24v lighting circuit - good or bad idea?

[SteamyTea]

46 minutes ago, jimseng said:

What if I want to woo a beautiful lady and the lights over the sofa are too bright

I have never gone to bed with an ugly woman, but have woken up with plenty.

[Alan Ambrose]

My analogy is this: an enormous amount of money, time and energy has been spent since the '80s trying to squeeze bits down a copper wire. It works, it isn't pretty and it doesn't work that well. Fibre is much simpler (ignoring the splicing tech) and it will probably be possible to improve from 1 Gbps to 10 or 100 without changing the fibre over.

 

Similarly, we can power and sort-of dim 3V or 4V white LEDs and 2V coloured LEDs from 230V. Cheap dimming and voltage dropping from 230V is kind of nonsense. It works-ish, but it sure ain't pretty and it's probably not possible to improve it much.

 

So, in the long term, low voltage DC is the way forward, especially given that LEDs are low power and thus low current (well compared with incandescent). Do we need low voltage lighting circuits? Well do we need heated seats, sat nav & phone connections in our cars? No we don't need them, but we sure want them.

 

One advantage, I think, is that 'extra-low-voltage DC' doesn't fall under Part P.

 

 

Edited September 21 by Alan Ambrose

[-rick-]

You have to be a bit mad to self build in the UK and going to this level of effort with lighting is a bit mad. But it's the kind of mad I like! I have been thinking about similar options.

 

Have you actually built and tested a prototype of this custom hardware?

 

The piece of advice I've taken from here and want to follow in anything I do is that if you do something a bit different or unusal, do it in a way that you could rip it all out and replace with something standard without much effort. So for me that means installing mains cabling in all the relevant places that would mean that the low voltage system could be replaced by just changing the fittings (no threading wires or breaking into walls/ceilings).

 

Another focus for me is to ensure that whatever lighting scheme I come up with works together well. If you just build a system for downlights that doesn't also plan to work with task and accent lights and also LED strips then you wont have a cohesive system. A ceiling full of downlights is in the end the bog standard developer option and options with variety and layers of lights is a nicer, more comfortable and more premium option.

[jimseng]

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Have you actually built and tested a prototype of this custom hardware?

Yes. It's actually an amalgamation of several projects I have done over the years. And the dimmer switches work well. The only bit I haven't done before is this many RS485 nodes over this distance. But it is well with RS485 spec and RS485 is decades old and very robust so I'm not that worried about it.
 

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you will stay single for ever

Suits me. My life is so much simpler now and I am getting too old for that nonsense. If I live long enough to be too old to go sailing I'll get me a couple of Whippets. 

[-rick-]

14 hours ago, jimseng said:

My plan is to have a 24v  dc "backbone" on each floor. I have yet to do the voltage drop calculations but it might be some fairly chunky DC cable (6mm? 4mm?) that then branches off, via a busbar to each room. The LEDS will have a common positive and then each negative will be taken back to the RGBW amplifiers on .5mm cable (8w at 24v is only about .33 amps so .5mm should be plenty) I will put up to 4 RGBW amplifiers (up to 16 channels) behind some sort of elegant service hatch in the service void in the wall in each room.

 

Sticking with what I said above about making it so it's easily convertable to standard. I've been thinking along the lines of radials and conventional lighting circuits. Plan your lights in groups that you suspect you want to control as one. Put convential mains wiring in for that either wired back to the switch or via a home run to a control panel that could be simply connected to a cable that also runs to the switch (the switch on the wall should have enough mains cables in it to provide full convential control, even if you don't use them). Also run a CAT5/RS485/DMX bus around that you can hook into your dimmers. I want to find dimmers that either go in the switch backbox/form part of the switch or can be accessed via the downlight hole or be in a central locataion. The idea of a service hatch in each room seems really ugly to me. Maybe you could put some art over it but seems best avoided. Having a dimmer located near each four lights with extra wires to those lights, means you could easily replace with standard lights if needed because the wires are already there.

 

If you have a wooden floor above then the plasterboard will likely be forming a fire-resistant layer, which will be limiting to what you can do behind the downlights. Do your own checking on this but I believe these days you need fire rated downlights and having the dimmers there may be a problem unless they can be installed within fire shrouds around the downlights, or you design the ceiling structure to accomodate.

 

Assuming you solve the fire issue but your dimmers are too big for downlight holes then one option is to look at bigger fittings in some places as a way of providing access. Designers tend to advocate for purposeful lighting rather than a boring grid of downlights so consider clustering with fittings like:

 

https://www.lightingstyles.co.uk/brushed-aluminium-twin-technical-spot

which both provides a bigger hole for access and more visual interest.

 

 

14 hours ago, jimseng said:

As for the power supply. I will probably start with a 500w 24v unit running off a 13amp plug as eventually I will have a 24v LiFePo4 battery tapped off my solar array. 80 x 8w MR16 bulbs is  640w, and that is with every single LED on at once so I don't think I need a massive supply. It works out at about 12 amps per floor, worst case. Over a 15 metre run that requires quite beefy cable if I want to obey the 3% voltage drop rule, but I will do some more calculations and start chunky and reduce it as I go further from the power supply.

 

I wouldn't plan to run direct from battery. Battery voltage will vary so your lights will be brighter/dimmer depending on how charged the battery is. Battery voltage will also often be above the nominal 24v, shortening the life of the bulbs. You will also likely find a modern high efficiency power supply converting from 240v to 24v is more efficient than your average 24v battery to 24v nominal supply. Solar system batteries want to be 48v minimum for efficiency anyway. Many solar systems use 400v batteries now, though personally I'd want to stick to 48v despite the lower efficiency so make it outside Part P.

 

14 hours ago, jimseng said:

 

I think I will run 2.5mm for the common positive and then the negatives will be .5mm. I have yet to have a conversation with the electrician as he/she/they don't know what I am planning. I might run singles in a ring for the positive, I will have to see what regs apply.  

 

Electrician will want singles to be in conduit of some form the entire run at least for mains voltages and as above I think it's wise to plan your wiring as if you might convert to standard mains fittings in future.

[jimseng]

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Battery voltage will vary so your lights will be brighter/dimmer depending on how charged the battery is. Battery voltage will also often be above the nominal 24v, shortening the life of the bulbs.

Not so with these really. I have checked. They are quite tolerant of voltage swings. But I am certainly thinking about retro fitting boring old nasty mains.
Has this thread drifted somewhat?

[-rick-]

1 hour ago, jimseng said:

Not so with these really. I have checked. They are quite tolerant of voltage swings. But I am certainly thinking about retro fitting boring old nasty mains.
Has this thread drifted somewhat?

 

Drifted from SMBS's original question I guess but it's all still about 24v lighting and how to go about it so compared to some of the other threads on here I think we are doing pretty well. You did ask for feedback on your approach

[SBMS]

As the OP after much consideration have decided to go standard mains with trailing dimmers for downlights and 24v strips where possible. I’ll be using the loxone system. I think my ethos is different to yours - but I’m also waaaaaay less electrically proficient than you! I want everything automated (I walk downstairs at night, presence sensors detect me, fade up stair lights etc) coupled with scene based lighting (a touch control has predefined scenes that controls the layered lighting based on what we are doing in the room). But good luck with your approach and maximum respect for trailblazing and trying something different! Would be great Hear how it goes.