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How do I install the 12V equivalent of a radial/lighting circuit?

  • I am about to renovate a small 40m2 apartment.
  • I do not want to touch the existing 240VAC cabling at all.
  • I am looking to have approximately 20-30 small LED lights of varying sizes throughout the apartment. Eg. there will be some RGBW strip on the ceiling down to some small (1 or 2 LED) accent lights in cupboards.
  • I really don't want to have to install 20-30 LED drivers
  • as far as possible, I want each LED (or group in some cases) to be individually switchable, and ideally dimmable.

The mental picture I have is a large 12V PSU with its output running through 20-30 MOSFETs and controlled by an Arduino. I will then run 12V pair to each of the light positions.

In practice I'd probably have 2-3 PSUs rather than one, but the architecture (central PSU, 12V radial) is what is important. There is space in the consumer unit for an additional module so I'd put my 12V circuit on its own RCBO.

As a principle, is this the right way to go?

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  • \$\begingroup\$ Doesn't sound great, but doesn't sound intrinsically terrible either. Even at low voltages, high amperages can cause overheating of wires and so on.. plus depending on the current draw vs wire thickness you might have significant voltage drop which might or might not matter (i.e. could shift color for RGBW stuff), so a lot of small issues that are implementation dependent. Overall kinda hard to give a specific answer. \$\endgroup\$ – Wesley Lee Feb 23 at 21:53
  • \$\begingroup\$ Thx @WesleyLee I was planning to be generous with the wiring gauge and if the runs get too long, that's when I'd split into a second PSU/Arduino. But the apartment is small enough that the maximum cable run would still be only 5-6m. I'll do a precise voltage drop calculation and swap in a 13V PSU if necessary. Although there are a lot of lights, the idea is that they will rarely be all on, and generally, the more lights that are on, the dimmer (via PWM) each one will be set. My intention is to keep the existing 240VAC lighting installed for the odd occasion where I need maximum illumination. \$\endgroup\$ – pinoyyid Feb 23 at 22:20
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    \$\begingroup\$ I think this question is off-topic. It deals with the use of electronics. It should be moved to DIY.SE. \$\endgroup\$ – Ariser Feb 27 at 10:03
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    \$\begingroup\$ @ariser if we reduce all system designs to "use" a significant portion of questions would be off topic here. \$\endgroup\$ – Passerby Feb 28 at 10:20
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    \$\begingroup\$ @ariser a question being useful to only one user has not been a close reason in probably a decade. Stack exchange welcomes all questions even ones that only helps one person, repository of knowledge, yada yada. \$\endgroup\$ – Passerby Feb 28 at 10:33
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You just described something like rail lighting system used in museum and such… they did it with halogen burners, but it applies to LED lamps too. They solved the power drop simply using bars as conductors and also hanging the lamps mechanically.

So it seems a fine thing if you are using an adequate wire cross section (adequate as in, depends on the distance). It is actually easy to predict the loss (it's just a resistor, you can find the wiring tables online)

One thing, however: some power supplies have a maximum length of cable supported on the output (for regulation reason, it's complex), just be sure to check it can handle your wiring. As for the group dimming/switching just do it in the obvious way, start with a 12V backbone/star/ring (depending on the placement) and then tap out the branches.

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Get a few 5m LEDSTRIPs with remote controls , stick it up and call it a day's work for $25 or get creative and buy a box full. You can easily reach an outlet.

They use IR remotes, so you have to aim and are practically cheap now. But get the white CCT you like and RGB for fun and W/m you need. Blocking direct light with indirect light is the trick to pleasant lighting for luminaire design.

enter image description here

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Let's start with your ideas concerning voltage.

12 V suck. Really.

Let's do some simple math. Assume you want to illuminate the whole area with at least 150 lx. A rough calculation gives the need for 6000 lm for basic brightness. In fact you will want to spend additional power on a lot of spots and you'll loose much light depending on the remittance of furniture, floor and carpets. You don't write anything about the number of rooms. Every wall makes it more difficult. My basic guess is, you will need 200 W at least to supply everything for full illumination.

Cabling and supply will have to carry 15 A or more to the lights. While in a 230V installation 15 A are a usual load for 1.5 mm² cables, in a 12V cabling it is a problem. In a 230 V installation a voltage drop of let's say 5 V is acceptable in terms of efficience and functionality. You will loose some percent of your power in the wiring and all appliances will work as expected. 5 V drop in a 12 V environment will make your lights stop working and efficiency abysmal.

If you really want to go for a SELV-supply installation, go for 24V. Cabling will be feasible and there's a vast number of lights and control gear out there for that voltage level. In fact 24V is defined as the "professional" voltage level in voltage controlled LED lighting and 12V is the "amateur" voltage level.

Now for installation in general

You will have to control your lights somehow. To adress this you will have to either use the features your already existing installation has or to add some functionality on top of that. If you refuse to use the switches already present, you will need either extensive cabling or wireless controls. I'm not a big supporter of all this wireless stuff but it may work if you carefully select your components.

A central PSU fostering hundreds of watts may be much more expensive than carefully selected individual control gear. On top if you exceed certain amperage on the output of your PSU you will have to provide circuit breakers for 12 V DC for the SELV circuit depending on regional codes. And circuit breakers for DC are ridiculously expensive.

If you want to dim and control your lights individually, keep in mind, that you still will have to supply individual control gears for single lights or local groups of lights regardles of the bus you're going to use. If you compare prices for integrated dimmable control gears with 230V input and dimmers for 12V, you will notice that it won't save you any money to put the voltage level conversion together into one device, as the number of electronic devices will stay the same.

If you want to add your own wiring to your home, take care of some details

  • if you install additional wirings in existing piping take care not to exceed the maximum number of wires. You will have to consult an electrician.
  • When using buses like DMX which aren't suited for building installation take care your ECGs use isolators to prevent "sum up of leakage currents".
  • When using buses like DALI be sure not to mix it with SELV-circuits inside a common cable. DALI has only basic insulation, it is allowed to route it together with 230V but not with SELV.

Update on 12V problems

I just want to go into some more detail, why 12V systems are problematic and inferiour to higher voltage SELV solutions. LED lights operating on 12V will contain some circuitry to ensure a fairly constant current over single LEDs or groups of them. There are two groups of lights available for 12V. Strip lights and retrofits for halogen systems. When searching the market you will find few other types.

In strip lights a small group of LEDs will operate independently on 12V to enable cutting the strip at convenient lengths. So there must be a current regulator for only few low power LEDs. As one can imagine that can only be a linear regulator to keep a reasonable pricing. A linear regulator is not necessary a bad choice for LED circuits. For 12V it is only possible to put 3 or 4 LEDs in series. For most white LEDs 4 LEDs are too much in terms of forward voltage. The linear regulator won't have enough headroom to regulate. So the 3 LED will typically reach a forward voltage of 9V something. The regulator has to waste the remaining 3 V plus minus the tolerance of the supply. That's around 25%. Due to run length of the strip and the supply cable the tolerances on the voltage can build up significantly.

The retrofits in turn have to deal with 12AC. They sometimes have some sort of switching regulator, but that is rare. They waste some energy in a rectifier, need a reasonable capacitor and have a linear regulator again. The capacitor typically is an electrolyte one, which doesn't like heat. Unfortunately a LED retrofit for 12V AC systems is prone to heat up strongly, as they don't have good thermal connection to housing and only feeble means of convection cooling. Lifetime is limited by the capacitor not the LED.

If you compare that to higher voltages, most of these problems are reduced drastically.

  • Absolute voltage drop over cabling and strip length will be smaller for the same output power.
  • Voltage drop relative to supply voltage will reduce by second order.
  • Considering an equal power drop for a linear regulator (let's stay with 3V headroom for this estimate), the regulator's loss will only be 12.5% of total power consumption.
  • As a smaller tolerance of supply voltage can be expected, the system can be designed to be even more energy efficient. This is done by selecting appropriate forward voltage binnings of the LEDs.
  • For higher voltages there are only dedicated DC supplies, so there is no further need to deal with rectifying and the need for filtering flicker.
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  • \$\begingroup\$ Thanks for the thoughts. Some questions if I may please. "Cabling will have to carry 15 A or more" - why? A typical single light will be 15W, with the maximum around 30W. I reckon that's 2-3A. The most light I need will be a very long (10m) LED strip, and I will probably run that at 24V. The rest are much smaller. Perhaps I didn't explain my architecture well, but I anticipate 3-5 cables to each room, each carrying a maximum of 20W. So I will have a lot of cables, but each relatively light. \$\endgroup\$ – pinoyyid Feb 28 at 20:04
  • \$\begingroup\$ "you will have to provide circuit breakers for 12 V DC " - I am planning to put the PSUs on 240VAC RCBOs, and then fuse each individual radial using simple blade fuses. Is this not OK? I take the point about 24V, so will change to that if I can find appropriate PSUs. My question is more about the viability of the architecture as a whole \$\endgroup\$ – pinoyyid Feb 28 at 20:04
  • \$\begingroup\$ Blade fuses are ok IMHO, as they are well suited for DC. The 15 A were a summary calculation. If you distribute it between different branches you can select thinner wires, but the issue with the relatively high voltage drop is still present. Just do a calculation for such a branch. \$\endgroup\$ – Ariser Mar 1 at 10:07
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Perhaps you should reconsider your idea.

  • Most LED lamps will come with their own driver that is 230VAC (or 110 depending on your region).

  • LEDs are current-driven and not voltage-driven, which means that if you have a 12VDC circuit, you will still need to have a driver for each lamp, defeating the purpose. The only case where a driver is not required is if you use LEDs that are current limited by a resistor, but in this case, the efficiency is low and defeats the purpose of LED.

  • Most white LED lightings are not 12VDC but rather operate around 30 to 60V, for efficiency reasons as many LEDs are put in strings.

This means, with a 12VDC circuit, most of the commercial lighting LED lamps won't work, you will have little choice of LED lighting that would work for 12VDC, besides the ones that are retrofitted to replace the old halogen, the choice will be limited and efficiency likely lower (More Amps for the same light output, P=R*I^2).

  • If your main supply dies, you are also out of all lighting until you get a new one, which can be very annoying if you need to order it.

  • It won't work with light regulators (the adjustment of intensity) while good drivers support it.

  • You would need to wire your house with some pretty thick cable, at 12V, if you have 15 lamps using 1A each (8W lamps), that would be 14-gauge wire. You probably can't use the neutral as ground path as the lamps would likely flicker, + safety issues.

  • It's also a safety concern. Having 12VDC running along 230VAC in house piping. If a short were to occur (damaged cable, rodents, water leak, miswiring) you may very well end up with your 12VDC circuit connected to your phase, and it will still work as those supplies are usually isolated, until the day someone touches it, it may cause death and you'd probably be legally responsible. It is not a problem with 230VAC alone because any short between the phase and another cable would trip the breaker. You could mitigate that by binding the supply 0V to GND, but the electrical code of your region should be checked.

  • LED Strips do look nice, however, they tend to break and die easily. I rented a few flat with LED Strips around, they all started to fail, come unglued, and falls, some led dies making dark spots.

All this, coupled with the amount of work to wire everything with 12VDC, it is difficult to find any compelling point to such implementation.

It may seem to be a fun project, but you probably will regret it down the line. You won't save much money, have an overall lower efficiency in addition to all the issues listed above.

If you want a smart system, there are some other ways to achieve that. Using smart lamps or a lots of IoT companies offers such products. You also have buses like EIB, but the cost will be higher than an arduino and some mosfets. You can also use cheap static relays (5-10$) to switch the 230VDC directly from an arduino signal.

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  • \$\begingroup\$ I find a lot of misconceptions here. There aren't that many "independent, ready to install" LED-lights on the market which are current controlled and/or voltages above 48V, as you suggest. Most professional LED-lights you are allowed to install with some reasonable distance from the control gear is designed for fixed voltages and mostly 24V. Please read datasheets carefully. The control gears with CC output are meant to be in-fixture mounted. \$\endgroup\$ – Ariser Feb 28 at 10:53
  • \$\begingroup\$ Binding 0V of 12V SELV to earth is a bad suggestion, because it is forbidden. It makes a PELV circuit out of a SELV one, and most fixtures and dimmers aren't allowed to operate in a PELV circuit. This is independend from local electrical code. However if the SELV circuits are routed in own cables along cables with 230V you are fine and safe with code as long as you don't exceed the permitted number of cables for a piping (check your code) \$\endgroup\$ – Ariser Feb 28 at 11:11
  • \$\begingroup\$ @Ariser amongst other things, I design lightings solution, so I'm pretty aware of what the market has and where the market is going. New single White LED chips now come at voltages around 10V, Lighting uses those in series. 6 leds in series gets you 60V string. Higher voltage for LED lighting makes sense as lower current, smaller driver that needs to do less work, and this is where the industry is going. You can check recent LEDs driver chips, they are designed for LED string voltages in the 50-80VDC. \$\endgroup\$ – Damien Mar 3 at 3:56
  • \$\begingroup\$ If a white LED has 10V forward voltage, then it is not a chip. It may be a lamp but not a chip. There is no compound semiconductor available with that forward voltage for visible light. When using unregulated LED lamps in a string with a CC-output driver, you have to take care of current legislation and electrical codes. In most cases you will realize that the driver and the lamps in series have to be installed inside a luminaire (aka fixture) which has to be certified according CE or UL, notably when you go over 60V in total or certain wattages. \$\endgroup\$ – Ariser Mar 3 at 14:57
  • \$\begingroup\$ @Ariser you should check before making assumptions. digikey.com/en/products/detail/cree-inc/MX3SWT-A1-0000-000AE8/… also you misunderstand electric code but I'm not going to make a class here, just go check by yourself led drivers and lamps. Or just go buy a lamp and disassemble it... \$\endgroup\$ – Damien Mar 4 at 3:50

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