EMERGENCY LIGHT

This circuit can be used as emergency light to be installed near You in any part of the house/apartment whenever You fear a sudden blackout due to frequent power grid malfunction, storms, intervention of circuit breaker in main electrical panel of the house, etc..

-n°1 power supply unit with output 12 Vdc, 1 A, including or not a cable with plug for the connection to domestic sockets (see also the example in the top right picture);

-n°1 cable with plug, to be connected to the alternate current connector of the power supply unit, if the latter does not include it;

-n°1 12Vdc relays with n°1 NC contact (see the example in the bottom right picture);

-n°1 12Vdc diode (code 1N4001 or similar);

-n°4 super bright LEDs, 5mm;

-n°1 set of electrolytic capacitors with minimum voltage of 15 Vdc, to be connected in parallel for a total capacity (sum of the capacities of single capacitors) of 100 milliFarad (or 100000 microFarad; see also the example in the middle right picture);

-n°1 set of electric wires salvaged from other electric circuits (length will vary according to the distance between components connected);

-n°1 set for soldering (soldering iron and soldering wire);

In the scheme You will find described the connections required between each component previously listed in the Supplies section. Hope it is enough simple also for those who lack the base knowledge of electric circuits. However, I assume that those interested in this circuit are aware of the risks of electric circuits, and can handle also the work required by this circuit without damaging neither them nor their houses.

Choose a plate or a box where to fix the components previously listed; according to what is available and what You prefer to work with, it may be made by plastic, metal, or even cardboard. I have built the prototype by putting the four capacitors into a cardboard box. Then the power supply unit has been fixed on the box with some adhesive tape.

You can dispose the components on the plate, or in a box, following the disposition shown in the circuit above, or You may choose to change it.

Identify contacts/terminals of each component to be used; online datasheets can help with this. 

Prepare the wires with the lengths required to connect each couple of contacts/terminals in the disposition of the circuit or selected by You.

After having soldered some terminals, You can check with a multimeter if the connection between components ends is good (it should show nearly 0 Ohm resistance).

After having completed and checked the last soldering, the circuit can be tested by putting the plug into a socket of the house. The capacitors will be charged, but the LEDs will not be on because the normally close contact (NC) of the relays will be open (the coil will be fed by the power supply unit).

After removing the plug the coil of the relays will not be fed anymore, and the NC contact will close, allowing the capacitors to feed the LEDs.

As You can see in the pictures, with the power unit on (lighted up in the picture to the left) the LEDs are off, while they are on once the power unit is off (no power unit light in the picture to the right).

Instead of removing the plug You can also switch off the power in the house/apartment, simulating a blackout.

If everything is OK, the LEDs will turn on like an emergency light.

This light can be used to have at least one small light available in any condition. By installing a handle on the unit, and removing the plug from the socket after the balckout, the unit can be brought around the house.

The light will last around 10 minutes, long enough to let You reach a portable flashlight, or an emergency generator (in case the generator doesn't start automatically).

You may actually just light a candle to have a small light independent from the electric system, but the candle will consume itself, and will emit CO2; this solution can be greener if You already have around the house all the components to build it.

As a final tip, the same circuit can be used to start automatically an appliance; all You have to do is replacing the battery of bright LEDs with the coil of a 12 Vdc relays with NO contact and the capacitors with a rechargeable battery of 12 Vdc (capacitors' charge would not be enough to actuate the relays). The NO contact will close in case of blackout and can then be used to start an inverter powered by batteries, or can start a motor generator (if the model allows it).

Hope You can enjoy this small circuit; I wish You a good work.