48V DC

Hello,

I am living (again) in an old House (built) 1911 and we are taking all old stuff out on a step by step basis. This included the whole electrical installation. As we are located in a small town and connected to the grid, there is the obvious 230V AC distribution in the house. But to use LED lights more efficient and economic:

There is an second 48 Volt Direct Current distribution installed. (And expanded from time to time.)
It is powered by an highly efficient 100 Watt converter that I bought for 20 Euro.
At the moment it completely powers the lights in two rooms and provides various dim lights.

This has a few advantages:
1. 48V DC is completely save. You can touch it without any harm (or feeling something else than the copper wires).
2. As only LED lights are used, it requires very little power.
3. As transmitted power is the product of current and voltage, only a small current is needed (compared to 12V, 5V, ...) installations. This makes it possible to use very thin cables (about 1mm x 2mm with a copper cross section of about 0,1mm².
4. The thin cables can be placed almost everywhere in the walls.
5. you can use your creativity freely. In the worst case you destroy an LED (at most a few euros) and create a short circuit (which does no harm – the power supply is designed to detect this and shuts itself off for a few secods).

So far I have used the following LEDs:
- 24V led module (using two in series)
- 12V lamps (didn't work out as they had integrated switching circuiuts that didn't like being chained together)
- a ligh power LED-chip (700mA, 35V) with a constant current regulator glued on a PC cooler (extremly bright but also extremly hot and subject to temperature problems)
- 500 warm white and 500 cold white LEDs ordered from China. They cost about 10€ per 500 LEDs, but do not reach the efficiency and brightness of the high-tech (and high-price) LEDs, but with some soldering (and added resistors to protect them from thermal runaway) they provide neat lights for decoration and when you do not need daylight brightness.

Some pictures will follow.

Greetings from northern Germany.

There are real efficiency advantages to low voltage DC, just as you suggest.

I would add one little detail, 48 to 50 volts DC is high enough that, under the right circumstances, it could mess you up.

The right circumstances would be, damp or wet conditions, a well grounded person, contact/circuit through both hands, or one hand and one foot (so far more current goes through your torso/heart. Some people are more sensitive than others. Some can notice/feel/be affected by anything over 30 volts.

Absolutely, 48V is safer than 240 V.

And your setup would automatically limit current to lower safer levels.

Here's a fuller discussion of how much and what kind of electricity can damage or kill you.

http://www.candlepowerforums.com/vb/showthread.php?261353-When-does-DC-voltage-become-dangerous

I'm totally not the safety nazi, you're an adult, you're smart, etc.

But, knowledge is power, so, more power to you.

A couple things I can think of that should be mentioned about DC, it cannot travel very far without losing some of the voltage. So for anyone with a remote system, or solar panels they are thinking of keeping the power in DC, the panels, controller, inverter and lines to the house need to be very, very close. AC, on the other hand, can travel quite far down a wire and still give you the voltage you need, which is why all those wires overhead on poles are AC and not DC.

Without an inverter to change the DC to AC for every appliance, all appliances would need to be DC and are very expensive, and I don't know where you would get parts for them or get them fixed, except with the original manufacturer. So literally every electrical thing you need to use has to be a DC version,, coffemaker, lamps, microwave, refrigerator, vacuum, printer, computers, TV, DVD players, electric razors, etc.

Sebastian, even with the converter, as you call it, you will still need to have AC to run large appliances like the fridge, printer, vacuum, so you'll need AC lines anyway, right? It seems like the LED AC bulbs use so little power, it wouldn't make much difference. Do you want two sets of electrical wires going through the house? Will you or future owners or repairmen remember which are which?

100 Watt converter/inverter isn't going to get you much more than a few LED lights. Not even a laptop or computer as the monitors use more than that.

If you are worried about safety of the AC, there certainly should be breakers in the system, and you can use power strips inside with built-in breakers that will shut off if too many appliances are plugged in at once, that could start a fire.

Troy:

I would add one little detail, 48 to 50 volts DC is high enough that, under the right circumstances, it could mess you up.

I agree, that it is certainly possible to kill yourself with it: Resistance is Futile
On the other side there is a huge difference between working on 230V AC and 48V DC. On the 230V I make sure not to have any contact to a conducting surface, shut off the power (if possible) and double check that there is no voltage on any wire. With the 48V DC cables I try not to short them, but the tension and concentration required otherwise is gone.

Cristo:
The range that power can travel depends on the resistance of the conductor (cables) and the current that flows in them. The choice whether one uses AC or DC only matters during transformation. An AC transformer is simple (two coils) compared to a high power DC transformer (which will involve DC -> AC -> AC -> DC conversion).

The different voltages for the appliances are a problem, but for now the 48V DC system is an experiment to explore the possibilities.

Using a coffeemaker with electrical power is not a great idea, as it requires a lot of power. And building an off-grid system that can provide some 2kW requires good batteries and electronics.

Lamps are certainly possible (this was the original reason to build this): The need for individual converters simply disappears (which is a big source of cost when using LED lights).

Vacuum: The "normal" deviced build for 230V AC will not work, but it is possible to modify them. The better idea would be to buy an vacuum for 24V DC and use that voltage everywhere.

100 Watt converter/inverter isn't going to get you much more than a few LED lights.

LEDs can be 10 times more efficient than incandescent light bulbs, so you can get an equivalent of 1000W out of the 100W power source.
When you look how the light is distributed, you may notice that half of it ends up in the wall behind or the ceiling above the lamp. There is another 2x gain possible when you can control the direction of the light (which is possible with most LEDs).

The power supply is enough to light the whole house, if not we are wasting too much energy! If it should really happen, that more power is needed, it is still possible to put a second power supply next to the first one.

The AC system is build according to the standards … There are fuses for each cable that make sure the current does not go above the allowed limits.
Nevertheless starting a fire is still possible... You can get 3.6kW out of a single cable!
I would love to get rid of the normal AC system, but for now the people that it for granted. Besides that until we have a proven power source in the house (which is an other topic) we still need the grid.
But still, when all the lamps and their switches are done with DC, the AC part will be reduced in complexity.

Now finally the photos (part 1/3):

two of these lights are used in a room with clay on the ground (I removed the floor, so it's the earth below the house) and on the walls.
They have 24V each and are connected in series.

Part 2/3:
These are cheap warm-white LEDs from china and they have proven not to be very efficient. These are probably the first and the last LEDs that I will buy without verified measurements and quality control.

15 of these LEDs are soldered together with an resistor around 100 Ohm. As the voltage-current curve of these LEDs varies with their temperature and they do heat up to about 30°C, it required some monitoring to make sure they won't damage them self.

Part 3/3:

These are cold-white LEDs build with the same principles as their warm-white counterpart.
I wanted to see how they could be integrated into the wall.

It was also possible to build a switch for them that is not as intrusive as the usual fat switches.
It required some care to prevent the clay from entering it, but it works!
I have allowed myself to make a closeup of it and to toggle it during the exposure of the photo.

Thanks for the pictures.

Agreed, the efficiency of AC vs DC has everything to do with the voltage and resistance of the conductors. At the same voltage, there are trivial differences in the efficiency of AC or DC.

And changing voltage these days is a whole new ball game. Transformers aren't the only game in town any more. Even for long distance high voltage lines, DC has distinct efficiency advantages over AC these days.

Sebastian, yeah, I do know that LEDs are way more efficient, but if we're talking about a whole house, there are going to be appliances that require more watts at a higher voltage, that's what I meant. Maybe your DC is just meant for one room you are experimenting on?

I would be more concerned about maxing out your 100W inverter. Inverters tend to heat up, which is very destructive to electronic devices. If the fan has to come on to cool it, it's using some of its own allotment. If it doesn't have a fan, it should, if you want it to last. The 100W inverters I've bought in the past didn't last more than a few years with daily use. A quality 300W or 500W inverter would give you a little more room to expand into another room, and not make the thing work so hard, and not cost much more.


I hope you have a main breaker, even on a DC setup.

Cristo Balete wrote:Sebastian, yeah, I do know that LEDs are way more efficient, but if we're talking about a whole house, there are going to be appliances that require more watts at a higher voltage, that's what I meant. Maybe your DC is just meant for one room you are experimenting on?

The appliances that require too much power or do not support 48V are not connected to it. So it's limited to the lights for now. And unless we switch the main power type there isn't a gain in using 48V for devices that already have an AC supply.
When 48V devices with higher power demands enter the house, I will probably use separate cables as they require more attention (I would like to avoid melting/evaporating the cables…). They will also get fuses.

Cristo Balete wrote:
I would be more concerned about maxing out your 100W inverter. Inverters tend to heat up, which is very destructive to electronic devices. If the fan has to come on to cool it, it's using some of its own allotment. If it doesn't have a fan, it should, if you want it to last. The 100W inverters I've bought in the past didn't last more than a few years with daily use. A quality 300W or 500W inverter would give you a little more room to expand into another room, and not make the thing work so hard, and not cost much more.

It is a used quality inverter [MEANWELL RS-100-48. They said it was used for commercial microwave devices, so it's designed to be used all the time. I have looked inside and it appears to be of good quality.

Cristo Balete wrote:I hope you have a main breaker, even on a DC setup.

There is a switch for the DC inverter on the AC switchboard if you mean that.