ischinca at plan.ceibal.edu.uy
Thu May 13 10:25:18 EDT 2010
Sascha, that's correct, once the 5V rail is loaded the 12V rail is properly
(properly depending on the power supply quality) regulated. Apparently,
switched power supplies need a proper load to correctly regulate voltage.
You may try something like 1A in the 5V rail. Be sure to use a resistor
which can tolerate 5W (4,7ohm, 9W for example) !
2010/5/13 Sascha Silbe <sascha-ml-ui-sugar-olpc-devel at silbe.org>
> On Thu, May 13, 2010 at 09:24:17AM -0400, John Watlington wrote:
> FWIW, I've also used a ATX power supply to power an XO-1, but stopped
>>> doing so once I discovered why the XO-1.5 would run from it: Being a cheap
>>> model, it regulated only the 5V rail, so the 12V rail dropped down to 9V
>>> with a switched-on XO-1 connected to it. The XO-1 barely coped (the power
>>> light started flickering some time ago, probably due to the power supply
>>> aging and delivering an even lower voltage than before) and the XO-1.5
>>> (without MPPT ECO) didn't like it at all (whining noise, LED off).
>>> Summary: If you're trying to replicate this setup, make sure your PC
>>> power supply regulates the 12V rail (just hook up some load and check the
> Many higher power supplies like AT/ATX power supplies don't
>> work properly when unloaded. I bet if you draw a couple of
>> amps from the +5V supply, you would find that the +12V supply
>> starts working fine.
> In what way is that different from what I wrote? Or are you saying that
> once I draw a certain amount of current from the 5V rail, the 12V one will
> be properly regulated (i.e. keeping the voltage stable at 12V +/- 10%
> regardless of the current draw on the 12V rail)?
> CU Sascha
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