Correct 12v transformer for mix of LED spotlights and LED striplights

[Naylor87]

Hi all,

I'm having some trouble working out which 12v transformer I should buy, or if there's even one available for what I want to do, and wondered if anyone was able to shed some light.

I want to install 4 LED spotlights, and 3-4 metres worth of LED striplight in my back yard. The total wattage for everything will be 44 Watts (5w for each spotlight lamp, and 24w for the LED striplight). My question is related to a mixture of LED spotlights and LED striplights on the same transformer. I keep seeing that LED striplights required a 'special' LED transformer/driver, as they usually require the transformer to provide DC directly to the strip light. However, most of the 12v transformers I've seen provide AC, which is then converted to DC by the LED lamps. I also see a lot with the online retailers of LED striplights that they advise to purchase a specific transformer with the strip light, but they don't mention why and if the transformer can be used for other lights too.

So my is there a transformer available that I can wire both LED spotlights and LED striplights in to? Or do most of the transformers out there already allow this, and I'm just being overly cautious? It would be great if I can run all lights off a single transformer, as it'll be a bit inconvenient (although not impossible) to have two separate ones. I can also provide info on what lights I'm looking at buying, I've not actually committed to buying them yet until I know what transformer I need.

Any advice is greatly appreciated, this is my first post so apologies if I'm missing something really obvious.

 

[EFLImpudence]

Use 240V light fittings.

 

[Taylortwocities]

Whssign

• Taylortwocities
• 16 Jul 2016

What he said

 

[Naylor87]

Thanks for the feedback. Is your suggestion for 240v due to my idea being unfeasible, or just a preference for 240v installations?

I was hoping to use a 12v setup for safety, power efficiency and installation flexibility reasons. I know 240v has it's advantages, but my preference at the moment is 12v - unless my idea is just not feasible of course!

Cheers.

 

[Taylortwocities]

You have 230v all over your house, is this some special location that needs extra protection that draws you to a 12v ELV option?

Power efficiency is about the same for both. The power is really related to the light output. 5 watts is 5 watts. With LED there is not much loss due to heat.

If you go the separate driver route you may find that you'll need to buy two. You might run into compatability issues as the requirments for the LED strips may be different to the spotlights.

The 230v LED items do have drivers, its just that the electronics is usually buried in each lamp or fitting. Advantage is that if the driver goes pop you've only lost one lamp.
If you go for the 230>12v driver option then if/when the driver fails, you in de dark!

 

[SFK]

Naylor,
For your Garden/Yard I do not see an issue for powering both basic (ie white 2 cable light strips, not coloured 4 cable light strips) 12V LED strips (like these: https://www.amazon.co.uk/s/ref=nb_sb_noss?url=search-alias=aps&field-keywords=white+waterpoof+strip&rh=i:aps,k:white+waterpoof+strip) and 12V LED Spots (like these https://www.amazon.co.uk/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=12V+LED+garden+light&rh=i:aps,k:12V+LED+garden+light) off a 12V DC LED driver if it provides enough Wattage.

Have a look at this that I wrote earlier today and see if it helps:
//www.diynot.com/diy/threads/decking-lighting-advice.466740/
sfk

 

[JohnW2]

You have 230v all over your house, is this some special location that needs extra protection that draws you to a 12v ELV option?

I suppose that depends on whether you regard a 'back yard' as being "a special location which needs extra protection"

Kind Regards, John

 

[Naylor87]

Thanks for the feedback all. I'm going to continue down the 12v route, it does appear that normal LED lamps tend to be able to handle AC or DC, whereas the LED strips usually only handle DC, so that pushes me towards a DC transformer.

Also thanks SFK for the link to the other post you commented on, useful stuff which has helped

 

[securespark]

you in de dark!

Street talk!

 

[winston1]

Thanks for the feedback all. I'm going to continue down the 12v route, it does appear that normal LED lamps tend to be able to handle AC or DC, whereas the LED strips usually only handle DC, so that pushes me towards a DC transformer.

There is no such thing as a DC transformer as by definition transformers provide AC without changing frequency. You even said in your first post, "most of the 12v transformers I've seen provide AC". So yes, as you say, most 12 v LED lamps can run on AC or DC whereas the strips are DC only.
You require a 12v DC power supply as stated in prievous posts.

 

[ericmark]

There are different ways to supply extra low voltage.

1) AC unregulated except by mains voltage at 50 Hz.

2) AC regulated at high frequency.

3) DC voltage regulated.

4) DC current regulated.

So to get these we have:

1) Wire wound transformer, these give a simple relationship to mains voltage, so if mains is at 230 Vac then output will be 12 Vac, but should the mains go up or down so will the output. With the old tungsten lamps they gave an advantage of thicker filament so the lamps lasted longer, but were not as good as the so called “electronic transformer” however today with LED lamps these work very well. There is no reason why you can’t add a rectifier and get both AC and DC from these units, although the DC would have a mains ripple.

2) The so called electronic transformer was used for many reasons, main one was it regulated the output so the quartz of the lamp was maintained at exactly the correct temperature, so it reflected the tungsten of the filament, if too cold the quartz would go black and the filament would rupture, but also the filament would rupture if too hot. Also they were cheaper to produce, because the frequency was so high the transformer inside became much smaller, however they also had some draw backs, because they were high frequency the output cables needed to be short, and there was often a minimum output. Although you may be able to rectify the output to DC this could result in illegal radio transmission and the limits to cable lengths mean these are not suitable.

3) The DC voltage regulated supply may well work with both types of lamp, however many of the MR16 compatible LED lamps are marked as 50 Hz so using DC could over load the rectifier inside the lamp, but I feel this is unlikely. So it likely could be used. With DC supplies the quality of regulation and smoothing effects the price and size, you do get some which are good enough for LED’s but likely not good enough for other DC equipment I would guess on no smoothing, these are often incorrectly labelled as drivers. Likely these will works for you.

4) The LED is a current dependent device, they are often packaged with components which make the voltage dependent instead, but the raw LED is current dependent, the device with controls the current is called a “driver” and you can get an array of LED’s all in series which can be powered by the driver at a set current 320 mA seems to be a common figure, the voltage is often 3 ~ 50 volt the 50 volt limit means they are classed as extra low voltage, although for DC it could go to 75 volt. Using a driver the LED output is typically 100 lumen per watt, but converting to voltage dependent and using a regulated voltage the lumen per watt will drop to around 60, in some cases as low as 25 lumen per watt. Although the driver may power your ribbon of LED’s it will not work the spot lamps.

The spot lamps which are designed for DC are more expensive, typical voltage is 10 ~ 36 volt and these often are 100 lumen per watt, they have a pulse width modulated driver built in which is why they are both efficient and have a large voltage range, the range does mean your not really worried about volt drop. Using DC spot lights and ribbon lights on the same supply is possible.

However 230 volt lighting is cheaper and a lot less hassle.

The big question is why do you want the ribbon lights and spots on the same power supply, if you really want ELV then why not two power supplies? You can have 12 Vdc and 12 Vac with one three core cable, although I would keep them separate.

I would call a fluorescent tube replacement a strip light, I assume you mean the ribbon cable?

So answer is you can use a 12 Vdc supply for both ribbon LED lamps and spot lamps, but the spot lamps are more expensive when designed for DC, you may get away with cheap AC spots on DC, but only way to find out is to try it. With a garden you do need to consider volt drop with extra low voltage so getting lamps rated 10 ~ 36 volts may be a good option.

 

[ericmark]

There is no such thing as a DC transformer as by definition transformers provide AC without changing frequency. You even said in your first post, "most of the 12v transformers I've seen provide AC". So yes, as you say, most 12 v LED lamps can run on AC or DC whereas the strips are DC only.
You require a 12v DC power supply as stated in prievous posts.

I would agree we normally consider a transformer to be a wire wound device with no electronics, however even when I started some 50 odd years ago we had rotary devices which would convert 230 volt AC to 12 volt DC or reverse 12 volt DC to 230 volt AC. Sometimes called rotary converters, but also called rotary transformers. They were wire wound and had no electronics, they were like small motors with no output shaft, some connected to a gear box allowing them to be manually turned to work a radio which at that time needed both high and low voltage for the valves. These were replaced with vibrators and static transformers as time went on. So even back in the war years we had DC transformers. You have been told many times the definition of a transformer is to change something to something else, and be it 230 to 12 volt or AC to DC, and robot to car, they are all by definition transformers, even if it is not normally considered to be a transformer in the electrical trade.

 

[winston1]

We are talking about transformers in the electrical trade however and they are defined by the IEC as AC devices that do not change the frequency. So sorry there cannot be a DC transformer.

 

[winston1]

Deleted.

 

[Naylor87]

Ericmark thanks a lot, exactly the information I was looking for!

I'm only just getting used to the technical terms, but glad I've at least avoided saying bulbs instead of lamps

The big question is why do you want the ribbon lights and spots on the same power supply, if you really want ELV then why not two power supplies?

The only real reason is that I already have an outdoor 240v single socket, and using a single power supply (which I intend to put inside an enclosure) will take up less space in my fairly tiny back yard. I'm not totally against using two power supplies, but wanted to understand how feasible using one was first.

However 230 volt lighting is cheaper and a lot less hassle.

Correct me if I'm wrong, but using 230v outdoors requires stricter rules when it comes to how and where it can be laid? Part of my cable runs will be laid on concrete, albeit within conduit and built in behind a bench so completely out of reach. My assumption was that having 12v running above ground in this way would probably be ok, whereas having 230v running above ground in this way probably wasn't a good idea, and probably wouldn't get past building regs. Also, the armoured cable I hear is quite difficult to work when it comes to connecting it to junction boxes etc. I may be wrong though so open to feedback on that!

So, if using a DC supply is possible for both light type (FYI yes it's LED ribbon not strip light), then I'm thinking something like this would be suitable - http://www.exteriorlightsuk.co.uk/product/LED-Driver-60w-12v-IP65

That particular transformer is recommended when purchasing these ribbon lights - http://www.exteriorlightsuk.co.uk/p...ip65-24w-cabinet-white-plastic-warm-white-led

For the spotlights then, I'd probably be looking at something like this, which looks like it supports AC & DC (according to the specs) - https://www.amazon.co.uk/EnergyBrite-GU5-3-White-Energy-Saving/dp/B009ZSWRPY

With 44w total, the 60w power supply seems sensible. I intend to use the whole LED ribbon.

Cheers