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Notes on power

From Steve Holton on the support-gang list, but good things to use when making your wiki resources for chargers...

The XO 'likes' around 12-14 volts, but should be able to charge
(slowly and inefficiently) down to about 9V.
DC-only and center pin positive. Both are critical.  Make sure you
check this for any re-tasked power supply you want to try.

I would avoid a power supply offering more than 25 volts, or less than
9. But these are unlikey anyway.

==CURRENT== "Amps"
The 'Amps" rating is a measure of how much current the supply will
allow a device to pull before (essentially) blowing an internal fuse
and killing the power adapter. You'll ideally want a supply that is
comfortable supplying about 1.5 amps (which is pretty beefy) because
then the XO will never ask for more than the power adapter can supply.

The risk of using a power supply with a smaller 'Amps' rating is that
the fuse will blow (in the power adapter) which will kill the power

Any power supply with a greater-than-1.5 Amps rating will be fine,
with the understanding that a) it will be unnecessarily more
expensive, and b) there's a risk that whatever is drawing the power
(the XO) will develop a fault and draw more than 1.5 amps, but less
than the overcurrent protection of the power supply, and so the
failsafe mechanism will fail to trip (a fancy way of saying the fuse
won't blow.)

==POWER== "Watts"
The other common rating of a power supply is the power, measured in
Watts. This is usually a rating of how much (maximum) the power
adapter will *consume* (so it's listed as an input parameter) and
includes power lost to the AC/DC conversion process.

The XO consumes 17 Watts of power at maximum draw. So if the power
supply indicates it uses less than 17 W, it won't supply a full 17 W
onward to the XO.

(That's important for the alternative energy folk as well: if you're
trying to find a solar panel, hand crank, wind turbine or perpetual
motion machine to run an XO, make sure it can supply enough power to
run a 15-20W lightbulb over a period of hours or you won't be matching
the standard power needs of an XO. That's a LOT of cranking over a
period of 2 hours.  Hand crank flashlight/cell phone rechargers
generally provide less than 5 volts and total power measured in
milliwatts. These just won't cut it for powering the XO.)

I have found two viable alternative power supplies:

The first  the 19V 1.84A (roughly 80 watts consumed) power adapter
from the Netpliance I-Opener mentioned above. The power plug is as
close to an exact part match as I've been able to find. (But it's not
green). The bad news; these are unsourcable parts.

The other is a 12V DC, 500 mA (0.5 Amp) power supply with a close-fit
plug. This unit:
1. is under-powered (only rated for 500mA vs. 1420mA for the OLPC Green supply)
2. gets hot when charging an XO.
3. has a loose-fit plug which occasionally needs 'wiggling'.
4. is NOT a lead-free device, so probably is not appropriate for children.

The good news is that these will recharge an XO (a good workaround
solution for someone who's only XO power supply has failed, leaving
their XO otherwise unpowered) and are available in my area. ($10 gets
you the 500mA power adapter, a 12V car adapter with the same plug, and
a wind-up flashlight/weather radio to boot)

Mchua 09:28, 22 May 2008 (EDT)

Ah ha!

So you're the infamous Chris! I've heard about you from Mel, and I think that I've spoken too everyone else at ilxo on irc or the phone except for yourself. Anyway. I was browsing the hardware articles you've been working on and I'm impressed. Good work. There is a pretty lively Flickr OLPC group that I manage, one of us should upload your photos as another method of distribution. Seth 21:05, 31 May 2008 (EDT)

Bridge Design Handout


Any chance of getting that bridge designer activity referenced in the lesson plan rewritten as an activity?

I went to the jhu site and played with it a little. It would seem to be a natural fit as an educational activity.

As a model railroader I also feel like pointing a couple of MR lists to it. Frequently there's the 'does this bridge make any sense' discussion.

Do you know what it is written in? Any encumbrances to using it? Or may the simplest solution be (ahem) reengineering it?

Rmyers 16:55, 8 June 2008 (EDT)

I like that idea, though I don't have a lot of time to put together a bridge building activity for the XO at the moment. I'll start doing some work on it toward the end of summer.


Power link dump Cjl 23:42, 8 June 2008 (EDT)


Human power

Bicycle power

IBM AC/DC combo power adapter

You might want to try to get your hands on a couple of "Lenovo AC/DC combo adapter 73P4503", this is the 72 watt version, I think there is also a 90 watt version. The tip works okay in the XO (maybe a little extra wiggle, but it works). The really cool part is that this can either plug into wall for AC source, or you can use the cigarette light adapter to plug into 12V DC source. Figure out what's inside one of these and you're well on your way. Cjl 17:38, 10 June 2008 (EDT)


Voltage_regulator is uncatagorized. But seems to be a work in progress. Could you categorize it please? 05:45, 2 July 2008 (UTC)

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