge will stop. The value of the reference voltage VD1 (stabilization voltage) should be equal to the sum of the voltage drop in the forward direction on VD2 + the voltage drop on R3VD3 + EMF of the battery and is selected for a specific charge current and specific elements. The EMF of a fully charged disk is 1,35 V [2].

With such a charge scheme, the LED as an indicator of the state of charge of the battery at the beginning of the process lights up brightly, as it charges, its brightness decreases, and when it reaches full charge, it goes out. If during operation it is noticed that the product of the charge current and the glow time of VD3 in hours is much less than its theoretical capacity, then this does not mean that the comparator on VD2 is not working correctly, but that one or more disks have insufficient capacity.

terms of Use

Now let's analyze the charge and discharge of the battery. According to TU (12MO.081.045), the charging time for a fully discharged battery at a voltage of 220 V is 20 hours. The charging current at C1 = 0,5 μF, taking into account the variation in capacitance and fluctuations in the supply voltage, is about 25-28 mA, which corresponds to the recommendations [2 ], and the recommended discharge current is twice the charge current, i.e. 50

ma. The number of complete charge-discharge cycles is 392. In the real design of the ACF, the discharge is carried out on a standard bulb of 3,5 V x 0,15 A (with three disks), although it gives an increase in brightness, but also due to an increase in the current from the battery in excess of that recommended by the specifications , negatively affects the battery life, therefore, such a replacement is hardly advisable, since in some copies of the disks this can cause increased gas formation, which in turn will lead to an increase in pressure inside the case and to a deterioration in the internal contact made by the Belleville spring between the tablet package active substance and the negative part of the housing. This also leads to the release of electrolyte through the seal, which causes corrosion and the associated deterioration of contact both between the disks themselves and between the disks and metal elements of the ACF structure.

In addition, due to leaks, water evaporates from the electrolyte, as a result of which the internal resistance of the disk and the entire battery increases. With further operation of such a disk, it fails completely as a result of the transformation of the electrolyte partly into crystalline KOH, partly into K2CO3 potash. It is for these reasons that charge-discharge issues need to be given special attention.

Practical repair

So, one of the three batteries "has gone wrong". You can assess its condition with an avometer. Why (in the appropriate polarity) briefly close each disk with the probes of an avometer set to measure direct current in the range of 2-2,5 A.

For good, freshly charged disks, the short circuit current should be within 2-3 A. When repairing an ACF, two logical options may arise: 1) there are no spare disks; 2) there are spare disks.

In the first case, this solution will be the simplest. Instead of the third, unusable disk, a washer is installed from the copper case of an unusable transistor of the KT802 type, which, moreover, fits well into most ACF designs in terms of dimensions. To make the washer, the leads of the transistor electrodes are removed and both ends are cleaned with a fine file from the coating until copper appears, then they are ground on fine-grained sanding paper laid on a flat plane, after which they are polished to a shine on a piece of felt with a layer of GOI paste applied. All these operations are necessary to reduce the effect of contact resistance on the burning time. The same applies to the contact ends of the disks, the darkened surfaces of which during operation are desirable for the same reasons to be reground.

Since the removal of one disk will lead to a decrease in the brightness of the HL1 glow, then a 2,5 V bulb at 0,15 A is installed in the ACF, or, even better, a 2,5 V bulb at 0,068 A, which, although it has less power, however, a decrease in current discharge allows you to bring it closer to the recommended according to specifications, which will favorably affect the life of the battery disks. Practical disassembly and analysis of correctable causes of disc failure showed that quite often the cause of inoperability is the destruction of the Belleville spring. Therefore, do not rush to throw away an unusable disk and, if you're lucky, you can make it work some more. This operation will require sufficient accuracy and certain locksmith skills.

To carry it out, you will need a small bench vise, a ball from a ball bearing with a diameter of about 10 mm and a smooth steel plate 3-4 mm thick. The plate is placed through a pad of 1 mm thick electric cardboard between the jaws and the positive part of the body, and the ball is placed between the second jaw and the negative part of the body, orienting the ball approximately in its center. The gasket made of electric cardboard is designed to eliminate the short circuit of the disk, and the plate is designed to evenly distribute the force and prevent deformation of the positive part of the battery case from notches on the vise jaws. Their dimensions are obvious. Gradually close the vise. Having pressed the ball by 1-2 mm, the disk is removed from the device and the short-circuit current is controlled. Usually, after one or two clamps, more than half of the charged disks begin to show an increase in short-circuit current up to 2-2,5 A. After a certain amount of stroke, the clamping force increases sharply, which means that the deformable part of the case rests on the tablet. Further clamping is impractical, as it leads to the destruction of the battery. If, after the stop, the short-circuit current does not increase, then the disk is completely unusable.

In the second case, simply replacing a disk with another one may also not bring the desired result, since fully functional disks have a so-called "capacitive" memory.

Due to the fact that during operation, the battery always has at least one disk that has a lower capacity value, which is why when it is discharged, the internal resistance sharply increases, which limits the possibility of a complete discharge of the remaining disks. It is not advisable to subject such a battery to some overcharging to eliminate this phenomenon, since this will not lead to an increase in capacity, but only to the failure of the best disks. Therefore, when replacing at least one disk in the battery, it is advisable to subject them all to forced training (give one full charge-discharge cycle) to eliminate the above phenomena. The charge of each disk is carried out in the same ACF, using transistor washers instead of two disks.

The discharge is carried out on a resistor with a resistance of 50 ohms, providing a discharge current of 25 mA (which corresponds to specifications), until the voltage across it reaches 1 V. After that, the disks are put into a battery and charged together. Having charged the entire battery, they discharge it to the standard HL until the battery reaches 3 V. Under the load of the same HL, the short-circuit current of each disk discharged to 1 V is checked again.

For disks suitable for operation as part of a battery, the short-circuit current of each disk should be approximately the same. The battery capacity can be considered sufficient for practical use if the discharge time to 3 V is 30-40 minutes.

Details

Fuse .U1. Observing the evolution of ACF circuitry for about two decades during repairs, it was noticed that in the mid-80s, some enterprises began to produce batteries without fuses with a current-limiting resistor of 0,5 W and a resistance of 150-180 Ohm, which is quite justified, since during a breakdown C1, the role of .U1 was played by R2 (Fig. 1) or R2 (Fig. 2 and 3), the conductive layer of which evaporated much earlier (than .U1 burned out by 0,15 A), interrupting the circuit, which is required from the fuse. Practice confirms that if a current-limiting resistor with a power of 0,5 W in a real ACF circuit noticeably heats up, then this clearly indicates a significant leakage of C1 (which is difficult to determine with an avometer, and also due to a change in its value over time), and it must be replaced .

Capacitor C1 type MBM 0,5 uF at 250 V is the most unreliable element. It is designed for use in DC circuits with the appropriate voltage, and the use of such capacitors in AC networks, when the voltage amplitude in the network can reach 350 V, and taking into account the presence of numerous peaks from inductive loads in the network, as well as the charging time of a fully discharged ACF according to specifications (about 20 hours), then its reliability as a radio element becomes very small. The most reliable capacitor, which has optimal dimensions that allow it to fit into ACFs of various design sizes, is the K42U-2 capacitor 0,22 μF H 630 V or even K42U 0,1 μF H 630 V. Reducing the charging current to about 15-18 mA, at 0,22 uF and up to 8-10 mA at 0,1 uF practically only causes an increase in its charge time, which is not significant.

Charging current LED indicator VD3. In ACFs that do not have an LED charge current indicator, it can be installed by connecting it to the circuit break at point A (Fig. 2).

The LED is connected in parallel with the measuring resistor R3 (Fig. 4), which must be selected for new manufacture or reduction of C1. With a capacitance C1 equal to 0,22 uF, instead of 0,5 uF, the brightness of VD3 will decrease, and at 0,1 uF, VD3 may not light up at all. Therefore, taking into account the above charge currents, in the first case, the resistor R3 must be increased proportionally to the decrease in current, and in the second case it must be removed completely. In practice, taking into account the fact that it is very unsafe to work with 220 V, it is better to select the resistance R3 by connecting an adjustable DC source (RIPT) through a milliammeter to point B (Fig. 3) and controlling the charge current. Instead of R3, a potentiometer with a resistance of 1 kΩ is temporarily connected, turned on by a rheostat to the minimum resistance. By increasing the RIPT voltage, the battery charge current is set to 25 mA.

Without changing the set voltage of the RIPT, turn on the milliammeter to open the VD3 circuit at point C and, gradually increasing the resistance of the potentiometer, achieve a current of 10 mA through it, i.e. half of the maximum for AL307 [2]. This moment is especially important for circuits without a zener diode, in which, at the first moment after turning on when charging C1, the current through VD3 can become large, despite the presence of a current-limiting resistor R1, and can lead to failure of VD3. In the steady state, R1 has practically no effect on the charge current due to its low resistance compared to the reactive (about 9 kOhm) resistance C1. When finalizing, VD3 is installed in a hole with a diameter of 5 mm, drilled symmetrically to the connector line in the housing between the supports of the spring contact connected to the HL1 coaxial output and the battery plus. The measuring resistor is placed in the same place.

Rectifier Diodes

Given the presence of a current surge at the initial charge of C1, to increase the reliability in the ACF rectifier, it is desirable to use any silicon pulse diodes with a reverse voltage of 30 V.

Non-standard application of ACF

Having made an adapter from the base of a worthless light bulb and the power connector of the radio receiver, the ACF can be used not only as a source of light, but also as a source of secondary power supply with a voltage of 3,75 V. At an average volume level (current consumption of 20-25 mA), its capacity is quite enough for listening to the WEF for several hours.

In some cases, in the absence of electricity, the ACF can also be recharged from a radio transmission line. Owners of ACF with LED indicator can observe the process of dynamic flashing of the LED. Especially exactly VD3 burns from "heavy" rock, so if you don't like to listen - charge the AKF, use the energy for peaceful purposes. The physical meaning of this phenomenon is to reduce the reactance with increasing frequency, therefore, at a much lower voltage (15-30 V), the pulse value of the charge current through the indicator is sufficient for its glow and, of course, recharging.

References:

1. Vuzetsky V.N. Charger for a rechargeable flashlight // Radioamator.- 1997.- No. 10.- P.24.
2. Tereshchuk R.M. etc. Semiconductor receiving-amplifying devices: Ref. radio amateur. - Kyiv: Nauk. thought, 1988

Author: S.A. Elkin

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