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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. 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 at all times to avoid draining your starting battery. Generally speaking, the alternator that comes with your engine will not provide sufficient output to meet the demand of the A/C system, especially with older systems.
However, if you have an in-board or IO propulsion system on your boat, there are many "high-output" alternators available in the marine after market which are easy, direct-swap-out replacements that will work nicely. Some "high-output" type alternators don't provide 50 amps when the engine is running slowly (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.
Most alternator manufacturers will provide a chart showing the output at various engine speeds and pulley ratios. 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 may have a hard time covering 100% of the power draw of the DC Breeze solely from the engine alternator(s), unless it is a newer unit. 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 cutty cabin sports boat 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, we will assume the the actual output is probably closer to 15 amps. Since we have two engines, we conservatively have a combined 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. |
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