How much power do I need? 

Under the rating conditions (85F inlet air, 86F cooling water), the system will draw 48 amps when running from a fully charged 12v battery bank.  This equates to 600 watts.  Systems operating from 24 volts batteries will draw 24 amps. This number includes the current draw of the seawater pump and the blower.  Like the actual system capacity, the current draw will also change under different ambient conditions.  If the water or air temperature is lower, the current draw will be reduced.  In both 12v and 24v systems, the actual battery voltage effects both the cooling capacity and current draw of the system.  A reduction in battery voltage due to low batteries or voltage drop in the wiring will result in lower cooling capacity and lower current draw.

How do I come up with enough 12/24v power?

Answering this question is key to obtaining a satisfactory DC Breeze installation.  Although the system is extremely efficient, it is easy to underestimate the amount of energy it takes to cool the air.  Nevertheless, it is not only possible to create a low-voltage A/C system which meets your needs, it is easier than you might think.  The important thing is to be realistic about your requirements and the amount of power you will need to meets them.  Viable sources of power include:

• Batteries
• Engine alternators
• Shore power battery chargers
• Solar panels
• DC or AC generators

Lets take a look at each of these individually to see which is the best choice (or combination of choices) for you.

Batteries -

To analyze the practicality of using battery power to provide your air conditioning, let's first review some useful battery facts.

• Lead acid batteries (including wet, sealed and AGM) come in two basic types - "Engine Starting" and "Deep Cycle".  Any battery bank used to power the DC Breeze should be of the "Deep Cycle" type.
• Deep Cycle batteries have a "20 hour rating" which provides the number of amp-hrs of electrical charge they contain when new and fully charged.  The amount of electrical power a lead acid battery can store is proportionate to its size and weight and remains relatively consistent between manufacturers and battery sub-types (wet cell, AGM, etc.).  This energy density is typically 24 watt-hrs per lb (1.9 amp-hrs @ 12.5v)
• To maximize battery life, lead acid batteries should not be discharged more that 60% before recharging.  Following this rule gives you a "usable capacity" of 14.4 watt-hours (1.15 amp-hrs @ 12.5v) per lb of battery weight.

Given these facts it is apparent that it requires 41.7 lbs of batteries to operate the DC Breeze at full power for one (1) hour*.  During this hour, the DC Breeze will remove 5,000 BTUs of heat.  To run the system continuously at full power from batteries for 8 hours would require a battery bank weighing 334 lbs.  A battery bank this size will require 2.7 ft3. (0.076 m3) of space.

Looking at it another way, we need to have 384 amp-hours (at 12.5vdc) of usable storage capacity available to us.  Since we don't want to discharge the batteries more than 60%, we will need a bank with a combined "20 hr" rating of 640 amp-hrs.  If we translate this into some commonly available battery sizes we find that, for 8 hours of continuous running we would need a bank consisting of one of the following**;

• Three (3) 8D size batteries (20.75" x 11.0" x 11.8")
• Four (4) 4D size batteries (20.75" x 8.75" x 10.8")
• Six (6) Group 31 size batteries (13" x 6.75" x 9.8")
• Seven (7) Group 27 batteries (12.0" x 6.8" x 9.5")
• Eight (8) Group 24 batteries (10.2" x 6.8" x 9.4")

If additional power were being drawn from the bank for other reasons (lights, refrigeration, etc), the bank size would have to be increased.

* This is determined by taking the amount of energy consumed by the DC Breeze when running at full power (48 amps) and dividing it by the amount of "usable power" contained in 1 pound of batteries (1.15 amps).  The same holds true to a 24v battery bank because both the number of amp-hours stored by the batteries and the current consumed by the DC Breeze are cut in half.

** Some combinations provide more than the required capacity.

Engine Alternators -

In many applications you will want to have air conditioning available while the engine is running.  In this case you will be using the engine alternator and charging system as the power source for the DC Breeze.  If the output of the alternator is equal to, or higher than the power consumed by the air conditioner, then no power is drawn from the battery bank.  In other words, the batteries are not "cycled" in any way while the air conditioner and alternator are running.  In applications where the engine will always be running whenever air conditioning is required (and the boat is away from the dock), it is possible to use nothing more than a small engine start type battery for your DC bank.  However, in such a case, your alternator MUST be capable of putting out 50 amps or more al all times.

Generally speaking, the alternator that comes with your engine will not provide sufficient output to meet the demand of the A/C system.  However, if you have an in-board or IO propulsion system on your boat,  there are many "high-output" alternators available in the marine aftermarket which are easy, direct-swapout replacements that will work nicely.  It is important to know that  even some "high-output" type alternators don't provide 50 amps when the engine is running slow (such as during trolling).  In this case, you would want to have at least some additional battery capacity is available to keep up with demand.  It doesn't take much.  Most alternator manufacturers will provide a chart showing the output at various engine speeds and pulley ratios.  It is a good idea to remember that most manufacturers rate their alternators under cold conditions.  Once the alternators warm up (which only takes a few minutes) the output will generally fall off by about 20%.

If your boat has outboard propulsion, you will probably have a hard time covering 100% of the power draw of the DC Breeze solely from the engine alternator(s).  In this case, you will want to add some reserve capacity to you battery bank to make up the difference.  Most outboard users find that the difference is relatively small and DC Breeze still offers an excellent solution to their air conditioning needs.  To take a closer look at this type of applications let's go ahead and make some assumptions.  We will assume that this DC Breeze customer owns a 2680 Coastal Runner from Glacier Bay Catamarans (no relationship to our parent company) equipped with twin Yamaha 150 four-stroke outboards.  The alternator on this outboard is rated at 35 amps at full throttle.  When the alternator is hot and the engine is running at trolling speeds, it is safe to assume the the actual output is probably closer to 15 amps.  Since we have two engine, we have a combined conservative output of 30 amps when trolling.  That leaves us 18 amps short of having enough power to sustain the air conditioning system.

Since this customer wants to set the boat up to provide full air conditioning for 6 hours of trolling, we need to come up with another 108 amps-hours of "usable" battery capacity to make up for the shortage of our alternators.  To get 108 "usable" amp-hours, we need a battery (or batteries) with a 20 hr rating of 180 amps (remember the 60% discharge rule).  If we add two (2) Group 27 batteries to the exiting "house bank" we will have sufficient power available to provide continuous air conditioning for six hours of slow engine speed.  Running the engine at faster speeds means that even less power is drawn from the batteries (since the alternator output would be greater) so the available air conditioning time would be extended.

Shore Power Battery Chargers -

The DC Breeze can be operated for extended periods when the boat is connected to "shore power" by using the boat's battery charger to supply the required DC current.  As with the alternator-power system, the batteries are not "cycled" so long as the charger is capable of putting out 48 amps (at 12v or 24 amps at 24v) continuously.  Used in this way there is no additional wear and tear on your battery bank.  The important thing here is to make certain that your battery charger can handle this output for extended periods of time without overheating.  Most, but not all, 50+ amp chargers will do this.  Be sure and check with the manufacturer of your charger to find out.  If necessary, increase the capacity of your charger or supplement it with a second unit.

Solar Panels -

The idea of using the same solar energy that is heating you up to also cool you down has tremendous appeal.  How practical that idea is depends on your budget and how much room you have for solar (photovoltaic, or PV) panels.  For most people on boats it will make sense to use PV panels to supplement other forms of charging but not entirely replace them. 

As mentioned in the beginning of this section, the DC Breeze requires 600 watts of power to run at full speed.  High quality crystalline solar panels (such those made by BP Solar) provide a "peak" output of about 11.5 watts per ft2.  The flexible, amorphous type panels have lower output.  On a boat in a tropical climate a realistic average over a 6 hour period would be about 50% of peak, or about 6 watts per ft2.  To reliably handle the entire power requirement of the DC Breeze would require 100 square feet of PV panels.  Not impossible, but not practical in most cases.

What is practical, is to use the panels to supplement other charging methods.  Although PV panels do not put out their peak power all the time, they do provide the most power at the same time the solar load is at its highest.  For this 2-3 hour window it is possible to average something much closer to peak output - maybe 80%.  Using two PV panels of the most popular size for boaters (BP Solar model BP380 - 47.4" x 21.1") you could reasonably expect 120 watts of usable solar power which would effectively reduce the energy consumed by the DC Breeze by 20% (to 480 watts) during this peak period.

Generators (AC or DC) -

One of the big advantages of the DC Breeze is that it makes air conditioning practical for boats that either do not have traditional AC generators, or want to have air conditioning without turning them on.  If you have a generator (either AC of DC) but would like to have air conditioning without the generator running, then you will want to set up your battery bank to provide sufficient storage to handle the "generator-free" run time you want.  later, when running the generator is less inconvenient, use it to recharge the batteries.  If you want to have the option of extended air conditioning operation, make sure your battery charger has sufficient capacity to provide 48 amps of 12v power while the generator runs (see Shore Power Chargers section above).

For boats with small DC generators designed for battery charging, DC Breeze is just what you've been waiting for.  Nearly all of these chargers create more that enough power to run the DC Breeze directly even while you  simultaneously charge the batteries.