15VAC 5Amp 75 VA Power Supply

Go to a swimming pool shop and get an old salt-water chlorinator.
They're usually about 12V 8A and will have the rectifier you need.
Add a filter capacitor and the voltage will jump into the range
you need. Should cost nothing - these things get thrown away all
the time.

Build one?
Do jaycar/etc sell a transformer that has those specs?

I use the JayCar toroids

One MT-2113 - 160VA 18VAC 8Amps - to power the DCC controller (Lenz
LZV100)
One MT-2132 - 300VA 18VAC 16Amps - to power each DCC booster (CVP
10Amp)

"Robert Small"





**  Make certain to have a reliable circuit breaker in series with the
secondary and suitable slow blow fuse in series with the primary.  Also, put
the tranny in a sturdy metal or plastic case to protect it from accidental
damage.

Toroidal transformers ( as sold by Jaycar etc)  do  ** NOT **  meet basic
safety standards for extra low voltage applications like model trains or
even halogen lighting.

Better use an ELCB or  "safety switch " on the AC power outlet too.




........   Phil

Care to elaborate? Is it something to do with the isolation not being
good enough? risk of insulation breakdown? or something entirely different?
What about using computer power supplies for things like model trains?

"Graham Fountain"



** Toroidals ( as sold by Jaycar etc ) only have " basic insulation "   -
ie just good enough to allow them to function as  transformers for a
reasonable life span and if  *never* accidentally abused. The insulation
used to separate primary and secondary windings is a soft polyester wrap
that melts * instantly * if you apply a soldering iron to it,  for example.
Not very impressive.

Low voltage transformers intended for use with portable electronic
appliances, model trains and 12 volt lighting systems etc are required by
Australian and international  LAW  to meet a much higher standards of safety
and reliability.

The actual requirements are much the same as for Double Insulation or Class
2  -  so that even if accidentally or deliberately overloaded to any
possible degree, the transformer will NOT burn up its own insulation or
otherwise become an electrocution risk to users.

Toroidal types are rarely seen in such applications, since it is near
impossible to make them comply with ALL the test requirements and yet still
have a size or cost advantage over other types.




......   Phil

We had in a circuit board that was exposed to the sun and it shorted.

Thanks Phil. I haven't had much to do with toroidals, so was curious. If
I'm reading you correctly, it is quite possible to make a compliant
toroidal, but to do so would be as expensive and bulky as a traditional
laminated transformer so there is no real point.

Probably the closest thing to toroidal transformer characteristics
which will allow insulation to SELV standards is an R-Core
transformer. They are not readily available though.
http://www.custommag.com/products/r-core.shtml

"Ross Herbert"
" Phil  Allison "





**  R- Cores are certainly good performers ( there is one inside the DSE
Q1803 CRO ) and well capable of being made to Class 2 requirements.  But  SO
is the once popular but now sadly neglected C-Core type.

C- Cores  ( C is for Cut )  are made by first winding a strip core similar
to a toroidal, but with two straight sides ( like a race track). Then the
core is cut precisely into two halves with a ( diamond ? ) saw and the ends
ground to a smooth matching surface to minimise any air gap.

The primary and secondary windings are formed on bobbins,  just as with the
R-Core, and the two C-Core halves are fitted together through the bobbin or
bobbins and then glued and clamped with steel bands.

C-Cores were made in Australia by firms like Ferguson and many others. For a
long time, DSE sold a single bobbin C-Core for the Playmaster Twin 40
amplifier, the M 0152.

Then the plastic wrap toroidal came along with great fanfare and ruined
everything.




........   Phil

On Fri, 20 Oct 2006 13:23:09 +1000, "Phil Allison"



Yep.. the good old C-Core. I had a whole swag of C-Cores left over in
'93 which I had to give away to a transformer manufacturer because we
couldn't use them since we were being closed down. They were the
choice core for Rolie Baldock (RIP) for his power transformer designs.
They were made in Australia by AEM from 1961 till just recently.
http://www.aemcores.com.au/CCores.htm

These days C-Cores and transformers using them are available for
purchase mainly from the UK/Europe. Most C-Cores these days are made
in China and possibly some European countries.

Nippon Core make a good range of cores of all types including C-Cores.
http://www.nipponcore.com/BAK%EF%BC%8D2006-6-17/pr.htm

 **  Groper Alert  !





 ** Then try Altronics.

They have a  M 2175L   for $35  rated at 15 volts and 8 amps.

It is NOT  a toroidal.

It has an inbuilt thermal fuse.




.........   Phil