Multi channel battery charger

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Multi Channel Battery Charger

Key requirements

• 15 batteries per unit.
• Charge batteries in 2 hours (Subject to limits per cycle time)
• OLPC must own the entire design.

Electrical

• The CPU will be and Atmel At91SAM7x family part. Either the 128 or 256 depending on how cheap we can get them in volume.

http://www.atmel.com/dyn/products/product_card.asp?part_id=3754

• Power source. AC 100V-230V. DC 9V-30V. The DC plug needs to be some sort of standard plug. Each battery needs 15W if its charged from totally empty. So 15 batteries is 225W. Meaning we will probably need a 300W power supply or so. 9VDC @ 300W means a 30 Amp connector.

Exterior devices

• AC In: IEC for 100 to 220VAC
• DC In: 9VDC to 30VDC 30Amp
  • Bill is going to find us a few connectors to choose from.
• DB9 for RS-232
• USB B connector (Its a USB device)
• Power switch
  • Need example switches
  • In addition to the power switch we are also going to need some sort of circuit breaker on the input. Considering the different voltage/current ranges for AC vs DC there will probably need to be one for each supply.
• Two indicator lights per battery channel
  • Red Led and Green Led. Use the same setup as in the laptop. Red, Green, and Yellow both are enabled.
• Battery Tray
• External laptop power DC cables.
  • 3 of the XO DC power cables available to the kids so they they can power their laptops while they switch batteries. This keeps them from having to turn off the laptops to switch batteries.
• (future) RJ45 10/100 ethernet connection

Software

• freeRTOS:

http://www.freertos.org/

• The charging software will be GPL licensed and OLPC must own the

copyright.

• • Slight exception to this for the first round of units. I plan to

reuse the existing BMS software and thus it will have to be closed source until that code is replaced with open source code.

FreeRTOS already supprts the Atmel chip. FreeRTOS has a special exemption that allows you to link closed code with FreeRTOS as long as you only use the API. If for some reason we can't then FreeRTOS offers a Royality free License you can purchase that lets you use it in closed applications.

Mechanical

• Density. Getting as many batteries as possible in as small a footprint is a goal.

• Physical Safety. Its got to be stable and hold lots of heavy batteries but not be able to fall over on top of a child. Who might be trying to climb on it to get his battery.

• Stackable. More vertical space is available than floor sq footage so an idea was to make them stackable. But see above point.

• Heat dissipation. Each battery needs 15W worst case and most of that power will be dissipated into the batery. I expect the electronics/battery to dissipate less than 1W/battery. PSU at 300W @ 85% efficiency is 45W.

• Enclosure. Metal. Except perhaps for some plastic for the battery holder. Having metal available to heatsink to should help in keeping the electronics from burning up in hot countries.

Datasheets

• File:At91sam7x128 256 pc.pdf Atmel CPU
• File:DS2756.pdf
• 30A connector