LinkSys courts Linux hackers with WRT54GL (LinuxDevices)

LinkSys courts Linux hackers with WRT54GL (LinuxDevices)

Posted Dec 15, 2005 12:45 UTC (Thu) by Duncan (guest, #6647)
In reply to: LinkSys courts Linux hackers with WRT54GL (LinuxDevices) by NRArnot
Parent article: LinkSys courts Linux hackers with WRT54GL (LinuxDevices)

> I've even seen a case where the Mk1 used
> 12V DC and the Mk2 used 7.5V AC, and the
> connector between the power brick and the
> box was the same size for both and not
> labelled.

It's still possible they were interchangeable, particularly if the 7.5
volt was a higher amp rating. Due to the way many DC power adapters work,
the same adapter may provide 12v @ 100mA (perhaps even 16v nearly open
circuit), but if the current rises to 250mA, it'll only provide 7.5v.
This on a 7.5v 250mA rated adapter. It will provide either one, depending
on what the draw is.

Also note that many low-power appliances have a fairly wide voltage
tolerance. They have to, not only due to the above, but because most of
the chips will be designed for the broadest use possible, often including
automotive/marine or battery operation, and those chips are generally the
most critical parts, unless voltage gets so high capacitors begin to pop
and current gets high enough to fry resistors. Nominally 12v automotive
systems can easily run 17 volts or higher on a full battery and little
accessory electrical drain. Nominally 1.5 volt batteries are actually
1.25 volt if rechargable-NiCad (and I believe NiMH versions are similarly
lower than nominal voltage ratings, but don't recall the specific value)
but source a far higher amperage if the resistance is low enough. On a
typical nominally rated 9v unit, 6 cells, then, output will only be 7.5
volts at full charge, even tho it's rated 9.

While 12v to 7.5v is probably one margin to the other, many portable units
will be perfectly happy on a wimpy 12 volt supply rated 100 or 150mA, when
the unit says 9v 200mA, or conversely, perfectly happy on a 9v 500mA rated
supply, when the unit says 12v 150mA. I've run 12v on 7.5v supplies and
the reverse as well, in a pinch, but I don't like to do it for long or
unsupervised, because either the unit or the power supply (depending on
which way one is going) often gets hot.

Thus, it's perfectly possible that the two were entirely compatible, if
the first only shipped with a 12 volt wimpy supply, due to cost, but was
really nominally 9 volt, while the second might have /still/ been
nominally 9 volt, but shipped with a heavier duty 7.5 volt supply that was
now cheaper.

Duncan

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