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Onboard Electrical Power


This section talks about the onboard electrical system. I have developed this setup over the 10 years that I have owned Andrea Lynn. I describe the various setups, the problems I encountered, and how I fixed them. In particular I discuss using wet cells, house and battery setup with a battery combiner, use of solar cells to charge batteries, and selection of equipment with reduced energy consumption. My goals are to produce a practical, simple, reliable, inexpensive, and field repairable system that I can understand. There are boat owners who like a lot of fancy electronics, who don't like to tinker with the wiring, or who can afford to have a marine electronics technician come out on short notice to fix things. I'm not one of these.

I don't cover basic 12V dc electrical concepts here as they are adequately covered elsewhere.

Disclaimer: I have taken great efforts at making sure that this information is accurate. However, I assume no responsibility for any consequences that you incur from reading this website. Please take the time to do your own research before doing any of the things discussed here.

Initial setup and its problems

When I bought Andrea Lynn, she had a pair of Gel cells, an alternator charger, and a typical orange 1-both-2-off switch. There was really nothing at the time to suggest that this setup would give me problems. My first inkling of trouble was when I ran out of battery power on an overnight cruise. I had to return under sail only. This took all day since the winds were light to non-esistent. What had happened is that I left the stereo and the anchor light on all night and ran the batteries down to the point that I could not start the motor. These together consume about 2.5 amps. I slept in a bit so these were on for about 12 hours. I also used some cabin lights that are 20 watts or 1.7 amps a piece for about 3 hours. I reckon that I used at least 35.1 amp hours of battery charge. This is quite a chunk of the capacity of one of these batteries. Both batteries were group 31 gel cells with close to 200ah of capacity if they were brand new. At this point these batteries were not new and were likely diminished by chronic under charging.

I started my learning process by attending a free Diesel Seminar put on by West Marine in Annapolis. I learned that one can tell if an alternator is generating electricity if it is hot to the touch. Shortly thereafter I bought the 12 volt dc bible.

On my big cruise I really had problems. In short, I wasn't sure that the alternator was charging so I had it fixed at The Hague Marina in Myrtle Beach, SC. This worked until I turned the 1-both-2-off switch from battery 1 to both. Since it was not a bridging switch it broke the connection between the alternator and the battery for a fraction of a second. This caused a voltage spike in the alternator and ruined the voltage regulator. The regulator started putting out higher voltage than the batteries could tolerate. I did not realize anything was wrong at the time. The only symptom was that the diesel acted like it was lagging - or that it had an extra load. I learned the awful truth at Stewart, FL when I pulled out a swelled up, hot, hissing gel cell and saw acid in the bottom of the battery box. I bought a new gel cell to replace it. I also installed a voltmeter and ammeter on the alternator output. I also installed another voltmeter and ammeter on the house input. I than ran the alternator and found that the output voltage was over 15 volts. I took the alternator to a shop where they replaced the regulator. Later in the cruise I bought a spare alternator just in case the present one was going to act up. I carefully monitored the voltage and amperage, conserved the batteries and maintained a strict operating schedule for the remainder of the big cruise.

After the big cruise I built this panel to accomodate the guages.

Switching to wet cells

Once I got the boat here, I took out the gel cells. I also took out the battery isolator. This is basically a pair of power diodes that allow current to go from the charging source to each of the batteries. But it does not allow current to flow from one battery to the other. It is important to keep paralleled batteries separated or else they tend to discharge into each other back and forth. They will go flat this way in a short period of time. But the diode type battery isolator incurs a voltage drop of 0.7 volts from the alternator output. Thus the alternator does not charge the batteries well. I put just one wet-cell battery in for now.

Gel cells have the advantage that they don't spill or emit fumes in normal situations. But they don't tolerate over charging. In fact, to get a proper charge on a gel cell requires precise control of the charging voltage with respect to the temperature of the battery. I could not see a practical, reliable and inxpensive way of achieving this on my boat. Also gel cells are much more expensive than wet cells.