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Home> Maintaining
your Continental and Lycoming engine
The addition of 1 or 2 ohms of resistance in the circuit caused by an oxidized
connector is significant. For example, in a 12 volt starter circuit drawing
40 amperes of current, the addition of 0.2 ohms of resistance drops the
current to the starter to 24 amperes. This drops the operating power from
480 to 288 watts. This is a 40% loss in operating power caused by a 0.2
ohm resistance. High current, low voltage circuits are resistance sensitive.
Voltage drop as a troubleshooting techniqueThe best method of checking for resistance is by measuring the voltage drop on each side of the circuit while current is flowing. What we actually measure is the resistance present in the circuit but displayed in terms of voltage. Total voltage drop is measured with the positive lead of the voltmeter prod toward the batteries positive post and touching the device's output terminal and the negative lead connected to ground. Current must be flowing in the circuit tested. If the meter reading is high (over .5 volt typically) then take separate measurements across each segment of the hot circuit; always with the positive prod toward the batteries positive post. You can check across solenoids, switches, lengths of cable, etc. Thus each segment of the circuit can be checked to find the fault. A similar check can be done on the ground side. Touch one prod to the grounded battery post and the other to the components ground connection. For example, you can check the return path from the engine mount back to the battery by touching one prod to the grounded battery post and the other to the engine mount. With the starter cranking the voltage reading is the amount of voltage drop in the return circuit; typically less than .5 volt. Similar check can be made on the alternator by turning on lights so that the alternator is producing appreciable current. Check total drop from alternator to battery.
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Don't
start thinking about your landing procedure --even if you're over water--until
you're on the way down. You'll have plenty of time then, and it'll break the
monotony. Parachute Sense US NAVY 1944