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221Re: [force_ev] Pb-acid Battery Charging

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  • David Roden (Akron OH USA)
    Apr 2, 2001
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      You are right, shallower discharges mean more cycles. Normally the right
      thing to do is charge as soon as possible after ~any~ significant
      discharge.

      However, to some extent, a lot of very shallow cycles (say, 20-30% DOD)
      can be less efficient in terms of the mileage you get out of a battery.
      The optimal depth of discharge (optimal in the sense of giving the most
      total distance before replacement) is around 50% per cycle.

      That said, the sulfation resulting from sitting for several hours in a
      partly-discharged state may very well more than offset any gain.

      Use common sense. Consider the amount of energy used from the battery,
      and how long it will be before it's next charged. If you've used only
      10% of the charge, and you'll use the car again in 2-3 hours, I wouldn't
      charge. But if you've used 30% and it'll sit for 8 hours, I'd charge.

      A few thoughts:

      First, make sure your charger is set up appropriately for the batteries
      you are using. Gel, AGM, and flooded types all require different charge
      profiles. Heck, different manufacturers have different recommendations,
      so if you've changed type or brand since installing the charger, make
      sure you're still charging correctly.

      Second, it isn't necessary for your charger to perform a full or even
      partial equalization on every cycle. It might not be a bad idea to, when
      at work, pull the plug a half-hour or so after your pack reaches 14.2
      volts per module (for gel) or 15 volts per module (for flooded).

      Finally, 1.5 to 2 years' life from the 12-volt marine batteries these
      cars use is pretty decent. In hot southern climates, sometimes you're
      doing well to get more than a year. Good flooded marine batteries like
      the Trojan 27TMH are BCI-rated at only around 300 cycles, and that's in
      trolling motor service (lots less strenuous than hauling around a 2100 lb
      car).


      David Roden - Akron, Ohio, USA
      1991 Solectria Force 144vac
      1991 Ford Escort Green/EV 128vdc
      1979 General Engines ElectroPed 24vdc
      1974 Honda Civic EV 96vdc
      1970 GE Elec-trak E15 36vdc
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