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Extra Low Voltage (ELV) refers to electricity supplies of 50v and below. These are usually DC, but need not be so.

Why Extra Low Voltage?... because the regional electricity Distribution Network Operators already use the term Low Voltage to refer to 240v (single-phase) and 440v (3-phase) which feeds our homes.

Over on the topic Anyone want to share costs on batteries, we've been discussing the merits of those batteries being grid-tied or off-grid.

In the course of those discussions I have dropped in a number of diagrams similar to this:

Off Grid battery5spB2

In this topic we are concerning ourselves with the bottom-right of that graphic.

These are devices in the home which can be run directly from the battery rather than via the 240v AC output of the off-grid inverter.

Why should we want to do that?

  • A householder is permitted to run their own cables and sockets for ELV. Employing a qualified electrician is not mandatory.
  • Devices powered directly from the battery will remain live in the event of a power-cut
  • It is more efficient to connect devices this way

Each time we pass the stored electricity through a conversion unit to change its voltage/frequency, we lose some of the energy in the process. It makes little sense to take the 48v DC from a Storage Battery, pass it through the Inverter to create 240v AC, and then use a 'transformer plug' to connect a landline phone at 12v DC.

This topic was modified 2 months ago 3 times by Transparent

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Interesting topic.

My portable marine fridge fridge freezer runs off only 12v, plugs into a 12v cigarette lighter type socket. I use it for camping. 

So begs the question how far could we go in the future in running much more appliances off 12v. Could a lot be run this way? 

Do we need standards for appliance manufacturers? What might the limits be in terms of the types of appliances and load? 

 

 

 


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Lots of questions arise from those points @jeff  Since there are few 'Standards' let me start by addressing the issue of which voltage to use.

Twenty years ago I attended a day-long symposium at the University of Bath, where most participants were European manufacturers/researchers in the field of high-brightness 'white' LED light. I have no idea why they thought to invite me, but it was an excellent introduction to a field of engineering which we now take for granted. 😎 

One interesting conclusion from the day was a call for all homes to be wired with 24v DC in addition to mains power at 230-240v AC. Over the years I have been doing precisely that, whilst learning what does and doesn't work.

Any move towards DC cabling in the domestic environment must surely start by acknowledging that 100-years use of lead-acid batteries has led us to a field which is dominated by three voltages: 12, 24 & 48v.

Let's suppose we wish to deliver these three possible DC voltages to drive a 'load' of 200w.

image

To derive the wire-size required to carry the current, I've looked at websites used by railway modellers like this. They have decades of experience with ELV and know how to operate within adequate safety margins. I've assumed we are running a pair of wires next to each other, with a voltage drop no more than 4% at room temperature 20-25°C

The price per 100m cable-drum is from CPC/Farnell, including VAT, and refers to the cheapest red or black wire which meets or exceeds the minimum specification. (For obvious reasons, please don't use brown/blue for ELV circuits!)

It is clearly very much cheaper to wire a house with 48v than with 12v or 24v because copper wire is expensive. However, there are very few devices available which can take 48v input. I have only one - an wired-network hub with Power Over Ethernet (PoE) capability.

Most home devices will require 12v or 24v, just as Jeff's camping fridge does.

Since I'm now starting afresh with a large-capacity 48v LiFePO4 battery, I will be taking 48v to my home 'distribution points' and then stepping down to the required voltages using DC-DC converters.

DC DC convertersSm
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@transparent

Thanks, interesting

May i ask what size wires you have decided to use then, are you going for the 200w capacity?

Have you an idea of what amount/percentage of your energy will be via the low voltage setup annually ? 

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@transparent

I am rather confused as to what you are actually trying to achieve.

It would appear that your intention is to take 48v DC, convert it to AC, then back to 12v DC, within a DC to DC Converter. rather than take 48v DC and convert it to 240v AC. Besides to cost of the DC to DC Converters along with additional wiring around your home you will have the power loss within the converter and additional cabling.

Unless you can get equipment rated for 48v DC, I cannot see any real gain, and if you move home in the future you may have to replace lots of DC powered devices that you can no longer use.


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Posted by: @jeff

May i ask what size wires you have decided to use then, are you going for the 200w capacity?

I think that would be lacking in adventure 🙂 

Here's an overview of the intended 48v wiring to the existing ELV wiring positions.

48vDistribution

And here's the DC-DC converter panel for the bottom of the server rack under construction:

48vServerRackSm

This server-rack location requires 19v for PC and monitors. 19v is commonly used for laptops too.

 

Posted by: @derek-m

I am rather confused as to what you are actually trying to achieve.

[...] if you move home in the future you may have to replace lots of DC powered devices

My house already has a high proportion of inbuilt 'devices' which operate at 24v. Here, for example is the light I made for the main living room:

LoungeLight10Sm

Remember, I started embedding 24v DC into the fabric of the building soon after attending the Bath Uni symposium. Initially these operated from a 1.7kW wind turbine supplying lead-acid batteries.

At 2m diameter, this living room light is very much a fixture. It wouldn't be taken to another house in the event of future move.

 

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Posted by: @jeff

Have you an idea of what amount/percentage of your energy will be via the low voltage setup annually ?

I'm now looking at this from the opposite viewpoint... using ELV unless there is a reason not to do so.

The current objective is to create a system which can run heat-pumps from off-grid battery as much as possible.

If we could do this for 20hrs/day, whilst reverting to mains-grid only for 4hours whilst the batteries are being re-charged, that would be good. Such an approach would reduce the adverse affects of heat-pumps on the Distribution Grid by 83% - which the DNOs would love!

Let me post here I diagram I first put on the OVO Forum over 3 years ago. It shows home devices which could be operated using the Auxiliary Load Control Switch (ALCS) feature inbuilt to our Smart Meters:

ALCSdevices2med

Notice how many of these devices require 240v AC to run them - mainly those with motors. But the heat-pump is by far the most significant because it is expected to operate 24/7.

If we can 'crack' the heat-pump issue, then it's really only the EV-charger which you probably wouldn't feed from a home storage-battery.

When customers apply to their DNO to connect Low Carbon Technology (Heat Pumps or EV Chargers) the form requires the Maximum Demand of the house to be calculated. I was pleasantly surprised to learn just how low this figure generally is. My own house (300m²) takes 20A before adding the EV Charge-Point.

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@transparent 

Are your ELV applications generally fixed wiring?  There is a fair amount of available 12V automotive plug in equipment, generally using cigarette lighter sockets -phone/laptop chargers, lights.  Would you use those, or are you bespoke / some other preferred plug and socket for use at ELV?  

20 years ago there would have been significant losses associated with converting 240V-5V dc, and very significant standby loss of 1-5W from the bulky 50Hz transformers.  They can be, and generally are now, significantly better - I think 100mW is common, and that is only going down.  

I like the resilience an ELV system gives in the event of a power cut, so I can see it being a great idea for lights, internet, maybe a few other low power things.  


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@transparent

Having worked on and helped design many highly complex systems over the years, one of the things that I learned fairly quickly was keep it as simple as possible. Adding complexity not only adds to the costs, but also introduces an additional point of failure.

I appreciate that you and a few others may like to experiment (I do so myself), but sometimes the benefits may not be as great as first envisaged. 

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@transparent

I welcome and indeed encourage your efforts to help mitigate the effects that both renewable energy production and modern energy appliances are having on the DNO's and the overall operation of the National Grid. I also feel certain that all involved will be more than happy to allow their customers to solve their problems. Don't get me wrong, I have been doing my bit for quite a number of years to become as 'grid neutral' as possible.

You can correct me if I am wrong, but there would appear to be two distinct, but often complimentary, main problems that both the DNO's and National Grid experience to a greater or smaller extent.

The first is matching supply to demand, which often entails transporting energy in bulk over large distances, with the cost of the required infrastructure and inherent losses.

The second is balancing the loading between the 3 phases, so that the infrastructure and losses can be minimised at a more local level.

The former will probably require the storage of electricity in bulk as more and more renewable generation comes on line, or the production of green hydrogen for use in gas fired power stations. Work is being carried out at the moment on the development of Iron-Air batteries for the bulk storage of electrical energy, which it is claimed will be a much cheaper alternative to Lithium batteries. Domestic storage systems may help to some extent, but will no doubt not always be located in the correct place and will not always be available for use.

I have been giving some thought to the second of the two main problems, balancing the loading phase to phase. I know that National Grid are not allowed to generate electrical power, but I'm not certain if the same restriction applies to DNO's. Also, does storing energy in batteries and then producing AC using an inverter count as generation? My idea to help balance the phases would be to have single phase inverters on each of the 3 phases at suitable locations within the local DNO network. Each inverter would be connected to a common battery storage system of adequate size. On the phase with the highest demand, energy would be drawn from the battery storage to help mitigate the loading, whilst energy from the lowest loaded phase could be drawn to charge the batteries via the inverter. This method may also help to alleviate the supply to demand problem.

I feel that the above would be much more cost effective than having individual domestic storage systems, and also would be much more beneficial to the DNO's, since it would be under their control. I also feel that much of the initial cost could be recouped from infrastructure and efficiency savings, and will eventually lead to savings for customers along with a more reliable and resilient electricity network.


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Posted by: @derek-m

Having worked on and helped design many highly complex systems over the years, one of the things that I learned fairly quickly was keep it as simple as possible.

In many cases I would agree. But I could easily apply that argument to the ubiquitous GU10 LED light bulb.

It's the most common type used in kitchens, which in turn is the room in the house which has a requirement for the highest level of illumination. As such the DIY warehouses sell far more of these than other LED bulbs. They would say "there is high customer demand".

Invariably the GU10 have the shortest lifetime of all LED types because the embedded electronics runs hot. This can't readily be dissipated within the confines of a bulb being fed from 240v AC.

So why should anyone consider changing away from such a simple product? After all, it's LED, so it must be efficient, mustn't it?

GU10

It's now 11 years since the UK ceased manufacture of incandescent bulbs. But the GU10 halogen bulb could hang on until September last year (2021) and still be sold 'whilst stocks last'.

The GU10 is expensive in the long term because you get through so many of them, whether they're LED or not. There have been better alternatives for the past decade, and I'm disappointed to see new houses being built close to me for a Housing Association which still have GU10 fittings in the kitchen ceilings.

Yes, it's more complicated to separate the LED light source from the electronics which supplies it. But I have no doubt that is the better solution.

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Posted by: @derek-m

I know that National Grid are not allowed to generate electrical power, but I'm not certain if the same restriction applies to DNO's. Also, does storing energy in batteries and then producing AC using an inverter count as generation? My idea to help balance the phases would be to have single phase inverters on each of the 3 phases at suitable locations within the local DNO network.

I discussed this very solution with my DNO in the initial year of the OpenLV Project to have monitored substations. Great minds etc....  😎 

DNOs too are not permitted to own generation assets. And Storage falls within that definition.

There is no such restriction on members of the wider community offering 'balancing services' to their DNO. This already forms part of the revenue streams handled by both DNOs and National Grid.

Since Western Power Distribution have generously provided a 3-phase connection to my house, you can see which way I'll be heading. 🙂 

3 phase

There are seven main categories of 'losses' which exist on the Grid. I've illustrated them in detail on the OVO Forum topic Balancing the Grid. Phase-imbalance is just one subsection within the 7th definition I've listed.

If you'd like to discuss these in more detail can I suggest

  1. we create a new topic about Grid Losses and the RIIO-ED2 Agreement for DNOs to take action to reduce these
  2. you copy the graphics from that OVO Forum article into that new topic as required. Either I own the copyright or else I have permission from Western Power to reproduce their material for purposes of education and public awareness.
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@transparent @derek-m @mars

As a general point i think it might be good to split out a few of the threads? 

Some the threads have quickly got into a lot of detail, great for some readers, other readers will glaze over.

As an example the posts around batteries went from asking for recommended installers and asking for comments on quotes from installers to quite a lot of detail on building your own batteries.

Unless there are different threads that cater for different types of customer it gets messy. I can't even put up a curtain rail these days following an injury.

I am all for education and knowing the detail and options is important and the shortfalls and costs and background etc. I really enjoy and value the detail. I wonder about who the target audiences are for the forum. Perhaps the forum will just self select to those that want lots of detail and be very hands on. That is fine also. But it will mean others don't contribute or ask questions. 

I don’t know if this post is useful or not. Just my thoughts. 


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Posted by: @robl

Are your ELV applications generally fixed wiring?  There is a fair amount of available 12V automotive plug in equipment, generally using cigarette lighter sockets -phone/laptop chargers, lights.  Would you use those, or are you bespoke / some other preferred plug and socket for use at ELV?

We're moving very fast into another area of discussion within the subject of ELV. I'll address what I've found out concerning connectors here. But please feel free to return to some of the matters already raised above.

Yes @robl - the majority of my ELV use is with fixed devices rather than those which can be plugged in. I'm in favour of both approaches. However, I'm currently renovating/extending a 1930s farmhouse and I'll obviously be running as much cabling for ELV lighting as possible whenever floor-boards are up!

There are many instances where I've run 24v cables for lighting or touch-sensors, but the light-units themselves or the controllers are still missing because I haven't yet found time to design them!

For example, here's an 'individually addressable' LED strip being installed in an aluminium 'corner bead' when I was busy plastering a room. It's not for 'flashy' lighting effects as more commonly offered by controllers bought from the Far East. But I have yet to develop the colour-fading/graduation system which I'd like, and the touch-interface to control it.

LEDfixStripSm

I also have two independent water-purification systems because we don't have mains water. One of these uses an innovative 24v LED-based UV light (265nm) which kills bacteria by denaturing the DNA.

UVlayoutSmLabels

 

ELV plugs and sockets:

Almost all DC connectors are the cylindrical 'barrel' type. The two most commonly found ones look almost identical, differing only by the central pin being 2.1mm or 2.5mm in diameter.

image

Unless otherwise stated, you should assume that these sockets can only deliver 1 or 2 amps. However, you can get 5A versions made by Switchcraft from Rapid Online, and I've used these to make 'wall sockets' in various places around the house. That effectively gives me a nominal 100w socket with a resettable over-current trip beside it.

WallSkt1

The company who make the 'best quality' ELV DC sockets are Lumberg. Their range is extensive, but UK suppliers like Farnell sell the most commonly used connectors. If you're looking for a plug to fit a laptop or an LCD monitor, start by considering their Product Code 1636 05 with a 1.4mm central pin.

Lumberg's range includes a 10A plug and socket 1636 07 & 1614 21. However, to achieve this current rating they take a fair bit of effort to couple and take apart again. The socket would need to be mounted on a substantial faceplate.

image

 

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Posted by: @transparent

A householder is permitted to run their own cables and sockets for ELV. Employing a qualified electrician is not mandatory.

So if I'm reading this correctly connections from (off grid only?) inverters to batteries (16S LiFePO4) is ELV.

Do you have any favourite reference works for how to correctly wire these ELV systems? How do you feel about the Victron Wiring Unlimited book as a starting point?


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