Ask PYS: Power

My 900W Coffee Maker is Triggering the Low Voltage Alarm, on Sep 05, 2017 asked:

My commercial salmon troller has a 1600W inverter drawing from a single 8D lead-acid battery which is isolated from the two other 8Ds at night when on anchor and the engine is off. The engine has an 80A alternator and is usually running 16-18 hours per day. The biggest load we put on the inverter is a 900W standard coffee maker, which we only use while the engine is running. While brewing coffee the voltage reading on the inverter display is usually in the mid 11s and the low voltage alarm occasionally starts going off. The voltage goes right back up when the coffee is done brewing. Is this type of use bad for the battery or hard on the inverter? I have size 4 cables going to the inverter, which is what the installation manual called for, and the run is only about 3 feet. - David

Thanks for contacting PYS about the electrical system on your boat.  A 900 watt load running off an inverter will be anywhere from 100 amps to 135 amps depending on the efficiency of the inverter. Sustaining that peak load for an amount of time on an 8D deep cycle battery (which is 260 amp-hours of capacity) will cause the battery voltage to drop significantly to mid 11 volts. As the battery ages, this sort of load will become more and more of a problem and the low voltage alarm on the inverter will be triggered. I’d recommend having a larger house bank, perhaps two 8D batteries, so proportionally the larger inverter draws aren’t as big in function to the battery capacity and therefore as the battery bank ages the inverter low voltage alarm won’t be triggered.