Whole-house 12v lighting circuit.

[epsilonGreedy]

I have been itching to pose this question on the forum. Given how eager folks here are to incorporate tomorrow's world in their new builds today, why is there little discussion of whole house 12 volt lighting circuits?

 

Many of the woes of mains powered LED lighting vanish as soon as cheap rectification electronics is removed from each bulb and instead the same function implemented centrally in a quality piece of kit. I must be overlooking something because this seems like a win-win decision for a new build.

 

p.s. To simplify the discussion let's ignore hi-end central mood lighting options.

[Jeremy Harris]

Cable size, voltage drops and a lack of DC capable switches is the simple answer.  I was going to do this, but no one makes a DC rated wall switch, and none of the wall switch suppliers would tell me what sort of current they would take at DC.  My best guess is that they would need to be de-rated to around 1/3 to 1/2 their AC rating (that's a pretty normal sort of derating for DC switching) and then none of the readily available switches will handle more than a few LEDs, certainly not enough for a room.

 

I did look at using a bank of relays to switch the 12V DC, so the switch current would be low and within the likely switch DC rating, but it all got too much hassle, so I ended up using separate 12V switched mode power supplies switched by normal 230V AC lighting circuits.

[SteamyTea]

10 minutes ago, epsilonGreedy said:

I must be overlooking something

Ohm's Law

As your voltage decreases, the current goes up, so there is no real saving to be made on the installation.

Then there are the rules about low voltage, extra low voltage and separated extra low voltage.

Not as simple as just trusting in low voltage.

 

Edit:

Bit cross post with Jeremy

Edited February 12, 2018 by SteamyTea

[Dee J]

What are the woes of mains powered led lighting? I get an LED lamp or fixture and plug it in... it works. Other than in some areas of bathrooms and swimming pools I've never understood the point of 12v lighting. And unless you run a lot of wasteful resistive droppers or linear regulators you'll still need the switch mode drivers similar to the mains based drivers....

[dpmiller]

many mains- LEDs (and not just the cheap ones) have regulators that are rather electrically noisy.

[Jeremy Harris]

26 minutes ago, dpmiller said:

many mains- LEDs (and not just the cheap ones) have regulators that are rather electrically noisy.

 

 

Very, very, true.  I had to do a lot of work replacing very noisy ones that completely blanked any radio in the house.  There is some real rubbish stuff around, and unfortunately it's not easy to sift the good from the bad without buying some and trying them.  I ended up replacing all the 230 VAC LED constant current supplies that came with all our kitchen ceiling lights, because of the electrical noise they created.

[dpmiller]

With cheapo MR16s I found that earthing the outer case/heatsink made a surprising difference, even when using a DC driver.

[epsilonGreedy]

26 minutes ago, JSHarris said:

Cable size, voltage drops and a lack of DC capable switches is the simple answer.  I was going to do this, but no one makes a DC rated wall switch...

 

If a home is wired for current 240v ac lighting standards then I guess the circuit is good for 3 amps i.e. +700 watts per wall switch.

 

At the other end of the scale a 60w (lumens equivalent) LED draws 6 watts including losses for some lashup of semi rectified cheapo circuitry embedded within the light. The more I learn about their design it is surprising these do not cook and blow within 5 minutes. At this point is it reasonable to conclude 50% loss in the embedded rectifier?

 

If so, surely a light switch capable of handling 750 watts and the sparkiness of 240 volts and the dangers of AC, will cope with the 12 watt draw of 4 x 12 volt DC LED ceiling lights.

[SteamyTea]

DC is great for creating an electrical arc.

It is not all about wattage.

 

This has been looked into a lot in the past, and if it is not available, there is a good reason for it.  It is too costly and complicated for normal housing.

[Jeremy Harris]

16 minutes ago, dpmiller said:

With cheapo MR16s I found that earthing the outer case/heatsink made a surprising difference, even when using a DC driver.

 

 

That's interesting.  I binned our MR16 fittings and replaced them with flat panel LEDs, run from a decent DC supply, and it made a big difference, but I'm wondering if part of that difference may be that I did make sure that the 0V side was connected to earth, so I have now earthed all the cases of these LEDs.  It could be that's what made much of the difference.

 

11 minutes ago, epsilonGreedy said:

If a home is wired for current 240v ac lighting standards then I guess the circuit is good for 3 amps i.e. +700 watts per wall switch.

 

At the other end of the scale a 60w (lumens equivalent) LED draws 6 watts including losses for some lashup of semi rectified cheapo circuitry embedded within the light. The more I learn about their design it is surprising these do not cook and blow within 5 minutes. At this point is it reasonable to conclude 50% loss in the embedded rectifier?

 

If so, surely a light switch capable of handling 750 watts and the sparkiness of 240 volts and the dangers of AC, will cope with the 12 watt draw of 4 x 12 volt DC LED ceiling lights.

 

 

The snag is that wall switches are not designed to switch DC at all, as they have really slow to operate contacts.  You may well get away with one running a very tiny load,  like 4 off 3W LEDs, but you will need a lot more LEDs than that to light a room well, especially a kitchen or utility room.  I have a total of 48 W of LED ceiling panels in our kitchen, and that's marginal, in my view.  I had to add supplementary LED strips under the wall units to get an adequate light level on the worksurfaces, and they add an addition load of around 12 W, so if I'd used 12V DC switched supplies then the wall switch would have been handling a total of around 60 W, or 5 A.  I doubt the switch would last long switching 5 A DC, but more importantly, it has no certification for use at DC, which could cause problems in the event of something going wrong.

 

The other problem is the vampire load from the power supply.  Even a really good switched mode supply may draw around 5% or so of it's rated power just when powered on with no load.  Add that up for 24v hours a day, 7 days a week, and it's apparent that it's quite a bit of wasted power, especially if the supply is rated for the whole house, or even just a single floor in the house.

[epsilonGreedy]

49 minutes ago, Dee J said:

What are the woes of mains powered led lighting?

 

My uneducated opinion has been formed by a JSHarris blog entry plus the following US podcast.

 

https://www.dotnetrocks.com/?show=1373

 

(Background info here https://www.dotnetrocks.com/?tags=Geek Out)

[Dee J]

49 minutes ago, dpmiller said:

many mains- LEDs (and not just the cheap ones) have regulators that are rather electrically noisy.

But what sort of regulator/driver do you use for 12v leds. Linear or resistive and you'll loose more energy in the regulator than you use in the led. And if you use switched mode you'll still run the risk of radio interference from poorly designed items.

[Jeremy Harris]

5 minutes ago, Dee J said:

But what sort of regulator/driver do you use for 12v leds. Linear or resistive and you'll loose more energy in the regulator than you use in the led. And if you use switched mode you'll still run the risk of radio interference from poorly designed items.

 

There  are some decent, metal encased, switched mode supplies, with decent filtering, that are not too expensive.  They are all made in China, but I've found that the supplies sold by LED Hut ( https://www.ledhut.co.uk/drivers-fittings-switches.html ) tend to be pretty good.

[Dee J]

2 minutes ago, JSHarris said:

 

There  are some decent, metal encased, switched mode supplies, with decent filtering, that are not too expensive.  They are all made in China, but I've found that the supplies sold by LED Hut ( https://www.ledhut.co.uk/drivers-fittings-switches.html ) tend to be pretty good.

But..... that's just a 12v constant voltage supply isn't it.... the mr16 lamp still contains either an energy wasting linear regulator or a potentially noisy switching regulator. I'd understand the point more if you were using good quality constant current drivers driving unregulated leds... but of course you'd need a constant current driver for each group or set of leds, and you'd still be switching the 240vac at the lightswitch...

[Jeremy Harris]

All the many MR16 samples I obtained just used an array of series/parallel connected LEDs to get close to 12V, plus a bridge rectifier (because the 12 V downlighter spec is 12 VAC) and a very low value dropper resistor.  There were small losses across the resistor and diode Vf in the rectifier, but these were modest, and little more than a cheap switched mode regulator.  They were free of any interference generating elements, too.  IIRC, the Vf of the white LED varied from around 3V to 3.3 V (with current and colour temperature), and they were wired in banks of three in series, giving 9 to 9.9 V to drive them.  The bridge rectifier included two diode Vfs of around 0.6 to 0.7 V each, so increasing the voltage required to around 10.2 V to 11.3 V.  The LEDs were run at between 20 and 30 mA, so the dropper resistor only had to lose between 1.8V to 0.7V.  It's not the most efficient system, but the total losses aren't that far off those for a typical cheap switched mode supply.

 

One thing I did find was that the multiple 5050 LED MR16s were not happy when driven with the small "electronic transformers" intended for normal halogen MR16s.  The reason was that these put out 12 VAC at around 20 kHz, and the bridge rectifiers in the MR16 LEDs weren't capable of switching that fast, as they didn't use fast recovery diodes.  The result was that they overheated and would eventually either smoke or unsolder the SMT bridge rectifier from behind the circuit board.  Running the same LEDs on 12V DC fixed the problem, and they barely run warm.

[Dee J]

Fair enough. Probably not enough resistive loss to worry about. 10percent of not much is not enough to worry about.

But I still don't have any problems with the various 240v led lamps I get from the wholesalers though. Used loads of GU10, ES and bayonet lamps with no ill effects. The only noise issue I have is a cheapy 12v switcher psu driving some resistor limited led tapes. 

[epsilonGreedy]

1 hour ago, JSHarris said:

The snag is that wall switches are not designed to switch DC at all, as they have really slow to operate contacts.  You may well get away with one running a very tiny load,  like 4 off 3W LEDs, but you will need a lot more LEDs than that to light a room well, especially a kitchen or utility room.  I have a total of 48 W of LED ceiling panels in our kitchen

 

In this example I would not want everything controlled by a single switch. Based on my current kitchen I would want 4 switches for manual mood arrangements e.g.  range hob illumination, lights above work surfaces, under wall cupboard lighting and pendants over the island.

 

1 hour ago, JSHarris said:

The other problem is the vampire load from the power supply.  Even a really good switched mode supply may draw around 5% or so of it's rated power just when powered on with no load.  Add that up for 24v hours a day, 7 days a week, and it's apparent that it's quite a bit of wasted power, especially if the supply is rated for the whole house, or even just a single floor in the house.

 

Would this also apply to upmarket gear as supplied by Victron Energy? The offgrid preppers would not tolerate such background wastage but I guess you are referring to the 240vac/12vdc function when enabled with zero load. I suppose the answer would be to added in a lithium iron battery and selectively charge from mains when battery voltage drops but now things are getting complicated. If I was going PV from day one it would be an easier decision to use 12v LED from day one.

[Jeremy Harris]

You still have to overcome the switch certification problem when run on DC.  I spoke at length with MK and they were adamant that their range of AC switches were not suitable for use on DC and could not give a derating factor.  Now I know people have used ordinary wall switches to switch DC, on boats etc, but the remains a problem with a house, where any fault could result in serious consequences, and may well impact on insurance cover.  I've no doubt that most of these switches would probably handle maybe 1/3rd of their rated AC current when used with DC, but their life may well be reduced because of arcing caused by their slow break characteristic.

 

My proposed solution was to fit DC relays, with fast acting, DC rated, contacts up in the ceiling void, switched by a very low DC current through the wall switch, with a snubber across it to reduce the risk of problems from switching the inductive load  of the relay.

[PeterW]

7 minutes ago, epsilonGreedy said:

In this example I would not want everything controlled by a single switch. Based on my current kitchen I would want 4 switches for manual mood arrangements e.g.  range hob illumination, lights above work surfaces, under wall cupboard lighting and pendants over the island.

 

Would this also apply to upmarket gear as supplied by Victron Energy? The offgrid preppers would not tolerate such background wastage but I guess you are referring to the 240vac/12vdc function when enabled with zero load. I suppose the answer would be to added in a lithium iron battery and selectively charge from mains when battery voltage drops but now things are getting complicated. If I was going PV from day one it would be an easier decision to use 12v LED from day one.

 

The question here is what are you trying to achieve ..?

 

12v is not a good voltage for anything DC in a house, it just happens to be a standard that’s been around for a while. If you really want DC then 36-48v is optimum and most of the PV panel providers would agree. If you are talking offgrid then that is a different concept to using off the shelf technology that is a replacement for 220VAC. 

 

Your next question would be capital vs ongoing. 220v LED bulbs are becoming cheaper and cheaper. 220VAC switching is cheap and needs no special products unless you get into complex dimmer circuits or HA (ask @Barney12 about this..) so unless you’re looking to massage a green ego or a take to the hills, what is currently on offer is the best you can go for. 

 

 

 

 

[joe90]

A lot of the technical stuff above went right over my head ?. Yes, I also considered a 12 volt dc ring initially in my build but previous threads convinced me not too. What might be good from those of you in the know is recommendations for actual products so Luddites like me know we are buying something worth having. ( I want some led flat panels for my kitchen!).

[epsilonGreedy]

27 minutes ago, PeterW said:

The question here is what are you trying to achieve ..?

 

Challenge convention.

 

This forum attracts those who are willing to challenge all and any existing precedent or practice in the British house building industry. Surely some of you find it incongruous that our lighting circuits are based on the needs of 1930's vintage lighting physics. We install multiple lighting circuits in our new builds each capable of delivering 1000 watts of AC power to 21st century light bulbs that only need 1 to 3 watts of DC power.

 

I think @jsharris did find it incongruous but encountered regulatory barriers and equipment deficiencies during his research.

 

Anyhow after starting this thread I do at least understand the time for whole house DC  is not here yet.

[chrisb]

I'm watching this thread with interest as I'm trying to find a solution to lighting in my extension, and later, the rest of the house.

 

Various illnesses, ailments, needs and preferences are pushing me towards multiple LED flat panels or downlighters in each room, with groups of them separately dimmable - example is a bedroom with 6 fittings, in two groups of three. Add to this a socket for a sensory lamp (think disco ball flashy lighty thing) and a socket for a desk lamp, all controllable from the doorway or thereabouts. Doing this with mains required 2x LED-compatible dimmers, and two switches. If I want to do this in one housing, then its got to be a grid switch, at about £55-60.

 

I'm already running OpenHAB for temperature data, integration with Alexa, and Logitech Harmony, and will likely start down the road of heating controls, so adding lighting control seems like a natural progression and maintains flexibility with an open platform. Family members use it too, so there is help at hand if I drop dead.

 

The problem i'm finding is reasonably priced wall-mounted in-room controls, and also controllable dimmers (if not in the same unit as the controls). I might be able to do something with the H801 12v LED drivers, but then I need a 12v LED fitting - far less choice than 240v. Also I've yet to find a suitable controller - as much as my son would love an android tablet stuck to his bedroom wall, that's not going to happen.

[Miek]

12v lighting makes sense in an off grid situation where you are trying to save power as much as possible. You can avoid the inverter being on the whole time just to run the lights. But as mentioned it's primarily a bugger to find a standard wall switch rated for DC. I use a standard switch to do this for about 24 watts of12v led  lights and it works OK (has been for about 3 years) , but I can tell that the switch is getting tired from all the arcing  and is not as responsive as it should be. 

[SteamyTea]

51 minutes ago, JSHarris said:

Now I know people have used ordinary wall switches to switch DC, on boats etc, but the remains a problem with a house, where any fault could result in serious consequences, and may well impact on insurance cover.

Same applies for boats, they also have rules for wiring, like caravans.

10 minutes ago, epsilonGreedy said:

This forum attracts those who are willing to challenge

 

11 minutes ago, epsilonGreedy said:

based on the needs of 1930's vintage lighting physics

There was a lot of DC back then, my Father worked for the local electricity board in High Wycombe.  One of his jobs was to change housing from DC to AC.

 

There is so much going for AC that, unless you are off grid, you gain nothing.