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Lithium Ion batteries — Parallax Forums

Lithium Ion batteries

UghaUgha Posts: 543
edited 2008-02-27 12:31 in Robotics
I happen to have a few of those prepaid cell phones handy... they have 3.6V lithium ion
batteries inside and I was wondering if I can put them in series to power a BOE-based robot
project with little to no problems?

I'd just put them back in the cell phones to charge so I figured this would be an easy source
of power for my BOE.

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-02-25 23:56
    I'd be careful of the lithium-ion rechargables.· If they're discharged at too high a rate, they can catch fire and, because of the lithium, a fire would be very dangerous.· There have been some impressive videos of laptop computers going up in a flare of flame with failures of their batteries.

    I'd stick with NiMH battery packs.· You still have to be careful of short circuits, but they're less dangerous.
  • UghaUgha Posts: 543
    edited 2008-02-26 00:11
    I thought if the lithium-ion has self-voltage regulation and temp cutoff, they are pretty safe to use? I'm pretty sure
    that these have those safeties built in. (I could most likely check)

    Do you have any recommendations for where to get cheap, small NiMH packs that'll work without any additional components
    on a BOE? Regular AA rechargables are well and good, but I'd like a little longer life per charge.
  • Mike GreenMike Green Posts: 23,101
    edited 2008-02-26 01:25
    AA NiMH cells come in different capacities.· I've seen some as low as 1200mAh and some over 2500mAh.· We're talking about twice as much capacity here ... and this is with the "cheap" cells being the ones with the larger capacity.· With a BOE, make sure to use 5 cells in series for a 6V battery.· You can use Parallax's 5th cell adapter or get a single AA cell battery holder from RadioShack and glue it on the BoeBot platform just over the steering ball, then connect it in series with one of the leads from the 4 cell battery holder.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2008-02-27 12:31
    AA NiMH batteries are the most convienent format because they are generic and individual cells. When a cell fails, you can swap it out. You can get cells prepacked as 2x, 3x, 4x and so on. But when one cell fails you loose the whole unit. I have a couple 900ma 4x units rated at 4.8volts that were intended for replacement units on cordless phones.

    I'd prefer the 1900mAh and above Lithium cells in a 7.2 volt format that are used in R/C airplanes if they didn't cost $40-60 USD each. NiMH AA cells are nearly up to 3000mAh in some cases, getting closer to alkaline in capacity. MiMH AAA cells are at about 900ma and though I have some I think they are somewhat less useful.

    The 3.6 Lithium cell is ideal for a lower voltage operation of the Propeller or the SX without a regulator. You could use your cell phone as the recharger. Just don't expect to suck all the power out of it. They should never be run lower than 1.8 volts [noparse][[/noparse]the SXes can be set to Brown Out above that limit at 2.4 volts].

    For hefty motors, I have an 8volt Gel Cell at 9Ah. The 6volts don't work with some regulators and the 12 volts just waste a lot in dumping heat.

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