April 2000 Telltale Page 3 - by Tom Winlow and Marcel Laroche.

Electrical systems on boats can be the source of annoyance. The environment in and around boats is anathema to electrical circuits with moisture causing corrosion which leads to the gremlins we all experience such as lights that don't work and instruments that give false readings. We hope to shed a little light on these maters in the next few articles.

Part 1 ­— Batteries

The heart of the system is the battery and the first thing to do is to determine the state of the batteries. There are different kinds of batteries -- lead acid, gel cell, and some newer exotics but for now we can concentrate on the lead acid and Gel cells. The big differences between these two types are cost and the charging requirements. This topic is a bit complex and we will cover it in another article. One point, however, Gel cells are easily damaged by overcharging. Batteries can be designed as starting batteries or house batteries, which are used for lights and radios and such.

House batteries are designed to be deeply discharged many times without damage, like what happens after a long weekend of partying up river with the tunes on till all hours, or the blender serving extra duty making margaritas.

Batteries can self-discharge over time and the first thing to check is the voltage. For this you need a voltmeter, preferably a digital meter that can accurately read 10ths or 100ths of a volt. Most of our boat batteries are nominally 12 volts and depending on the state of charge (that is how much energy is stored in the battery) will read around 12 volts.

The following table provides a reasonable guide to the charge state of the battery.

• 12.7v 100% charge
• 12.45v 75%
• 12.2v 50%
• 11.9v 25%

Measuring the battery is simply a matter of connecting the positive lead from the meter -- usually red, to the positive terminal on the battery marked with a + sign, and the negative lead -- usually black, to the negative battery terminal marked with a -- sign. Care should always be taken when working around batteries with tools. If you should happen to drop a wrench across the battery terminals it could result in serious injury. Molten metal can explode as the battery discharges through the metal wrench.

Another test that can tell the state of a lead acid battery is to measure the electrolyte condition. A Hydrometer is available from Canadian Tire for a few bucks that can determine this. Assuming you have lead acid batteries that are not sealed, simply remove the cover from the cells and draw some fluid into the instrument and read the charge condition on the floating scale.

If the battery has been recently charged it may read okay but will not properly start the engine or provide lights for very long. In this case take it to someplace such as Canadian Tire where they can do a load test. A load test will simulate the condition, for example, when the battery is trying to start the engine. The equipment used can determine if the battery can be saved or whether it needs to be replaced.

It may be worth mentioning that batteries vary a lot in price, and it is never more true than with batteries that you get what you pay for. The heavier the better, and of course, the more expensive. For example a high quality marine house battery, size 4D will cost about $400 and a good starting battery will cost $135.

Another thing about batteries is that they like to be kept clean. Wipe all dirt and grease from the case and terminals before installing them this spring. Take a small wire brush and give the terminals a good cleaning. Coat the terminals with vaseline (engine oil will do in pinch) before attaching the cables which will prevent corrosion and a poor connection. Make sure the cells all are filled with distilled water (a few pennies at the pharmacy) and away you go.

Finally, what about the idea that batteries should be stored on wood and not on a concrete floor. I can see no good reason for this if the case is clean and dry, but, as Pascal would argue, the cost of a bit of plywood to sit the thing on is so small that you should do it. Also charge them once or twice over the winter to keep them topped up.

Next time we will look at finding high resistance connections and how to sort out the failed lights on the mast!