Low Voltage Lighting transformer problem

[Ben Mack]

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
--
Ben Mack
Watchfront Electronics - Bespoke R&D - http://www.watchfront.co.uk/
Watchfront Internet - ADSL, Colo - http://www.watchfront.net/
Are you bricking it? - Firewalls - http://www.firebrick.co.uk/

[Mike Barnes]

In comp.home.automation, Ben Mack wrote:
>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

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

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

--
Mike Barnes

[Ben Mack]

In article <bB0UtmvRf2TEFww$@g52lk5g23lkgk3lk345g.invalid>, Mike Barnes
<april2006@mikebarnes.fsnet.co.uk> writes
>You could post this to uk.d-i-y as well. Lots of experts there.

good plan, ta
--
Ben Mack
Watchfront Electronics - Bespoke R&D - http://www.watchfront.co.uk/
Watchfront Internet - ADSL, Colo - http://www.watchfront.net/
Are you bricking it? - Firewalls - http://www.firebrick.co.uk/

[Ian Shef]

Ben Mack <nospam@ben.watchfront.co.uk> wrote in news:xJ
$M8oCS3zTEFwlj@delirium.watchfront.co.uk:

> 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

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!

--
Ian Shef 805/F6 * These are my personal opinions
Raytheon Company * and not those of my employer.
PO Box 11337 *
Tucson, AZ 85734-1337 *

[Ben Mack]

In article <Xns97B17B1D27294vaj4088ianshef@138.126.254.210>, Ian Shef
<invalid@avoiding.spam> writes
>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.

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
--
Ben Mack
Watchfront Electronics - Bespoke R&D - http://www.watchfront.co.uk/
Watchfront Internet - ADSL, Colo - http://www.watchfront.net/
Are you bricking it? - Firewalls - http://www.firebrick.co.uk/