Using Inverters for operating marine AC with ships 12-24 VDC power supply.

The Pros and Cons of operating Marine HVAC systems with the ship's 12-24 DC Volt power supply.

Operating marine air conditioning systems with the 12 or 24 volt DC ship's power supply is possible, and in many commercial and military applications and some recreational applications, desirable, but for the typical recreational boat owner it's frequently impractical for numerous reasons:

Operating with 12 or 24 volts DC current is often limited by the lack of a sensible and adequate power supply.
It's foolhardy to run a 300 HP engine at fast idle while at anchor to spin an alternator that requires only a few horsepower.
On a smaller engine, the large alternators required (200 plus amps) usually require multiple belts and may place an unacceptable side load on the front crankshaft bearing, voiding the engine warranty.

It's impossible to overcome the V=I/R formula, whereby a typical 16,500 BTU air conditioner that requires about 13.5 amps @ 120V, requires about 135 amps @ 12VDC, therefore you will need about a 200 amp alternator with beefed up engine wiring harnesses to comfortably produce a continuous 135 amps to operate a single, typical 16,500 BTU air conditioner.

The voltage drop is very high with low voltages, therefore with 12 volt HVAC equipment you will need to run very heavy, battery cable like, power supply wires, which are not only expensive, but also heavy.

Running off of the batteries is also usually impractical because you will need a huge bank of batteries to operate the air conditioning equipment overnight, and you would certainly give your alternator an incredible workout in the AM, possibly overwhelming it.

For smaller recreational applications, we usually recommend the consumer consider a small (2,500+ watt) portable generator if one wants to operate the air conditioner overnight. It's extremely important to avoid carbon monoxide poisoning, somewhat limiting the possible locations where the generator can be placed, and we always recommend the use of at least one high quality CO detector on board!!

Other manufacturers do supply 12 volt HVAC equipment, however because the components are such small specialty runs on the assembly line they are usually very expensive. We believe it's actually less expensive and far more desirable to purchase one of the many highly efficient, reliable and relatively inexpensive inverters so that you can utilize the lesser expensive, standard, over-the-counter air conditioning equipment. An added benefit is the elimination of your battery charger because these inverters usually have very powerful and sophisticated battery charging circuits in addition to the inverter!

If, however, you wish to run the AC while underway and you do have or can install a large alternator, this can be a very sensible installation. We have done just this as a test on a USCG 47 MLB several years ago with great success. The existing alternators were huge and under-utilized, and they now heat and cool the entire vessel with two 16,500 BTU Flagship Marine units via a Trace inverter while underway, and on the shore-power while dockside.

Our OEM relationship with Xantrex Technology, Inc.(they recently purchased Trace Engineering, Statpower Technologies, Cruising Equipment Corporation and Heart Interface), enables us to pass along very substantial savings to our customers as evidenced by the few models that follow:

Flagship Marine, Inc., 2427 SE Dixie Hwy., Stuart, Florida 34996 - USA
Phone: 772-283-1609 Fax: 772-283-4611 Wats: 800-316-6426 sales@flagshipmarine.com

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