Transformer question (only slightly OT)
ajp166 at bellatlantic.net
Mon Sep 4 20:26:08 CDT 2006
>Subject: Re: Transformer question (only slightly OT)
> From: ard at p850ug1.demon.co.uk (Tony Duell)
> Date: Tue, 05 Sep 2006 00:07:10 +0100 (BST)
> To: cctalk at classiccmp.org
>As a result, I feel wall-warts are dangerous in the UK. They do not
>contain na internal fuse, so could in theory draw nearly 30A from the
>mains before the circuit fuse failed. The mains transformer primaty of
>the wall-wart is supposed to burn out in a safe way, my experience
>suggests this is not always the case.
Wall warts, least here in USA must be fused internally or have a thermal
interupter (usually the blow open). I've forcably opened a number of
warts to replace protective devices.
For many projects I use a standard 12V regulated DC wart and if higher
voltages are required a simple multivibrator or switching regulator driving
a suitable hunk of ferrite does nicely. It allows me to work inside
without scary high potentials floating around and also solves the problem
of "the right transformer". If warrented I bury the HV system in a
seperate enclosure on the chassis and bypass the leads so the switching
noise is hidden and in the case of tube (valve) designs keeps it looking
"correct" while saving the annoying and sometimes messy job of winding
a custom mains transformer.
>I _never_ use wall-wards plugged straiht into the wall. Putting them on a
>fuesed extension lead is somwhat safer. Altough personally I prefer a
>decent transformer with fuses in both priamry and secondary circuits.
Not a bad thing to do even here. Though I do it to assure all the warts
are powered OFF when not in use not so much for safety but wasted power
>> Another thing to have on your shop outlets is GFI protection. It could
>> save your life.
>It can also be a right royal pain when a main filter has enough
>unbalanced current to trip it. Ad it won't protect you if you're
>relatively well insulated from ground but manage to connect yourself
>between live and neutral or equivalent.
Still it's some assistance for some cases. Perfection is a goal.
>I use a GFI (RCCD, whatever it's called this week) in placees where there
>could be dangerous leakage (sockets for outdoor appliances, in the
>darkroom (a mixture of electrics and water, after all :-)), and so on.
>But I don't have one on my workbence, nor do I want one.
I have a mix of outlets on the bench some GFI protected some not. When
I'm testing and working on line powered gear I used the GFI protected.
Items that are known and in use I use the direct. Never hurts to have
a good isolation transformer too. A recent addition to the bench power
is a BIG RED BUTTON for those times when an unambigious off NOW is desired.
Power safety is a good thing.
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