Direct Current in the home

PeterRT: 
 

With more and more in the home being powered off DC (Direct Current) supplies, e.g. Battery & Solar Panels, then wouldn't it be more economical to consider extending the regulations to cover DC in the home avoiding the need for transformers?

For example, this is particularly appropriate now that lighting is dominated by LED.

Then hopefully no L.E.D. light flicker.

Z.

I think the authors of the current regs BS7671 think they do already cover the  use of LV and ELV DC in the home, with a nod to other standards for things like telecom equipment.

Solar panel strings of less than 1kV are covered, as are SELV and PELV DC systems.

 I suspect what you are really wishing for is for someone to decree a standard voltage and or harmonised set of connectors, and sadly that is as far off as ever it was.

Mike.

PeterRT: 
Unfortunately I do not have a copy of the current regulations as they are very expensive for the occasional read for interest.

Yes, for DC in the home I would expect to see a standard voltage, maximum power, standard plugs and sockets etc so I can go to a specialist technician and get it done.

Peter.

BS 7671 is in a good place for DC systems, but product standards for household products are not yet up to speed.

Standard voltages for AC are not stated in BS 7671 … they are in BS EN 60038 CENELEC Standard Voltages.  This standard has the following preferred voltages for DC equipment below 750 V DC: 6, 12, 24, 36, 48, 60, 72, 92, 110, 220, 440. However, the standard does not have preferred values for DC distribution. In fact, it only specifies (Table 1) AC distribution in terms of three-phase star/delta or three-phase delta.


In terms of electrical accessories, these are largely dependent on product standards, which are yet to be developed. This IET publication contains a commentary on the suitability of common standards for protective devices, accessories, etc., for use with DC: 

Interesting that in the BS EN 60038 CENELEC Standard Voltages, that the usual 28 volt DC used on many aircraft is missing, as is the rather unusual 112 volt DC as used on the Vulcan, Valiant and Viscount turbo-prop aircraft. 

Clive 

At least the preferred voltages do not include 8 volts, 16 volts or 32 volts all of which must be nearly extinct now.

The 28 volts used on many aircraft is I believe obtained from a 24 volt nominal battery, 12 lead acid cells. Should be about 28 volts in flight as battery on float charge.

The older BR era diesel locomotives were often said to use “110 volts” . This was a 96 volt nominal lead acid battery, 48 cells. averaged about 110 volts on charge.

nor does it include the common 5V used for ‘USB’ phone charger.

I'm not sure that you can standardise things in the current climate - if anything we seem to be diverging rather than converging.

Mike

      There is no standardisation amongst my laptops and gadgets on the DC voltage they expect for recharging.  Deriving an appropriate voltage is easy when starting with 230v AC, a suitable transformer, rectification, maybe switch-mode clipping, and smoothing.  But if you start with DC then I guess you would need a rotary converter or, when the required voltage is lower than supplied voltage, I suppose you could use a woefully inefficient voltage divider.  May I suggest that in UK we stick with the distribution of alternating current electricity to domestic customers.

ARE: 
 

   But if you start with DC then I guess you would need a rotary converter or, when the required voltage is lower than supplied voltage, I suppose you could use a woefully inefficient voltage divider. 

Solid-state DC-DC converters are common now, and very efficient. 

 May I suggest that in UK we stick with the distribution of alternating current electricity to domestic customers.

I don't think DC distribution in the public network is being considered at present (never say never, though, it was still present in some UK towns until 1960's I believe).

But for some purposes, DC circuits within buildings are definitely on the increase.

ARE: 
 

      There is no standardisation amongst my laptops and gadgets on the DC voltage they expect for recharging.  Deriving an appropriate voltage is easy when starting with 230v AC, a suitable transformer, rectification, maybe switch-mode clipping, and smoothing.  But if you start with DC then I guess you would need a rotary converter or, when the required voltage is lower than supplied voltage, I suppose you could use a woefully inefficient voltage divider.  May I suggest that in UK we stick with the distribution of alternating current electricity to domestic customers.

I think you may be a couple of decades behind on power supply technologies.

Conversion of AC to DC is now done using switch mode power supplies.  The AC is rectified to DC.  The DC powers a high frequency AC oscillator, which incorporates a small lightweight transformer.  The output is rectified back to DC again.  It works out lighter weight and more efficient than a traditional iron cored transformer.

DC to DC converters are available off-the-shelf for a wide range of voltages.  Again they are switch mode power supplies configured as boost or buck converters, to raise or lower the voltage respectively.  No moving parts are required, and the efficiency might be 85 to 90%.