OT: Need P/S specs for Power Sentry USB hub (was OT: Need

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Mon Feb 23 17:54:50 2004

> AFAIK, *almost all* wallwarts were center positive. If the outer ring is
> going to the ground plane, that *should* be the clincher, but... as they
> say about assuming things...

The problem comes what that design of connector (we call it a 'coaxial DC
power connector over here') is used on a device that has internal
batteries too. Theres's a switch contact which breaks when the plug is
inserted, but that connects to the _outer_ contact of the plug. And
conventionally, that switch is connected in the +ve line. Certainly a lot
of devices over here are outer +ve...

When 2.5mm or 3.5mm hack plugs (OK, mini and submini phone plugs to you),
then it's conventional to have tip +ve. And the switch contact on those
sockets is on the tip connection.

A popular wall wart in the UK has a cross-shaped plug with the 4 arms
being a 2.5mm jack, 3.5mm jack, 2.1mm (interal) coaxial power connector
and a 2,5mm coaxial power connector. I've seen them where the tip of the
jack plugs corresponts to the outer of the power connectors. Conversely,
I've seen them where the tip of the jack plugs corresponds to the inner
of the power connectors. The only way to be sure is to check it with a meter!

> The reason for this is supposed to be that if a barrel connector is
> center-negative and is grounded, if the barrel touches any part of the
> circuit that's grounded (which is usually a pretty fair amount) it will
> short out the PS and possibly do bad things to the circuit. The risk is
> _lessened_ when the barrel is negative.

Indeed. There's also a panel mount version of the connector -- I use it
quite a lot -- where the outer is connected to the panel mounting
bush/nut. That had better be at ground potential !

Received on Mon Feb 23 2004 - 17:54:50 GMT

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