Cabling LED Application

[Russell Seddon]

I apologise for what must seem an elementary question to most of you:

I have need to power a series of LED lamps (in total, up to 60). I am trying to understand if I must run a 220v AC circuit from which each lamp connects its own driver, or if I can use 2 or more ‘big’ drivers and connect each lamp to a DC circuit.

Each lamp comes with the following specification, printed on the box:

10 watt
12 v
50/60 hz
20 Ma

I have successfully sized 220v circuits before by applying the simple V x A = Watts equation and then calculating my maximum wattage load. But if I try this approach with my lamps at 12v 10w each I seem to need a cable the size of a tree-trunk. I am obviously misunderstanding something fundamental about DC/LED applications.

I can see availability for ‘30 amp’ 12v drivers, these take as input 220v 350watt 50/60 hz at 1.6amps, and as output 12v (+/- 0.5) 25a 300w (why a ‘30 amp’ driver outputs 25 amps is a mystery to me).

But would I be right to suppose that one of these units would power up to 30 (to be safe, 25) of my 10W lamps, if I connected them in parallel? And if that is correct, what kind of cable would I need? Would not a 25 amp cable be overly-substantial for a sting of LEDs; and why does the box say that each unit is only 20 Ma?

Any help or advice on this would be gratefully received.

Russell.

 

[Russell Seddon]

Okay, thank you all, I am very appreciative. On balance I think that I need to absorb the cost and inconvenience of providing each lamp with its own 10w driver, attached to a parallel-wired 220v circuit. I will operate them on two switches, one for each side of the barn. The eaves are designed such that I can attach each lamp, driver and junction box to a small plate that will remain out of sight.

If I have any more questions I will post here: this is a most helpful forum.

All the best

Russell

 

[grantr37]

.

 

[grantr37]

These LED lamps will have no additional circuitry inside apart from a fusible resistor and a diode, these are AC ones which are swappable in place of the halogen bulbs/lamps, you can get a whole led system with drivers quite cheaply these days which will light up a wooden barn ceiling quite well and can be hidden on top of the stone work.

I imagine you will be able to find a setup that will work well otherwise you may need a power supply unit for every 2 fittings

What you would probably want to do as well is to split up the lights into several groups independently switched because there could be a very high inrush current on switch on which may cause a driver or switch to overload. This may also mean that you might need additional (or more powerful) drivers to keep within the limits of the drivers.
If you want to have a small number of drivers then it is generally best to distribute the 230V (in smaller cables) as far as possible and then radiate out from the driver to keep the 12V cables as short as possible.
Along the eaves of a long room is not usually an easy place to position drivers in an inobvious way.
If the lights were split into four groups then you should be able manage the cable size reasonably, inrush current would be dependent on the light itself, but PTC resistors may help limit this if you have a space for a hot component.

A good idea in some applications but PTC (positive temperature coefficient ) resistors are usually just for temporary limiting and also tend to run at upwards of 80c temperature