Electromechanical protection in chargers. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells
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Chargers (chargers), as a rule, are equipped with an electronic system for protecting against short circuits at the output. However, in amateur radio practice, there are still simple chargers, consisting of a step-down transformer and a rectifier. The necessary components in order to assemble electronic protection are not always available. In this case, simple electromechanical protection can be applied using relays or multiple-acting circuit breakers (for example, automatic fuses or AVMs in residential electricity meters). Advantages of the proposed protection: simplicity and absence of expensive semiconductor devices. Its disadvantage is high inertia.
The speed of relay protection is approximately 0,1 s, with the use of AVM - 1...3 s.
When the battery (or battery) is connected to the output of the device, relay K1 is activated and connects the charger with its contacts K1.1 (see diagram).
In the event of a short circuit, the output voltage will drop sharply, the relay winding will be de-energized, which will open the contacts and disconnect the battery from the charger. Re-enabling after troubleshooting is carried out by the button SB1. Capacitor C1, charged to the output voltage of the rectifier, is connected to the relay winding. Resistor R1 limits the current pulse in case of erroneous switching on, when the short circuit at the output has not been eliminated.
Resistor R2 limits the short circuit current of the rectifier diodes. It can be omitted from the circuit if the diodes are designed for pulsed currents of this value. Otherwise, resistor R2 is required. However, it should be remembered that the output voltage of the charger in this case must be greater by the value of the voltage drop across the resistor R2 at the rated charging current. AVM protects against overcurrent, which relay protection cannot do. An automatic fuse (or switch) is connected in series with the relay contacts. AVM resistance is about 0,4 ohm. In this case, the resistor R2 can be omitted.
The parameters of the structural elements depend on the type of memory. For example, for a charger for car batteries, it is necessary to select a relay for a rated voltage of 12 V with a permissible current of at least 20 A. These conditions are met by the REN34 relay (passport KhP4.500.030-01), the closing contacts of which should be connected in parallel. For a charger with a rated current of up to 1 A, you can use the RES22 relay (passport RF4.523.023-05). Capacitor C1 - oxide (K50-12, K50-16, etc.).
Author: D. Ataev, Sterlitamak; Publication: N. Bolshakov, rf.atnn.ru
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