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Old April 26th 06, 03:33 PM posted to uk.d-i-y
Ben Mack
 
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Default Low Voltage Lighting transformer problem

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/

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Old April 26th 06, 04:12 PM posted to uk.d-i-y
fred
 
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Default Low Voltage Lighting transformer problem

In article , Ben Mack
writes
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

Look for another cause to the problem, 100pF/m for the T/E over 3m still
gives 4k impedance at 125kHz so unlikely to be causing your 6V problem.
Look at minimum load, maximum load, wiring faults & faulty transformer.
--
fred
Plusnet - I hope you like vanilla
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Old April 26th 06, 05:26 PM posted to uk.d-i-y
Dave Plowman (News)
 
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Default Low Voltage Lighting transformer problem

In article ,
Ben Mack wrote:
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


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

--
*You sound reasonable......time to up my medication

Dave Plowman London SW
To e-mail, change noise into sound.
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Old April 26th 06, 05:46 PM posted to uk.d-i-y
Ian Stirling
 
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Default Low Voltage Lighting transformer problem

fred wrote:
In article , Ben Mack
writes
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

Look for another cause to the problem, 100pF/m for the T/E over 3m still
gives 4k impedance at 125kHz so unlikely to be causing your 6V problem.
Look at minimum load, maximum load, wiring faults & faulty transformer.


http://en.wikipedia.com/wiki/skin%20effect
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Old April 26th 06, 06:07 PM posted to uk.d-i-y
[email protected]
 
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Default Low Voltage Lighting transformer problem

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


it doesnt at all. Look for a bad connection or too many bulb watts for
the transformer. Bear in mind multimeters may read the 12v wrong if its
not sine wave.


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


tronic TFs are high frequency, toroidals are 50Hz.


NT



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Old April 26th 06, 07:20 PM posted to uk.d-i-y
fred
 
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Default Low Voltage Lighting transformer problem

In article , Ian
Stirling writes
fred wrote:
In article , Ben Mack
writes
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

Look for another cause to the problem, 100pF/m for the T/E over 3m still
gives 4k impedance at 125kHz so unlikely to be causing your 6V problem.
Look at minimum load, maximum load, wiring faults & faulty transformer.


http://en.wikipedia.com/wiki/skin%20effect


Only 5% increase in impedance on 1.5mm2 @ 125k
--
fred
Plusnet - I hope you like vanilla
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Old April 26th 06, 07:34 PM posted to uk.d-i-y
Andy Wade
 
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Default Low Voltage Lighting transformer problem

fred wrote:

Only 5% increase in impedance on 1.5mm2 @ 125k


Only 5% increase in *resistance* due to skin effect, perhaps, but a huge
increase in *impedance* due to the inductive reactance...

--
Andy


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