WINDY NATION TrakMax 30L User Manual page 28

TrakMax 30L User Manual
Revision 1.0
7 APPLICATION
7.1 B
ATTERIES
Batteries come in different sizes, types, amp-hour capacity, voltages and chemistries. Here are a few guidelines
that will help in battery selection, and ensure that the batteries are properly maintained. The best source of the
most appropriate settings for the TrakMax will be from the manufacturer or supplier of the batteries.
7.1.1 Automotive Batteries
Automotive and truck batteries are designed for high cranking power – not deep-cycling. Do not use them
unless no other battery type is available. They simply will not last long in a cycling application.
7.1.2 Maintenance-Free Batteries
This type of battery is often sold as a RV or marine battery, but is rarely appropriate for use with a PV
system. They typically have an additional reserve of electrolyte, but are vented. This is not the same as a sealed
battery.
7.1.3 Deep-Cycle Batteries
Best suited for use with PV systems, this type of battery is designed to be more deeply discharged before being
recharged. Deep-cycle batteries are available in many sizes and types. The most common is the vented liquid
electrolyte battery. Vented batteries usually have battery caps. The caps may appear to be sealed, but are not.
The caps should be removed periodically to check the level of electrolyte. When a cell is low, distilled water
should be added after the battery is fully charged. If the level is extremely low, add only enough distilled water to
cover the plates before recharging. The electrolyte volume increases during the charging process and the
battery will overflow if it is filled all of the way up before recharging. Use only distilled water because impurities
will reduce battery performance. A popular and inexpensive deep-cycle battery is the "golf cart" battery. It is a 6-
volt design, typically rated at 220amp-hours. RV and marine deep-cycle batteries are also popular for small
systems. They are usually referred to as Group 24 or Group 27 batteries and are rated at 80 to 100 amp-hours
at 12volts. Many larger systems use L16 batteries, which are usually rated at 350amp-hours at 6-volts each.
They are 17 inches high and weigh about 130pounds. 8D batteries are available with either cranking or deep-
cycle construction. Purchase only the deep-cycle version. The 8D is typically rated at 220 amp hours at 12 volts.
7.1.4 Sealed Batteries
Another type of battery construction is the sealed gel cell. They do not use battery caps. The electrolyte is in the
form of a gel rather than a liquid, which allows the batteries to be mounted in any position. The advantages are
no maintenance, long life (800 cycles claimed) and low self-discharge. Absorbed glass mat (AGM) electrolyte
batteries are also acceptable. Their electrolyte is contained in mats between the battery plates. Sealed batteries
reduce the maintenance requirements for the system and are good for remote applications. They are much
more sensitive to the charging process and can be ruined in as little as a day of overcharging.
7.1.5 Battery Sizing
Batteries are the fuel tank of the system. The larger the batteries, the longer the system can operate before
recharging is necessary. An undersized battery bank results in short battery life and disappointing system
performance. To determine the proper battery bank size, compute the number of amp-hours that will be used
between charging cycles. Once the required amp-hours are known, size the batteries at approximately twice this
amount. Doubling the expected amp-hour usage ensures that the batteries will not be overly discharged and will
extend battery life.
7.1.6 Equalization Charging
Approximately every month, some batteries may need to be "equalized." Since the individual cells of the battery
are not identical, some cells may not be fully charged when the charging process is completed. If the batteries
have been left in a discharged condition for long periods of time, the plates will have sulfates on them from the
electrolyte. If the sulfate remains on the plates for an extended period of time, it will harden and seal off a
percentage of the plate area, reducing the capacity of the battery. By equalizing the batteries before the sulfate
hardens, the sulfate is removed from the plates. Batteries with liquid electrolyte may become stratified.
Stratification concentrates the sulfuric acid into the bottom of the cell while the top becomes diluted. This
corrodes the lower portion of the plates, reducing battery life. Mixing of the electrolyte by the formation of gas
bubbles during the equalization process reduces stratification. Two methods can be used to determine if a
battery needs to be equalized. If possible, measure the voltage of each individual cell while the battery is at rest
(not being charged or discharged). A variation of 0.05 volts between cells indicates an imbalance exists. If the
Page 28 of 29
windynation
05/06/2015