Help! Seems I´ve fried yet another transformer

[Planapo]

One of my cold light sources is a version for the American market of a 'made in Germany/EU' product (branded Leica, manufactured by Schott).
It came with a no name transformer to use it with our national grid (230 V, 50 Hz). The transformer is a device of its own and has a socket to insert the light source's American-style plug.
The light source works with a 150 W halogen bulb and, according to its label, takes up a max. power of 200 W. The transformer is labelled to be used with up to 200 W.

To be on the safe side I´ve set the light only to level 4 (max. is 6). Recognizing a slight smell, I thought well, the devices are new and smell a bit when warming up. But the smell got stronger and before I could reach the transformer to switch it off, I was already sitting in complete darkness (it was night and when shooting I have the room lights switched off).
Since then the transformer is dead, but its fuse is intact.
Well, I thought maybe the transformer was falsely assembled and got another one of the same model as a replacement. But, darn, the same thing happened again!
Meanwhile, I´ve found out that the transformer´s fuse will only melt in case of a short circuit, and not if the transformer is overloaded.

Now, with my knowledge of electrostatics and electrodynamics being rather theoretical and pure than practical and applied I hope people here aboard who read this and have better knowledge of electronics than me can help me with my questions:
Is it possible that the electronics of the high-quality light source, maybe due to their stabilizing abilities, cause an overload of the transformer (labelled for max. 200 W) albeit I use the light source (labelled 200 W) only on level 4 (out of 6 and hence I assumed P < 200 W) or damage the transformer in another way?

Or is it because it´s probably a Chinese junk transformer not really strong enough to cope with the 200 W Power that it is labelled for? (And presumably the CE mark on it is a fake too.)
What transformer should I get to use my 'American' cold light source safely with the German/European grid?

I know that your replies will be helpful as always and thank you in advance very much.

--Betty

[Harold Gough]

Goods should be suitable for the purpose for which they are sold.

You should take it up with your retailer.

[rjlittlefield]

Betty,

Check the frequency rating of the light source. If it says only "60 Hz" (and not for example "50-60 Hz"), then your problem may be due to increased power consumption caused by the wrong frequency. I once fried several power supplies for a small electronic device by using supplies rated for 110-120V 60 Hz (US standard) on transformed German power at 110-120V 50 Hz. In that case the mains transformers were so huge they were not bothered, but if your transformer is already on the edge, it might be pushed over. Buying a larger transformer might work, or it might just move the failure to the light source, making your problem even worse. (My failed supplies would sometimes run for days too warm but apparently OK, only to fail at some awkward moment.)

If your light source is 60 Hz only, the most practical solution probably is to sell it and buy one rated for 50 Hz. There do exist frequency converters of various designs, but they are generally expensive and would be pointless clutter in your workspace.

On the other hand, if the light source is rated for 50-60 Hz, then I don't know what the problem is and I will eagerly await answers from other people.

--Rik

[Planapo]

Thanks Harold and Rik,

Yes, Harold I´ve emailed twice to the retailer, but until now have got no answer.

Rik,
on the Schott light source the label reads:
"120 V AC 60 Hz 200W
100 V AC 50/60 Hz 200W"

and on the transformer it reads:
"step-down converter
fuse protection

input: 220 V/240 VAC 200 W 50 Hz
output: 110/120 VAC 60 Hz

for electric products up to 200 Watts"

--Betty

[rjlittlefield]

Betty, this is a tough one.

I'm suspicious the label on the transformer is wrong. It's not so easy to input 50 Hz and output 60 Hz. Mere coils of wire on a magnetic core won't do the job. On a no-name device, I'm inclined to think this claim is a labeling error. If you still had a working transformer, I would suggest to borrow a meter and measure it, but I guess that's not possible at this time.

Anyway, quite possibly the transformer is putting out 50 Hz.

But then if it's really putting out 110-120V at 50 Hz, it's also over spec for the light source, which essentially says 100-120V at 60 Hz but only 100V at 50 Hz. (100V at 50-60 Hz is the Japanese power standard; they run 50 Hz in eastern Japan, 60 Hz in western Japan [ref].)

If you can prove the transformer labeling is wrong, then you have good claim to get your money back on those at least.

That leaves you with the problem of getting a transformer that really does put out 100V at 50 Hz, so as to be strictly what the light source wants. It seems like such things should be available, since that's what would be required for Japanese standard equipment in Germany.

--Rik

[puzzledpaul]

A possible alternative (if having difficulty getting a suitable transformer) would be to consider getting a variable transformer (variac).

This is a non-solid state device that'd let you set whatever voltage you wanted in the range 0 > 230v ac ... and (if you have access to a meter) set the supply voltage whilst actually supplying current / under load conditions.

pp

[Harold Gough]

This may be no different from what has been suggested.

In the early 1970s I had access to a thyristor. If you look that up on Google you will find all kinds of circuits. What I had was about the same size and appearance as a combined clock/timer and plug for a domestic appliance.

With the thyristor, you interposed it between the device and the mains. Turning a large dial by hand permitted continuous control of power from zero to full. It was used for an "electric bunsen burner", a mini electric fire in a staliess streel funnel. Thus, the heat could be very finely controlled.

Harold

[rjlittlefield]

For controlling a heating coil, thyristor and Variac are roughly equivalent, but for driving another power supply, they can be wildly different.

Thyristors and other small lightweight dimmers are switching devices; they work by either delivering the full instantaneous mains voltage to the controlled device, or none at all. The Variac is essentially a tapped transformer; it delivers a full continuous cycle of power at some fraction of the mains voltage.

I would be fairly comfortable using a Variac to provide reduced voltage to the separate power supply of a dimmable light source. But I would be very nervous about trying to feed the output of a switching dimmer into another power supply that was not rated for full mains voltage.

--Rik

[Planapo]

As a similar problem was partly addressed in a recent thread, I was reminded of my own troubles back then, and thought I should post the happy ending of my transformer odyssey:

An electrical engineering technician, whom I had consulted, explained to me that, although the Schott light source is labelled as drawing 200 W, a transformer that can handle much more power is needed due to some higher electric oscillations that would occur when running the light source.

I now use a voltage transformer that is made for up to 500 W, switchable between step up and step down, so it could also be used for running European devices on the U.S. grid, and so far it seems to do the job nicely, except for the humming sound it makes, but on the other hand that sound reminds me to pull the plug when my work is finished.

The transformer I use is the model "THG-500W" from this supplier:
http://www.nipponamerica.com/catalogue/jpg_NA-306.htm

--Betty