Batteries

[last updated: 2022-11-20]
Li-ion batteries
battery projects
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Misc Notes:

• Max charge current (amps) for lead-acid batteries is 25% of AHr capacity
• AH rating: determine how long it takes to discharge to ~50 percent capacity.

On this page ...

• Battery C-rating
• Coin cell batteries
• NiMH batteries
• LiPo link
• multiple-battery packs (usu. LiPo)
        battery internal resistance

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• Battery C-rating:
  The "C-rating" of a battery (at least usually but not always???) is its A-hr capacity divided by one hr (ie. same number, with units converted from A-hr to amps)
  For example, a 2 A-hr battery will have a C rating of 2 amps.
  When you specify what current (ie. amps) a given battery type (ie. its specific chemistry) can be charged or discharged with, you'll do so in multiples of C.
  For example, a ... battery might be charged at 0.5C, and discharged at 0.1C. This means, say for a 2 A-hr battery (with C = 2a), you can charge it at a rate of 1a, and should discharge it at or below 0.2a.
  Charging faster than recommended can overheat and explode. Discharging faster than recommended may also overheat, but mostly will damage the battery's future A-hr holding capacity.
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• Coin Cells:
• Alkaline:
  • Coin cells with ID's that start with 'L' are alkaline cells, with a nominal voltage of 1.5V.
  • Alkaline batteries like LR1154 (aka LR44) is 11mm diam and 5.4mm thick.
• Lithium:
  • Coin cells with ID's that start with 'C' are Lithium batteries, and have a nominal voltage of 3V.
  • CR2020 coin cells are 20mm diam and 2.0mm thick
    CR2016 are 20mm diam and 1.6mm thick
    If the thicker one will fit into the holder, it will work just fine, with slightly longer life.
    If the thinner one will fit snugly, it will work just fine, with slightly shorter life.
  • Amp-hr capacity:
    [most of below is from: (link to:) batteriesAndButter ]
    2032: Nominal rating: 230mAh (C = 0.23)
    230mAh at 1mA (0.005 C)
    460mAh at 0.5mA (0.002 C)
    150mAh at 3.0 mA

    1612: 40 mAh
    1620: 75 mAh
    1632: 125 mAh
    2012: 55 mAh
    2016: 90 mAh
    1220: 35 mAh

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• "standard" NiMH rechargable batteries are ~ 1.5v
  lifespan: ~ 1000 cycles
  heavier, lower power capacity
  lower discharge rates
  best to charge with a pulse charger
  charge at 1.5C

• If you have a battery pack made up of some number of batteries in parallel,
  and you charge it (ie. all batteries in the pack are getting charged at the same time),
  then the amount of charge each battery receives will depend on its internal resistance.
• If some batteries in your pack are eg. much lower resistance than other batteries,
  then they will end up being more fully charged than other batteries in your pack that have higher internal resistance.
• In order to keep your battery pack balanced, with all batteries about the same charge,
  all batteries in your pack should have about the same internal resistance.
• If your pack is not balanced, you can help the situation by breaking apart the pack and charging each battery by itself. Of course this might not be convenient.
• Measuring battery internal resistance:
• For starters, measuring DC resistance as below is only a reference point
  that can be used to compare batteries, or compare how a battery ages over time and use.
  DC resistance ignores effects of internal or external circuit capacitance and inductance and frequency.
• Vbu = battery voltage unloaded
  Vbl = battery voltage under load
  Rl = load resistance
  Rb = battery internal resistance
  then:
  Rb = (Vbu – Vbl) * Rl / Vbu
• Another method uses a small AC signal...
• See also: (link to:) Battery University

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