Part 3: Kehren grinned happily when we checked the boat again at 4:45 p.m.By Capt. Bill Pike — January 2003
I took startup readings (with the unit fully operational) at 2:45 p.m. with the sun beating down mercilessly on the flush foredeck of the Harley and an outside temp of 93°F. An astonishingly small amount of power was entering the inverter from the battery bank: 12.4 volts x 40 amps = 496 watts (watts = volts x amps). And an equally astonishing amount of power was exiting the inverter, bound for the air-conditioner: 117 volts x 4 amps = 468 watts. No doubt about it, the amperage draw of the Avi-Air unit was considerably less than the draw reported for most off-the-shelf production A/Cs in the 6,000-Btu size range—just 4 amps.
Kehren grinned happily when we checked the boat again at 4:45 p.m. The temperature inside was 75°F, according to our thermometer, and the unit was off, an excellent state of affairs that turned out to be the pattern for the rest of the night. Each and every time I ventured forth from the house to check the boat (at two-hour intervals, more or less), the temperature inside was 75°F and the unit was off.
The final readings Kehren and I recorded the next morning at 7 a.m. were just as astonishing as the ones we’d taken the previous afternoon. The same amount of power was entering the inverter from the batteries, more or less: 11.9 volts x 38 amps = 452 watts. And pretty much the same amount of power was exiting, bound for the air conditioner: 117 volts x 3.6 amps = 421 watts.
There was one more piece of good news: While my final readings indicated the interior temperature of the boat had held steady at a cool 75°F all night, an “energy monitoring device” Kehren had modified for A/C work showed that the system, despite its small size, had actually run just five hours during the total elapsed time of the experiment.
The implication here was obvious. Since it was reasonable to assume that operating our air-conditioner for just five hours had used up just 200 AH (40 amps x 5 hours) of our total 610-AH battery-bank capacity, it was also reasonable to assume that there was plenty of juice left in the batteries for continued cooling. In fact, if Kehren’s energy monitor was right, there were nearly 100 AH left before our batteries were even half-discharged.
“So I think the experiment proves my point,” Kehren concluded confidently as we helped Motro shut the system down. “With or without a genset onboard, you can run a high-efficiency marine A/C all night and be comfortable. No problem!”
“Cool!” I replied.
Avi-Air Marine A/C Phone: (305)940-1996
This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.