A123 M1 Lithium cells for robot power

The Lithium Iron Phosphate (LiFePO₄), also know as Lithium nano-phosphate, M1 cells produced by A123Systems promise to provide a high performance rechargeable cell, substantially lighter than NiCads, suitable for use in fighting robots, without the disadvantages of current LiPo technology (fire risk, short life, fragility, limited maximum charging rate, high cost).

Advantages of A123 M1 Lithium batteries

• Lightweight - finished 33V 2.2Ah (73Wh) battery pack = 0.9 kg.
• Similar cost to good NiCads, or considerably cheaper on eBay
• High current ability - up to 70 Amps continuous discharge - over 30C. Less when built into a pack.
• Fast charging - up to 4C - can be fully charged in under 20 mins.
• Safe - Do not suffer from thermal runaway. Enclosed in a metal case.
• Long life - over 1000 cycles if not abused.
• Only require a very simple voltage cutoff charger, or even simpler constant voltage charging, if not balancing.

Disadvatages

• Life will be reduced if cells are over charged, so cells in a pack need to be carefully balanced, or a cell monitoring charger used.
• The cells will be damaged if deep discharged - must avoid any cell being discharged below 2 Volts.
• Do not like getting hot - if the cells get to over 60ºC, their life will be reduced significantly, although this may be acceptable in this sort of application.

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John Reid 2007