How to Check if a Diode Is Bad

How to Check if a Diode Is Bad

Diodes are semiconductor devices that conduct current in one direction only, and are commonly made from silicon or germanium. Diodes have two terminals -- an anode and a cathode -- with the cathode being marked by a line painted on the body of the diode. Current is allowed to flow from the anode to the cathode, but is blocked in the other direction. This property is used most commonly in rectifier circuits, which change alternating current to direct current. Diodes are also used to protect components in a circuit if the power is connected the wrong way around, blocking the flow of current to stop damage being caused. Although diodes rarely fail, it can happen if they are exposed to voltage or current above their rated limits.

Things You'll Need
Digital multimeter
Soldering iron
Desoldering braid
Pliers


Instructions
Unsolder one leg of the diode if it is part of a circuit, otherwise the other components in the circuit may affect the results of the test. Heat the solder pad around the diode leg until the solder is molten, and then gently pull the leg through from the other side using pliers. Soak up any excess solder with desoldering braid, leaving the hole clear.

Set the multimeter to its diode test mode, denoted by the circuit symbol for a diode which looks similar to an arrow. If the multimeter does not have a diode mode, set it to the lower end of the resistance range.

Place one probe from the multimeter on to one of the diodes legs, and the other probe on to the other leg. Note the reading obtained, and then swap the positions of the probes and note the new reading.

Interpret the results. If you get an open circuit in one direction indicating the current is blocked, and a low resistance reading in the other direction, the diode is good. If there is an open circuit in both directions, the diode has failed with an open circuit. If there is a low resistance in both directions, the diode has failed with a short. In both cases the diode should be replaced.

How to Charge a Car Battery Through a Cigarette Lighter

How to Charge a Car Battery Through a Cigarette Lighter

An automotive electrical system normally has one or more power accessory points. These accessory points are often cigarette lighter outlets. However, most vehicles manufactured since the 1990s contain dedicated power accessory outlets.


Many automobiles have their cigarette lighter outlets wired so that the outlets only work when the automobiles are running. However, power accessory outlets are usually hardwired to the battery, and are always active.


A power accessory outlet may also be used as a means to trickle charge an automobile battery. Some accessories, such as solar battery chargers, are designed to take advantage of the bidirectional nature of a hardwired power accessory outlet.



Things You'll Need
Automobile with hardwired power accessory outlet
Solar battery charger with automotive cigarette lighter plug


Instructions
Place the solar battery charger, shiny-side up, on the automobile's dashboard.

 A solar charger must have the shiny side (left cell) exposed to light to generate electrical energy.
Plug the battery charger plug into the power accessory outlet.

Allow the battery to charge for approximately six hours, and then unplug the charger from the power accessory outlet.