18650 Cells

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What it it?

https://www.google.com/search?q=18650+cells&client=ubuntu&hs=KUs&source=univ&tbm=shop&tbo=u&sa=X&ved=0ahUKEwj8xPLHwdLfAhULtIMKHTQ3ADUQsxgIKw&biw=1438&bih=738

General Performance

  • 10A discharge, self-protection circuit inside.
  • 3.7V
  • 3 Ahr
  • 18 minutes of 37W
  • 10W for 1 hour
  • 100 of these give 1 kWhr
  • 45g each, so 1 kWhr weighs 4.5 kg.
  • At this density, ultra light cars (500 lb total) - will have 30 miles per kwhr.
  • 1kwhr ~ 4MJ - so about 1/10 kg gasoline. Given gas is 20% efficient in cars, we have 1/2 kg equivalent. Tbis gets us to about 240 mpg equivalent.
  • With 1 kW solar added- that gets us to about 400 mpg equivalent.

Discharge Characteristics

  • Can 18650 cells really discharge at 10A rate? Yes! [1] - Panasonic goes up to 20 amp rate. 6S (6 cell) packs are 22v. 10 of 6s cells, if discharged at 20A, give a 200A welder for 6 minutes. See Discharge Rate.
  • Crappy ones can be as low as delivering 2.5A each - [2]. With 100 of these, that's still a 250A welder which has a weight of 5 kg for the batteries. Still impressive.
  • Discharge rate of 20A yields temp increase to 50C - [3]

Specs

  • Note actual spec from a buyer on Amazon - [4]

Reviews

Management

  • While specs say 250 cycles for 15A discharge - Multiple thousands of cycles are possible when charged to 80% and drained to 30%. - [5]

Cost

  • From <$1 to $7 each - so choose wisely -
  • Cheapest - [6]
  • Best - Samsung 30Q - 3000 mAh - $3 in bulk - [7]
  • These appear to be on spec at 3000 mAh - [8].
  • Cycle life and specs - [9] - 250 cycles to 70% of rated
  • 1000 cycles at 6A discharge rate bottoming at about 60% capacity for 2000 cycles? - [10]. So these last pretty long.

Links

External Links