Ceska verze

Test wall socket with current limiting

     Introduction: 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 :). These 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.
     Description: 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.

The schematic of the current limiting test wall socket.

Parts prepaded for the construction

Halogen lamps rated 230V 300W and 500W.

Mounting the wall outlet socket to the hole from one of the fans.

Almost completed

Test with shorted output

Completed. The top cover comes from different ATX.

Added: 8. 11. 2011