[Peripherals] Fwd:Replacement power adapters

[Ixo X oxI]

I thought to cross-over a discussion about needed power adapters for the
XO-1 Laptop.
-iain

---------- Forwarded message ----------
From: Steve Holton <sph0lt0n at gmail.com>
Date: Thu, May 22, 2008 at 5:38 AM
Subject: Re: [support-gang] Replacement power adapters
To: "Community Support Volunteers -- who help respond to help AT laptop.org"
<support-gang at lists.laptop.org>


On Thu, May 22, 2008 at 1:21 AM, Ixo X oxI <ixo at myna.ws> wrote:
> Some interesting news on compatible adapters...
>
> I just recently purchased a Linksys (or was it a D-Link?) wireless
adapter,
> and the adapter fits like a charm. (12 V 2.25 amp)
>
> So that got me thinking, and dug through my pile of various adapters.
>
> (Laptop - IBM Thinkpad 770E), 16V , 3.36 amp
> (Laptop - HP pavalin ze1250),  19V , 3.95 Amp

Best fit I've found was the power brick supplied with the Netpliance
I-Opener boxes. Sadly, those are even harder to find than the real
OLPC ones.

>
> Also just in the last few days, I've developed some connections with two
> local electronics recyclers who can set aside a select few of specific
items
> for me.  One of the items I was thinking could be power adapters... with
the
> correct plug end.....
>
> So...  can the XO really handle ANY DC voltage between 12V and 24V ?  Any
> amps ?
>
> Will all of the above work ok? What is the best range (or most effective
> combination) for Amp's and total wattage ?  (i.e. 12v @ 1amp vs 24v @ 500
> milli-amp = 12 Watts)

==VOLTAGE== "VOLTS"
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
adapter.

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)

--
Steve Holton
sph0lt0n at gmail.com
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