Notebook Emergency Power Circuits

SAFETY NOTICE: The AC line power in this circuit CAN BE LETHAL! Not only to you, but to your power supply, battery(s) and your radio equipment. Use extreme caution during construction and testing. If there is a severe wiring error, an additional EXPLOSION HAZARD MAY BE PRESENT. DO NOT TOUCH any part of the circuit while it is powered and be ABSOLUTELY certain that it is working properly. Use a 9 volt transistor battery and an incandescent lamp to simulate the power supply, battery and load instead of your actual equipment. Invest in a meter to verify that the AC line power is not in contact with the DC powered sections of the unit and that DC polarities are correct.

Use a plastic enclosure for this project, it really simplifies construction. You may use a low amperage 2 prong line cord (AC line polarity is not a concern and AC power used is minimal). You may add a 1/8 Amp fuse to one of the AC lines to provide additional protection, if you wish. The plastic enclosure itself provides the insulation for the 1/4" bolts used as terminals for the DC connections.

Actual construction is not critical. The parts may be located anywhere inside the enclosure. There are some points, however, that you need to consider.

1. Keep the AC powered wiring as far away from the DC wiring as possible. If the two need to cross paths, try to do so at a 90 degree angle.
2. The DC wiring paths for the power supply, battery, and the load must be at least 12 gauge. "Mega" speaker cable works just fine for this. All other wiring may be small gauge hookup wire.
3. You MUST provide individual external fusing for ALL wiring connected as the "load", this is NOT OPTIONAL. If you do this, you do not need fusing for the power supply or the battery. The "load" side fuses are to protect the external wiring from becoming a FIRE HAZARD.
4. None of the "load" side fuses should be rated greater than 25 Amps @ 30 Volts.
5. If the total calculated load connected to this unit is greater than 25 Amps, then add a external fuses to the power supply and battery inputs rated at 25 Amps.

These construction notes may seem to be harsh safety warnings at first, but nothing is more important than personal safety. Secondarily, property protection issues (explosions, fire, etc...) affect us all in the the same manner, they are also safety related in one way or another.