24V Led Lighting - Cable size confusion

[gunnermanms]

Hi All

I am having 24V Led lights installed in my garden. Its 12m in length drawing power at 16W per M.

The LED comes with 0.5mm of tails which i want to extend.

The distance from the strip to the LED driver is 25m in a single length.

Using online calculators to gauge which sized cable i need, its recommending 10mm or 16mm SWA cable to stay under 3% voltage drop but this seems excessive to me.

For info: My LED Driver is 230V Input, 24V output. Rated up to 350W Supply.

Can anyone advise?

 

[Brother Blue]

Yes that is the kind of cable size you would expect for that.

You will also probably have issues with voltage drop along the length of a single atrip 12m long and fed from one end only,

 

[plugsandsparks]

Put driver close to LEDS

 

[gunnermanms]

Put driver close to LEDS

Unfortunately that isn’t an option.

If I need to use 10/16mm cable then that is fine by me. I just wanted to make sure I haven’t got it wrong and miscalculated

 

[DefyG]

its recommending 10mm or 16mm

There is a massive difference between the two sizes 'IT' (Online Calculator?) cant recommend both. Its got to be one or the other, given that the same installation criteria for the formulae.
I would suggest you get a local electrician to size the cable properly.

 

[Risteard]

Unfortunately that isn’t an option.

Why not? It would be crazy not to if at all feasible.

 

[gunnermanms]

There is a massive difference between the two sizes 'IT' (Online Calculator?) cant recommend both. Its got to be one or the other, given that the same installation criteria for the formulae.
I would suggest you get a local electrician to size the cable properly.

Two sizes as there’s two install locations with varying cable runs. Shorter run has a 10mm recommendation. Longer run has 16mm

 

[DefyG]

Two sizes as there’s two install locations with varying cable runs. Shorter run has a 10mm recommendation. Longer run has 16mm

That wasn't clear (ie. 2 lengths) from your original posting.

 

[James]

Can you not use a constant current led string and driver?
That would remove the volt drop calculation and just require the cable to be specified for the max current of the driver.

 

[Brother Blue]

Can you not use a constant current led string and driver?
That would remove the volt drop calculation and just require the cable to be specified for the max current of the driver.

You would still need to ensure that the combined forward voltage of the LEDs plus the volt drop in the cable is less than the maximum voltage output of the driver.

 

[James]

You would still need to ensure that the combined forward voltage of the LEDs plus the volt drop in the cable is less than the maximum voltage output of the driver.

Agreed but, the calculator the op is using is trying to achieve less than 3% volt drop at 24v or about 0.75v
Even if the driver had a max of 32v that will give over 10 x the original volt drop allowance .

It would be worth speaking to the lighting supplier and specifying a system that works with sensible cable sizes.
It is somewhat ridiculous to be using a 16mm cable for a load less than 200w

 

[Brother Blue]

Even if the driver had a max of 32v that will give over 10 x the original volt drop allowance .

We can't know that without knowing the forward voltage of the LEDs. We only know that they are configured to work on a 24V constant voltage supply at the moment.


To change to a constant current supply they would need to be re-configured into a series circuit which would drastically change the required input voltage.

It is somewhat ridiculous to be using a 16mm cable for a load less than 200w

Yes, it's completely daft, and with a little lateral thinking I'm sure it could be easily solved.

 

[sunray]

Well we know it's 24V at 192W = 8A

What's difficult about a CC 8A source capable of 33V using 1mm² cable?



Apart from the 70W loss.


Splitting the run in half and running it in series on 48V will bring it down to 4mm²

 

[Brother Blue]

Well we know it's 24V at 192W = 8A

What's difficult about a CC 8A source capable of 33V using 1mm² cable?

24V 192W when configured for a constant voltage supply.
The load would need to be reconfigured in order to operate it on a constant current supply.
To operate reliably on a constant current supply all of the individual LEDs would need to be connected in series, The voltage required from the cc supply would be the sum total of the forward voltages of those LEDs.

If you connected an 8A cc supply to the load as it is then it would most likely destroy the LEDs sooner or later.

 

[sunray]

24V 192W when configured for a constant voltage supply.
The load would need to be reconfigured in order to operate it on a constant current supply.
To operate reliably on a constant current supply all of the individual LEDs would need to be connected in series, The voltage required from the cc supply would be the sum total of the forward voltages of those LEDs.

If you connected an 8A cc supply to the load as it is then it would most likely destroy the LEDs sooner or later.

Not until they start failing, then yes.

 

[Brother Blue]

Not until they start failing, then yes.

They will fail fairly quickly as the cc supply is supplying too much current to the LEDs nearest to the supply. Once one has failed the current through the others will increase and the process of staging the LEDs will speed up.

Current from the cc supply will not divide equally between the parallel connected LEDs, the resistance of the conductors connecting them will affect the current distribution and lead to excess current flowing through the first set of LEDs, destroying them.

 

[mainline]

The most efficient way to run high power LEDs is using a series circuit with a constant current LED driver. Running a series circuit helps to provide the same amount of current to each LED. This means each LED in the circuit will be the same brightness and will not allow a single LED to hog more current than another.

 

[w0z]

I thought these were led strings so the leds are effectively in parallel?
Can you provide a link to the leds?
Are you sure it's 16W/metre that sounds very high?
Is your supply constant voltage or constant current?
You'll need to either split the length into 2 or power from both ends.
If you split into 2 you could use 2 lower rated supplies (I would, more availability and cheaper)
I don't understand why you would need SWA for 24v when much cheaper low voltage cable will suffice?

 

[EddieB]

If it were me I'd get that driver moved closer to the strip, if running a 16mm swa is not an issue there must be a compelling reason why the driver can't be relocated

 

[w0z]

Unless I've misunderstood wouldn't it make more sense from a £ point of view to use muti stranded in a conduit and put the power supply indoors ? And I doubt the lighting strips would look any different at 4 or 5% less volts anyway (say up to 1 ohm for the cable).