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Alternator Source Power Relay Energizer Circuit?

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May 12, 2018
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Can you guys out there help me? During some non related maintenance, I noticed that the wire wound resistor on this circuit (attached to the battery box) has failed as the lead has corroded through.

It looks like the value of the resistor is 4.7 Ohms which would make sense to pull in the main solenoid.

I have never noticed any problems caused by these two components being open circuit but I have never flown with a really flat (or failed) battery. The circuit diagram is as below. I assume the purpose of the diode and resistor are designed to operate the main power relay in cases where the battery becomes completely flat (or perhaps fails and ends up open circuit).

I assume the diode is to allow the DC to flow one way only and the resistor is to drop a little voltage as the alternator voltage might be a 14.8 volts or a bit higher.

Can anybody explain/ confirm my assumption is correct relating to the purpose of the circuit - after all it says more or less this in the circuit diagram. Also does anybody know if the value of the resistor really is 4.7 Ohms? - See circuit diagram below and the relevant part highlighted in yellow.

IMG_20180615_105057.jpg


Relay Energizing Circuit.jpg
 

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