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24v DC house lighting

 
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mr brightside



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PostPosted: Sat Jun 22, 2013 7:49 pm    Post subject: 24v DC house lighting Reply with quote

I've been considering the pros and cons of installing a separate 24v lighting circuit in a house. It would be powered from a bank of lead acid cells which would either be charged by solar panels or by off-peak mains 240. All the bits and bobs needed to set it all up could be got from a chandlery, as narrowboats are 24v. Anything that partially releases you from a reliance on mains power has to be a good thing even if in the end you break even on the long term costs. I can't see a reason not to wade in personally, can anybody else?
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adam2
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PostPosted: Sat Jun 22, 2013 8:46 pm    Post subject: Reply with quote

I doubt that it would make economic sense, but would still recomend a battery powered lighting circuit as a preperation for both short term breakdowns or rota cuts and for any longer term emergency.

12 volts might be better than 24 unless a large system is being contemplated. 12 volt lighting and small appliances are more widely available.

Please take care, a study of this thread is recomended
http://www.powerswitch.org.uk/forum/viewtopic.php?t=5455&highlight=safety+using+batteries
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mr brightside



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PostPosted: Sun Jun 23, 2013 11:35 am    Post subject: Reply with quote

adam2 wrote:
I doubt that it would make economic sense, but would still recomend a battery powered lighting circuit as a preperation for both short term breakdowns or rota cuts and for any longer term emergency.

12 volts might be better than 24 unless a large system is being contemplated. 12 volt lighting and small appliances are more widely available.

Please take care, a study of this thread is recomended
http://www.powerswitch.org.uk/forum/viewtopic.php?t=5455&highlight=safety+using+batteries


Cheers for the link, what makes you think it wouldn't make economic sense?

The reason i was considering 24v is because it keeps the current down and 24v travels better than 12v. I probably wouldn't go for any complicated charging and switching systems like some posters on the other thread (UPS etc.); i'd probably manually monitor the battery condition with a meter of some sort and throw an isolator to supply 240 to the charger with a Sangamo timeclock contact used to enable charging at off-peak times only. A contactor could probably be used somewhere to good effect. I'd also fuse each fitting separately from an automotive type fuseboard- just my personal preference, and probably wire it all in low smoke singles in low smoke plastic conduit. Conduit can easily be brought into junction boxes and toggle switches for the fittings can easily be mounted into plastic junction boxes.

I'd also only look to have enough light to move around the house and cook/eat by, low light doesn't bother me. It'd all be a bit industrial looking but it wouldn't matter to me as i don't have Kirstie Allsop and Phil Spencer to dinner.
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adam2
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PostPosted: Sun Jun 23, 2013 12:22 pm    Post subject: Reply with quote

If you calculate the capital costs of a battery charging system, versus the energy produced and the value thereof, then it compares poorly with grid tied PV or indeed many other investments.

BUT I would still go for it as insurance against short or long term failure of the public electricity supply.
If the lights go out regulary, or permanently ! how much is a KWH worth then ? many times todays price I suggest.

For a maximum demand of up to about 200 watts I would go 12 volts, unless unusually long cable runs are innvolved.
200 watts is only about 17 amps at 12 volts.
Perhaps 3 circuits each on a 10 amp fuse, but only loaded to about 6 amps each.

If you go for 24 volts, then I would think twice about vehicle type fuses, although these are rated at up to 32 volts, the breaking capacity is very limited and arguably insufficient if a fault occurs close to the battery.

For 24 volt systems I normally use mains rated equipment, which is fairly cheap.
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adam2
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PostPosted: Sun Jun 23, 2013 12:39 pm    Post subject: Reply with quote

For a maximum load of 200 watts you can get a lot of light with modern lamps.

Cooking area, 3 lamps. Living room, 3 lamps. Hall/landing/stairs, 3 lamps.
4 bedrooms and 2 bathrooms/showers/toilets, 1 lamp in each, 6 in total
Shed, workshop, and porch, 1 lamp each or 3 in total.

18 lamps in total, which presuming 11 watt CFLS is just under 200 watts.
The average load would be less as it would not be normal to use every lamp at the same time.
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adam2
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PostPosted: Mon May 01, 2017 1:17 pm    Post subject: Reply with quote

Whilst I stand by my previous remarks as being accurate at the TIME I POSTED THEM, technology moves on and 24 volts is increasingly worthwhile.

Until just a few years ago, 12 volts was far preferable to 24 volts for small scale standby lighting.
12 volt lamps were available in much greater choice and often of greater efficiency than 24 volts.

These days it is unlikely that incandescent lamps would be much used for emergency lighting.
LED would be the first choice in most cases, with fluorescent or CFL as possible alternatives.
A good selection of high efficiency 24 volt LED lamps are available, and for larger scale lighting needs 24 volt CFLs are available in larger wattages than 12 volt ones.

Many of the new LED lamps are multi voltage and may be used on 12 volt or 24 volt installations, or indeed on 16 volts if anyone still uses 16 volts these days.

Take care with 24 volts DC, although there is virtualy no electric shock risk at 24 volts, the risk of fire is significantly greater at 24 volts than at 12 volts. 24 volt DC installations should be done to the same standard as mains voltage equipment.

12 volts is still probably preferable to 24 volts for very small installations due to safety, simplicity and a cheaper battery.
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clv101
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PostPosted: Mon May 01, 2017 8:11 pm    Post subject: Reply with quote

After a few discussions with our electrician, I think we might end up going for 24 rather than 12V. Driven by cabling and voltage drop considerations. At 12V, a ~30m lighting circuit with ~40W of LED, which may well be all on at the same time, is looking at 14% voltage drop on 2mm2 cable and 9% at 3mm2. Anything fatter than 3mm2 starts getting expensive/hard to work with. Running a separate cable to each light fitting would cut the loads, but require a lot of cable!

At 24V, the voltage drop is obviously the same, but it's half the percentage/power.

I'm not seeing a great choice of LED lamps at 24V though. I recently bought a few of these at 12V, 6W, warm white, 3, which are excellent: http://www.ebay.co.uk/itm/172425606902?_trksid=p2057872.m2749.l2649
They don't saying anything about operation at 24V - think they might work!?
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adam2
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PostPosted: Mon May 01, 2017 8:57 pm    Post subject: Reply with quote

Presuming a fixed wattage, the voltage drop at 24 volts is not half (in percentage terms) of that at 12 volts, but is one quarter. Consider the following example.

A 12 volt circuit with a load of 10 amps has a voltage drop of 10% or 1.2 volts.
At 24 volts the load current for the same wattage will be only 5 amps and the voltage drop will be 0.6 volts, which is 2.5%.

In practice, a 10 amp circuit wired in 2.5mm cable will be fine for any likely domestic lighting circuit. 200 watts wont fully load the circuit, and 200 watts is a lot of LED lighting.

Don't forget some non standard socket outlets for 24 volts, for table lamps, floor standards and the like fitted with 24 volt bulbs, and of course for the Christmas tree lights !
The old type round pin mains outlets have become an unofficial standard for 24 volts.
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adam2
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PostPosted: Mon May 01, 2017 9:15 pm    Post subject: Reply with quote

clv101 wrote:
----

I'm not seeing a great choice of LED lamps at 24V though. I recently bought a few of these at 12V, 6W, warm white, 3, which are excellent: http://www.ebay.co.uk/itm/172425606902?_trksid=p2057872.m2749.l2649
They don't saying anything about operation at 24V - think they might work!?


I have purchased the exact same lamps from fleabay, long term durability unknown, but they seem OK and are certainly very cheap.
I would expect instant failure at 24 volts.

24 volt LED lamps are very common now, suppliers include

http://www.onsolar.co.uk/OnSolar-12V-24V-LED-Light-Bulbs.shtml
Who have a range including lamps with two switch selectable brightness settings, and also 24 volt LED floodlights.


New suppliers crop up almost daily on fleabay. Key search terms include "24 volt bayonet cap" or "24 volt b22" or "24 volt e27"
Such search terms will include incandescent bulbs of course, but these are now so rare in b22 or e27 bases that most of the search results will be LED lamps.
Any fleabay search for LED bulbs or lamps turns up largely MR16 style lamps.
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Last edited by adam2 on Mon May 01, 2017 9:21 pm; edited 1 time in total
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adam2
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PostPosted: Mon May 01, 2017 9:20 pm    Post subject: Reply with quote

Another supplier
https://www.12vmonster.com/collections/12v-24v-led-lamps-and-light-bulbs
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clv101
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PostPosted: Mon May 01, 2017 11:07 pm    Post subject: Reply with quote

Yes, looks promising. 24V is looking a lot more viable. I hadn't appreciated the cable lengths when 2-way switching and the routing practicalities are considered.
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adam2
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PostPosted: Mon May 01, 2017 11:46 pm    Post subject: Reply with quote

Regarding two way switching, remember that the perhaps lengthy cables to/from 2 way switches will only be carrying the load current of one or two lamps and not the whole circuit current.

I would be inclined in most cases to use 2.5mm cable from the fuse box to each switch and onwards up to and including the penultimate switch.
The switched feed from the light switch to the lamp, and also from the penultimate switch to the last switch may be done in cheaper 1.5mm cable.

I would suggest that in most cases that 3 core and earth cable be run from the switch to the lamps. That permits of the use, or potential future use of light fittings with two lamps or two groups of lamps each separately controlled. That gives a choice of two or three lighting levels without any need for dimming.

A certain amount of wire in 2 way lighting circuits may be saved by a rather odd circuit layout known as "Philadelphia switching" In theory it is prohibited, but I have used it 12 or 24 volts, never for mains.
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adam2
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PostPosted: Sun Dec 03, 2017 2:34 pm    Post subject: Reply with quote

clv101 wrote:
Yes, looks promising. 24V is looking a lot more viable. I hadn't appreciated the cable lengths when 2-way switching and the routing practicalities are considered.


Cable lengths and the voltage drop therein on 2 way lighting circuits can often be reduced by a rather odd type of circuit often known as "American switching"

Standard two way light switches are used, but contrary to normal practice, the positive and negative supply wires are connected to terminals "L1 and L2" at both the switches. The lamp is connected between the common terminals of the two switches.

If a positive and a negative feed are required at or near each switch position in any case, perhaps for other lights, then a considerable economy of cable results.
This arrangement has the drawback that the polarity at the lamp holder varies, so it WILL NOT work with a lamp that is polarity sensitive.

This arrangement is also DANGEROUS at mains voltage and has been prohibited for many years. It should only be considered at low and non dangerous voltages.

O/T trivia, the internal lights in some London black cabs are wired thus, in order that the passenger or the driver may turn the lights on/off, safe enough on 12 volts, and works fine. Until the driver fits an LED bulb that is polarity sensitive and therefore only works half the time !
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