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Thread: 12 volt house circuit with PWM dimmable lighting

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    Default 12 volt house circuit with PWM dimmable lighting

    Has anyone created a separate 12v circuit in their house ?
    advantages/disadvantages ?

    primarily for 12v LED lighting, but also to replace a pile of existing transformers: chargers, modems, routers, etc

    for the lighting I am planning on having a single 12v transformer (size to be determined based on the final number of lights I use) and powering all of the lights from this.

    ------------+
    | ------> (controller/switch) -----> LED Light(s)
    transformer | ------> (controller/switch) -----> LED Light(s)
    | ------> (controller/switch) -----> LED Light(s)
    ------------+

    the controller/switch will be a programmed Microchip controller which will allow me to dim the lights with PWM.

    this does give all of my lighting a single point of failure, but you can easily buy another 12V transformer usually the next day if anything goes wrong, so i'm not particularly worried there.

    in the long term I am also considering replacing the transformer with a deep cycle battery/solar panel setup.
    by my (crude) calculations a small 12v 28ah battery should be able to power around 10 x 3W in the evening no worries. re-filled during the day with a 80W solar panel. - this was the bare minimum from what I calculated. you could have a larger solar panel/battery if you wish to spend more money - at this point i'm trying to stick to what I can find in my shed.
    either way, the circuit will automatically switch back to mains power in the event the battery is running low.


    all just theory so far !
    I do however have a pile of different LED downlights, microchip controllers, and transfomers coming in the post very soon and am keen to start prototyping a setup.

    can anyone see any floors in my setup (excluding the solar/battery stuff for now) as i'm no qualified sparky.. but I do have a decent amount of experience with electronics and microcontrollers

    cheers
    jimmy !



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    since my quality ascii diagram didn't come through here is a nice picture


    cheers

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    The biggest issue I see you coming across is good old fashion voltage drop.

    If your cable runs from the transformer are even moderately long you'll find you'll need a rather large cross sectional area cable to keep 12volts up to the lamp.

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    I am no electrician or have any idea of prices but I wouldnt think a suitable transformer would be cheap plus cable, polarised 2 pin outlets etc.
    Also the transformer would be on all day every day consuming power whether its supplying or not.
    Correct me if I am wrong but do I remember correctly standard AC light switches dont like DC current ?
    I certainly like the idea of using solar panel/batterys to be a supplementary lighting system but to go wholly solar is a real major expense.
    There is a house near me that is totaly solar and it cost thousands even with Govt Subs to install and from what I have been told, they have to watch their consumption dilligently.
    Even so the system needs to be boosted by the generator set.
    I stand unequivicably behind everything I say , I just dont ever remember saying it !!

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    We have a fair bit of 12volt totaly separate cabling power through the house. And in all honesty we wouldn't do it again...

    Each bedroom has two 12volt light (as well as the normal 240v lights). 12v feeds goto 12v power outlets for corner lamps, ambiance lighting, and - my speciality down the hall way - a nice multi cycling colour set of leds in the roof.
    I installed 4 12volt lights around the perimeter of the house. Will light up all the garden and surrounds 'just ok' nicely.

    It turned out to be a nightmare and a costly one at that. But once you are half way, it's financialy 'hurtfull' to pull out.

    As Mudcrab says. Be prepared to have THICK cable.

    I used thick cable to the house, then along the roof i made 'junction' points of which i feed into the individual berdooms etc.

    You need to do some research on how much power 1 80W panel will give you.
    A Deep Cycle battery is fine, but you will need a regulator for that as well as you probably know.

    It's all nice to have 12v power. But once you weigh up the cost (as I didn't, i'd like to say 'we didn't), but i can't), it's not cost effective.

    1kW of grid power is only 20c..!!

    Put some low power ambiance lights in on 240v and enjoy the cheap price.

    We have 12 Trojan T105's supplied by 12volt 70W-80W panels on the roof and the back shed.
    We run the house at night on 240v volt from the Batterys as well via a 1000W PSW Invertor with 2 seperate 240v runs into the house.
    And also 3 seperate runs directly off the battery bank of 12volts that go into the house.



    As i said. To me anyway, it's not worth it - at all. When we show people, they go Oohh, and Ahhrr with comments of how good it is. But they have no idea as to the cost.

    We actualy had (used to now), have a lot of power blackouts, which led us (me), to look at independant power.
    I must say that we have had a few BO's since and it's been funny to have the neighbours, comment on the fact that we were the only house with 'power'.

    But what's wrong with a few candles and such. The kids love it and it makes a change.

    And if the world ends, we are going to charge addmission to have hot water, hot food and lights etc...


    If you want to do it as some sort of project, then fine. You'll learn a lot about voltage drop - Ω resistence with copper cable, and the basic inefficencies of solar power and battery storage.

    For each input and output you LOOSE power. To make up for that, you need better )aka more), solar panels, better battery's (or more), thicker cable (go for your life), better regulator (buy one now that does the job, or buy a bigger one in case you expand - but a bigger one will be rated (and perform poor), to low efficiency due the low input!), better connections (thicker is better), and the list goes on... The more 'connections' you have the more 'loss' and 'resistance'.

    Good luck.

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    thanks for the quick responses guys!

    that was another question I had forgotten to ask
    I was looking at starting with a cheap transformer like this to drive the lighting


    would this thing suck down the full 15A as soon as I plug it in ?
    or does it only draw what it needs from the power point

    I think that initially I will just stick with the 18-20 LED downlights in the roof.
    we're in a small Queenslander house and no more than 5-7m of cable should reach each light.
    to save costs - I plan on cutting out and reusing the existing 240v lighting cabling already there.
    and luckily the previous owners went overkill for all cabling and I have quite heavy duty solid core cabling used for all the existing lighting.

    I will actually be creating all my own light switches to handle the light switching/dimming.
    using an off-the-shelf plate (Clipsal or similar) with 2 vertical stainless touch pads stuck on top to handle the dimming (drag your finger down the pads to dim/turn off, drag them up to brighten the lights).
    i'll be using a Microchip mTouch capacitive touch controller behind each switch to handle the PWM.
    I don't imagine each switch costing more than $8-10 (7-8 switches)... possibly less as I already have a pile of surplus electronics and microchips.

    by controlling each light with a microchip I can plug these into a PC controlled I/O (like an Arduino or Fusion USB) for total house automation.

    cheers
    jimmy

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    Hey Jimmy

    The power supply will only draw what you connect to it - 2 x 50w = 100w
    keep in mind ohms law, 10Amps at 240v is equal to 200A at 12V and there will be losses changing from AC to DC - just keep it well ventilated

    I like your idea of the dimmers.... and with the LED lighting the load will be stuff all load and therefore the voltage drop will be stuff all as well, hopefully a win win for you


    goodluck


    f
    有段者

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    Quote Originally Posted by jimmyb View Post
    Has anyone created a separate 12v circuit in their house ?
    i have , sort of. my house alarm power supply is always on and happens to be 13v DC , so i ran some good fig8 cable and use that to power the doorbell , the telephone answering machine , charge a dustbuster and a small nightlight in the hallway.

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    I run my lights off 12VDC. The source is off grid solar.
    Actually the entire solar system is now 24V which runs inverters and a buck converter floats a 12V rail which powers the house lights. (MR16's).
    I run 16mm^2 cable (I have heaps of the stuff) so voltage drop isn't an issue. The setup I have disconnected the 240V transformers and use the 240V to drive a relay which switches the 12V to new 12VDC MR16 sockets. That way I can use the normal 240V light switches and the current draw on the 240VAC side is minimal compared to driving halogens or even LEDs.

    I've been looking for a way to eliminate the 240VAC from the circuit by finding some other convenient way to turn the 12V circuit on and off like the existing light switch on the wall without having to put extra switch plates in etc.

    I had more cause to think about the circuit yesterday during a blackout. Aha ! My lights are solar, they'll work just fine without grid power. DOH !!! the control circuit is dead !
    The sound of one hand clapping ! <slaps forehead>
    Yes I am an agent of Satan, but my duties are largely ceremonial.

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    Default 12V Lighting

    Prior to leds being practical for household lighting we lived for many years with off grid solar the main high current being at 12V with a additional small 12V pv & battery to give a 24V rail for ni-cad chargers & my soldering iron and bench psu.
    Halogen globes gave better lighting than tungsten car bulbs but the most profound improvement was the release of the philips 20W cfl globe. We found the cfl lamp ran well on a square wave inverter with conversion losses being less than 10% so for 22/23W we could have the same lumens as a 75W GLS globe and only need a 1/20th of the cross sectional area of copper as the conductor.
    My neighbour discovered by adjusting the frequency of the inverter you could 'tune up' the load and get slightly better current efficency.
    Life span of the 240V cfl's and RFI were much better than using 12V converters on the same style PL tubes due to the effectiveness of the high voltage electronic balast.
    In our suburban debtors prison I'm thinking about having a changeover hard-wired feed from the same 20+ yr home brew 300W inverter to run CFL's rather than having to scramble for the extension cords and epod's to run lights in a blackout.
    If you need a dependable and long lasting 12V CFL (compact fluro lamp) with low rfi the Sundaya brand is a exceptional and has a pre-heat start up.

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