18 Jan
2009
18 Jan
'09
1:22 p.m.
Most of the electrolytic problems I've seen
associated with age have
been with the ones inside of sealed "wall warts" where the heat from
the transformer eventually cooks the juices out of them. Short of
cracking open a fused-together housing, the only viable alternative
is to replace the whole thing.
A lot of wall-warts over here are held together with screws, often with
'security' heads (why???). At least they can be opened and repaired,
although whether it's worth doing is debatable.
How I hate those things! No standard on the connectors--a wart
So do I, but for a rather different reason. I think they're unsafe. The
normal UK mains plug contains a cartridge fuse (the plug is rated to
carry 13A, the circuit it's plugged into is normally protected by a 30A
fuse/breaker, the cartridge fuse in the plug is normally 3A, 5A or 13A).
These wall-warts often contain no fuses at all, even though they plug
straight into the 13A-rated socket outlet, so in the event of a fault,
the plug/socket and internal wiring of the wall-wart could be carrying up
to 30A _continuously_ (the circuit fuse/reaker would not operate under
those conditions).
One common type of 'universal' wall-wart over here has an output cable
ending in a cross-shaped plug, the arms of the cross being a 2.5mm jack
plug, a 3.5mm jack plug, a 2.1mm coaxial power plug and a 2.5mm version
of that. Also coming out of the moulded coss are 2 short cables, one
ending in a 1.3mm coaxial power plug (the old 'Walkman' type) and the
other in a press-stud clip similar to that found on PP3 type 9V batteries
(the indea being you can connect that in place of the battery in a radio
or whatever to powerit from the wall-wart).
The problem is that the press-stud contacts can easily short to the outer
parts of one of the other connecotrs which can put a dead short across
the output of the wall-wart. With no protecitive devices in the circuit,
the transformer gets very hot and bothered. I've had them get hot enough
to melt the plastic case, and after I unplugged it, I noticed that the
transformer primary was still continuous, so presumably the thing would
have carried on getting even hotter.
putting out 20vac will often have the same plug as one
putting out
3vdc, they often don't have the same brand on them as the device
Soma 'universal' wall-warts over here have an output lead ending in a
moulded 2 pin socket. You get an assortment of little adapters witha 2
pin plug on one end to fit that socket and a jack plug, coaxial power
plug, or whatever on the other side to fit the equipment you want to
power. The adapters fit either way round in the socket so as to be ale to
have 'tip +ve' or 'tip -ve'.
Anyway, I found you could buy a pack of all the adapters and also a cale
with the socuket moulded on one end and, IIRC, bare wires the other. I
simply fitted 4mm plugs on that end. Used with my DC bench supply or a
multi-tapped transformer that I have, it'll replace just about any wall-wart.
Not a solution if you don't know what the requirements of the unit you
want to run are (and for some odd reason the wall-warts are often marked
with their output, but the equipment is rarely marked with its power
requirements). but useful if you can't find the wall-wart but know what's
requried.
they're powering, take up 2 or more slots on a
power strip and can't
be reliably operated from a power strip mounted under a table top,
lousy wire leads and hidden fuses. The nadir of 20th century
technological innovation...
I still can't see anything wrong with a good-quality mains transformer in
an earthed metal box with primary and secoondary side fuses. That's what
I normally uild to replace wall-warts.
-tony