Batteries

Boomershoot Mecca has solar power to keep the Wi-Fi going year around. Some of the batteries were over five years old and weren’t holding a charge. Some were three years old and I wasn’t too sure about them. I purchased four new sealed batteries and replaced all the old ones over Thanksgiving.

The batteries don’t handle really cold temperatures well and there is no heat at Mecca. At times it gets well below zero so I put some scrap insulating foam board underneath and on top to retain a little bit more heat until I can make something a little more permanent for the winter.

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I brought the two year old batteries home, charged them, and did some tests. They have about 70% of their claimed storage capacity. I took them back to Idaho earlier this month for use at a different site.

Brother Gary, his dog Roscoe, and I took them the last 0.3 miles across the field on plastic toboggans over a few inches of snow:

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The other site is underneath the power tower you see at the top center of the picture. It is a Wi-Fi relay station to get Internet service from Mecca to brother Gary’s house. The batteries there have been working for a couple years but were a little marginal in terms of recommended capacity. As they aged I was concerned that one dark and extremely cold January the batteries would fail. Putting in additional batteries now will ensure it makes it through this year and I won’t have to make the trip across the field on snowshoes over four feet of snow pulling 100+ pound batteries. I will test their capacity each August or September when access is easy by driving across the field and replace them as needed.

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12 thoughts on “Batteries

  1. To help keep them warm in the winter, an good insulated box, and use a 12v water heater in a like 5 or so gallon water tank as a shunt for the wind/solar when the batteries are full as a heat source. It would not have to dump a lot of heat in to the water to keep a good insulated box above 50f all winter long and that will help the batteries last longer.

    • I’ll have to do the thermodynamic math on that suggestion but it sounds like a good idea. The batteries themselves generate a fair amount of waste heat in both charge and discharge modes. They also have a lot of thermal mass. The box would have to be convertible to “summer mode” too.

      During some weather conditions of the winter there can be no surplus solar for weeks at a time. I have been thinking of making my own wind power generator which could take up the slack in those dark months.

  2. Dagamore may be on to something; a very heavily insulated box (rigid polyisocyanurate is 6.45/inch, so ~8 inches = ~R50, although I think I’d figure a way to get ~R75 – 12 inches) would not require much calorie input to maintain temps well above freezing.

    Could H2O solar panels be used to provide the warm water dagamore mentions, or a small on-site wind driven electrical generator to power a resistance heater?

    The “water tank” of course would require an antifreeze solution capable of withstanding temps at least 10% below the lowest temp expected, and be constructed of material that could withstand expansion caused by freezing liquid should the vagaries of nature drive temps below that. The larger the thermal mass, the better, 1″ OD PEX is .875″ ID, my math says 5 gallons = 160 ft. which may be impossible to accommodate inside an insulated box, but using tubing to contain the liquid thermal mass may allow using powerless thermal siphoning to circulate the liquid. Flexible PEX tubing is flexible enough to survive freeze/thaw cycles – the weak point is the fittings. Batteries outgas, so whatever insulated box is built would require venting of some sort.

    Is it feasible to buils an underground vault for the batteries? I’d guess frost level at Mecca is around 4 ft but going down that far would reduce the insulation requirements substantially and it might be possible to reach/exceed that 4 ft number with above-grade earth berming. Ground temps at ~4 ft are probably ~15-20 degrees above freezing.

  3. That’s all rubbish. The best way to keep your batteries warm is to shove them inside of a dead tauntaun.

  4. Pretty amazing how much they degrade in such a short time. I just finished doing a Li-ion battery swap on a smaller device that was less than a year old and only holding 84% of the charge it held when brand new.

  5. I wonder about cold and batteries. It’s not clear why it would matter. What I do know matters is serious cold IF the battery is not well charged. The reason is that the melting point of battery acid depends significantly on the state of charge of the battery. A fully charged battery is very hard to freeze; I don’t remember the number but it doesn’t seem likely except in Antarctica or Thule. A battery with low charge is quite another matter, that can freeze in a good USA winter.
    Ever since I’ve kept my batteries on tractors and mowers on a float charger — a very small and dirt cheap device — I haven’t had to replace batteries or worry about jump-starting the snow blower in the middle of winter.

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