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Aug 20, 2022
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A new idea for a capacitor fuse instead of an incandescent bulb

Most radio amateurs, when testing their homemade products powered by the mains, use an incandescent lamp as a fuse. For example, if you need to check, say, a switching power supply, then the first switch-on is done through a serial connection with an incandescent lamp. Due to the fact that if there is a short circuit in the circuit, the lamp will simply light up and no consequences in the form of sparks and burnout of the tracks will occur. This is the most classic method, but there is one big drawback: the power is limited, which means, say, a power tool or other powerful device cannot be checked with such a circuit. It is quite simple to get out of the situation – by collecting an analog of a fuse on capacitors.

A new idea for a capacitor fuse instead of an incandescent bulb

What you need

The following device will require electrolytic capacitors of relatively large capacity and, more importantly, designed for high voltage. Suitable parts can be found in an old computer power supply. Work progress below.

A new idea for a capacitor fuse instead of an incandescent bulb

The ratings of the soldered capacitors are 220 uF 450 V. By soldering, they are connected with negative terminals. As a result of this (remember the formula), we get a non-polar capacitor with a capacity of 110 microfarads, designed to work in a network with a voltage of up to 900 volts. The voltage margin is very correct. Given that the values ​​​​of the AC voltage at the peak of the sinusoid reach 400 V.

A new idea for a capacitor fuse instead of an incandescent bulb

Three resistors of 10 kΩ, 2 W each are connected in parallel. When the resistors are connected in parallel, the power adds up and the result is a resistor of 6 watts. Resistors are soldered in parallel with the positive terminals of the capacitors. Resistors are needed to discharge capacitances during operation.

A new idea for a capacitor fuse instead of an incandescent bulb

DIY capacitor fuse

Next, a simple chain is assembled.

A new idea for a capacitor fuse instead of an incandescent bulb

At the ends of its network plug and network voltage splitter. The device assembled above from resistors and capacitors is soldered into the gap of one of the network wires of a two-wire line.

A new idea for a capacitor fuse instead of an incandescent bulb
A new idea for a capacitor fuse instead of an incandescent bulb

An ordinary light bulb is turned on in one of the sockets of the splitter. A voltage of 220 V is applied. Capacitors and resistors connected in series to the network have practically no resistance to alternating current. The lamp is on.

A new idea for a capacitor fuse instead of an incandescent bulb

And then the most interesting. If a plug with shorted contacts is inserted into the free socket of the voltage splitter, then … Short circuit? Explosion? Not at all. There is no short circuit. The lamp just goes out. And the type of lamp does not matter. Everything works with both LED and conventional incandescent lamps. Miracle? Of course not. The explanation is simple.

A new idea for a capacitor fuse instead of an incandescent bulb

In fact, no short circuit occurs. After all, there are electrolytic capacitors in the circuit. And the current in the circuit will be limited by the voltage drop across them. Simply put, the capacitors start working, creating a capacitive load.

A new idea for a capacitor fuse instead of an incandescent bulb

Where else can such a device be used? Interested to hear your use cases. There is enough power even for a drill without a noticeable voltage drop.

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