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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". Battery banks 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-hrsof electrical charge they can deliver 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)
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●To maximize battery life, lead acid batteries should not be discharged more than60% before recharging. Following this rule gives you a "usable capacity" of 14.4 watthours (1.15 amp-hrs @ 12.5v) per lb of battery weight. We can see 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")
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●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 whenrunning at full power (48 amps) and dividing it by the amount of "usable power" contained in1 pound of batteries (1.15 amps). The same holds true for a 24v battery bank because boththe number of amp-hours stored by the batteries and the current consumed by the DCBreeze are cut in half.
** Some of these combinations provide more than the required capacity |
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