Keep Them Warm
Lead-acid batteries like to be kept warm. For optimal function, batteries should be kept between 75 to 80° F. In this range, they’ll accept and deliver tons more electricity. Guaranteed! Cold temperatures slow down the chemical reactions in batteries, reducing the amount of electricity a battery can store.
Although batteries can’t be housed in cold rooms, care must be taken to avoid exposure to high temperatures as well. High temperatures increase the release of explosive hydrogen gas, known as outgassing.They also increase water loss, which reduces battery fluid levels. Higher temperatures also lead to higher rates of self-discharge in batteries. (As a rule, older batteries lose charge faster than new batteries.)
If you can’t maintain batteries in a 75 to 80° F range, at least ensure they’re housed in a room where the temperature ranges between 50 and 80° F. Rarely should batteries fall below 40° F or exceed 100° F. Whatever you do, don’t store batteries in a cold garage, barn or shed. Besides delivering less electricity, they won’t last long. They could even freeze under certain conditions, causing their cases to crack, spilling acid and creating a dangerous mess.
Batteries should not be stored on concrete floors. Cold floors cool them down and reduce their rate of chemical reaction and their capacity. Always raise batteries off the floor.
Ideally, batteries should be housed in a separate, conditioned (heated and cooled) battery room or in a battery box inside a conditioned space to maintain proper temperature. Battery boxes are typically built from plywood. An acid-resistant liner is required to contain possible acid spills. Lids should be hinged and sloped to discourage people from storing items on them. As a side note, batteries should be located as close to the inverter and other power conditioning equipment as possible. Doing so minimizes power losses.
Ventilate Your Batteries
Batteries release potentially explosive hydrogen gas when being charged, so battery boxes and battery rooms containing flooded lead-acid batteries should be well ventilated (Figure 7.3). This allows hydrogen to escape. Never place batteries in a room with a gas-burning appliance or an electrical device, such as a water heater, even if the enclosure is vented. A tiny spark could ignite the hydrogen gas, causing an explosion. Note that this applies to the inverter
Fig. 7.3: Battery Vent System. (a) An outdoor battery room should be well insulated and possibly heated and cooled to maintain temperatures in the optimum range. A passive vent system is needed to allow hydrogen gas to escape. (b) Indoor battery rooms need not be insulated, but require venting.
and all other conditioning equipment. Although you want them near the batteries, they should not be in the same space.
Keep Kids Out
Battery rooms and battery boxes should be inaccessible and locked if young children are present. This will prevent children from coming in contact with the batteries, risking electrical or acid burns. Although electrocution is not a hazard at 12, 24 or 48 volts, dropping a tool or other metal object on the battery terminals could result in an electrical arc that can cause burns, or could result in an explosion of the battery, resulting in acid burns.
Avoiding Deep Discharge to Ensure Longer Battery Life
Keeping flooded lead-acid batteries warm and topped off with distilled water to replace water lost during charging ensures a long life span. Longevity can also be ensured by keeping batteries as fully charged as possible. Like many technologies, lead-acid batteries last longer the less you use them. That is to say, the fewer times a battery is deeply discharged, the longer it will last.
This topic (like so many others) is complicated. While deep discharging reduces the lifespan of a battery, what renewable energy users want from batteries is not simply for them to last a long time but to cycle a lot of energy. Theoretically, you’ll get the most bang for your buck by cycling in the 40 to 60 percent deep-discharge range.
It’s also important to recharge batteries as quickly as possible after deep cycling. For long life, you should also never leave batteries at a low state of charge for a long time. This results in the formation of large lead sulfate crystals, described earlier. Unfortunately, achieving these goals is easier said than done. If your system is small and you don’t pay much attention to electrical use, you’ll very likely overshoot the 40 to 60 percent mark time and time again.
One way of reducing deep discharge is to conserve and use electricity efficiently. Conserving energy means not leaving lights and electronic devices running when they’re not in use. It also means getting rid of phantom loads. Energy efficiency means installing energy-efficient lighting, appliances, electronics, etc. You can also adjust electrical use according to the state of charge of your batteries— in other words, cut back on electrical usage when batteries are more deeply discharged and shift demand for electricity to times when the batteries are more fully charged. You may, for instance, run your washing machine and microwave when the wind’s blowing and your batteries are full, but hold off when batteries are running low.
To track battery state of charge you can install a digital amphour or watt-hour meter. These meters keep track of the amount of electricity stored in a battery bank each day. They also indicate the amount of electricity drawn from the batteries. In addition, they keep track of the total amount stored in a battery bank at any one time — how full the batteries are. This information is used to adjust consumption. If batteries are approaching the 40 to 60 percent
discharge mark, you may hold off on activities that consume lots of electricity. Or, you may run your backup generator to charge the batteries.
Watering and Cleaning Batteries
To maintain batteries you must also periodically add distilled water. This replaces water lost during charging. Water loss occurs by electrolysis, the splitting of water molecules in the electrolyte when electricity flows into a battery. Electricity splits water molecules into hydrogen and oxygen. (Electrolysis is the source of the potentially explosive mixture of hydrogen and oxygen gas that makes battery room venting necessary.)
Hydrogen and oxygen produced during electrolysis are both gases. These gases can escape through the vents in the battery caps in flooded lead-acid batteries, lowering water levels. Water can also evaporate through the vents in a flooded lead-acid battery at any time, and a mist of sulfuric acid can escape through the vents during charging, depleting fluid levels.
All of these sources of water loss add up over time and can run a battery dry. When the plates are exposed to air, they quickly begin to corrode. When this happens, a battery’s life is pretty well over.
To prevent batteries from running dry, check battery fluid levels regularly. Many experts recommend checking batteries monthly. Others recommend checking batteries every two to three months. When replacing fluid, be sure to only add distilled or deionized water, and do not overfill batteries. Never use tap water. It may contain minerals or chemicals that will contaminate the battery fluid, reducing a battery’s life span.
The tops and terminals of batteries may also need to be cleaned with distilled water and paper towels or a clean rag. When cleaning batteries, be sure to wear gloves, protective eyewear and a long-sleeved shirt you don’t care about. If you get acid on your skin, wash it off immediately with soap and water.
When filling batteries, be sure to take off watches, rings and other jewelry, especially loose-fitting jewelry. Metal jewelry will conduct electricity if it contacts both terminals of a battery. Such an event will leave your jewelry in a puddle of metal — along with some of your flesh. One 6- or 12-volt cell can produce more than 8,000 amps if the positive and negative terminals of a battery are connected. In addition, sparks could ignite hydrogen and oxygen gas in the vicinity, causing an explosion. Shorting out a battery can also crack the case, releasing battery acid.
Also be careful with tools when working on batteries — for example, tightening cable connections. A metal tool that makes a connection between oppositely charged terminals on a battery may be instantaneously welded in place. The tool will become red hot and could also ignite hydrogen gas, causing an explosion. Wrap hand tools used for battery maintenance in electrical tape so that only one inch of metal is exposed on the working end; that way it can’t make an
electrical connection. Or buy insulated tools to prevent this from happening. Try to have a set of these insulated tools dedicated just to battery maintenance. That way you won’t grab the insulated wrench for another project and then use whatever non-insulated wrench is at hand when it comes time for battery maintenance.
You may also have to clean the battery posts every year or two. To clean the posts, use a small wire brush, perhaps in conjunction with a spray-on battery cleaner purchased at a hardware store. To reduce maintenance, coat battery posts with Vaseline or a battery protector/sealer, available at hardware and auto supply stores. This protects the posts and the nuts that secure the battery cables on the posts.
Equalization
To get the most out of batteries, you need to periodically equalize them. Equalization is a controlled overcharge of batteries.
Why Equalize?
Periodic equalization is performed for three reasons. The first is to drive lead sulfate crystals off the lead plates, preventing the formation of larger crystals that reduce battery capacity. In addition to coating the plates, the large crystals can also flake off, removing lots of lead from the plates.
Batteries must also be periodically equalized to stir the electrolyte. Sulfuric acid tends to settle near the bottom of the cells in flooded lead-acid batteries. During equalization, hydrogen and oxygen gases released by the breakdown of water (electrolysis) create bubbles. They mix the fluid so that the concentration of acid is equalized throughout each cell of each battery, ensuring better function.
Equalization also helps bring all of the cells in a battery bank to the same voltage. That’s important because some cells sulfate more than others. As a result, their voltage may be lower. A single lowvoltage cell in one battery reduces the voltage of the entire string. In many ways, then, a battery bank is like a camel train. It travels at the speed of the slowest camel.
Although equalization removes lead sulfate from plates, which restores function, some lead flakes off the plates during equalization and settles to the bottom of the batteries. As a result, even properly equalized batteries lose lead over time and never regain their full capacity.
How to Equalize
Equalizing batteries is a simple process. In those systems with a gen-set for backup, the owner simply sets the inverter to the equalization mode and then cranks up the generator. The inverter controls the process from that point onward. In wind/PV hybrid systems, the operator can also set the controller to the equalize setting during a storm or period of high wind. The controller takes over from there.
How often batteries should be equalized depends on whom you talk to and how hard you work your batteries. Some installers recommend equalization every three months. If your batteries are frequently deep discharged, however, you may want to equalize more frequently. If batteries are rarely deep discharged, they’ll need less frequent equalization. For example, batteries that are rarely discharged below 50 percent may only need to be equalized every six months.
Rather than second guess your batteries’ needs for equalization, it is wise to check the voltage of each battery, using a digital volt meter (multimeter), every month or two. If you notice that the
Fig. 7.4: Hydrometer. Hydrometers measure specific gravity. Low specific gravity indicates that the battery needs recharging, perhaps even equalization.
voltage of one or two batteries is substantially lower than others, it’s time to equalize.
Another way to test batteries is to measure the specific gravity of the battery acid using a hydrometer (Figure 7.4). Specific gravity is a measure of the density of battery acid. Density is related to the concentration of battery acid — the higher the concentration, the higher the specific gravity. If significant differences in the specific gravity of the battery acid are detected in the cells of a battery bank, it is time to equalize.
If at all possible, use your wind turbine to equalize batteries in off-grid systems. You’d be amazed at how well this works. As a final note on the topic, be sure only to equalize flooded lead-acid batteries. A sealed battery, either gel cell batteries or absorbed glass matt sealed batteries, cannot be equalized! If you try to, you’ll ruin the battery.
Reducing Battery Maintenance
Battery maintenance should take no more than 30 minutes a month. To reduce maintenance time, you can install sealed batteries. Another way to reduce time spent babying batteries is to replace factory battery caps with Hydrocaps (Figure 7.5). Hydrocaps capture much of the hydrogen and oxygen gases released by batteries when charging under normal operation. The gases are recombined in a small chamber in the cap filled with tiny beads coated with a platinum catalyst. Water formed in this reaction drips back into the batteries, reducing water losses by about 90 percent.
Another option is Water Miser caps. They capture moisture and acid mist escaping from batteries’ fluid, reducing water loss by about 30 to 75 percent.
Yet another way to reduce maintenance is to install an automatic or semiautomatic battery filling system (Figure 7.6). Dan uses a manually operated Qwik-Fill battery watering system manufactured by Flow-Rite Controls in Grand Rapids, Michigan (sold
Fig. 7.5: Hydrocaps. These simple devices help reduce battery watering by reducing water losses.
Fig. 7.6: Battery Filling System. Distilled water can be fed automatically to battery cells or manually pumped into them through plastic tubing. Both approaches save a lot of time and energy and help to keep battery fluid levels topped off to ensure battery longevity.
Fig. 7.7: Battery Filler Bottle. If you can access your batteries relatively easily, this filler bottle is one of the easiest and most economic means of adding distilled or deionized water to them.
online through Jan Watercraft Products). He’s found that this system works extremely well even after many years of service and has turned battery maintenance from a chore to a pleasure. Although they’re a bit pricey, the systems quickly pay for themselves in reduced maintenance time and ease of operation. The convenience of quick battery watering overcomes the procrastination that leads to costly battery damage. A cheaper alternative is a half-gallon battery filler bottle (Figure 7.7).
