Knock Knock Page 2

Maintenance Q & A — July 2002
Maintenance Q & A — July 2002
By Capt. Ken Kreisler

Knock Knock
Part 2: Charging Voltage, Epoxy Failre, and more
 More of this Feature
• Part 1: Detonation, Oil Filter, and more
• Part 2: Charging Voltage, Epoxy Failure, and more

 Related Resources
• Maintenance Q&A Index

The flow on my pressurized water system has dropped to less than half of normal. How should I troubleshoot this problem? C.S., via e-mail
First check the electrical components, including the pump itself, wiring, switches, and the pressure sensor. Look for any corrosion buildup or loose or burned wires. If everything seems fine, try to localize the problem, checking to see if it's on a particular line or on just the hot or cold water side. Once you determine this, look for a restriction in that water line, perhaps a kink or a place where something is lying on a hose. Also check for a leak by looking for water accumulation, being mindful that water can run some distance before it's visible.

The water filter is a frequently overlooked trouble spot. It may not be tightly affixed, or its gaskets may be leaking. If it's clogged, you may observe spitting or hear rattling when the tap is turned on. Finally, check the mesh screen in the faucet end, which can become blocked by corrosion or mineral deposits.

What does the charging voltage of a battery mean? J.A., via e-mail
The battery charging voltage is the voltage measured across the battery terminals during charging. It consists of the battery voltage plus the voltage drop due to the internal resistance of the battery; the battery's internal resistance opposes the charging voltage, so the voltage produced by the charging unit must always be higher than the battery voltage when the battery is being charged.

The on-charge voltage is affected by temperature, electrolyte concentration, plate area in contact with the electrolyte, age of the battery, impurities in the electrolyte, and the state of charge and gassing.

Gassing, consisting of hydrogen produced at the negative plates and oxygen at the positive plates, temporarily increases the battery's internal resistance because of the gas film formed on the surface of the plates. Plates with hard and crystalline sulfate deposits also cause the internal resistance of the battery to increase.

What could have caused the bond on my epoxy job to fail? G.T., via e-mail
There are several possibilities. The first is insufficient cure time. Check with your manufacturer for correct cure times and mix ratios. The second is that resin-starved joint epoxy has wicked into a porous bonding surface. You'll have to clean things up by sanding and wetting out the bonding surfaces before applying the thickened epoxy. Make sure to re-wet very porous surfaces, especially end grain wood.

You could also have had a contaminated bonding surface, or the bonding area may have been too small for the load on the joint. Resanding and cleaning will help. For a too-small bonding area, consider using fillets, bonded fasteners, or, depending on your skill level, scarf joints. Finally, if you applied too much pressure during clamping, this could have caused the epoxy to be squeezed out of the joint.

Need help with a maintenance problem? Write to Maintenance Q & A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail: No phone calls, please.

Previous page > Detonation, Oil Filter, and more > Page 1, 2

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

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