LED Footlights

[adam2]

That link works. It is a pity that they use brown and blue for extra low voltage wiring, I rewire them with red and black wires.

WHY?

The standard for ELV changed at the same time as LV. If anything all of your old red/black should be changed to brown/blue.

 

Thinking further the red/black was often wrong and realistically the new should, more often than not, be brown/grey replacing red/blue.

 

 

Of very little real world importance either way.

Blue/brown is widely used for the simple reason of availability.

 

Blue/brown is arguably correct for extra low voltage AC PROVIDED THAT one pole of the supply is grounded, and that blue is used for the grounded pole. For an ELV AC supply with neither side grounded then both sides are live and brown/grey as above should be used in theory. Now where can I buy some twin flex with brown and grey cores ? I suppose that someone might make it, but I have never seen any. Note for example that brown/grey SHOULD be used for 110 volts AC from a safety isolating transformer with earthed center tap. Has anyone ever seen this this done ? I have, precisely once and then only for fixed wiring. Flexible cords were blue/brown.

 

For DC it is even more complicated and the approved colours have recently changed AGAIN.

 

Old, old DC colours.

DC mains supplies. Positive outer = red, negative outer=blue, center wire =black.

2 wire circuits derived from a 3 wire system, black=neutral, red=live (no matter if the live side was positive or negative)

 

ELV DC such as batteries. Red=positive, black or blue Negative. When polarity unimportant, ELV DC was sometimes both wires white to distinguish from mains voltage AC or DC.

 

Old DC colours

Grounded neutral=blue

Positive=brown

Negative=grey.

 

So 3 wire DC mains were meant to be positive outer=brown, negative outer=grey, center wire=blue

 

2 wire DC circuits were meant to be blue=grounded neutral, live=brown if negative, and grey if negative. Never seen it done in the wild.

 

New new colours for DC

Red for positive, was brown, White for negative, was grey, grounded neutral remains blue. Anyone ever seen this done ? If you buy a small battery with attached wires these are almost always red for positive and black for negative.

 

So back on topic, I would not worry about colour codes on ELV stuff, except that the blue should preferably be used for the grounded side if any.

[alistermorton]

FWIW I've found that driving LED tape with a mosfet off an Arduino PWM pin gives a smoother dimming response than you'd expect - certainly better than the cheap dimmer pcbs from the bay - so you might be pleasantly surprised. I wonder if it slews the M/S ratio intead of just jumping.

[sunray]

Well I have worked in many DC situations, I won't start with any details of the days of Blue, Orange, Green & Brown as I never got to learn the useage. However... see any pattern arising?

That link works. It is a pity that they use brown and blue for extra low voltage wiring, I rewire them with red and black wires.

WHY?

The standard for ELV changed at the same time as LV. If anything all of your old red/black should be changed to brown/blue.

 

Thinking further the red/black was often wrong and realistically the new should, more often than not, be brown/grey replacing red/blue.

 

 

Of very little real world importance either way.

Blue/brown is widely used for the simple reason of availability.

 

Blue/brown is arguably correct for extra low voltage AC PROVIDED THAT one pole of the supply is grounded, and that blue is used for the grounded pole. For an ELV AC supply with neither side grounded then both sides are live and brown/grey as above should be used in theory. Now where can I buy some twin flex with brown and grey cores ? I suppose that someone might make it, but I have never seen any. Note for example that brown/grey SHOULD be used for 110 volts AC from a safety isolating transformer with earthed center tap. Has anyone ever seen this this done ? I have, precisely once and then only for fixed wiring. Flexible cords were blue/brown.

All of my 110 work in singles is done with grey, why would it not be? Yes I have used correct coulours in flex but the cost is prohibitive at more than double with yellow sheath and more like quadruple in any other colour but not many options available.

 

For DC it is even more complicated and the approved colours have recently changed AGAIN.

 

Old, old DC colours.

DC mains supplies. Positive outer = red, negative outer=blue, center wire =black.

2 wire circuits derived from a 3 wire system, black=neutral, red=live (no matter if the live side was positive or negative)

Sorry I want to disagree with that one, you are nowhere near the first to mention it so so it's either 'my mate says' or a version of regs I haven't had sight of, I imagine the later but please bear in mind I haven't seen them all. Going back further to old, old, old it was red(or orange)/blue for everything so in a system with +ve & -ve supplies there was a horrible mix of red and blue on the earth bar (This was very apparent in old Strowger telephone exchanges where one will see pretty much every colour used for 'earth' connexions). I've never knowingly come across red used for negative but in large systems like I work on one doesn't tend to look any further than the relevant part.

IME red/black and blue/black was standard for a lot of years however many equipment manufactures seemed to use red/green/black with green neutral/0V. To complicate it further control panel manufacturers tend to have their own wiring colour codes.

 

ELV DC such as batteries. Red=positive, black or blue Negative. When polarity unimportant, ELV DC was sometimes both wires white to distinguish from mains voltage AC or DC.

 

Old DC colours

Grounded neutral=blue

Positive=brown

Negative=grey.

 

So 3 wire DC mains were meant to be positive outer=brown, negative outer=grey, center wire=blue

 

2 wire DC circuits were meant to be blue=grounded neutral, live=brown if positive, and grey if negative. Never seen it done in the wild.

Just look in modern telephone exchanges, I have 10mm² fig8 twin flex of grey/blue in stock. I also may still have 6mm² brown/brown ident shaped used for a DC supply which sat on top of another DC supply.

 

New new colours for DC

Red for positive, was brown, White for negative, was grey, grounded neutral remains blue. Anyone ever seen this done ? If you buy a small battery with attached wires these are almost always red for positive and black for negative.

I've not come across anything like this in recent work however did work in an American company where black +ve, red neutral & white-ve about 20 years back but their AC was white neutral red & black 2ph lives.

 

So back on topic, I would not worry about colour codes on ELV stuff, except that the blue should preferably be used for the grounded side if any.

So summary one may expect to see pretty much any colour used for pretty much any potential.

 

Edited July 14, 2021 by sunray

[Junior8]

I'm now wondering whether, slightly counter-intuitively, a non-dimmable fixture might actually be better in this application. The dimmable ones often seem to contain drivers to cope with the unhelpful phase control dimmers that they're expected to be used with so perhaps the non-dimmable ones are more simple and hence easier to PWM? Lamps with a simple dropper resistor won't dim with a triac dimmer but are perfect for PWM. Is my thinking way off here?

 

I don't think it's counter intuitive at all, back when such foots were in use they were as likely to be on a blackout switch as a dimmer. Remember they are the last reminders of gas instals...

 

 

 

[Shez]

I don't think it's counter intuitive at all, back when such foots were in use they were as likely to be on a blackout switch as a dimmer.

Just to clarify, I do want them to dim. What I'm wondering is whether lamps marketed as non-dimmable might actually dim better with the type of dimmer I plan to use than those marketed as dimmable for use with a different type of dimmer.

[sunray]

I don't think it's counter intuitive at all, back when such foots were in use they were as likely to be on a blackout switch as a dimmer.

Just to clarify, I do want them to dim. What I'm wondering is whether lamps marketed as non-dimmable might actually dim better with the type of dimmer I plan to use than those marketed as dimmable for use with a different type of dimmer.

One of theproblems with non dimmable lamps is they are designed to work at full brightness regardless of supply, as such they will remain on until the last sniff of power disappears.

[alistermorton]

As an experiment I've connected non dimmable MR16s and "kitchen bulb" capsule lamps (G4?) to a PWM dimmer and they stay on at full brightness down to about 30% then flash until they snap off at about 10%

[timsabre]

As an experiment I've connected non dimmable MR16s and "kitchen bulb" capsule lamps (G4?) to a PWM dimmer and they stay on at full brightness down to about 30% then flash until they snap off at about 10%

 

Behaviour varies widely though depending on the design of the driver circuit - which can differ even in different batches of supposedly the same product. Most non dim lamps have a big capacitor across the supply so will run at full until there isn't enough power coming in to keep the cap charged at which point they will flash. Dimmable lamps also have the cap but take a copy of the incoming PWM signal and use it to control the power driven to the LED.

 

The best thing is to find lamps, tape or filaments which use resistor-dropper control and drive them with a PWM dimmer (DMX tape dimmer or similar).

Dimmable 240V lamps dimmed with a trailing edge/phase cut dimmer can work quite well but often will not dim smoothly in from black - but you can sometimes bodge around this by holding them at a low dim level where the electronics remains powered but the LEDs are not lit or lit very dimly.

Edited July 15, 2021 by timsabre

[DrV]

If your dimmer packs have pre-heat this can be handy for maintaining the low level that Tim describes. If you consider the pre-show requirement to give them a burst of power, to switch them on, to be akin to striking a discharge lamp then we're using familiar procedures!

[timsabre]

We tried the pre-heat trick at my local theatre which had dimmable LED lamps installed in the balcony front houselights. Seemed to work fine, then half way through the show a selection of the lamps started randomly flashing. I had control from the lx desk so I had to edge up the dimmer setting until it reached a point where they stopped flashing but weren't on too bright. Was embarrassing.

[Shez]

The best thing is to find lamps, tape or filaments which use resistor-dropper control and drive them with a PWM dimmer

That's the golden goose. Sadly when it comes to lamps, it's not a feature that anyone advertises. Fleabay seems to have a reasonable supply of bare 3V filaments - useful if constructing ones own DIY lightbulbs was a thing?

 

 

As an experiment I've connected non dimmable MR16s and "kitchen bulb" capsule lamps (G4?) to a PWM dimmer and they stay on at full brightness down to about 30% then flash until they snap off at about 10%

I've just tried a "non dimmable" MR16 too (an "Aurora Enlite"). Slightly better results - from full downwards: a bit of a step down from 100-90%, smooth dimming down to about 20%, bit of strobing down to about 10% then snap off. At a couple of narrow levels in the smooth dimming range, there was a bit of slight strobing. Still unusable in this application but nicely demonstrates the unpredictability of these things.

Edited July 15, 2021 by Shez

[adam2]

I think that the simplest and most reliable solution would be to use the 3 volt LED filaments as sold on ebay. Connect 3 in series on a 12 volt DC supply, or 6 in series on a 24 volt DC supply. A ballast resistor is essential to limit the current to the proper figure.

Dimming via a suitable PWM dimmer. With a high enough frequency, smooth dimming to almost zero should be achievable.

 

 

[Shez]

I think that the simplest and most reliable solution would be to use the 3 volt LED filaments as sold on ebay.

I've yet to move into 3D printing but imagine it should be reasonably simple to construct a frame that would hold half a dozen filaments (by their connecting wires) in a visually pleasing pattern. Assuming they don't kick out too much heat of course!

[J Pearce]

I think by the time you're soldering filaments onto a 3D printed frame it's all got a bit much for footlights. Probably simpler to cut a small plate of aluminium and cover it in warm white LED tape. It'll be brighter, it'll last longer as it has good heatsinking, it's far more durable and storable, and it'll take half the time to build.

 

 

I have had perfectly reasonable results out of the little G4 capsule lamps though, the tall COB ones do a reasonable candle flame imitation too. If you want a quick and cheap solution it's hard to beat. Just check product photos to see what is a chip (usually won't dim) and what is a resistor (and sometimes a diode or two).

[adam2]

LED filaments could be assembled very simply and cheaply by use of "tag strip" tag strip on fleabay

 

Solder to a suitable piece of tag strip 6 LED filaments and a small power resistor to limit the current to about 0.3 A Paint the dark coloured tag strip white to reflect the light. Tag strip, LED filaments, and resistors are cheap and assembly very simple. 6 LED filaments would give a similar light to a 60 watt incandescent bulb, providing that the led filaments are spaced well apart to aid cooling reliability should be excellent. A 500ma fuse in series with the assembly would be prudent just in case the LEDs go short circuit.

24 volt DC supply via PWM dimmer.