since 1940

How to check the starter solenoid

When dealing with high current circuits, a fraction of an ohm is enough to produce poor, or no operation. For example, in a 12 volt starting circuit drawing 40 amperes of current, the addition of 0.2 ohms of resistance due to an oxidized connector drops the current to the load to 24 amperes. This drops the operating power from 480 to 288 watts. This is a 40% loss in starter operating power caused by a 0.2 ohm resistance!

Checking the circuit without a load would take a resistance of anywhere from a few hundred ohms to thousands of ohms to show a 0.2 volt drop. The best method of checking the solenoid is to disconnect the lead from the starter and connect it to a battery load-meter tester. Activate the relay and check the voltage on each side of the relay. A 0.1 volt drop is normal for a new or near new relay. Any more than 0.3 volt drop, replace the relay. 

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Disclaimer: sacskyranch.com contains abundant information relating to aircraft maintenance. The information provided  is not intended to supercede or supplement the F.A.A. approved  maintenance and/or operator’s manuals. Those F.A.A. approved manuals must be utilized when performing maintenance and/or operating aircraft.