FUSE-“PHOENIX”

Overcurrent, short circuit for power supply… To protect against this scourge in the apparatus used old world as the means of fuses. Some are mounted in a special cartridge-holders, others are soldered in the circuit Board that simplifies the design itself, but complicates the replacement of burned out “inserts” healthy.

 

Lately in stores appeared a third type of fuse is resettable. Like the fabulous Phoenix bird, the funds for the protection of electrical and radio equipment capable of “self realization”. But not by magic, but due to the special properties antipregnancy plate of plastic, is made on the basis of the crystalline polymer in the thickness which are dispersed mass of particles of conductive carbon black. Both the plane of such plates is covered with metal (plated) and fitted with wire or tape conclusions.

In normal operating conditions taken as the norm, carbon particles dispersed in the plastic, in contact with each other and with evaporated electrodes, creating a plurality of parallel-to-serial conductive paths to lpa6 (Fig. 1A). However, when overcurrent fuse plate-“Phoenix” heats up. There is a transition of the polymer in the amorphous state and a sharp increase in the volume of plastic to push the carbon grains so that there is only a very small amount of conductive chains (Fig. 16). Accordingly, the jump increases the ohmic resistance antipregnancy plate, depending on temperature (Fig.2). In the result, the electric current is practically disabled. Such as protecting equipment, can last indefinitely, it is supported by a small leakage current lyr

 

From the variety of resettable fuse most popular in Amateur radio use, “Phoenix”, the designation which is the abbreviation MF-R (MF-S) and the number expressing the maximum operating current in tenths (see table). They are available in three distinctive versions (Fig.3). Modifications designed to protect batteries from short circuit and overheating during the charging process, the tape is provided with conclusions.

 

 

As the fuse wire with a fusible insert, the performance of Phoenix is strongly dependent on the ratio of the overload current relative to Inom. Model MF-R040, for example, when 6 A trigger for 0.1 sec and ten times faster — at about 10.5 A.

 

Are eliminated when the reasons that caused tamperers, fuse”Phoenix” for some time cools, returning to your original working state. Of course, the process of self-healing is influenced by the ambient temperature.

 

A typical graph of the effect of temperature on the resistance of the fuse-“Phoenix”

 

Samoustraniajutsia the fuse with a wire (a,b) and belt (in) conclusions

 

Led as status indicator of fuse-“fencs”

 

Circuit diagram and circuit Board pseudospectra machine for the intermittent electric scoreboard or other load

 

Protecting the load circuit are so specific fuse, it is advisable to introduce at least the simplest alarm to his condition, for example, by means of a led (Fig.4). About the serviceability of the load circuit can be judged by the glow of HL1. Protective when it is turned off the voltage supplied to the led falls sharply, and goes out HL1. With the elimination of damage to the circuit and cooling of the Phoenix the conductivity of the latter again becomes high. Indicator recovery functions, the readiness of the guard to work, and is the resumption of the LEDs.

Properties of fuse”Phoenix” can be used in the design of a fairly simple machine to periodically turn on the load (Fig.5A). When power switch SA1 opens the compound transistor VT1-VT2, the collector circuit of which the winding of the electromagnetic relay K1, closing contacts 4 and 5. Through the fuse FU1 and the lamp EL1 begins to leak current, the magnitude of which is critical for “Phoenix”. After a delay, going to warm up antipregnancy plate, the fuse operates, causing the locking of the composite transistor and consequently, de-energizing relay coil K1. Contacts 4 and 5 open, removing the load lamp EL1. After cooling, plates (and hence self-healing “of the Phoenix”) reopened the compound transistor VT1-VT2 and the whole process repeats.

 

Key features self-healing of the most common fuses series MF-R and MF-S

 

The job of an electrical circuit of such a machine it is desirable to debug on a breadboard. As a power source, it is preferable to take a small 4-volt battery. Lamp (or group of lamps) shall be designed for a voltage of 3.5 to 4 V and a current of about 1 A.

 

For switching of such loads is the best fit relay RES-9 with a coil resistance of 30 Ohms. And if instead of the lamp EL1 solder the resistor, is composed of two parallel-connected resistors MLT-2 to 10 Ohms, can be used and the second normally open contact of the relay (circuit diagram not shown) to enable a more powerful lamp or appliance powered by the lighting circuit.

 

The fee for the installation of the already established machine is easy to make a one-sided foil of the PCB or Micarta. The required shape pseudopath wire Board you can get, cutting the foil to the insulating base.

P. YURYEV