Controllable "fairy lights"

[samchurchill]

Hi,

 

I'm after a bit of advice... I've been asked to provide some "fairy lights" which will be criss-crossed across a 2m diameter circular truss and I'd like to be able to control them a little - just really going from static to various speeds of flickers/fades and perhaps an overall flash, which likely means I need to get them controlled by our console (Chamsys MagicQ). I have an ArtNet to WS2811 / WS2812B / SK6812 / SK2801 / SK8860 controller but wondered what lamps I can get reliably in the next couple of weeks (i.e. likely not from China at the moment)? Here are some things I've thought of, but I haven't quite found the right product yet...

 

• Ideally they'd look as similar as possible to "normal" warm white fairy lights, but I'm open to those where each light is in a small translucent ball (i.e. I don't want to have to worry too much about whether they twist around when being hung, so they need a large "field of view")
• RGB would be a bonus, but would likely just run them on a constant warm white colour
• Each light could be a different pixel, but not essential at all
• Could have separate strings of lights on different "dimmers"
• Ideally they'd have a small twisted cable as opposed to the colourful 3-wire cable that can seen on lots of WS2811 LED strings
• I'd prefer LED (as opposed to 240V strings) for safety
• Could purchase or hire, but my preference would be to purchase

 

Any help gratefully received!

 

Sam

[TomHoward]

Could you find a 3-circuit chasing warm white string, cut the end off and run it off one of those 3ch DMX led drivers meant for RGB tape - tend to run a reasonable voltage range.

 

I’ve just made a set running at 18V off a Makita battery for a truck with wireless dimming but used artnet receiver into DMX and just used one of those dinners rather than going WS281x, it’s only one static circuit though not multiple

 

For ease of identifying circuits etc you could just wrap three static sets together.

 

Beware of the two-circuit chasing lamps as they often run off one string with have the diodes inverse, you could probably drive it as two circuits again with some rectifying but it would take more thinking about.

 

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F112978858890

[samchurchill]

Could you find a 3-circuit chasing warm white string, cut the end off and run it off one of those 3ch DMX led drivers meant for RGB tape

 

Sounds perfect, I’ll see what I can find! Now, what to Google?...

 

Or, thinking about it, would I simply apply +ve voltage from both ends of the string for one of the ones that uses diodes?

Edited March 9, 2020 by samchurchill

[DrV]

...

Or, thinking about it, would I simply apply +ve voltage from both ends of the string for one of the ones that uses diodes?

 

The ones I have seen which have back to back diodes were wired for a 31V supply as follows:- take 10 LEDs in series to give a 31V string. Take another 10 in series to make another string. Now connect the two strings in parallel with the anode end of each string connected to the cathode end of the other. Applying 31V one way round lights one string and applying it the other way round lights the other. To get all of them lit you just apply 31V a.c.

[indyld]

Applying 31V one way round lights one string and applying it the other way round lights the other. To get all of them lit you just apply 31V a.c.

 

Ouch. Is there a more robust diode with a decent reverse voltage in each chain? I mean, I guess it doesn't matter but makes me anxious.

Edited March 9, 2020 by indyld

[DrV]

Applying 31V one way round lights one string and applying it the other way round lights the other. To get all of them lit you just apply 31V a.c.

 

Ouch. Is there a more robust diode with a decent reverse voltage in each chain? I mean, I guess it doesn't matter but makes me anxious.

Not in the ones I saw but provided both strings remain connected the reverse voltage can't exceed the forward voltage. It's no different from connecting a single pair of diodes back to back.

[alistermorton]

Those back to back sets are PWM driven with an H bridge to enable them to fade in and out. Not difficult but a little more involved than simply switching the power off and on.

[bigclive]

Applying 31V one way round lights one string and applying it the other way round lights the other. To get all of them lit you just apply 31V a.c.

 

Ouch. Is there a more robust diode with a decent reverse voltage in each chain? I mean, I guess it doesn't matter but makes me anxious.

 

The way modern strings are configured is in large parallel sections of inverse parallel LEDs that are then wired in a series group to make up the required string voltage. Usually ten sets for around 30V, but sometimes 8 sets for 24V.

That means that the max reverse voltage across any LED is capped to around 3V by the alternate polarity LEDs in the string.

 

Controlling these strings is a nuisance as the supplied controllers are usually current limiting and swap the polarity for "multi-channel" flashing effects.

 

When static they are actually reversing polarity at a fairly high speed.

 

I'd recommend avoiding them where proper control is required. Even with just static on you'll probably have to add an extra resistive load to give a dimmer something it can work with. The electronic supplies should only be switched and not dimmed.

[DrV]

I did actually make up some controllers for a load of them using H-bridge stepper motor chips driven by an Arduino. Worked quite well. I think I may have detailed it in a post on here about a year ago.

[TomHoward]

We were using this kind of LED PWM dimmer, cutting off the LED's power supply and dimming it on the string after the power supply-

 

As said a lot of them use LEDs wired in both directions to give two circuits and pulse between them, so driving them is a bit of a nightmare.

It would probably be easier to find 3 static strings that run in the 12-24V range and twist the three together

[samchurchill]

Thanks for the great info, some of which I must admit is a little too advanced electronics for me!

 

So, do we think a couple of lengths of https://www.amazon.co.uk/gp/aw/d/B01DAEKDMW (possibly cut into shorter lengths) with a https://www.amazon.co.uk/GIDERWEL-Channel-Decoder-Controller-DC12V-24V/dp/B07Q9Y2KLZ/ fits the bill?

 

Sam

[TomHoward]

You won’t need 12 channels of control, 3 should do.

Those LEDs claim 24V so they should be okay to use.

 

They’ll be wired in about 8s, and each 8 lights or so the twisted wires will go from being 3 wires twisted together down to 2 wires, which is the feed into the next section.

You could cut it there or just order two strings and twist them together.

 

If you’re running two whole strings, it will probably draw more current than the supplied power supply could give, as you’d be combining them into one string at the controller, so you may need a higher current 24V power supply.

 

3ch controller: https://www.amazon.co.uk/Candybarbar-Professional-DC12-24V-Decoder-Controller/dp/B07WBYMVX7/ref=mp_s_a_1_7?keywords=3ch+led+DMX&qid=1583789115&sr=8-7

[samchurchill]

Just wanted to say thanks all - the kit arrived today and is working exactly as I need it to! Thanks again