Electronic transformer

[mahinda jayasinghe]

I have an electronic transformer to drive 12V halagen lamps.
I checked the output voltage without connecting bulb. I am not getting any volts. Input is 240V ok.

I connected the lamp and it is working ok and read voltage 30v.

If I check output voltage without lamp( open circuit o/P voltage) I get nothing.
It seems to be a faulty one.
What is the theory behind it, how it works. It is Australian made.

Many thanks.

 

[williB]

what scale are you on ? AC ? DC?
i am thinking that if you were on the DC scale you wouldnt get a reading with the open circuit transformer..

 

[yantronic]

Some switch mode PSU do not operate without load.

Since the electronic transformer is probably a switch mode PSU of sorts, try and connect a load resistor across the transformer before tessting.

 

[mahinda jayasinghe]

I checked on both scale (AC and DC). Without load I dont get any reading. With load (I used 12v Halagon lamp, I belive this ia a resistive load), I can read 29V on AC scale.

Why do not I get any reading (On this electronic T/F) at Output ( open circuit voltage).
How electronic T/F works.

 

[Nigel Goodwin]

I checked on both scale (AC and DC). Without load I dont get any reading. With load (I used 12v Halagon lamp, I belive this ia a resistive load), I can read 29V on AC scale.

As it's not a sinewave output, you can't measure it with a simple meter on AC, these are calibrated ONLY for sinewaves, and also ONLY for low frequencies. You would need a true RMS meter to read it, as duscussed elsewhere recently in a thread about buying a new multi-meter.

Why do not I get any reading (On this electronic T/F) at Output ( open circuit voltage).
How electronic T/F works.

As you've already been told, it's very likely the PSU won't run without a load - most switch-mode PSU's don't run properly without a load, and some would self-destruct!.

 

[Sebi]

Most of electronic halogen-lamp supply don't run without recommended minimum load. The output voltage coming direcly from HF transformer, so the output some rectangular AC (50..250kHz) without voltage feedback.

 

[TheOne]

Most of electronic halogen-lamp supply don't run without recommended minimum load. The output voltage coming direcly from HF transformer, so the output some rectangular AC (50..250kHz) without voltage feedback.

Are you sure? The filament will act as a nice antenna and radiate harmonics. I am not sure that it would be allowed in a lot of countries that's strict on EMI levels.

 

[Sebi]

Yes, unfortunately sure. I was just curious and opened a defected device... The transformer have two secondary winding parallel, and go to output. After repair i reconnected the sec. windings in seriel, and work fine with Weller soldering iron and 30W bulb since 5years.

 

[TheOne]

I doubt if those will ever find their way into the US or countries that enforce the CE mark

 

[JimB]

Most of electronic halogen-lamp supply don't run without recommended minimum load. The output voltage coming direcly from HF transformer, so the output some rectangular AC (50..250kHz) without voltage feedback.

Are you sure? The filament will act as a nice antenna and radiate harmonics. I am not sure that it would be allowed in a lot of countries that's strict on EMI levels.

Quite correct!

These things are noted for radiating VERY high levels of broadband noise.
The installation instructions usually specify a maximum length to the cable from the transformer to the lamp, and so squeeze past the European EMC regulations.
But how many electricians installing these things read the words, let alone understand why?

JimB