Battery

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  • A combination of one or more electrochemical cells, used to convert stored chemical energy into electrical energy.


Contents

[edit] Using Batteries

Most BEAMbots are solar powered, so batteries aren't usually a huge issue. Some BEAMbots, though, have sufficiently-high energy requirements that they really have to run on batteries. These tend to be more compex robots such as walkers.

Once you've made this decision to use batteries, have a couple of ways you can go:

You'll pick your batteries based largely on what's available (given your budget), whether your bot will be recharging the battery from solar cells (if so, you'll want a fairly low voltage battery), and how big your bot is going to be (9V batteries are none too light).

[edit] Battery chemistry

A number of battery chemistries are available. The following comparison chart comes from the January, 2002 issue of Embedded Systems Programming:

Chemistry Vnominal (V) Max. load current (C) Energy by weight (Wh / Kg) Energy by volume (Wh / L) Operating Temperature (deg. C) Rechargeable? Life cycle (recharges) Shelf life / self discharge
Alkaline 1.5 150 375 -20 to 55 No - 5 years to 80%
NiCd 1.25 >2 45 - 80 125 -40 to 60 Yes 1500 20% / month
NiMH 1.25 0.5 - 1 60 - 120 180 -20 to 60 Yes 500 30% / month
Lithium Ion 3.6 1 100 270 - 325 -20 to 60 Yes 50 - 100 10% / month
Lithium polymer 3.7 0.2 120 - 160 230 - 270 -20 to 60 Yes 500 10+ years
Lead acid 2 0.2 30 80 -20 to 60 Yes 200 - 500 5% / month
Zinc air 1.4 300 1150 -20 to 60 No - 3-12 weeks to 50%
Silver Oxide 1.55 130 500 -20 to 60 No - 2 years to 84%

Note that here load current is expressed in units of C (which is just the Amp-Hour rating of the battery divided by 1 Hour).


[edit] Battery Availability

A number of types of small batteries are available to us:

  • "Button" cells -- 1.25V each; alkaline or NiCad; these are the smallest in size, but also have a fairly low energy storage capacity
  • 9V battery cells -- alkaline only. 9V alkaline batteries are made up of 6 clustered cells in a can. You can pull open this can (carefully) with pliers to pull out the small cells (which are a bit smaller than AAA batteries). Since these aren't rechargeable, I don't use them much.
  • Cordless phone 'batteries -- these are easily salvaged (and in high availability, if you go through cordless phones as often as I do) NiCad batteries -- most output 3.6V, which is just right for most BEAMbots.

[edit] Also See:


[edit] External References




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