Is there any reason you cannot convert a 110v power supply to run off 240v
by using any split primary toroid mounted inside the unit concerned?

i.e. make safe all secondaries and take the 110v from half the series
connected 0 ----110v --0----110v primary?




Cheers,


Gareth.

Forgot to include "i.e. using the toroid as an autotransformer"

Følgende er skrevet af Gareth Magennis:
Is there any reason you cannot convert a 110v power supply to run off 240v by
using any split primary toroid mounted inside the unit concerned?

i.e. make safe all secondaries and take the 110v from half the series
connected 0 ----110v --0----110v primary?

Not /any/. Of cause it need to be powerful enough.
And it needs to fit :-)

Is it possible to change the mains transformer from 110 to 240v?

--
https://www.paradiss.dk
Ting til konen eller kæresten.
Eller begge.

"Leif Neland" wrote in message ...

Følgende er skrevet af Gareth Magennis:
Is there any reason you cannot convert a 110v power supply to run off 240v
by using any split primary toroid mounted inside the unit concerned?

i.e. make safe all secondaries and take the 110v from half the series
connected 0 ----110v --0----110v primary?

Not /any/. Of cause it need to be powerful enough.
And it needs to fit :-)

Is it possible to change the mains transformer from 110 to 240v?

--
https://www.paradiss.dk
Ting til konen eller kæresten.
Eller begge.



There is enough room inside the unit to mount a toroid of sufficient
capacity.

Which is why I asked the question.


Is there any reason you can't just put in a toroid as an autotransformer?
This is pretty much a cheap no brainer if there are no issues with that.



Gareth.

Sounds like you want to run a US/Can tuner or someting with a UK/EU amp. Is that what it is ?

If so, the current drain is so low it is fine.

Now if you wanted to run a US/Can amp off the split primary of a tuner or preamp or something, that would be a problem.

Of course you have to treat this like mains wiring.

wrote in news:36e2101e-bd5e-4084-a83c-
:

Of course you have to treat this like mains wiring.


.... and check that the creepage distances, clearances, insulation etc. of
the 120V PSU's isolation barrier are adequate for 240V operation.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & 32K emails -- NUL

"Ian Malcolm" wrote in message
...

wrote in news:36e2101e-bd5e-4084-a83c-
:

Of course you have to treat this like mains wiring.


.... and check that the creepage distances, clearances, insulation etc. of
the 120V PSU's isolation barrier are adequate for 240V operation.





The 120v PSU is receiving 120v from the autotransformer.

The difference is that this autotransformer has unused secondaries and is
not designed to be used as an autotransformer.

The question is whether this is an issue or not.


Gareth.

Gareth Magennis wrote:

Is there any reason you cannot convert a 110v power supply to run off 240v
by using any split primary toroid mounted inside the unit concerned?

i.e. make safe all secondaries and take the 110v from half the series
connected 0 ----110v --0----110v primary?


** The idea is quite useable and the available power output is the same as the nominal rating of the tranny. Current in the load comes equally from each half winding with this connection - so there is no imbalance.

But there are safety issues with using auto-transformers to power 120V appliances from 240V - particularly with old US and Japanese equipment that does not employ a safety earth conductor.

If the AC supply has live/neutral reversed or simply no connection to neutral - then the 120V appliance winds up with 240V on one or both AC connections.

Many such appliances, particularly items of audio gear, have low value capacitors ( ie 0.047uF, 400V ) linked from one side of the incoming AC to chassis and this cap will definitely not stand up to 240V AC for long - hence the popular title "death cap".

This cap *MUST* be removed and a 3 wire AC lead fitted in order to make the old item safe to use with a stepdown auto-tranny.


..... Phil

On Sun, 12 Apr 2015 17:39:56 -0700, Phil Allison wrote:

** The idea is quite useable and the available power output is the same
as the nominal rating of the tranny. Current in the load comes equally
from each half winding with this connection - so there is no imbalance.

I had thought that would not be the case. Can you explain the current
flows at the output centre tap, please? (I am happy with an assumption of
a perfect transformer.)

Mike.

Mike wrote:

Phil Allison wrote:

** The idea is quite useable and the available power output is the same
as the nominal rating of the tranny. Current in the load comes equally
from each half winding with this connection - so there is no imbalance.


I had thought that would not be the case.

** Really - you have some odd thoughts.


Can you explain the current
flows at the output centre tap, please? (I am happy with an assumption of
a perfect transformer.)


** That is a near impossible task without the benefit of diagrams.

Suffice to say that equal currents flow in opposite directions in each half of the series connected windings combining in the load to become double.

FYI: In a normally connected transformer, primary and secondary currents flow in the opposite sense to each other - from the AC supply *into* the primary and *out of* the secondary to the load.

Draw it and see.


..... Phil

On Sunday, April 12, 2015 at 9:58:58 AM UTC-7, Gareth Magennis wrote:
Is there any reason you cannot convert a 110v power supply to run off 240v
by using any split primary toroid mounted inside the unit concerned?

i.e. make safe all secondaries and take the 110v from half the series
connected 0 ----110v --0----110v primary?

In addition to 'all secondaries', you'd want to avoid electrifying the (now
unused) 110V mains plug and its cord, of course.

Gareth Magennis wrote:


... and check that the creepage distances, clearances, insulation etc. of
the 120V PSU's isolation barrier are adequate for 240V operation.


The 120v PSU is receiving 120v from the autotransformer.


** That claim is only generally true for isolation step-down transformers.

With an auto-transformer, it DEPENDS on getting everything right all the time.

The supply neutral must remain connected to the neutral side of the auto tranny AND the neutral side of the appliance's AC connection.

A simple loose connection on the neutral pin of the plug means that 240V AC appears on each AC conductor in the appliance. Sure, the appliance does not work but that is no barrier to insulation or AC side capacitor failures.

I would never suggest using an auto tranny step-down with any appliance that did NOT have a 3 wire lead with safety ground connection.



.... Phil

"Phil Allison" wrote in message
...

Gareth Magennis wrote:


... and check that the creepage distances, clearances, insulation etc. of
the 120V PSU's isolation barrier are adequate for 240V operation.


The 120v PSU is receiving 120v from the autotransformer.


** That claim is only generally true for isolation step-down transformers.

With an auto-transformer, it DEPENDS on getting everything right all the
time.

The supply neutral must remain connected to the neutral side of the auto
tranny AND the neutral side of the appliance's AC connection.

A simple loose connection on the neutral pin of the plug means that 240V AC
appears on each AC conductor in the appliance. Sure, the appliance does not
work but that is no barrier to insulation or AC side capacitor failures.

I would never suggest using an auto tranny step-down with any appliance that
did NOT have a 3 wire lead with safety ground connection.



.... Phil



Thanks to all.

My use for this method would be convert low power audio equipment, mostly
designed for both 110v and 240v use, and has a grounded IEC inlet. e.g.
keyboards, rack mount equipment etc.
Sometimes the 110v versions that find their way to the UK are not
convertible without changing the mains transformer or entire SMPS.

Having to cart an autotransformer around to gigs is inconvenient, and unless
you change the IEC socket to something else you risk connecting the 110v
unit to 240v and blowing it up.
So it makes more sense to me to incorporate an autotransformer inside the
unit itself, if there is room to safely do so.



Cheers,


Gareth.

Gareth Magennis wrote:

"Phil Allison" wrote in message

The 120v PSU is receiving 120v from the autotransformer.


** That claim is only generally true for isolation step-down transformers.

With an auto-transformer, it DEPENDS on getting everything right all the
time.

The supply neutral must remain connected to the neutral side of the auto
tranny AND the neutral side of the appliance's AC connection.

A simple loose connection on the neutral pin of the plug means that 240V AC
appears on each AC conductor in the appliance. Sure, the appliance does not
work but that is no barrier to insulation or AC side capacitor failures.

I would never suggest using an auto tranny step-down with any appliance that
did NOT have a 3 wire lead with safety ground connection.


My use for this method would be convert low power audio equipment, mostly
designed for both 110v and 240v use, and has a grounded IEC inlet. e.g.
keyboards, rack mount equipment etc.
Sometimes the 110v versions that find their way to the UK are not
convertible without changing the mains transformer or entire SMPS.

Having to cart an autotransformer around to gigs is inconvenient, and unless
you change the IEC socket to something else you risk connecting the 110v
unit to 240v and blowing it up.
So it makes more sense to me to incorporate an autotransformer inside the
unit itself, if there is room to safely do so.


** Or you could just fit a 230V:110 toriodal step down tranny like this one from Farnell:

http://uk.farnell.com/multicomp/mcta...65?ost=9532765

90mm dia and only weighs 1kg.



..... Phil

"90mm dia and only weighs 1kg. "

Sounds like it might even fit in the case and be done with it.

Then of course you halve the fuse rating, it goes right where the cord comes in, not AFTER what you add to the unit. In fact it should go after the switch as well and go off when you shut it off. Why keep bothering electrons needlessly ? So you are merely interrupting the wires going to the original power transformer primary. That way, you also don't have to **** with the casps across the switches and any of that. If it has those buck wound noise filters you might have a slight problem but I doubt it. gonna change 1 kV caps to 2 kV ? No reason to I think. If anyone does, say so, I am all ears. but t here sahouldn't be more than 1 kV on a 220 line either.

And then you put a sticker on it to that effect, the lower fuse rating included.

Actually, half might be too low because of inefficiency and cause nuisances.. If it was three amps use a two. If it is less than two amps, just don't really worry about it. If you must, put another fuse of the original value after the output of your transformer. But anyting less than an amp is already so safe you don't need to go farther. Ground faults are a different subject, but you don't seem to have that problem, right ?

Oh, and you could permanently attach the cord and then supply 110 V for other US components. That might be more than you wan to do but it's a thought.

"Phil Allison" wrote in message
...

Gareth Magennis wrote:

"Phil Allison" wrote in message

The 120v PSU is receiving 120v from the autotransformer.


** That claim is only generally true for isolation step-down transformers.

With an auto-transformer, it DEPENDS on getting everything right all the
time.

The supply neutral must remain connected to the neutral side of the auto
tranny AND the neutral side of the appliance's AC connection.

A simple loose connection on the neutral pin of the plug means that 240V
AC
appears on each AC conductor in the appliance. Sure, the appliance does
not
work but that is no barrier to insulation or AC side capacitor failures.

I would never suggest using an auto tranny step-down with any appliance
that
did NOT have a 3 wire lead with safety ground connection.


My use for this method would be convert low power audio equipment, mostly
designed for both 110v and 240v use, and has a grounded IEC inlet. e.g.
keyboards, rack mount equipment etc.
Sometimes the 110v versions that find their way to the UK are not
convertible without changing the mains transformer or entire SMPS.

Having to cart an autotransformer around to gigs is inconvenient, and
unless
you change the IEC socket to something else you risk connecting the 110v
unit to 240v and blowing it up.
So it makes more sense to me to incorporate an autotransformer inside the
unit itself, if there is room to safely do so.


** Or you could just fit a 230V:110 toriodal step down tranny like this one
from Farnell:

http://uk.farnell.com/multicomp/mcta...65?ost=9532765

90mm dia and only weighs 1kg.



..... Phil




Oops, didn't know they existed.



Cheers,


Gareth.

Ha, should have read the post properly and clicked the link.

I assumed that was an autotransformer, but yes, the 2 x 55v secondaries
would do the job and fit in a keyboard.



Gareth.

Phil Allison wrote:


Can you explain the current
flows at the output centre tap, please? (I am happy with an assumption of
a perfect transformer.)


** That is a near impossible task without the benefit of diagrams.

Suffice to say that equal currents flow in opposite directions in each half of the series connected windings combining in the load to become double.

FYI: In a normally connected transformer, primary and secondary currents flow in the opposite sense to each other - from the AC supply *into* the primary and *out of* the secondary to the load.



** My friend Rod Elliot (of ESP fame) has just added a section to one of his articles on transformers to cover the strange goings on with
"auto-transformers".

So we have suitable diagram to look at.

http://sound.westhost.com/xfmr2.htm#s19

Please note the safety warnings in the article, mains voltage auto-transformers are hazardous.


.... Phil