# Low Voltage Lighting transformer problem

• posted

Hi

I've installed some 12V halogen lights in some shelves, such that I have to mount the transformer remotely. I used 3m of normal 1.5mm^2 lighting cable to connect the transformer to the lights, having calculated a

300mV drop across the cable (30mV/A/m x 3.3A x 3m)

However in practise I'm losing around 6V in the cable, and have discovered that the transformer output is 125kHz, not 50Hz, explaining the bad attenuation in the cable

So my question is - do all compact dimmable 12V transformers have high frequency outputs?

I don't have space for an old-fashioned 50Hz transformer

Cheers

• posted

You could post this to uk.d-i-y as well. Lots of experts there.

(yes, that's really the name of the group)

• posted

In article , Mike Barnes writes

good plan, ta

• posted

Ben Mack wrote in news:xJ \$ snipped-for-privacy@delirium.watchfront.co.uk:

I suspect that something else is wrong. I don't know what gauge wire corresponds to 1.5mm^2, but if you were expecting 300 mV drop on ordinary lighting wire at 50 Hz, there shouldn't be that much more at 125KHz.

As an experiment, use a short wire to put the "transformer" very close to the lights and see what happens. It could be that the "transformer" can't handle this load or is broken.

If the transformer is OK, then solutions include: Heavier wire. More wires in parallel. Separate wires from the "transformer" to each light. Twist the two wires to each other to lower the inductance. (probably not very effective at this frequency)

Good luck!

• posted

In article , Ian Shef writes

It turned out it was down to frequency - if you're interested there's an interesting thread on uk.d-i-y, same subject as this. Someone gave the maths showing a 6V drop at 125kHz

I've now fitted 50Hz toroids and all working great

So a lesson learned for me - watch out for high frequency transformers!

Cheers

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