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- Wiring transformers
June 24, 2006, 6:48 am
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i was wondering if wiring a transformer for an amplifier power supply
(such as jaycar MM-2007 for the kit KC5038) is dangerous.
does it involve exposed high voltage parts, or is it simply a matter of
screwing the primary wires into a mains plug?
i've done some electronics in university and made some audio effects
before - but of course i'm extremely wary of meddling with mains
Re: Wiring transformers
** Sure is - if you do not do the job safely.
** The primary has short leads that must NOT be fitted directly into a plug.
The MM-2007 transformer MUST be put into a sturdy enclosure ( plastic or
metal) and attached to an *approved* mains lead or IEC type inlet ( ie
Jaycar PP-4005). Connecting the short leads to the mains lead can be done
with screw terminal strip like the Jaycar HM3194.
If you need to fit a power switch, best use an all plastic (ie rocker)
Any *metal shaft* switch used in the AC power MUST have its body connected
to AC supply ground - usually by mounting it to a metal box that is
connected to supply ground. That metal box must be connected to the AC
ground wire with a ring terminal fastened with a nut, bolt and star or
The MM-2007 is fitted with a primary thermal fuse and has the primary and
secondary on separate halves of a plastic bobbin. This makes it inherently
Re: Wiring transformers
You didn't get much advice did you? I got a nice litle four page leaflet in
the latest Dick Smith kit I picked up (a power supply board oddly enough)
entitled "A Safety Guide to Mains Wiring and Handling for the Project and
Kit Builder". Email me ( rover109 at bigpond dot net dot au) a postal
address offline and I'll drop it in the mail for you.
But the answer to your question about whether mains wiring a psu kit is
dangerous is No, not if you can make a neat soldered joint and if you do the
You should put your project in a box, either metal or plastic to eliminate
any chance of contact with 240v when it is finished.
If a metal box, it is even more important to use three core mains cord and
connect the green wire to the box and the transformer frame. Often easiest
to trap a solder lug under one of the transformer mounting nuts. Use a star
washer for effective contact.
Heat shrink tubing is your friend. Get some from same place you buy the
project bits and use it to insulate the 240v soldered connections to
transformer lugs, on\off switch lugs etc. Shrink it with a hair dryer, an
electric paint stripper gun or at a pinch with a butane lighter flame.
Use a rubber grommet where mains cord passes thru case and anchor cord
inside case with a cable clamp to relieve any strain on the connections.
Basically, it is YOU who is eliminating the possibility of contacting 240v
and you do it with commonsense construction practices.
We all start somewhere, in my case in the laundry at the age of 13 while my
oblivious parents were in the lounge watching the Dean Martin show. I
suppose I could have been smoking dope or making out with another 13 year
old. You have the advantage of being an adult with more disposable income
for decent parts so I say go for it.
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