Test wall socket with current limiting

Description: Individuals who frequently build, repair, and test equipment powered by mains voltage may encounter unexpected hazards, such as loud explosions, equipment destruction, flying components, tripped circuit breakers, and power outages. These incidents can be mitigated by utilizing a test wall socket designed to limit maximum current, prevent tripping of breakers, and reduce potential damage to the tested device. This tool is particularly beneficial for testing switching power supplies. The primary components of the device are light bulbs that limit current in the event of a short circuit in the tested device. Incandescent bulbs can serve as power resistors, but they offer better availability compared to resistors, despite the potential for significant power loss. Another advantage of using bulbs is their lower cold resistance, allowing them to function similarly to a variator or PTC; until a fault current occurs, the voltage drop across them remains minimal. Halogen bulbs rated at 230V and 300W or 500W are selected for this application. By using switches S1 and S2, three power combinations can be achieved: 300W, 500W, and 800W (with both lamps in parallel). The power input of the tested equipment must always be significantly lower than the rated power of the light bulbs to avoid excessive voltage drop. The device is housed in a metal case from an ATX PC power supply, which includes two fans. The power input is connected using the original cable connector, while the output is a standard socket located in place of one of the fans. The second fan remains to cool the bulbs and is powered by a miniature transformer (Tr1) and rectifier. The operation of the device is straightforward: connect the input to the mains and the tested device to the output socket. Caution is essential, as the device operates at mains voltage, necessitating careful construction and handling. The bulbs generate significant heat, posing risks of fire, burns, or damage to surrounding objects. Supervision is required during operation.

The test wall socket serves as a crucial safety device for those working with high-voltage equipment. Its design allows for a controlled testing environment where the risk of catastrophic failure is minimized. The use of light bulbs as current-limiting elements provides a unique advantage; they not only limit current during a fault condition but also offer a visual indication of power flow. When a fault occurs, the bulbs will illuminate, signaling the user to investigate the issue before any further damage occurs.

The selection of halogen bulbs rated for 230V and 300W or 500W is intentional, as these bulbs can handle high power while providing a significant amount of light. By configuring the switches S1 and S2, the user can easily select the appropriate power level for the testing procedure, ensuring that the tested device operates within safe limits. The parallel arrangement of the bulbs allows for increased power handling, providing flexibility depending on the requirements of the test.

The housing of the device in an ATX power supply case is an innovative repurposing, offering both structural integrity and cooling capabilities. The inclusion of fans not only aids in dissipating heat generated by the bulbs but also enhances the overall safety of the device by preventing overheating. The use of a miniature transformer and rectifier to power the cooling fan ensures that the design remains compact and efficient.

In summary, this test wall socket is an invaluable tool for electronics engineers and technicians. Its design prioritizes safety while providing essential functionality for testing high-voltage equipment. Proper usage, along with vigilant supervision, will ensure effective operation and minimize the risk of accidents associated with mains voltage testing.Anyone who frequently builds, repairs and tests equipment powered by mains voltage, will certainly have met with an unpleasant surprise when the plug inserted into the socket (or later) - loud explosion, destruction of equipment, flying pieces of components, circuit breakers tripped, darkness in the whole house and smoked plug :). Th ese surprises can be prevented using described test wall socket which serves to limit the maximum current, prevents tripping the breakers reduces the amount of destruction of the tested device. Especially useful for testing switching power supplies. The main part of the device are light bulbs, which in case of short circuit in the tested device limits the current.

Incadescent bulbs can be used as power resistors, but the advantage bulbs is better availability compared with resistors, with a loss of hundreds of Watts. Another advantage of the bulbs is less resistance in cold state, so they behave as a variator or PTC, and until the fault current, voltage drop on them is just a little.

I chose halogen 230V 300W and 500W. With the switches S1 and S2 can I thus choose three combinations: 300W, 500W and 800W (both lamps in parallel). Power input of tested equipment must always be much smaller than the rated power of light bulbs used to prevent significant voltage drop.

I built the device into the metal case from the ATX PC supply (with two fans). Power entry is solved with the original cable connector, the output is classical socket located instead of one of the fans. The second fan is left to cool the bulbs. This fan is powered by a miniature transformer Tr1 and rectifier. How to use the device is very simple: connect the input to the mains and tested device to the output socket.

Attention! The device operates at mains voltage, and accordingly is necessary to construct and work with it. Bulbs produce large amounts of heat - there is risk of fire, burns or damage to surrounding objects. Never operate this device without supervision.