The Almighty Battery

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Wiring and Enclosures

The most important thing you need to know about batteries is that they produce explosive gas when charging. Batteries should be kept in an enclosure completely isolated from anything else (even switches and breakers can spark when used and ignite the gas). This enclosure should be equipped with a vent that exits the box above the top of the batteries and travels

level and/or upwards to fresh air. It is not a good idea to put batteries in your house; instead, build them their own home away from yours. A small insulated structure for lead-acids works well in cooler regions. Placing the enclosed, vented box inside a heated building such as a shop or garage can also work very well in cold areas.

Interconnects between batteries should be beefy. A one-eighth-inch copper bus bar, or some similarly adequate material, can be bolted between terminals for this purpose. Be sure when making connections that contact surfaces are perfectly clean (a bit of sanding can clean up surfaces, if needed). Add some anti-oxidation compound to keep connections from crusting up during use. When making cable interconnects use a large copper cable (don't use aluminum. Most conditions will require at least 2/0 copper; if you get welding cable, it bends very nicely). Get professionally crimped lugs on the ends. It's not a bad idea to add solder, electrical heat/shrink wrap, and then electric tape over the whole thing. If you size your interconnects to your system's needs and properly build and install them, you will rarely run into a situation where they fail.

Finally, always fuse anything coming from or going to the battery bank with a properly sized fuse rated for DC usage. Also, I usually ground an entire off-grid system at one point to an eight-foot ground rod connected with 4/0 copper cable straight to the negative lug of the battery bank.

Maintenance

All battery banks occasionally need to be equalized. This is a process where the voltage on the system is run up higher than the normal "full" voltage (to 15 volts or higher on a 12-volt system, 30 for a 24volt). In a bank, cells that perform better continually will rise ahead of others that lag behind. Running the voltage up to excessive levels brings all the cells in the bank up to full, increasing their life span. It also mixes the electrolyte and reduces sulfation (see "Lead-Acid Dilemma").

The banks must be equalized every three months. The duration of this process differs among battery types and brands. Many chargers and charge controllers have a built in equalization mechanism, enabling you, with a simple push of a button, to raise the voltage to the numbers required by your system to complete this task. Disconnect any DC appliances during this process, as the high voltage may damage them.

It's also good to check each cell with a hand-held volt meter or hydrometer and note any cells with large differences from the rest. One bad cell can put a drain on the whole system and cause your storage to drop well below what you'd intended to have on hand.

Finally, as mentioned earlier, in the case of ni-cads, it's good to completely discharge them a couple of times a year. This helps avoid a strange chemical "memory," which can cause ni-cads to function improperly.

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