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Topic Title: Garden lights
Topic Summary: 200va transformer
Created On: 21 January 2013 09:26 PM
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 21 January 2013 09:26 PM
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GJH

Posts: 501
Joined: 24 January 2008

I have a customer who wants some garden lights.

He has already got about 8 fittings installed (20w each) and has asked me to have a look at them because they don't work.

He has got a 60va transformer and a 105va transformer. The 60va feeds 2 lights and is ok.

The other 6 are fed from the 105va transformer. I think he has overloaded the 105va as there is no voltage coming out of the secondary side and so I propose to install a 200va transformer.

There are 3 seperate cables out to the lights. What is the max length I can have for each cable? 2 lights on each.
 21 January 2013 09:32 PM
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slittle

Posts: 3485
Joined: 22 November 2007

Are we talking about 12v lamps ?

If so, 20w is about 1.6 Amps @ 12 Volts.

Cable length can be as long as you want. The only issue you'll have is getting a bit of 240mm into the fitting :-)

You could probably cope with loosing a volt down the cable without too much loss of light. Depends really on the size of cable you intend to use.


Stu
 21 January 2013 09:45 PM
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Legh

Posts: 3482
Joined: 17 December 2004

Originally posted by: slittle

Are we talking about 12v lamps ?

If so, 20w is about 1.6 Amps @ 12 Volts.

Cable length can be as long as you want. The only issue you'll have is getting a bit of 240mm into the fitting :-)

You could probably cope with loosing a volt down the cable without too much loss of light. Depends really on the size of cable you intend to use.

Stu


Lol, 240mm2 ? sounds like your designing elv lighting for an airstrip runway.
Good idea for flying in illegal Turkeys

I would have thought 4.0mm2 flexible cable at 25m will give you a VD of approximately 1.0v. I would look at <20m to be on the safe side....

Legh

Legh

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 21 January 2013 09:47 PM
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broadgage

Posts: 1282
Joined: 07 August 2007

You can not, or at least should not, feed 6 lamps each of 20 watts from a 105 VA transformer.

Are these electronic transformers ? if so they are probably not suitable for garden lighting.
The permissable cable length for such transformers is very limited indeed, not just due to resistive voltage drop but also inductive and capacitive effects which are very pronounced due to the high frequency.
Over long cables on the output of an electronic transformer also lead to radio interference.

Unless the cables are improbably short, you will need either a copper/iron transformer or a DC power supply for garden lighting.
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