Old disco lighting - LED conversion

[DJ Jules]

This article will give you a lot of useful info Jules - a lot of what I posted comes from here http://www.tbideas.com/blog/build-an...power-rgb-led/

Thanks for that, I almost feel like I know what I'm talking about now I understand the issues with creating a constant current source now - that article was very good at describing the issues about dealing with different forward voltages.

Some solutions look like they set the current limits in software by adjusting the PWM ratios.. not really what you want for a retrofittable solution.

Yup, I reckon that's how a lot of them do it, probably explaining the high failure rate of LED's in some devices...

Julian

[dicky]

@juski
Yes you are correct - a constant current source per colour - however you still have the problem of the forward voltage drop difference on the Red. If you are looking at 30W LEDs (10w per colour) then you have about an extra 11V to drop at a current of around 235ma = 2.6W of heat to dissipate either in a resistor or the FET providing the constant current source (or a combination of a constant current plus a series resistor I would imagine)

Not too bad but for a 90W RGB (30W per colour) then on the red chain (which is three chains of 10 led in parallell) you have 11V x 700mA x 3 = 7.7W !!

One thought I had was to put around 20x 1N5404 3 Amp rectifiers in series with the Red. Each 1N5404 has a forward voltage drop of 0.5V (I just measured a few) so that would drop 10V across the diode chain with very little heat dissipation per device. Plus they are very cheap http://www.ebay.co.uk/itm/50-x-1N540...item43bbcb79b5 and would solve the problem unless I missed something

In the case of the light I want to upgrade, you already have in the existing circuitry three Power FETs that no doubt already provide the constant current - so I think it is just a matter of increasing the LED supply voltage to around 33V-36V and then getting rid of the excess 11V on the Red possibly as just described



Rich

[DJ Jules]

One thought I had was to put around 20x 1N5404 3 Amp rectifiers in series with the Red. Each 1N5404 has a forward voltage drop of 0.5V (I just measured a few) so that would drop 10V across the diode chain with very little heat dissipation per device.

Watch out for this as the voltage drop is proportionate to the current drawn (varying from 0.6v at 50ma to 1v at 1a: http://www.cliftonlaboratories.com/1...rd_voltage.htm In reality this just means you wouldn't need as many as you might think...

Julian

[dicky]

Interesting post Julian - cheers

It would seem I am on to a possibly workable idea though and less Diodes is a positve attribute and less money

All I can realistically do a the moment is set something up on the test bench once the LEDs arrive and get some real life measurements

Bear in mind I am not trying to accurately drop enough volts on the red chain to make the power dissipation in the FET/seiral resistor the same as for the green/blue - I'm just trying to bring the voltage difference into a more manageable region for high powered LEDs

Rich

[funktions]

im not overly worried about cooling issues at the moment. just the possibility of upgrading the "light" source to stand out a little more and not have to worry about lamp failures. the heat generated could be an issue in a working environment, although im more of a I want to try it and see then sort any possible issues, sometimes too much thought and planning create what if moments these then snowball.. although I do see adding it as a light source to certain other devices would make more of a benefit by having to remove a huge transformer running low voltage high wattage lamps. some of the older lights are positively excessive in the weight department. I like the 812's and im sure I have gone excessive with 100w but I love a challenge and I doubt the heat created will be anywhere near the discharge laps even if I do have to replace the cooling fan fitted technology has improved somewhat in many areas I wonder what they would create with todays technology to rival it. yes im sure I would love a viper airfx or 2 but slightly excessive for a disco lighting rig..

[Andy P]

Not being funny here but there could be a very good market out there for upgrading old or underpowered units as they go cheap enough and the component cost seems minimal. I have a set of lex boxes and the construction is pretty solid, if they could be upgraded I'd be well happy as I love the effect and they are great with haze, just a little dim for my likings.

[funktions]

so, bigger is not always better, got the thing all connected up and fitted. it saturated the inside with light but not a lot went the way we wanted it to, so a little fiddling around and had a reasonable result even with using some optics to focus but need to find a high wattage low diode count, although we got it correctly focused up it needs more of a focused beam, so we played with some other lights and again had mixed results. narrow beam high power single diode is defiantly the way to go.
but boy was it bright. excessively bright, like erm ... what can we do with it bright. heat dissipation was a bit of an issue but not as horrific as I had thought, with the fans running I think it would have been manageable.
so onwards and upwards bit more investigating to do have found some interesting 5 degree white diodes but at £45 each they will be staying there. special order from the states so add shipping and the fact customs will also want a percentage.

[dicky]

Can you post up some pics mate of your results?

Also did you try a LED reflector and lens like this http://www.ebay.co.uk/itm/1-set-100W...item2a3bb66ae4

Rich

[funktions]

Can you post up some pics mate of your results?

Also did you try a LED reflector and lens like this http://www.ebay.co.uk/itm/1-set-100W...item2a3bb66ae4

Rich

yes I did use reflector and lens, should have taken some pictures sorry were so intent on getting at least something working it was jumping from one to another.

the reflector and lens did improve the light a lot, focal length was good but because there is such a lot of light in a large area it seems to be wrongly used if that makes sense. and oh my gosh how bright, we switched on for a quick second to see if it was working and I had this image of a square burnt into my retina for a few minutes and I was not even looking fully at it.
might benefit from having a reducing reflector on it to try and condense the light into one spot, its good for a flood but focused beam no.
the heatsink we ordered for it was the wrong one , we ended up with a 50watt even though I ordered 100watt size so it did get very toasty but it kept the chip working without fan cooling whilst we moved things around to adjust angles.
we tried a moonflower effect and obviously the size of the chip blocked a lot of light from a frontal positioning, so we went angled side on and had the majority of the beams on one side only. so that didn't work. we tried the 812 with a 5w head torch and it had more light output than the 100w chip. we might have to try a silvered tunnel effect almost ending at the gobo wheel to get a more focused beam.
personally the research we did before did point to having a very narrow beam.
we even tried using an led of this type of design http://www.ledhut.co.uk/new-6-watt-g...FbHKtAodHHsAbg
it had an interesting effect for the moonflower that kinda looked very different.

we think something less than 10 degrees would make a difference but would also need to be around the 30watt area single chip
results we found..
a lot of wasted light.
inability to condense this light,
no real intensity to it just bright.
need a larger heatsink and or fan combination.
no one does replacement led conversions as the technology is not really there to replicate the focused beam required to replace the good old hid or filament lamp.

if you want me to post you our chip and driver to play with for a bit your more than welcome. although I now seeing it living out its days as an outside lamp but again got to try and fit it into an old housing I have more fun and games...

[dicky]

Intersting findings there Jules

I'm actually looking at upgrading an LED fixture (3x3W RGB) to either 3x10W or 3x30W so have probably some different issues to what you were finding with old halogen powered lamps - in particular i would imagine the high wattage LED to have a similar beam dispersion angle as the original low powered one

However I do have some old incandescent 'Colour Dynamics' lights here I could play with too. The came amongst the stuff I got free from the closed nightclub after I bought all the working stuff

Rich