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Thread: 12v supply to multiple points

  1. #1
    Automated Home Jr Member CableTie's Avatar
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    Default 12v supply to multiple points

    Has anyone any experience of installing multiple 12v supplies to various places in the home. With the amount of 12v eqipment now (printers scanners telephones automated curtains etc) I thought it would make sence to install one main 12v transformer feeding various points arround the house to get rid of all those ugly transformer plugs.

    Any info appreciated such as wirring configurations, transformer availability, cable, modular fittings etc

    Thanks all

    Paul

  2. #2

    Default Re: 12v supply to multiple points

    Hi Paul,

    This has been covered several times before on UKHA_D and whilst at first glance this may seem easy to do there are several pitfalls to be aware of.

    1. The power supply would need to be capable of quite a high output current to power multiple devices.
    It is absolutely VITAL that suitable fuses are used to limit the current available to any single cable otherwise there is a very real fire risk.

    2. If you use a switch mode power supply and something shorts it out, its own internal protection may well shut it down faster than a fuse blew on the cable causing the fault. This would lead to loss of all 12v powered equipment. Also switch mode power supplies oftern then need to be disconnected from the mains before they will start up again.

    3. The equipment itself. Many items of equipment are connected upto other devices eg Printers to PC's. Each of these devices have ground connections which are connected to the power input in some way.

    For Scanners, Printers etc it is fairly safe to assume that the negative side of the PSU is connected to ground internally, however for many other items particularly audio and video equipment, neither the positive or negative may be connected to the ground rail as it may generate s pseudo ground internally so that internal circuitry can be powered from +6 and -6V etc.

    If devices using different internal grounding methods were fed from the same power supply it could short out the supply and damage either the PSU or the equipment.

    There is also a risk of creating "ground loops" when item of AV equipment are connected together by more than one common connection which could easily occur using a common power supply when items are distributed around the house.

    In the case of telephone equipment, oe of the reasons that a power supply "conforming to BS6301" is specified is again because the power supply is conncted to the internal circuitry, but unlike the items described above, no part of a telephone is connected to ground. At the exchange, one wire (A wire) is connected to ground and is effectively 0V. The other wire (B wire) is the power supply which is nominally -50V (note that it is NEGATIVE). If you were to measure the voltage on the phone line when idle you would get 50V across the pair, testing to earth you would get a small voltage on the A wire and approx -50V on the B wire due to slight differences in ground potential between your house and the exchange. If you were to test when the phone is in use you would find about 10V across the pair and one wire would be about -20V the other about -30V as the whole phone line is raised above ground potential. If you were to connect your common power supply to the phone it would tie the phone line down to ground thereby unbalancing it and at best putting severe hum on the line, at worst it would effectively take the phone permanetly off hook and rendering it out of action.

    Without wishing to put you off completely, if you are powering your own devices and you know how they are wired internally then a centralised power supply is possible. Likewise there is no problem connecting devices that you dont know the internal circuitry off PROVIDED that they DONT connect to anything else except by wireless or infra red.

    If an item originally has a power supply with an AC output then you cant connect it, also watch out for polarity. Most power supplies are center positive but there are some that are center negative!

    Hope that helps

    Keith

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    Automated Home Jr Member CableTie's Avatar
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    Default Re: 12v supply to multiple points

    Thanks Keith for taking the time and trouble to provide such useful information, very appreciated. So at this moment in time it looks as though this is not a viable option. I think I will just drop a conduit in and box to each room just in case some future developments allow this to take place easily :lol:

    Its a shame that these ugly transformers take up a power outlet and clutter neat installations of equipment, especially when going to such lengths to de clutter installations.

    Thanks again Keith

    Paul.

  4. #4

    Default Re: 12v supply to multiple points

    Quote Originally Posted by CableTie
    Its a shame that these ugly transformers take up a power outlet and clutter neat installations of equipment, especially when going to such lengths to de clutter installations.

    Thanks again Keith

    Paul.
    How about applying a little lateral thinking.....

    Get a blank module for your chosen style of faceplate ( or just drill a hole in a blank part of the faceplate) and fit a 2.1mm DC power socket to it.

    Use a 2 core flexible cable (preferably 1.0mm or more to avoid any problems with voltage drop) and run them back to Node 0

    You could use CAT5 by bunching wires together but as you are not sure what voltage or current you will be handling, I personally would opt for proper flex.

    Terminate all the cables onto 2.1mm DC sockets using a suitable PLASTIC enclosure hidden inside your rack.

    Mount some 13A plugboards inside the back of the rack (ensuring you chose ones with as wide spaced sockets that you can find) and plug all the power supplies in there.

    Granted it doesnt remove the wall warts but it does declutter the rooms AND it doesnt matter how the device treats its power supply because it will still be using its own.

    Each device would then just need a short cable to connect it to the wall outlet.

    If you wanted to be really flash you could also mount an BiColour LED on the faceplate as well. These are the two legged ones that have a red/green LED connected in inverse parallel so that with one polarity they show green, with the other they show red.

    Just use a 1K resistor in series with it and then have a Green LED showing to indicate a Positive supply, Red indicates a Negative supply (red for warning ). As an added advantage, if the power supply was AC the LED would appear to be yellow.

    Hope that helps

    Keith

  5. #5
    Automated Home Jr Member CableTie's Avatar
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    Default Re: 12v supply to multiple points

    Thanks Keith !

    I have already installed cable on my curtain track points to take 12v so I might as well install some points in each room and do as you say. The building of the Node Zero bit may take a while (sooooooooo much to do ) but I will get round to it eventually. I think it would be a worth while project if it tidies everything up.

    Cheers for your time and trouble. (its just made me look even harder at your switcher :lol: )

    Cheers Paul.

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    Default Re: 12v supply to multiple points

    I'm sure I saw somewhere on the web, a 12V transformer with two 3.5mm outputs.

    I'm not sure what the Ampage would be.

    If anyone know's of such a device, please reply back - I have the same dilemma - too many transformers in the house!

    Thanks in advance.

  7. #7
    Automated Home Legend TimH's Avatar
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    Default Re: 12v supply to multiple points

    darkknight,

    This might do the same thing for you:
    http://tinyurl.com/beugx or
    http://www.maplin.co.uk/Module.aspx?...20lead&doy=3m2

    This next bit is a cut & paste direct from the website:
    Five 2.1mm DC power plugs connected together in a daisy chain. The end of the chain is terminated with a DC line socket into which the original power supply plug is inserted. This can then power several items simultaneously, such as guitar effects pedals, etc. The input socket will suit a 2.1mm or a 2.5mm DC plug. The 2-core lead 1.8m long and is rated 1A 75Vdc.
    Price = GBP 2.99 each :-)

    HTH,

    Tim.

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    Default Re: 12v supply to multiple points

    Nice!

    Shame the cables don't look all that long... I'd have to bring some of my devices closer together.

    I assume whether the polarity of the inner and outer part of the cable will be matched in the outputs ?.

    One other question about these ('cause I was cr@p at physics) :

    If my 12V adapter is rated at X Amps, would this same Ampage drive through to the 5 peice splitter ?

    Or would I have to potentially buy a 5x more powerful 12V main adapter if I were using 5 peices of equipment ?

    Thanks.

  9. #9
    Automated Home Legend TimH's Avatar
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    Default Re: 12v supply to multiple points

    Quote Originally Posted by darkknight
    I assume whether the polarity of the inner and outer part of the cable will be matched in the outputs ?.
    That's my assumption too :-)

    Quote Originally Posted by darkknight
    If my 12V adapter is rated at X Amps, would this same Ampage drive through to the 5 peice splitter ?

    Or would I have to potentially buy a 5x more powerful 12V main adapter if I were using 5 peices of equipment ?
    If you have 5 devices each consuming 200mA that gives a total consumption of 1000mA, or 1amp. Therefore you need a 1amp power supply to simultaneously feed all devices.

    Sometimes the power supplies included with each bit of kit supply more than the minimum required so you might be able to run a couple of devices from one wall-wart, but it depends on the individual supplies and devices (e.g. a 3Com router I bought needs 1amp at 12volts but was supplied with a 1250mA 12V adaptor, so I could, in theory power another device up to ~250mA).

    Oh, another thing, the adaptor I linked to had _2.1mm_ DC plugs - check these will fit the kit you intend to power-up. The power injection socket will suit a 2.1 or 2.5mm plug.

    I think CPC (www.cpc.co.uk) also do similar leads.

    HTH,

    Tim.

  10. #10
    Moderator toscal's Avatar
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    Default Re: 12v supply to multiple points

    Taking Katman's idea a stage further. IF you are only going to use a positive DC supply, then it might be an idea to put in a diode bridge rectifier at the face plate. I do this quite a lot when working with DC voltages. What this will do is make sure that the +ve is always the +ve connection and the -ve is always -ve. Even if the connections at the supply end are reversed. I come from the school of if a connection can be reversed at some point it will be no matter how careful you are. Its just an added safety feature.

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