Battery Powered Air Conditioning

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.


Oct 5, 2007
Vessel Name
Anastasia III
Vessel Make
Krogen 42
I was looking over Mermaid's product line and found this copy on their smallest AC.
M5: 5,200 BTU Cabin Air Conditioner

Smallest footprint on the market and weighs in at 31.5 lbs. for the unit, and 4.7 lbs for the electrical box! This unit has a rotatable blower and tapers down to a "V" shape for those odd angle discharge installations. We use 4" ducting and recommend a minimum of 2, 4" round supply grills with this installation.

This unit will run off the new Honda eu1000i 1,000 watt portable generator, while in cool mode. Another option is to use a Statpower 1,800 watt inverter and 450+ amp hours of battery power and you can anchor out (one average) for one night. We have actually had success operating the Mermaid Model M5 off as low as a 1000 Watt Inverter and only 400 amp hours of battery power, however, longer operating times, it is recommended to use a higher wattage inverter and a bit more battery power.

On average, this unit is designed to cool cruisers up to 26' and sailboats up to 28'. All M5 models include a programmable digital thermostat. Pump Not Included.

5,200 BTU Cabin Air Conditioner Specifications
Running amperage:
Cool = 4.4 amps, R/C = 5.5 amps.
Add approximately one amp for the standard seawater pumps.
Start up amperage is calculated by running amperage multiplied by 1.8.

COOL ONLY UNIT: L-15" W-11.5" H-11.5
REVERSE CYCLE UNIT: L-18" W-12" H-11.5"
This is from their master distributor:
At this point there are a variety of DC air cond , mostly tiny made for the truck 18 wheeler cabin market.

There is even one that uses Eutetic plates (frozen brine tank) to store the cool , instead of batteries.
REd Dot and Dometic are just 2 ,

That all sounds good, but in the real world it would take a hell of a battery bank to run even this small of an a/c unit. Sounds like they are figuring just running the a/c and a perfectly effecient inverter for just 8 hours. It ain't gonna happen.

Do the math, and if you JUST run this unit for 8 hours, including pump, and an 80% effecient inverter, that would take 5.4 amps times 8 hours times 10 times 1.2*for the inverter brings you to 518 amp hours, which would take at least a 1,000 amp hour battery bank, and be drawing nothing else but the a/c. Reality it would take something like a 1,500 to 2,000 amp hour bank to get away with this. That's a BIG battery bank.
A better matched inverter would be 90% and DC unit is even better ,

but the saving grace (same with fridges and freezers) is they seldom have a 100% duty cycle.

If it runs only half time the numbers aren't too bad.

And most of the battery only use should be at night when the insolation is far less.

1000A of batteries is not that hard and 300A a night wont harm the set , the real question is weather most folks will pay for the ability to restore a 1000A batt set.

Sure not going to be done with the cheapo engine alt or a rewound from Balmar.

Top Bottom