Systems+Engines

Ask Sail: Solenoid Surgery

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Gary Horvath of Grand River, Ohio, asks:

When I purchased my 1993 Hunter 33.5, I found the previous owner had installed a high-output alternator with an external regulator on the three-cylinder Yanmar engine. He also installed a simple pull switch near the engine’s control panel to manually energize the field voltage to the alternator. His practice was to start the engine, then engage the field to the alternator, I assume to control starting current by eliminating “in-rush” current on the un-energized field.

I had a hard time remembering to turn the switch on and off, so I eliminated it by tying the field to the load side of the ignition switch. Since then, when first pushing the start button, I sometimes get no response. Releasing and pushing the button a couple of times finally engages the starter. Interestingly, I had the same problem with my last boat, which had a single-cylinder Yanmar engine.

Is my theory of in-rush current to the alternator field pulling down the battery valid? I am thinking about reinstalling the pull switch or installing a time-delay relay that will energize the field after the engine reaches oil pressure. What do you think?

Nigel Calder replies:

I don’t believe your alternator has anything to do with this. The in-rush current to the field winding is only a fraction of your cranking current. The contact points on your start button may be corroded and periodically making poor contact, but my guess is the points and contactor ring inside your solenoid on the starter are burned up. Periodically these burned-up parts are aligning and won’t transmit cranking current. Can you hear the solenoid on the starter clicking when you push the start button?

If you put a voltmeter across the terminals on the start button or across the two heavy-duty terminals on the solenoid, you should see around 12 volts until the button is pushed, then you should see close to zero volts. Test the start button switch first. If it continues to show 12 volts when the engine won’t crank, then the switch is the problem. If instead the solenoid continues to show 12 volts when the engine won’t crank, then it most likely is the problem.

It’s easy to check the points on the solenoid: just disconnect the various wires and cables from the end of the solenoid, and then take out the screws holding the cap and pull the cap off. Be warned, though: there is a spring in here you don’t want to drop in the bilge! On many solenoids you can turn the points around and flip the ring over to get new contact surfaces.

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