New Batteries for Mindego Repeater

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    This weekend Linda, W6LJB, and I swapped out the old batteries and replaced them with shiny, new ones.  The original batteries were old when we got them, were not deep cycle and didn’t fare well.

    Old batteryOld and new batteries

    Car and truck batteries are designed to give a big surge of current while starting an engine, be recharged almost immediately and then to just idle along while the lights, accessories, ignition and so on run from the engine driven alternator.  Starter batteries have thin plates (to pack in more surface area, for the high current) use high strength alloys to resist vibration and leave space at the bottom of each cell, for any broken or loose plate material to drop off without shorting out the plates.

    In contrast:  Deep cycle batteries use thicker plates to withstand multiple, deep cycles and have a lower alloy content, which results in less gas generation while charging.  The batteries that we installed are also AGM or absorbed glass mat construction where the electrolyte is held against and between the plates by a glass fiber blotter.  Since the electrolyte is completely absorbed, the batteries can operate and be transported in any position, and the individual cells are capped with pressure relief valves so there is no flammable or explosive gas.  AGM batteries can withstand more vibration and higher charge rates than GelCels.

    The new batteries are 12 Volt, 35 Ampere hour and weigh 25 pounds each.  Battery Systems in San Jose carries these in stock and they are $75 a piece.  Combined we now have 140 Ampere hours of standby capacity which will hold the repeater for roughly 40 hours of standby or 7 hours of continuous transmission.  For long life, we ought to limit the discharge to only half these amounts, but this still gives us plenty of time to start a backup generator.

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