Providing Resistance

Maintenance Q & A — August 2001
Maintenance Q & A — August 2001
By Capt. Ken Kreisler

Providing Resistance
Testing a solenoid, battery gassing, and more.

 More of this Feature

• Part 1: Q & A
• Part 2: Q & A continued

 Related Resources
• Maintenance Q & A Index

Is there any way to test the solenoid for the tilt motor on my stern drive? D.P., via e-mail

While this solenoid is completely sealed and nonserviceable, you can perform a simple test to see whether it is operating correctly.

Connect a voltmeter to the solenoid’s two large terminals. They are for the battery and motor; the small one is for the switch control. Next connect a carbon pile voltage regulator as shown in the illustration and reduce the voltage to six volts. A carbon pile voltage regulator varies resistance as pressure is applied to its pile of carbon disks. When pressure is increased by a spring, the stack is compressed and resistance drops; when pressure is reduced via a solenoid, there is more air between the disks, and since air has high resistance, overall resistance increases.

Adjust the carbon pile until the ohmmeter shows a complete circuit. When it does, the carbon pile meter should be reading somewhere between six and eight volts. If more than eight volts are required to complete the circuit, the solenoid is likely defective and must be replaced.

What happens when a battery gases during recharging? R. L., via e-mail

In order for wet cell batteries to be completely recharged, it is necessary to raise battery voltage beyond what is known as the gassing point. This is the voltage at which the battery electrolyte begins to bubble and gas is given off. If the charging stops before this point, some lead sulfate deposits formed during discharging remain on the plates, damaging the battery. Left unattended this can build up over time and will destroy a cell and eventually the battery itself.

To ensure a battery is completely charged, test each cell with a hydrometer. A reading between 1.26 and 1.30 for each cell indicates a high state of charge.

While replacing some brass screws, I found that most of the heads snapped off as I attempted to remove them. What could have caused this? A.N., via e-mail

Brass screws are an alloy of copper and zinc. In the presence of moisture, the two metals react galvanically, resulting in a loss of zinc. This leaves mainly brass, a relatively weak metal, which can result in the screw head snapping off when trying to back the fastening out. To avoid this situation use stainless steel or bronze screws.

Next page > Q & A continued > Page 1, 2

This article originally appeared in the June 2003 issue of Power & Motoryacht magazine.

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