Running 240V Transformer at 120V

[Monty]

I recently purchased a halogen lamp from the UK which has an input
transformer with the following specs:

COMELIT
MOD: TL50U/4-UK MAX 50VA

PRI: 240 V ~ 50 HZ
SEC: 12 V ~ 4.16 A (PRI 240V 1-2)
SEC: 9 V ~ 3.2 A (PRI 240V 1-3)
SEC: 6.5V ~ 2.3 A (PRI 240V 1-4)

The transformer powers a 50W halogen bulb. One 240V power lead goes
into pin 1. The lamp has a four-position switch: apparenlty one
position is off, and the other three positions switch the 240V input
power into pins 2, 3, and 4 on the primary side of the transformer.

I want to use the lamp in the US. Do I need to replace the transformer
altogether? If so, any suggestions on how to find one of matching
specs and size? If I can rewire or otherwise use this transformer,
what are my alternatives? (I assume I could use an external 120v->240v
step up transformer, but that seems likely to be inefficient.)

thanks!

mk

 

[Tim Wescott]

I recently purchased a halogen lamp from the UK which has an input
transformer with the following specs:

COMELIT
MOD: TL50U/4-UK MAX 50VA

PRI: 240 V ~ 50 HZ
SEC: 12 V ~ 4.16 A (PRI 240V 1-2)
SEC: 9 V ~ 3.2 A (PRI 240V 1-3)
SEC: 6.5V ~ 2.3 A (PRI 240V 1-4)

The transformer powers a 50W halogen bulb. One 240V power lead goes
into pin 1. The lamp has a four-position switch: apparenlty one
position is off, and the other three positions switch the 240V input
power into pins 2, 3, and 4 on the primary side of the transformer.

I want to use the lamp in the US. Do I need to replace the transformer
altogether? If so, any suggestions on how to find one of matching
specs and size? If I can rewire or otherwise use this transformer,
what are my alternatives? (I assume I could use an external 120v->240v
step up transformer, but that seems likely to be inefficient.)

thanks!

mk

Unless the transformer has a split primary specifically for the purpose
of running at either 120 or 240 V you would have to rewind the
transformer. This is a fun and challenging task, but you'll spend less
time if you flip burgers until you've earned enough to buy a new lamp at
Home Depot.

 

[Joerg]

Hello Monty,

I want to use the lamp in the US. Do I need to replace the transformer
altogether? If so, any suggestions on how to find one of matching
specs and size? If I can rewire or otherwise use this transformer,
what are my alternatives? (I assume I could use an external 120v->240v
step up transformer, but that seems likely to be inefficient.)

Short answer: Probably yes. No. Transformer.

I brought a couple of Artemide Tizio lamps from Europe that are
excellent for viewing large schematic plots. The big one contains a 55W
automotive halogen bulb. Could have bought new ones here but they are
very expensive (no, Tim, can't buy these at Home Depot).

So I rigged up a transformer to feed them 230V.

Regards, Joerg

 

[Pooh Bear]

Unless the transformer has a split primary specifically for the purpose
of running at either 120 or 240 V you would have to rewind the
transformer. This is a fun and challenging task, but you'll spend less
time if you flip burgers until you've earned enough to buy a new lamp at
Home Depot.

Ah ! The joys of transformer winding.

I seem to doing it regularly these days.

Graham

 

[Monty]

Ah. Mine is a Nemo Italiana Luce, so I am in the same situation. I was
thinking of replacing the transformer that is internal to the lamp, but
no luck yet finding one that has the same taps and the same dimensions.
Probably I am best off with a 240->120V transformer on the power line.
(I assume that I need something rated at 50W or more... right?)

 

[Joerg]

Hello Monty,

Probably I am best off with a 240->120V transformer on the power line.
(I assume that I need something rated at 50W or more... right?)

Depends on the bulb. If it is a 55W like mine I'd go for a transformer
of 100W or more. I needed >1000W because some other stuff is hanging on
it as well. To save weight and space I built a few that took in 125V
which is our local line voltage and put out 100V (Japanese line
voltage). Then I connected the secondary in series with mains and got
225V, just about right for gear from the European mainland. You need two
fuses if you do that.

Be careful with a straight 1:2 step-up. In many places in the US the
line voltage is between 125V and 130V. 260V would be a real stretch for
some European stuff. That can turn capacitors into spacecraft.

Regards, Joerg

 

[Rich Grise]

I recently purchased a halogen lamp from the UK which has an input
transformer with the following specs:

COMELIT
MOD: TL50U/4-UK MAX 50VA

PRI: 240 V ~ 50 HZ
SEC: 12 V ~ 4.16 A (PRI 240V 1-2)
SEC: 9 V ~ 3.2 A (PRI 240V 1-3)
SEC: 6.5V ~ 2.3 A (PRI 240V 1-4)

The transformer powers a 50W halogen bulb. One 240V power lead goes
into pin 1. The lamp has a four-position switch: apparenlty one
position is off, and the other three positions switch the 240V input
power into pins 2, 3, and 4 on the primary side of the transformer.

I want to use the lamp in the US. Do I need to replace the transformer
altogether? If so, any suggestions on how to find one of matching
specs and size? If I can rewire or otherwise use this transformer,
what are my alternatives? (I assume I could use an external 120v->240v
step up transformer, but that seems likely to be inefficient.)

If you can make it impossible for anyone to touch any part of the lamp,
there's a possibility that you could run it right off the 240V in the
normal household supply, like your dryer or stove.

But you have to be _absolutely sure_ that no part of the mains can
EVER touch any part of the lamp that's accessible to human contact.
It's also probably a violation of code and who knows how many safety
regulations, but if you can _guarantee_ that it's 100% isolated, and
double- or triple-insulated, just run it off a 240V outlet.

Probably cheaper and less trouble to get a new lamp, but I've seen
people do stupider things.

All of the usual disclaimers apply here, don't try this at home,
I take no responsibility for any injury, dismemberment, or death,
and so on; I don't even recommend it.

Officially. (wink, wink, nudge, nudge) ;-)

Cheers!
Rich

 

[Joerg]

Hello Rich,

But you have to be _absolutely sure_ that no part of the mains can
EVER touch any part of the lamp that's accessible to human contact.

That is usually a prerequisite in Europe. For example, if the lamp is
sold in Germany their 230V power plugs are not polarized. Neither is
there a clear scheme of which side is hot and which is neutral in a
power outlet. Found that out the hard way as a kid (bzzzt...zing).

Regards, Joerg