Rechargeable Batteries

Ricardo's concept The power could come from rechargeable batteries, either in an internal compartment or an external box. The OLPC project has a range of power options we could use. This page has a lot of conventional and speculative ideas by various people http://wiki.laptop.org/go/Battery_and_power .

Social Network for Recharging Batteries

One option is to organize people like a Sneakernet, to take batteries to a place with mains electricity for re-charging, even if the battery has to pass down a chain of 10 people to get there and back. I think I said on Worknets that in the early days of radio in the 1930s, people took batteries to their local electrical store for re-charging. People had 2 batteries, one to use and one at the store being re-charged.

I've added a Paid Battery-Delivery Service to KnowledgeWork, as one way to earn some extra income and provide a useful service.

Calculating Battery Life

Calculating battery life

• Power (Watts) is Voltage (Volts) times Current (Amperes)
• Energy (Joules) is Power (Watts) times Time (Seconds)

• 15000 Joules = 150 Watts * T seconds
• T Seconds = 15000/150 Seconds = 100 Seconds = 1.6 Minutes

• 45000 Joules = W Watts * 700 Hours
• 45000 Joules = W Watts * 700 * 3600 Seconds
• W Watts = .018 Watts

• .018 Watts = 1.5 Volts * A Amperes
• A Amperes = .012 Amperes = 12 mA

A rechargeable mobile phone battery may provide 1000mAh x 5 V = 5 watt hours.

Calculating Screen Refreshes

A 1/8 VGA Kent display requires .022 Joules for each screen refresh. How many screen refreshes (or keystrokes) can it allow for with 3 AA batteries?

• 120000 Joules = N Refreshes * .022 Joules
• N Refreshes = 5,454,545 Refreshes

If the 1/8 VGA Kent display is used for typing 60 words per minute, where each word is an average of 5 characters, then there are 5 refreshes per second, which is .11 Joules per second, which is .11 watts. A VGA display would be less than 1 watt even with continuous typing.

Flash Drive Editor

The total power used by the FlashDriveEditor would be:

• < 2.5 watts for the Linseed processor
• < 1 watt for the display in use
• .75 watt for USB flash drive in use
• < .6 watt for the keyboard
• .01 watt for each USB standby

OneLaptopPerChild laptop will consume about 2 W of power during normal use, compared with 10 to 45 W for conventional laptops.

Car battery for storing electricity

What might be the role of a car battery as storage of electricity (perhaps from Solar energy) for a FlashDriveEditor?

From Ricardo - If you're interested, here's a beginner's guide to Wind Power and Battery Storage, showing all the main parts.

http://www.homepower.com/files/beginner/WindPowerBasics.pdf

It says that if you have a back-up petrol/diesel generator, you may only need it for 50 to 200 hours per year.

It also says, in section 6 'Battery Bank', that systems that are used just to deal with power-outages/cuts can use ordinary car-batteries, as the batteries are fully charged most of the time. However, systems that work on their own need 'Deep-Cycle' or 'Deep-Discharge' batteries, that often go from fully charged down to almost fully discharged. These will be more expensive and difficult to obtain in developing countries.

The One Laptop Per Child Wiki page at http://wiki.laptop.org/go/Battery_and_power explains why Deep-Discharge batteries are needed. The plates on ordinary car-batteries are thin and sensitive to deep discharge. They experience 'premature end of life' if discharged below 10 Volts.

AboutThisPage

• FlashDriveEditor=We want low power and to be able to use standard AA batteries so that they are easily available. Rechargeable AA batteries are then optional. The AlphaSmart Neo runs for 700 hours on 3 AA batteries. Battery recharging might depend on the Sneakernet.
• (just a remark. In these cases it would be extremely useful to use nested pages. Batteries might appear in several contexts, So it would be much better to use FlashDriveEditor/Batteries etc. FranzNahrada - I just want to add that the question of evolving into sustainable information venues by being considerate and careful with namespaces is really an important and urgent issue for me)