Generic name for USA style of mains transformer?

[N_Cook]

Well I only see it in USA kit. A toroid but flattened into an elipse shape
in plan view and a coil around each straight section. The curved ends of the
ring are exposed. Laminated core construction so easy coil winding ?

 

[N_Cook]

Well I only see it in USA kit. A toroid but flattened into an elipse shape
in plan view and a coil around each straight section. The curved ends of the
ring are exposed. Laminated core construction so easy coil winding ?

Not sure if you are referring to a 'flat pack' or a 'C' core
transformer. The Flat pack has squared 'U' shaped laminations, so if
you look at the core the lams are stacked [like in the common 'EI'
tranformer with the coil on the centre leg], but the two coils are on
the legs of the'U'.
The C core is more like what you describe with the core curved around
at each end and is made by winding the lamination strip around a
rectangular form, then compressing it on each long side to bond the
lam together, then cutting it in half midway along the 'long' side and
polishing the cut ends. Two coils are wound in the conventional manner
then the core halves slipped in and clamped [we used to use steel band
wrapped around the perifery of the core]. The ends could be epoxied
together, but that introduced a tiny air gap that affects the core
performance. This core design came, originally, from Germany IIRC. I
believe that the ones we were using back in the '60s came from Vacuum-
Schmeltz [sp?]

Neil S.


"image" searching on
"C core " "mains transformer"
didn't show any like the one in front of me
http://www.jacmusic.com/lundahl/images/tube_trafo.jpg
is similar but this one has a core more circular in cross-section , or maybe
circular , under an all over moulded epoxy-like coating .
I will take a pic tomorrow
I can't see how the core could be moulded over the joins and then couils
placed over, no other bracing strips around the core .

 

[Trevor Wilson]

Well I only see it in USA kit. A toroid but flattened into an elipse
shape in plan view and a coil around each straight section. The
curved ends of the ring are exposed. Laminated core construction so
easy coil winding ?

**Sounds like an 'R' core tranny to me. Excellent isolation, but higher loss
than a toroidal.

 

[Trevor Wilson]

Well I only see it in USA kit. A toroid but flattened into an elipse
shape in plan view and a coil around each straight section. The
curved ends of the ring are exposed. Laminated core construction so
easy coil winding ?

**Like these?

http://www.custommag.com/products/r-core.shtml

 

[N_Cook]

**Like these?

http://www.custommag.com/products/r-core.shtml

Yes it would seem R-Core, eg
http://www.dibao-transformer.com/Image/productimage/R-core-transformer-30VA.
png

I wonder how they are made.
Coils formed and laid over the bare cores which are then joined somehow
farely seemlessly and then perhaps 4 sections of quartered pre-moulded epoxy
covers slid over the cores and under the coils and plastic welded into place

 

[Phil Allison]

"N_Kook"

Yes it would seem R-Core,

http://www.dibao-transformer.com/Image/productimage/R-core-transformer-30VA.png

I wonder how they are made.

** An R-core is wound with one continuous strip of steel - tapering at each
end to get a round cross section. The two plastic bobbins are made as halves
and glue together around each straight limb of the core.

There are also gear like teeth on the ends of the bobbins - allowing a
machine to spin them on the core while an operator feeds them with wire.

Then the bobbins and wire ends are secured and an overall insulation wrap
applied.

A steel claming frame is finally attached to allow chassis mounting.

Clever - huh ?


..... Phil

 

[N_Cook]

"N_Kook"

http://www.dibao-transformer.com/Image/productimage/R-core-transformer-30VA.
png

** An R-core is wound with one continuous strip of steel - tapering at each
end to get a round cross section. The two plastic bobbins are made as halves
and glue together around each straight limb of the core.

There are also gear like teeth on the ends of the bobbins - allowing a
machine to spin them on the core while an operator feeds them with wire.

Then the bobbins and wire ends are secured and an overall insulation wrap
applied.

A steel claming frame is finally attached to allow chassis mounting.

Clever - huh ?


.... Phil

Ah! its now so obvious, had me scratching my head.
I never thought of winding the bobbins while on the core, yes clever.
I'd worked out how fully enclosed toroidal transformers with solid cores
were wound, a few months back, even made a sort of m/c for doing it, but
this type had me flumoxed

On a side matter relating perhaps to their efficiency.
The one in front of me gives off various voltages and the associated DCs are
marked on the overlay (no schematic available).
All the DC voltages , amplifier but just quiescent no load, all the actual
DC levels are about 10 percent less than the overlay marked DC. If one of
these C or R type cores is knocked/ abused / thermal stress/vibration and
the closure face opens up muicroscopically, could that cause a 10 percent
drop in secondary voltages?

 

[Phil Allison]

"N_Kook"

Phil Allison

http://www.dibao-transformer.com/Image/productimage/R-core-transformer-30VA.
png

Ah! its now so obvious, had me scratching my head.
I never thought of winding the bobbins while on the core, yes clever.
I'd worked out how fully enclosed toroidal transformers with solid cores
were wound, a few months back, even made a sort of m/c for doing it, but
this type had me flumoxed

On a side matter relating perhaps to their efficiency.
The one in front of me gives off various voltages and the associated DCs
are
marked on the overlay (no schematic available).
All the DC voltages , amplifier but just quiescent no load, all the actual
DC levels are about 10 percent less than the overlay marked DC. If one of
these C or R type cores is knocked/ abused / thermal stress/vibration and
the closure face opens up muicroscopically, could that cause a 10 percent
drop in secondary voltages?

** Nope.

Look elsewhere for the explanation.



..... Phil

 

[Phil Allison]

"N_Kook"

Look elsewhere for the explanation !!!!!!!!!!!!!


Increase of DC saturation characteristic of iron powder over time?

** What " iron powder " ?

Wot an annoying bloody imbecile.




..... Phil