Electrical Power Considerations

The Com-Pac 19 did not have a battery when I purchased it. All electrical wiring was installed and appeared to be in working order except for the steaming light on the mast. The in mast wire for this navigation light had been worn down to bare conductor by a failed grommet and would need to be replaced. Electrical tests however showed that bow and stern navigation lights were in good operating order.

The Com-Pac 19 is designed to carry one group 24 deep cycle battery in a storage box located in the starboard side lazarette. This results in about 130 minutes of battery capacity at an electrical load of 25 amps. At lower electrical loads, the battery would have substantially higher capacity. There appeared to be sufficient room to increase the battery capacity to two group 24 batteries. If necessary, the larger group 27 batteries could also be accommodated with some minor carpentry work. Two of these fully charged and new group 27 batteries would supply 25 amps for about 6 hours before giving up the ghost.

The literature on batteries indicated that if you expected to get any useful life from your investment, you should not drain them below 50% of their total charge. Additionally, batteries should be recharged as soon as possible. Charger electronics have improved over the years so a "Three Stage" charger was the desired solution if at all possible. This is as opposed to  less expensive shunt controllers that only serve to turn the connection between a current source and the battery on or off.   This would enable the batteries to be fully charged and retain a full charge over more of their useful life.

Since my definition of comfort (as well as safety) required access to electricity for periods of one or more weeks away from shore facilities, I would need to be able to recharge the battery while underway. While some outboard motors are advertised as having charging options, this capability is limited to about three amps at 12 volts for motors in the five horsepower range. A great number of hours of motor operation would be required to fully recharge a battery at this low current. This would not really be a practical option.  The option of hauling one or more 50 pound batteries from the boat to a shore facility for a quick charge every four or five days was also not too attractive.  Equally unattractive was the suggestion to stop at a marina overnight (with occasional surcharges for electric hookups) just to charge the batteries.

The option of purchasing a small four cycle gasoline powered generator for both battery recharging and providing 110 volt AC was a real consideration. Generators of this type are light weight, portable, and might even be available on the used market at a reasonable cost. Even though the noise from these units has been much reduced in the modern designs, I did not want to go this route if I could avoid it. This was not a purely rational decision but was really a matter of personal preference.  Since  I would need to have 110 volt AC power on board for occasional use of power tools such as a small drill or saber saw, I did purchase a 300 watt inverter.  This would provide a limited supply of "Houshold Power" when needed.

This left a solar panel, wind generator, or towed water charger as options either individually or in combination. The wind generator was rejected immediately since a set of fast spinning blades on a small boat would pose a significant safety problem. The solar panel idea was very practical for even a small sailboat and the concept of a towed water generator was interesting until I saw that the only unit readily available on the market was selling at about $1,100.

A Few Words About Solar Panels

The amount of useful electricity produced by a solar panel depends on the amount of available sunlight, the ambient temperature, and the orientation of the panel to the sun. Solar panels are rated by their Peak Power; however, for the middle of the United States and a random orientation to the sun, an approximation is that a solar panel in summer will produce about 4 to 6 amp hours per day at 12 volts for every 10 watts of peak rated power. My estimated electrical requirements were 12 to 14 amp hours per day so my intention would be to obtain a solar panel with around 30 watts of peak power.  Additional money would be spent on a good charge controller. This would serve to ensure that the battery would always be at maximum charge and would also extend the life of the battery bank.

The reading that I did on solar panels pointed out that while there are several methods of manufacturing for solar panels, most types of panels reduce their output voltage as the temperature rises.  Therefore, when mounting solar cells, it is necessary to allow for circulation of air underneath the panel to prevent overheating and the resulting reduction in voltage.  The worst case is with the so called self regulating panels (listed as having 33 cells rather than 36 cells) that are often sold at a discount.  While the suppliers often claim that no voltage regulator or charge controller is required with this type of cell, the panel may not produce  sufficient voltage in very hot climates to fully charge a battery.

With the correct choice in a solar panel, the silent operation, 10 to 20 year life, and no moving parts for maintenance of this setup added to the attractiveness of this concept. By installing a large battery for storage and using electricity with some care, I could be self sufficient with my needs for power and still relatively comfortable.  For the curious, the mounting details for the solar panel are on the photographs page.

Recharging NiCad (Nickel Cadmium) Batteries on Board

After one season using the boat, I had accumulated an array of battery powered devices and gadgets.  Most of these were purchased with power adapters so that they would also operate directly off the 12 volt deep cycle battery using a common cigarette lighter type plug.  However, for several of these devices (small flashlights and GPS especially) a long power cord was not really desirable or practical.  While daysailing, I could always count on availability of fresh batteries at a nearby convenience store.   However, I wanted to be prepared for cruises with several days or more "on the hook" and bringing large supplies of batteries would  not be my idea of a good thing.

I determined to solve this problem with a fast charger for "AA" size NiCad batteries that would operate directly from a 12 volt source and recharge a set of 4 batteries in 2 to 3 hours or better.  Unfortunately, considerable searching for a commercial unit failed to turn up a suitable device since most will only trickle charge a battery in 4 to 8 hours at a 75 to 100 mA charge rate.  I finally turned up a kit from Ramsey Electronics that had all the capability that I was searching for.  This kit (called Dr. Nicad Model DN-1) can be configured to recharge a set of 1 to 8 identical NiCad cells simultaneously.

I built my kit to fully recharge a set of 4 "AA" NiCad batteries ( 550 mAHr) in 2 to 3 hours at a conservative 250 mA charge rate.  The less common (and much more expensive) high capacity "AA" NiCad batteries (1,100 mAHr) could be charged in the same time period by setting the unit up to supply a charge current of  500 mA. Another major advantage of this kit is that it is designed to optionally discharge the batteries before starting the charge cycle.  This prevents the build up of a "memory" in the NiCad battery that will lead to a loss of charge capacity.  Using this feature, older niCad batteries that have developed a low charge memory can be cycled from full charge to complete discharge several times to restore their capacity.  Using the standard capacity NiCad cells, my Magellan 2000 GPS will operate continuously for 7 to 8 hours with a set of fully charged batteries (no backlighting) or about 4.5 hours with the backlight on continuously.

Taking my time, the kit took about 2 hours to solder all the components (about 50) to the printed circuit board and check the work before turning it on.  This job requires care, a magnifying glass, a good 25 watt pencil type soldering iron and good color vision.  A matching case for the unit is available from Ramsey for $15 but the same size case is also available from Radio Shack at a $6 savings (Part #270-214).  While the kit is designed with soldered jumpers to set the maximum time of charge and the battery charging current, a selector switch could be installed to make this field adjustable if you have many different battery packs to recharge.  I may alter the kit at a future date if this becomes necessary.

This page was last updated:  09/14/00 05:09:11 PM