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Confusion between current and capacity

Jan 1, 2003

I was disappointed in the article "Electrical needs" in Ocean Voyager 2001. Unfortunately, the authors have confused the electrical unit "amps" with "amp-hours," causing difficulty in reading the material and casting some probably undeserved doubt on the technical accuracy.

Getting down to basics: Electrical current is the rate of flow of electrical charge. Current is measured in amperes (abbreviated as amps). This is analogous to the number of gallons per minute of water flowing in a pipe. Battery capacity, on the other hand, is measured in ampere-hours, the amount of current multiplied by the number of hours the current flows. This is analogous to the number of gallons of water stored in a tank.

The error first appears in the second paragraph with "a single 110-amp deep-cycle battery." In most instances in this article, substituting "ampere-hours" for "amps" is actually the correct unit, as in line eight of the second paragraph, which refers to "the wimpy 55-amp alternator."

The inconsistency causes confusion in some areas. For example, on page 14, third column, we are left to wonder if 120-watt Kyocera solar panels provide 21 amps of current, which seems high, or do they deliver 21 ampere-hours of charge during the four-hour period?

On page 16 it is stated that the wind generators "charge at a consistent 10 amps," so they deliver "80 amps of energy in a single eight-hour night." This was multiplied out correctly, but energy is certainly not measured in amps.