recycling chargers

[John Watlington]

On May 13, 2010, at 10:18 AM, Sascha Silbe wrote:

> 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 voltage).
> 
>> 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)?

Your latter statement is correct.
There is usually a "main rail" (+5V or +3.3V) which must be loaded
for the "auxiliary rails" (+12V) to be regulated.

Cheers,
wad