Selv

[sparkysteveward]

I've recently installed a SELV transformer (original one was removed by a French electrician 3months ago!). Having connected the 230v supply to the 'pri' end, I haven't got any output voltage (looking for 11.5v DC). I took it back to my supplier & got a replacement but it too is showing no output voltage. Am I missing a trick (this is my first contact with SELV) or have I just managed to get hold of 2 duff transformers?

 

[Jabbajaws]

what are you using to test your voltage? Is your instrument capable of reading SELV, as daft as it sounds...

 

[Darkwood]

If its an electronic transformer like for a LV lamp then it monitors resistance of output and wont supply voltage till conditions for which it was designed are met, if you've got standard wound transformer you said your measuring d.c. output from an a.c. input, if its just a standard wound transformer then youll need a rectifier to convert to dc... you info is vague but hope it helps

 

[Richard Burns]

LV lighting transformers run at high frequency and do not supply an output until connected to a load.
If you supply power to the input and just use a voltmeter across the output the will be no reading.
Easiest way to test them it to wire them up to a light and see if it works! Can also clamp one of the wires whilst on load and measure the current and using P=VI estimate the voltage.

 

[MarkieSparkie]

As others here have hinted LV lighting "transformers" are more strictly electronic converters which contain a "free running" HF oscillator, like most oscillators they require a minimum load before there is enough positive feedback for it to oscillate, connecting a high impedance (most digital and some analogue) meter to the "secondary" or load terminals does not draw sufficient current to initiate oscillation, hence there is no (or mVs) output voltage.

 

[sparkysteveward]

Hi Guys,

Thanks very much for the info. Yes it is an electronic converter. I haven't applied a load as yet but from your replies, I'm sure it'll work. I couldn't believe I'd bought 2 duff converters.

Thanks again