12V & 5V 'Structured Cabling'?

[FrodoOne]

Is there any practical or regulatory reason I couldn't / shouldn't run 12V feeds back to a central 7A 12V DIN transformer in my CU for blinds and 12v kit

If you run cabling from a supply capable of supplying something like 7 A through walls, ceiling spaces etc. you must protect the wiring from over-current at the source with a suitably rated fuse or circuit breaker, in the same way as any other "house wiring" is protected.

 

[bernardgreen]

The idea of 12v to 5v adapters is going to be the same as having 240vac to 5vdc adapters

A 12 volt to 5 volt convertor module is far easier to create and does not require the same degree of insulation that mains voltages need between input and output.

For what it is worth.

In the 1980's a community of three ecologically minded families wired their three house renovations for 12 volt DC electricity. They were off-grid and at the time were dependent on a couple of windmills for power. It appeared to work well using vehicle lamps for lighting and car batteries for windless nights.

Mid 1990's they installed the pipe work to feed water from a water fall to a Pelton wheel and generator. The decision was made to remain with 12 volt supply to the houses. The generator's 230 volt AC output was used for small machinery in the workshop.

Their 12 volt supply is ideal for 12 volt LED lights and a few "cosy colour" tungsten lamps which are using zero carbon electricity.

 

[JohnW2]

If you run cabling from a supply capable of supplying something like 7 A through walls, ceiling spaces etc. you must protect the wiring from over-current at the source with a suitably rated fuse or circuit breaker, in the same way as any other "house wiring" is protected.

Indeed. Many overlook the fact that it's current that can damage cables and cause fires, regardless of voltage ... and probably required by regulations (at least in the UK, the regs don't, in general, distinguish between ELV and LV).

However, as added 'reassurance', assuming that we're talking about SMPSUs, any half-decent one will have in-built overload (including 'short circuit') protection - and even those which are not 'half-decent' will probably stop oscillating if significantly overloaded.

Kind Regards, John

 

[Gasguru]

Sending 12 or 5V down long cables is asking for trouble.
The end devices would be designed with the expectation that the power supply cabling is perhaps a meter of less.
How would they cope with the significant interference picked up on a cable perhaps 10s of meters? In addition the device may not cope with high voltage spikes
generated when initially powered up (high inrush currents combined with long cable inductance).
Load regulation (ie. how much the voltage varies with current draw) would be poor.
USB is a hugely complex protocol often you'll require more than +5V and Ground.

Normally Point of Load (POL) is the better solution...run a higher voltage (say 24V) to the required locations and convert that down to 5 or 12V.
With switched mode converters efficiency can be 90% of higher.

 

[plugwash]

I've certainly seen a old PC power supply faced with a short through some hookup wire (don't know the exact size but probablly around 22 or 24 AWG) burn the insulation off the hookup wire and belch smoke out the fan.

Interestingly the PSU still worked afterwards.

 

[333rocky333]

Indeed. Many overlook the fact that it's current that can damage cables and cause fires, regardless of voltage ... and probably required by regulations (at least in the UK, the regs don't, in general, distinguish between ELV and LV).

However, as added 'reassurance', assuming that we're talking about SMPSUs, any half-decent one will have in-built overload (including 'short circuit') protection - and even those which are not 'half-decent' will probably stop oscillating if significantly overloaded.

Kind Regards, John

I recall back in the 90's at least 2 major fires where 12 volt halogen lamp heat melted the lampholder wiring causing a dead short, it was quite common to find each lamp wired in 1mm flex back to 300va or more proper transformers with a single unfused output.
The copper was found to have melted through the insulation the entire length.
You was meant to buy a splitter box that converted the single output to numerous fused outlets, but many did not bother.

 

[JohnW2]

I've certainly seen a old PC power supply faced with a short through some hookup wire (don't know the exact size but probablly around 22 or 24 AWG) burn the insulation off the hookup wire and belch smoke out the fan. ...

That's hardly surprising. I obviously don't know what the capabilities of that 'old PC power supply' was, but these days there are plenty of ATX PSUs around that are specced to provide at least 45A/50A at 12V and at least 20/25A at 3.3V and 5V - so a current adequate to melt a piece of hookup wire would probably feel nothing like an 'overload' to such a PSU

Kind Regards, John

 

[B Wilde]

Sending 12 or 5V down long cables is asking for trouble.
The end devices would be designed with the expectation that the power supply cabling is perhaps a meter of less.
How would they cope with the significant interference picked up on a cable perhaps 10s of meters? In addition the device may not cope with high voltage spikes
generated when initially powered up (high inrush currents combined with long cable inductance).
Load regulation (ie. how much the voltage varies with current draw) would be poor.
USB is a hugely complex protocol often you'll require more than +5V and Ground.

Normally Point of Load (POL) is the better solution...run a higher voltage (say 24V) to the required locations and convert that down to 5 or 12V.
With switched mode converters efficiency can be 90% of higher.

Thanks, that's helpful - Perhaps 24V over Cat5 with a small 5V converter like the example below tucked behind the 'load' e.g. the alarm or touchscreen panels I'm considering?

https://www.aliexpress.com/item/329...exp_id=41967241-9058-4e26-9882-17963224a7a0-0

 

[Gasguru]

I would not want a power supplies from ebay/aliexpress in my house...I'd want to see a proper datasheet showing the spec.
Have a look at YY Control Cable.

 

[Harry Bloomfield]

I've certainly seen a old PC power supply faced with a short through some hookup wire (don't know the exact size but probablly around 22 or 24 AWG) burn the insulation off the hookup wire and belch smoke out the fan.

Interestingly the PSU still worked afterwards.

It would have gone into current limiting. I have a 13.8v 50amp supply here, a repurposed BT telecoms 50v job.

 

[JohnW2]

It would have gone into current limiting. I have a 13.8v 50amp supply here, a repurposed BT telecoms 50v job.

Indeed - as I said ...

.... However, as added 'reassurance', assuming that we're talking about SMPSUs, any half-decent one will have in-built overload (including 'short circuit') protection - and even those which are not 'half-decent' will probably stop oscillating if significantly overloaded.

Kind Regards, John

 

[DIYWell]

Perhaps I'm missing the point, but the idea of using high voltage is to lower the current requirements and voltage drop doesn't become a defining issue.

Also, the mains can be regarded as an infinite supply with no internal impedance since no matter how hard you load it in your house, the incoming supply voltage won't be changed by it. If you load your 12V supply, the psu output voltage will drop. If you overload, current protection can be an issue.

Voltage supplied by newer USB chargers is not fixed. The Quick Charge 3 spec allows compatible chargers and devices to negotiate and raise the voltage to 9V for the initial charge section.

Run cat6 to rooms, put patch panels in cupboards. You can always inject PoE if you need to power a device. PoE is about 48V with a current limitation depending on the PoE device type. Think 500mA to shy of 1A.

 

[JohnW2]

Perhaps I'm missing the point, but the idea of using high voltage is to lower the current requirements and voltage drop doesn't become a defining issue.

Certainly one of the main points for considering it.

Also, the mains can be regarded as an infinite supply with no internal impedance since no matter how hard you load it in your house, the incoming supply voltage won't be changed by it.

Not by very much, but it certainly will change (drop), otherwise Mt Ohm would have to turn in his grave!

If you load your 12V supply, the psu output voltage will drop.

It will. However, if you loaded the mains supply with the same current, the voltage would drop by the same amount. If that voltage drop were, say, 3V, then the fall from, say, 240V to 237V would be of no consequence, but the drop from 12V to 9V might well be a problem. The point, of course, is that for a load of given power, the current (hence voltage drop) will be much less at mains voltage than at 12V.

Kind Regards, John