Ben Mack wrote:
Well thanks all for your most informative replies, most impressed by the
knowledge on this group, particularly Andy's maths!

The problem was due to frequency (see below) and is now sorted :-)

In article , Andy Wade
writes
The problem here is caused by the inductance of the cable, which I
figure will be roughly 0.9 uH per metre. For a 3 m run that's a
reactance of about 2 ohms at 125 kHz, so with the 3 A load current
mentioned the voltage drop will be about 6 V - more or less as observed :-)

Excellent :-)

The only solutions are to get the electronic 'transformer' nearer to the
luminaires, or use a real 50 Hz (iron-cored) transformer.

We found some 50Hz toroids from Maplins that work a treat over the same
wiring, proving the wiring was OK and frequency was the issue. So well
done Andy - your maths was spot on

We had some fun and games finding space for the bigger transformers, but
now all sorted

Regarding the idea of a terminating capacitor, I will have a play with
that when I get a mo, sounds an interesting possibility

Oh, and the reason for 12V lamps - we needed some very shallow
downlighters to fit into milled recesses in the underside of shelves,
and couldn't find any 230V lamps slim enough. And halogens for
aesthetics

In article , Dave Plowman (News)
writes
TLC have a cable calculator for LV lamps. Dunno if it will help with your
problem.

http://www.tlc-direct.co.uk/Technica...ltageDrop.html

Mmmm, seems they made the same mistake I did - they reckon 3m of 1mm^2
T&E will drop 0.4V driving 12V 40W

In article , fred writes
As and aside, I'm a bit taken aback that this is an issue at all as this can't
be an uncommon situation and this is the first word of it I've ever seen on
the group, there's always a first time I suppose.

So am I, I was most surprised!

I guess 125kHz is pretty high, I checked some other transformers that
ran around 30 - 50kHz so less of a problem, though still noticeable. And
sparkies normally seem to fit a transformer by each light fitting,
certainly for ceiling downlighters which I guess is the most common app

Well you live and learn, many thanks all!

Cheers


other shallow lights:
screwfix.com numbers

round:
38701
87529
6000hr bulbs: 21975

strip:
22239
98307
68183
95961
23953
17886
15608

and if youre vision is really going, 10383


NT