12v lights on roof terrace

[ChickenBhuna]

Hi there

I am planning to install a couple of 12v LED spots on my roof terrace. The plan is to install a 12V transformer inside my property to an existing (and currently unused) FCU in an upstairs cupboard.

I will then run standard 2 core 12v cable from the transformer through a window frame and over a short section of roof onto the roof terrace. Here it will connect into an IP66 junction box, which will then connect to a switch and a couple of outdoor 12v spots. I would also like to install a 12v USB charging point (I found something intended for marine applications, so suitable for outdoor).

My proposed wiring diagram is below.

I've done my voltage drop calcs and I'm confident 1.5mm cable will suffice. The total wattage will be well below 30w.

Any comments on this as an approach? Anything in particular I need to be concerned about?

Given all the outdoor runs will be 12v, I'm working on the assumption I don't need any special armouring or conduit.

The transformer I'm looking at is here:

https://www.amazon.co.uk/gp/product/B083PRGPG7/ref=ppx_yo_dt_b_asin_title_o00_s08?ie=UTF8&psc=1

Any comments or thoughts welcome.

CB

 

[ericmark]

It seems reasonable, I would fuse and switch supply to the power supply as switch mode power supplies don't last for ever, and you will need to ensure lamps OK for use with DC many are marked 50 Hz, USB power supplies I have found with 12 volt don't give 2.1A so you have to be careful selecting.

The 12 volt DC LED is often rated 10 - 30 volt with a switch mode driver built in, so volt drop should not be a problem, but 12 volt DC is often not really 12 volt, my 12 volt radio is rated at 13.8 volt with max 14.2 volt and will not give full output at 12 volt, they are designed for cars, caravans and boats which use lead acid batteries that need over 12 volt to charge, so may be better to use vehicle voltages so you can use stuff designed for vehicles.

 

[ChickenBhuna]

Thanks Ericmark. The transformer will be connect to the existing FCU which is fused (3A) and switched. Do I need anything more than this?

Noted on the lamps.

I have managed to find a 12v USB point which will do 2.1A:

https://www.amazon.co.uk/gp/product/B07SL9FB5Y/ref=ppx_yo_dt_b_asin_title_o00_s09?ie=UTF8&psc=1

Tested it with the power supply and seems to work great.

 

[bernardgreen]

but 12 volt DC is often not really 12 volt,

in the worst case Switched Mode Power Supplies ( SMPS ) the 12 volts DC can be a series of variable voltage high frequency pulses that average out to be 12 volts. Pulses as high as 36 volts has been seen in one SMPS. A low price is not an indication of a worst case item and a high price is not an indication of a good quality item

The high frequency pulses can upset the operation of LED drivers ( those built into the 12 volt lamps ) leading to unstable operation of the lamp.

 

[winston1]

It does say on it LED driver so I’d hope it was OK.

 

[SFK]

Chicken,
A bit of a similar situation and what I did was as follows:

1) My 12V Cable run was 22meters, so I was very conscious of Voltage drop with this site showing significant voltage drop for me when using 0.75mm2 cable. But I found that 1.5mm2 cable was difficult to get into the small connections of my 12V Power Supply/Driver, so I went with 0.75mm2.
Over the 22m for me the LEDs worked perfectly okay and I am happy with the brightness, but it should be noted that I cannot tell if they are significantly dimmer as I never made a comparison. And you might notice this more.

I used 0.75mm2 Black 'rubber' or 'pond' cable as more durable and less noticeable on fence (where I attached it). For carrying the 12Volts I did not use the Earth lead, I used Brown as the +12V and Blue as 0Volts.
[To utilize all the copper in the cable You could join the Earth and blue lead and use as 0Volts, as this would reduce returning resistance and reduce voltage drop.]
http://www.screwfix.com/search?search=Tough+Flexible+Cable
https://www.toolstation.com/pitacs-3-core-flex-rubber-cable-3183trs/p80794

2) Joining 12V Cable together or to lights I used these:
https://www.ebay.co.uk/sch/i.html?_...ne+Protection+Sleeve+Connectors+IP66&_sacat=0

3) Switches
To control the lights outside I used outdoor (240V) switches with the 12V cable going in and out using cable compression glads.
https://www.screwfix.com/c/electrical-lighting/outdoor-switches/cat3360010
http://www.screwfix.com/p/tower-male-comp-gland-black-20mm-pack-of-2/80851

4) For the 12V USB supplies I used (like you) 12V USB designed for boats and cars, placed inside a waterproof enclosure box:
https://www.ebay.co.uk/sch/i.html?_...0&LH_TitleDesc=0&_osacat=0&_odkw=12V+boat+car
https://www.screwfix.com/c/electrical-lighting/weatherproof-switches-sockets/cat830538

SFK

 

[ChickenBhuna]

Thanks for sharing SFK - a very similar situation!

 

[SFK]

Pleasure.
Note that I use these 3W spots as low power, cheap, directonally bright, waterproof. But might not be suitable as quite directional
https://www.amazon.co.uk/LemonBest®-Outdoor-Garden-Spike-Spotlight/dp/B01IQY6OSI/ref=sr_1_2?dchild=1&keywords=12v+3W+spot+lights+outdoor&qid=1589282640&sr=8-2

Others here:
https://www.amazon.co.uk/s?k=12v+spot+lights+outdoor&ref=nb_sb_noss

SFK