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How to Keep Them Alive for Years & Years...
With flooded batteries, corrosion of terminals and cables is an ugly nuisance that causes resistance and potential hazards. Once corrosion takes hold, it is hard to stop. The good news is that it’s easy to prevent! Apply a non-hardening sealant to all of the metal parts of the terminals before assembly. Completely coat the battery terminals, wire lugs, nuts, and bolts individually. A sealant applied after assembly will not reach all around every junction. Voids will remain, acid spatter will enter, and corrosion will begin.
Special compounds are sold to protect terminals, but you can get perfectly good results using common petroleum jelly (Vaseline). It will not inhibit electrical contact. Apply a thin coating with your fingers, and it won’t look sloppy. If wire is exposed at a terminal lug, it should be sealed airtight, using either adhesive-lined heat-shrink tubing or submersible rubber splice tape. You can seal an end of stranded wire by warming it gently and dipping it in the petroleum jelly, which will liquify and wick into the wire.
It also helps to put the batteries over a floor drain, or in a space without a floor, so that they can be rinsed with water easily. Washing the battery tops about twice a year will remove accumulated moisture (acid spatter) and dust. This will further reduce corrosion, and will prevent stray currents from stealing energy. Batteries that we have protected by these measures show very little corrosion, even after ten years without terminal cleaning.
Moderate the Temperature
Batteries lose approximately 25 percent of their capacity at a temperature of 30° F (-1° C), compared to a baseline of 77° F (25° C). At higher temperatures they deteriorate faster. So it’s good to protect them from temperature extremes. If no thermally stable structure is available, consider an earth sheltered enclosure. Where low temperatures cannot be avoided, get a larger battery bank to make up for the loss of capacity in the winter. Avoid direct radiant heat sources that will cause some batteries to get warmer than others.
Use Temperature Compensation
When batteries are cold, they require an increase in the charge voltage limit in order to reach full charge. When they are warm, they require a reduction in the voltage limit in order to prevent overcharge. Temperature compensation is a feature in many charge controllers and in the chargers of some inverters. To use this feature, order the accessory temperature probe for each charging device, and attach it to any one of the batteries.
©1999 Windy Dankoff
Lead-acid batteries are often considered to be the “weak link” in renewable energy systems.
However, today’s renewable energy batteries are better than ever, and so are the devices that regulate and protect them. Battery failures are rarely the fault of the batteries themselves! Follow these guidelines to avoid most battery problems.
Size a Battery Bank Generously
The battery bank is the foundation of the power system. Don’t skimp here! A good working minimum size can be based on your estimate of seven days of energy storage. Keep in mind that after one year of service, it is not advisable to enlarge a battery bank by adding new batteries to it. Doing this will cause mismatch problems and stray currents between the newer and the older sets. Instead, anticipate your growing energy needs by sizing the set properly from the start, perhaps to twice the minimum (seven day) size.
Avoid Multiple Strings
The ideal battery bank is the simplest, consisting of a single series of cells that are sized for the job. Higher capacity batteries tend to have thicker plates, and therefore greater longevity. Having fewer cells will reduce both maintenance and the chance of randomly occurring defects. For example, suppose you require a 700 amp-hour battery bank. You can approximate that by using three parallel strings of golf cart batteries (220 AH), or two strings of the larger L-16 style batteries (350 AH), or a single string of larger industrial batteries.
It is advisable to have fewer than three parallel battery strings if possible. Battery banks with multiple strings are more likely to develop cells with unequal states of charge. Weak cells will be difficult to detect because they will “steal” from the surrounding cells. The system will suffer as a whole and will cost you more in the long run.
46 Home Power #69 • February / March 1999
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