We’ve been testing a few of our AC items with the Kill A Watt meter and have some interesting findings to report. The data which follows is on the 115VAC side of our power system.

To get watts multiply the amps by 115 volts. When looking a t this in terms of inverter supplied power, we would normally factor in an additional 20% loss for conversion factors.

• MacBook Pro, 17″ screen – .33 amps
• Sony Vaio 17″ – .40 amps
• 17″ Samsung 740BX monitor -.4 amp
• Icom charger for VHF – .05 amp
• Canon Camera battery charger – .08 amp
• HP printer (6980) at idle – .05 amp
• Ethernet hub power supply – .04 amp

If we measure the terminal strip as a whole into which two VHFs, the printer, ethernet  power supply, and MacBook Pro all are connected it totals .43 amps, or 50 watts. Allowing for inverter conversion inefficiencies, will bring this to 60 watts. Add in the idling current of the lightly loaded inverter ads another 15 watts, for a total of 75 watts. Divide by 24 volts and we are at three amps.

Now leave this on 24 hours and suddenly the batteries have lost 75 amp hours to seemingly innocuous little items. That is as much as the two freeers and fridge probably use. We can put this back into the batteries, once we are underway with the engine mounted alternators, in about 20 minutes. Sitting at anchor for a few days this consumption starts to add up.

If you are taking this power from a stacked set of inverters (stacked f or heavier loads) the idling current is multiplied times the number of inverters, which is why we have single a inverter set up for lighter loads and turn it off at night.