Content:
- Design
- DIY surge protector
Design
The device looks like an extension cord with a shutdown button, this is partly true, but in addition to the block with sockets, filter elements are additionally located. They are just needed to protect against power surges, filtration interference and parasitic harmonics.
In the simplest surge protector, there is only varistor. This is a semiconductor device that, when a certain voltage is exceeded, turns into a resistor, goes into a short circuit. As a result, the circuit breaker installed in your home may trip, or, if the pulse is short, then its energy will be dissipated by the varistor in the form of heat. This element is used in surge protectors and power supplies to protect against high voltage surges. Depending on the type of varistor, it can extinguish pulses of different magnitude.
This version on a varistor is the cheapest, but apart from voltage surges, it does not protect or filter from anything. Interference continues to ooze into the network and interfere with surrounding and powered equipment.
To filter high-frequency harmonics, L, LC and RLC filters are widely used, which can also be installed in the line filter.
In addition to such options, there are also models where the power cord passes through a ferrite ring, or makes a couple of turns around it. In fact, this is another L (inductive) element that is needed to filter the high-frequency component of the interference.
DIY surge protector
The simplest filter circuit consists of a switch and a varistor, this is how it looks:
V1 is the varistor, its marking is "471", which means that its actuation voltage is 470V, while the larger its diameter, the more energy it can extinguish without exploding. Thus, the larger the varistor you put, the better, if only it fits in size. Here is an example of a surge protector assembled according to this scheme, but in the factory version. This is a cheap device that only dampens high voltage pulses. At the same time, it can irrevocably fail with a particularly strong surge.
In order for your surge protector to really be a noise filter, you need to add another filter element - a choke.
Circuits are, of course, good, but how to make a surge protector from available tools? Simple enough! Almost always, an amateur has something to tinker with, you can find an old unnecessary or non-working power supply, it has such a filter at the input. It remains only to evaporate it. In the photo, it stands in the corner of the board closest to us. This part consists of a ferrite core and a lacquered copper wire wound around it.
This is a choke with two windings, a phase passes through one of them, and a zero through the other, thus the inductance is part of the mains filter and reduces the level of interference.
By the way, the power supply unit can work without it, many Chinese people make their goods this way, it is often found in cheap power supply units for a computer and not only. Because of this, such a large amount of unwanted interference occurs on the network.
If you have not found such an element in your stocks, you can look for a ferrite ring with a magnetic permeability of 400-2000 Nm and wrap it with lacquered copper wire PEV-2 (you can use the primary winding with a 50 Hz network transformer) with a diameter of 0.5 mm, it depends on the power of the load that you want connect. Wrap it around the ring as shown in the picture, after wrapping it with several layers of dielectric, for example: electrical tape, varnished cloth, Kapton tape.
Use a wire with a high-quality, undamaged varnish. And after winding, for reliability, cover the part with several layers of varnish. The loop at the end must be cut, ideally, immediately wound with two parallel wires.
A good diagram that is easy to do with your own hands is as follows:
And here is a specific version of its implementation "in hardware". A couple of filters from the PSU are taken as the basis.
Capacitors it is better to use ceramic or film. They can also be removed from the power supply, they are often found there near the network connector in a rectangular parallelepiped case.
If there is an unnecessary power supply unit, you can simply cut off a part of the board with a filter and use it. Here is an example in the photo showing what you need to saw off to get a surge protector in a couple of minutes. Just be careful not to bridge the board layers with metal filings, this can lead to a short circuit. And be sure to place the finished device in a non-conductive case for safety.
And here's another version of the pattern for repetition. It is she who is used in many ATX power supplies:
A surge protector is a useful and simple device that is not difficult to make yourself at home. And if we consider that many have several unnecessary, inoperative devices, it turns out that spare parts are literally lying under our feet. Therefore, making a device that can prolong or even save the life of expensive equipment is a very profitable business. Finally, we recommend watching a few interesting video instructions for assembling a homemade surge protector:
Related materials:
- How to make an extension cord with your own hands
- How to choose a voltage regulator
- What is overvoltage in the network