House renovation, how to a good electrical system oriented to MySensors?

[TRS-80]

This post is deleted!

[TRS-80]

@mfalkvidd said:

Common household electrical cables are 12 AWG, which is rated for 20 amps maximum. That means you can use a maximum of 240W at 12V. It is recommended that you don't exceed 80% load, which is 16A/192W.

Yes but in the U.S. that is 20 Amps @ 110V = 2,200 W.

Which kind of throws all the rest of your calculations off a bit. :)

Also, OP is in Italy, my understanding is mains in Europe are like ~220 or whatever. I'm not sure if that comes on one leg or not (in the U.S. we also have 220V circuits for larger loads like dryers and pumps, but we get the 220 by putting 2 legs of 110 together). So I have no idea what the average size house wires are in Europe...

At any rate, some additional careful and knowledgeable planning definitely should be done. This is doable, but not something you want to rush into without proper planning...

[mfalkvidd]

@TRS-80 said:

Yes but in the U.S. that is 20 Amps @ 110V = 2,200 W.

Which kind of throws all the rest of your calculations off a bit. :)

Yes. If you use regular voltage, you will of course get regular wattage. But that's not what this thread is about, unless I misunderstood the OP's question about running on 5/12V.

[TRS-80]

@mfalkvidd said:

Yes. If you use regular voltage, you will of course get regular wattage. But that's not what this thread is about, unless I misunderstood the OP's question about running on 5/12V.

What I meant was, when you say that 12AWG is usually good for 20 Amps, that is in a home circuit which assumes 110V.

However, if you are only running 12V, couldn't you run more Amps? Or is wire sizing strictly based on amperage?

[mfalkvidd]

@TRS-80 yes it is only based on amperage. In Sweden, where we have 230V mains the same cable can be used to transfer 20*230=4600W.

http://www.homedepot.com/c/factors_to_consider_when_wiring_your_home_HT_BG_EL H has some information on cable selection.

[tbowmo]

It's a bit complicated. The problem is that the lower the voltage, the higher the amperage is needed to be, to keep the same output wattage on the string.

if you are not running sufficient wiring on the low voltage bus, you'll get into troubles with voltage drops across the wires (ohms law). And THAT would also lead to heat dissipation on those wires (Again, ohms law)

Power dissipation on the wires would be something like : (I²)*R = P. Where I = total current drawn, R = wire resistance, and P = Watt dissipated.

[yancym]

Interesting conversation. I can't help but throw a fly in the ointment, as they say. Have you calculated the cost of all this additional infrastructure? Wouldn't it make more sense if you are going to this level of implementation, to go with a standard system like zWave/ZigBee modules, or something else on the open market? It's plug and play into any existing standard home electrical infrastructure. In addition, they are all fully certified products for home use and limit your risk of liability should you have an electrical fire or anything else that could be attributed to your self built system.

Don't get me wrong, I like MySensors and am using some point solutions that make sense for me. I myself have contemplated putting in a full blown MySensors environment for control of devices, but I'm having a hard time justifying the costs and risk in doing so. In addition, I won't plan on staying in my house forever, so the potential resale could be more difficult with a non standard infrastructure.

Just some thoughts to consider. Would love to hear some additional ideas on the topic.

[bruno]

The house at the moment is completely without the electrical system, so for me the price, at the end, will be the same of a traditional system.
Also today i decided to not use a drywall with electrical pipes inside, but to use external electrical system like this just for idea:

So all is more easy (installation, maintenance and price).

I think to never resell this house in future, but if this will happen i can convert it to a traditional system in a relatively easy way.

It's true that is more simple and secure to use a commercial system, but in this way i will loose the taste to realize the whole system :)

@TRS-80 : In Italy we have 220V mono-phase for civil installation and 380V tri-phase for civil/industrial installation (usually for industrial machine or for a farm like mine).
And wire size usally are 1,5mm for lights (10A) and 2,5mm for sockets (16A).

[alowhum]

I wanted to revive this topic, as I'm noticing this is becoming a little more common.

If anyone would now build a second DC system in their home, how would you go about it?

I get the sense that the industry is standardising on 48 volts for this. It's also a common output for photovoltaic systems, so you could connect a solar system quite easily.

@bruno, what did you go for in the end?

I've been donated a large spool of speaker wire, so I could retrofit something in my home. Since Arduino's can take 12v input voltage, I was thinking it would make things nice and simple if I used 12v. I could buy a PC power supply (Andres Spiess seems to dig those) and hook that up somethere in the middle.

• Would a 12v system be a bad idea in a small city apartment? At what apartment size should 12v no longer be considered?
• If many 12v devices share a wire, does that lead to any weird side effects?

[skywatch]

For any system using such low voltages it is best to run them as AC and then rectify near the point where DC is required as the losses in the cables will be large if DC is sent along a 20M run of cable.

There will also be less induced noise on the (DC) power lines if you do this.

[alowhum]

Thanks. But my apartment is only 10 from front to back. I thought that if I place the power source in the middle, then the maximum distance to an endpoint is about 5 meters. The same as the maximum length of USB extension cords.

Would you still recommend against it for those lengths?

[scalz]

@alowhum
it could work. voltage drop mostly depends on the load, wire size, voltage source and cable length. You could also use ethernet cable, it's quite cheap and shielded, and you could use pair of wires for power etc. This might reduce a lot the voltage drop if it's an issue.
you can find voltage drop calculator on google.
Be careful, some cheap arduino have cheap/fake 12v ldo, which can heat and die when running on 12v after a while

[alowhum]

Thanks! Ethernet cable is a great idea (since it's also used for power over ethernet it makes sense). Unfortunately I've already been donated some speaker wire. It's gauge is larger than ethernet, and it's made of copper, so I think it should be ok.

[skywatch]

@alowhum In that case I would suggest you try it with 'floating cables' and see how it goes.

It may be 5M direct, but by the time you have routed the cables it could be a lot more. Cable cross-sectional area will have an impact too. But as you add more nodes with sensors, diaplays etc then the issue will be more pronounced.

Be sure to check the max rated voltage and current of the cable you eventually use. Also check it is compliant with any building/electrical regulations as a fire caused by non-compliant installation will often result in insurance being denied.

If you can, run the cable as a loop as this will minimise voltage 'sag' at the end of a run.

[alowhum]

Thanks for the advice @skywatch! You're right about the distance increasing, for sure. Then again, if the voltage drops from 12v to, say, 10 volt, would that matter? The Arduino itself will still bring it down to 5, and it can handle anything between 6 and 12 as an input on the jack plug?

What do you mean with running it in a loop? Where could I learn more about that?

[Sasquatch]

@alowhum said in House renovation, how to a good electrical system oriented to MySensors?:

What do you mean with running it in a loop? Where could I learn more about that?

wires in the loop:
PSU-----GW----Node1----node2
|____________________________|

Use switching regulators to keep current down.

[skywatch]

@alowhum Voltage drop will be proportional to the current drawn by devices, so it may be acceptable at first but get worse as more items are added to the system.

As for the 'loop' look on google for 'ring main wiring'. Essentiall instead of a power line going from psu to a number of nodes in a single spur that ends with the last node, the connection for the last node goes back to the psu.

Bit like I said, just run some of the cable you want to use across the floor and try it out before installing it all.

@Sasquatch that is not the way a power ring main is wired, sorry if I was not clear on what I meant. Hopefully it will be clearer after seeing it on google/youtube. Also, for a mains powered system a linear regulator might be a better choice. Not as efficient I agree, but less noisy output and the power savings would not likley show on the electricity bill! ;)

[Boots33]

@alowhum There will be a wealth of information out there on the net and probably also at your local library. look for resources about remote cabin power systems and also even the larger 5th wheeler type caravan systems will be helpful reading. You will also need to check your local building codes to see if there are any rules to be adhered to.

When we built our house (about 15 years ago, long before i discovered MySensors :) we ran a low voltage backbone cable throughout the house. From this backbone we ran smaller cable drops to every room in the house. Many of these are still not in use but as others have said the cost of running wires is relatively cheap when you are building. Of course we still have mains power as well and use the low voltage system to compliment this.

In those initial years the 12v system was used primarily for lighting systems such as night lights etc. As time progressed we installed 12v outlets in the bedrooms and these now are used to power bed/reading lamps. The small 12v downlights have also proved to be very easy to convert over as well. These were initially halogen bulbs but now there is a good range 12v LED replacements for just about any type of socket. Once I discovered MySensors and home automation then the 12v system became even more useful now powering several nodes and even the gateway.

Right from the start we ran our system from a battery with solar charging and in 15 years it has never let us down. Voltage drop will always be a thing to watch, but with LED's low power draw and as you have surmised the ability of arduinos to run well below 12v it will usually be of little practical concern. Unless of course you are thinking of running more than lights and nodes.