Transformers from 240 v to multiple 12v luminaires?
Transformers from 240 v to multiple 12v luminaires?
(OP)
I'm based in the UK and intending to install display lighting to a long narrow exhibition space app 80ft. x 18 ft.
To minimise cost I want to use standard Quartz Halogen 12 V spot reflector bulbs suspended from pairs of catenary stretched-wire conductors by a simple system of my own devising, using brass double-screw connectors of various sizes (cut out of the ordinary polythene connector blocks that you can buy in strips anywhere)- the first pair of these are the largest size available, and clamp L-shaped brass rods (3mm brazing rod)to the stretched conductors; the next pair connect short, flexible - but thick - copper wire links to the ends of the brass rods; and the third pair connect the copper wires to the pins of the spot-bulbs.
This way I can manually twist the spots to point in any direction I choose - and they'll stay there - without the expense of a fancy shop-bought connection system - with 4 different spotlight spread angles available this gives me a very versatile system.
The conductors will be either high strength braided brass picture-hanging wire - the stuff they use in public art galleries to hang big pictures -or if that turns out not to be strong enough, or too stretchy if it heats up with the current, stainless steel rigging-wire - the high-conductivity stuff that they use to double for radio aerials on yachts.
There will be perhaps 100 of these spots at up to 50 Watts each,in perhaps 2 - 4 switched groups - or possibly ALL fed off one 12v supply if it's feasible, so I need a transformer from 240 v mains, capable of carrying up to perhaps 400 amps load in the 12 v secondary (ouch - sounds a lot! well- maybe 200 amps, or 100 amps for 4 groups of 25 lamps)The transformers that are specifically designed for use with 12v lighting typically can only cope with 3 or 4 lamps at most, so I need something industrial:
Questions (I'm not an electrical engineer!):
1) Is this a sensible proposition at all?
2) Where can I source such a transformer in the UK?
3) Am I right in thinking that, for transformers, bigger=more efficient?
4)Air-cooled? Oil-cooled??
5) Is there a welding transformer with as low as 12V output that might do the trick at lower cost?
6) Does anyone know of a source of high-conductivity + high tensile strengh catenary cable designed for this application?
7) will the catenary wire melt with these currents? I could always run solid copper bus-bars parallel with the catenaries and cross link at intervals - but now it's getting silly!!
- Those are my practical questions - now for some theoretical ones that have occurred to me as a result of puzzling over this:
8)With alternating current, the voltage, hence current, drops to zero every half-cycle(?) 100times? 50times? per second; so the temperature/luminosity of the filament of an incandescent bulb is constantly going up and down - the bulb is 'out' for part of each cycle. (Hence 50 Hz stroboscopic effects).
Would, therefore, direct current at the same 240 voltage produce more perceived light? Would the filaments, spared the presumed stress of constantly heating-up and cooling down, last longer?
(None of my electrical engineer acquaintances has been able to answer this one - but they're all high-voltage distribution-grid specialists.)
9) Supposing direct current WOULD result in greater efficiency in converting electrical energy into light, and/or a longer life for the bulb filaments, would the losses involved in having a large power rectifier in the circuit negate any advantages? (not to mention the capital cost of the rectifier!)?
9) If NOT, and there WOULD be significant advantages to DC, where can I get such a rectifier, to match the transformer?
Any advice and comments gratefully received - any rebukes for naive stupidity humbly borne.
Dick Q
To minimise cost I want to use standard Quartz Halogen 12 V spot reflector bulbs suspended from pairs of catenary stretched-wire conductors by a simple system of my own devising, using brass double-screw connectors of various sizes (cut out of the ordinary polythene connector blocks that you can buy in strips anywhere)- the first pair of these are the largest size available, and clamp L-shaped brass rods (3mm brazing rod)to the stretched conductors; the next pair connect short, flexible - but thick - copper wire links to the ends of the brass rods; and the third pair connect the copper wires to the pins of the spot-bulbs.
This way I can manually twist the spots to point in any direction I choose - and they'll stay there - without the expense of a fancy shop-bought connection system - with 4 different spotlight spread angles available this gives me a very versatile system.
The conductors will be either high strength braided brass picture-hanging wire - the stuff they use in public art galleries to hang big pictures -or if that turns out not to be strong enough, or too stretchy if it heats up with the current, stainless steel rigging-wire - the high-conductivity stuff that they use to double for radio aerials on yachts.
There will be perhaps 100 of these spots at up to 50 Watts each,in perhaps 2 - 4 switched groups - or possibly ALL fed off one 12v supply if it's feasible, so I need a transformer from 240 v mains, capable of carrying up to perhaps 400 amps load in the 12 v secondary (ouch - sounds a lot! well- maybe 200 amps, or 100 amps for 4 groups of 25 lamps)The transformers that are specifically designed for use with 12v lighting typically can only cope with 3 or 4 lamps at most, so I need something industrial:
Questions (I'm not an electrical engineer!):
1) Is this a sensible proposition at all?
2) Where can I source such a transformer in the UK?
3) Am I right in thinking that, for transformers, bigger=more efficient?
4)Air-cooled? Oil-cooled??
5) Is there a welding transformer with as low as 12V output that might do the trick at lower cost?
6) Does anyone know of a source of high-conductivity + high tensile strengh catenary cable designed for this application?
7) will the catenary wire melt with these currents? I could always run solid copper bus-bars parallel with the catenaries and cross link at intervals - but now it's getting silly!!
- Those are my practical questions - now for some theoretical ones that have occurred to me as a result of puzzling over this:
8)With alternating current, the voltage, hence current, drops to zero every half-cycle(?) 100times? 50times? per second; so the temperature/luminosity of the filament of an incandescent bulb is constantly going up and down - the bulb is 'out' for part of each cycle. (Hence 50 Hz stroboscopic effects).
Would, therefore, direct current at the same 240 voltage produce more perceived light? Would the filaments, spared the presumed stress of constantly heating-up and cooling down, last longer?
(None of my electrical engineer acquaintances has been able to answer this one - but they're all high-voltage distribution-grid specialists.)
9) Supposing direct current WOULD result in greater efficiency in converting electrical energy into light, and/or a longer life for the bulb filaments, would the losses involved in having a large power rectifier in the circuit negate any advantages? (not to mention the capital cost of the rectifier!)?
9) If NOT, and there WOULD be significant advantages to DC, where can I get such a rectifier, to match the transformer?
Any advice and comments gratefully received - any rebukes for naive stupidity humbly borne.
Dick Q





RE: Transformers from 240 v to multiple 12v luminaires?
I also want to connect up a large number of 12V halogens without the expense of hundreds of expensive transformers - Please see my post about series wiring 12V lamps, it may give you something to think about as an alternative solution... but be aware I'm not yet sure it will work :) and you couldn't use bare wires.
I don't think any thin catenary can carry 100A plus!! (without voltage drop, and the wire perhaps getting hot enough to give out more light than the fittings - I think you want white light, not bright orange!!
Well, not unless it's the kind of steel rigging wire you'd find on the QEII <G> - above 10-16 square millimetres cross section.
I doubt such a big 240:12V transformer exists, and if it did, it would be extremely expensive, heavy and probably noisy.
BTW, yours is a fascinating question about the effects of AC or DC on lamp filaments. I hope someone answers that!
Best regards and good luck, Mark
RE: Transformers from 240 v to multiple 12v luminaires?
I'd still like to get some informed opinions about the AC/DC effects on perceived light intensity and filament life - it's one of those things that nobody ever queries.
Dick Q
RE: Transformers from 240 v to multiple 12v luminaires?
RE: Transformers from 240 v to multiple 12v luminaires?
RE: Transformers from 240 v to multiple 12v luminaires?
RE: Transformers from 240 v to multiple 12v luminaires?
A few phone calls to local lighting reps and referrring to lighitng catalogs will provide you plenty of options.
All 12 lamp and luminair manufacturers offers a series of light fixtures with 12V tranformers that are either built in each head or one common xfmr for a group of light(remote but mounted close to the ligting track or group of fixtrues).
This are standard accesories offered for low voltage lighting, do not reinvent the wheel.
Even by any engineering principles, you want to bring 240V service as close to the load (lamps) as possible before transforming to 12V. Your desing sounds like a clap-trap with all due respect. I am sure you are good at what you have expertize in.
Trying to light a 'exhibition' space and then skimping on lighting trasnformer cost or Do-it-yourself concept sounds oxymoroic.
RE: Transformers from 240 v to multiple 12v luminaires?
RE: Transformers from 240 v to multiple 12v luminaires?
RE: Transformers from 240 v to multiple 12v luminaires?
RE: Transformers from 240 v to multiple 12v luminaires?