Applying LED strips

[phaenius]

Hi to Eurobricks community,

I am a new user and this is my first post, I hope I don't infringe any rules, if so, please tell me. I have a question about the LED strips that can be applied to various LEGO models. I bought some strips that have 4 LEDs in parallel and where I want to apply them there is really only room for 2 or maximum 3. I want to ask you guys if some of you applied LED strips and how shall I deal with it. Information is scarce from where I bought it and I don't know what to do. Is it ok to cut (with scissors) the strip so that I can stick only 2 or 3 LEDs? Or should I try to mask the extra ones? Also, the strips have some pre-applied glue, it's auto-adhesive. Is it ok to use this or shall I use extra glue? Don't want the strips to fall off. Any tips in general about this is highly appreciated. Thanks.

[MAB]

Obviously I do not know which LED strips you have but normally if you can cut them, then this is either marked with a line or if there is a line of electrodes where they join to the next section then you can normally cut through the electrodes to separate the sections, but you cannot cut anywhere else. For example here, you can have a group of three but you cannot cut just a single one:

 

 

If yours look different to this then it is probably a good idea to post an image of them or a link to the product.

 

[phaenius]

Thanks MAB. My strip looks very similar to your picture posted. I don't know if I am allowed to post pictures because of being new here. I also wanted to know if it's a common practice by people who mod their kits with LEDs to cut excess lamps or usually those are hidden somewhere.

[DeCommander96]

1 hour ago, phaenius said:

Thanks MAB. My strip looks very similar to your picture posted. I don't know if I am allowed to post pictures because of being new here. I also wanted to know if it's a common practice by people who mod their kits with LEDs to cut excess lamps or usually those are hidden somewhere.

You can post pictures, but since Eurobricks doesn't host images, it has to be from Flickr, or an image URL

[Thierry-GearsManiac]

You can post remotely-hosted pictures ([insert other media] - [insert image from URL]). No restriction to some specific picture hosting services : if you own some website-hosting server space, you can put your pictures there and link to them too.

Being in electronics, I can say that, on 12V strips (the most common ones), for electrical reasons (using less power while staying not much sensitive to slight input voltage variations), LEDs are arranged in series of 3 with one current-limiting resistor. Therefore one can only have multiples of 3 LEDs on a cut strip.

Then I guess that, when wanting other numbers of LEDs, one has to either hide the unused ones, or modify the strip itself (changing the resistors values, re-wiring some PCB traces...)... or even design one's own lighting solution, for example, when only one LED is needed (there are plenty of online tutorials, but if you need further help, you can still ask me).

 

[neonic]

Lights, always good 

Like already said by other members, most of those led-strip can be cut. Where you can cut is shown by mostly a little scissor. I have one I use for lighten up my bottles and cut strip too, no problem.
Only I think it is too bad too cut and use only three leds of a led-strip?

Quote

 I don't know if I am allowed to post pictures because of being new here.

Why not? 

Maybe you can post a photo of what your model and lights? Maybe there also other 'solutions'?

[phaenius]

Thanks everybody for the answers. Here are the strips. Sorry for the dust.

https://ibb.co/dm0ST4N

https://ibb.co/3MsvsNf

[MAB]

You can cut those individually. Just cut through the copper pieces and you will be fine.

 

[phaenius]

Thought so, thanks. I didn't find any resistors or any voltage divisors, could it be that those LEDs are individually fed directly from the power box (which I presume delivers 9V)? Also, in your opinion, is it worth cutting the strip (if I do it, there's no turning back) or should I mask somehow (not easy) the extra lamps? If I cut the extra lamps, the light from the area will be reduced, but if I don't, there will be leaking light where I don't want to from the extra lamps.

[Thierry-GearsManiac]

Cutting the strip can be more or less "reversed" by re-soldering the cut copper pads together (through a short wire).

I noticed on the pictures that this LED strip is very unusual : power LEDs, probably between 20mA and 100mA, slightly smaller than the 5630 type.

Technical specs for the LED strip (circuit), the LEDs and even the power supply (constant voltage or constant current type ? For any length of this LED strip ?...) would help to solve the numerous problems.

Moreover they seem to be wired directly in parallel, without individual resistors (unless the LED case embeds it, but it would be much more unusual). And having LEDs wired in parallel is usually bad because the current sharing isn't well controlled (and when one LED gets disconnected, then the other ones receive more current, then may fail in cascade because they would get overloaded more and more).

Personally, because of the above remark, I don't trust very much this LED strip. In order to gain full control of the current in each LED of it, more advanced hacks would be needed (cutting the strip in single LED bits, powering each of them with individual series resistors, whose values would have to be chosen, depending on the LED forward voltage and the supply voltage... like when designing a LED circuit from scratch).

 

Have you got any idea about the kind of lighting your LEGO designs would need, and if strong miniaturization is a concern, as well than aesthetics (hiding the wiring) ?

Some of these informations would help choosing the right lighting solution :

- a "long" (several cm) row of LEDs, above/around a stage for example ==> a standard 12V LED strip where the "multiple of 3" constraint won't matter so much (you can center the cut strip), especially if the LEDs are close to each other.

- shorter rows of LEDs

- LEDs arranged in an array

- single LED, either direct lighting or remote lighting (light pipe)

 

[MAB]

^ Some of these strips do have resistors in the casing.

I tend to use WS2812B strips or matrices, as these can change colour via an arduino. Or if using white light only, I often go for a traditional LED (5mm) as these fit through and get held by the hole of a technic brick.

[phaenius]

Thanks Thierry and MAB. I am not an expert (like many of you here), I just bought the whole set and it came with the lights included. I can post a pic with the strips lit, don't know if it helps. Thierry, you are right about the strips, I don't know where the resistors are, maybe they are inside the caps, I don't know if it's a good idea to connect a LED directly to the power source, but I'm not an expert. Some sort of resistor should be inserted to limit the current flow. Now you gave me something to think. If I cut the strip, there should be less bulbs. But maybe there is some current limiter somewhere, after all I have 5 strips (2 white, 2 red and one yellow) and they light the same, no matter how many strips are connected to the distributor. Besides, the controller's battery can hold different voltage at any given point (may be partially discharged), so I don't think that cutting one bulb should make a difference, after all ALL bulbs are connected in parallel (4 X 5 in total). I have an extension distributor that can hold 9 strips and is connected directly to the central command control (don't know how to call it, since it holds the battery, the bluetooth receiver and the control over 4 ports in one sealed unit). I can make pictures with it if anyone is interested. The kit is not an official LEGO product, I can post the name, but I don't know if I'm allowed, since it could be considered advertising.

[Thierry-GearsManiac]

@MAB :

I remember about fitting a 5mm LED into a technic brick's hole, but it was so tight that the LED's body could not be inserted on its full length without risking breaking the LEGO brick or rendering this insertion permanent.

 

@phaenius :

- if you intend to use other power sources (perhaps LEGO ones through the use of a cut LEGO power cable), never connect LEDs directly to them or they'll burn out instantly. Limiting resistors or constant current source modules will be required

- I'm indeed curious about the whole lighting kit (either its specs, or reverse-engineering it). And for the concern of it being considered as advertising, perhaps the problem may arise if its brand is a LEGO clone (some are legal and can be discussed here, some others are not and we must not talk about them, for not advertising them), or not : I guess that universal non-LEGO-related lighting kits can be talked about here (after all, some other people do add custom LED lighting to their designs). Instead of pictures, the name of the lighting kit or a link to its supplier's and/or manufacturer's page is possible too.

[phaenius]

It's not a LEGO clone, I think it's a MOC clone, after MOC-6687.

I will put some pictures later with the central unit and LED strips lit. No brand is visible.

Edited September 10, 2019 by phaenius

[Thierry-GearsManiac]

On my side, after thinking, according to some clues, I may make this assumption about your LED strips : if they are :

• powered on a 9V supply (typ. batteries)
• directly connected to this supply without any extra resistor

then :

• each LED package probably embeds 3 LED dies in series, each one having a forward voltage drop of approximately 3V (typical for blue/white LEDs)
• the current limitation may rely only on the LEDs' intrinsic resistance (and the batteries' one too), but with the drawback that slight voltage variations lead to large current variations (this resistance is low : a few tens of Ohms) :
  • when the battery charge drops only a bit, the light intensity will decrease significantly
  • one can't power the LEDs on a 12V power supply without instantly overloading = frying them

 

 

[phaenius]

Bellow are some pics. The first two are with the control box (contains commands, battery and receiver), next is with the LED strips distributor (clearly 9 ports in parallel) and the last one is with LED strips connected and lit.

https://ibb.co/7n3RVds

https://ibb.co/QMrT1w7

https://ibb.co/tXpSFJd

https://ibb.co/NyP5x47

Edited September 11, 2019 by phaenius

[MAB]

15 hours ago, Thierry-GearsManiac said:

@MAB :

I remember about fitting a 5mm LED into a technic brick's hole, but it was so tight that the LED's body could not be inserted on its full length without risking breaking the LEGO brick or rendering this insertion permanent.

 

Yes, not all 5mm LEDs are equal, If you do get a tight one, then you can use sandpaper on the edges to remove a little of the plastic casing to get it to fit into a technic hole. Also, I don't mind them getting stuck. Technic bricks are cheap enough and in fact with some of mine I actually glued the LED in place so they do not come out if a wire is accidentally pulled.

[Thierry-GearsManiac]

@phaenius:

After a look at your pictures, I see that the power distribution board has a resistor (SMD, probably 0603 size) in front of each LED strip connector ==> my assumption of three LED dies in each LED package is probably wrong.

And since you have red and yellow LEDs, their forward voltages are lower (around 1.8V for red and 2.0V for yellow, versus around 3.0V for pure green and blue/white LEDs).

==> the resistors do matter and are dimensioned for supplying 4 times the nominal current of a single LED (4 LEDs / strip, assuming equal current sharing between paralleled LEDs although it's wrong)

==> don't cut your strips, otherwise you'll overpower = fry your LEDs ! (unless you hack the strips in order to insert extra resistors or reuse only the cable with the female connector in order to build a custom LED circuit)

For further hacking purposes, it would be interesting to make the following measurements :

• the supply voltage (on the black cables' solders)... I guess around 9V since it is today's LEGO standard
• the LED strip voltages for each colour (on the surface-soldered terminals of the PCB connectors where the strips are connected)
• the resistor's value (on one of the resistors' terminals, with power turned off and everything disconnected)... unless its value code (3-4 digits or 2 digits + 1 letter) can be read by the help of a magnifier

 

[phaenius]

Thanks, Thierry. Meanwhile, I managed to find a workaround for the front LEDs, I wrapped them around the whole beacon set and the length was just fine, the auto-adhesive is very strong, it holds. The light is spread on the sides and on the back, but all-in-all it gives a nice effect.

https://ibb.co/3pFgPNW

With the tail lights shouldn't be a problem, since it seems they wrap fine around the whole lights block. The yellow lights are just for the sake of it, don't find any use for it, it just looks kitschy, I believe this strip is for the light coming from underneath the car. I saw some cars in real life, look awful, like a Christmas tree, but hey, if it's there, I don't find any place for it. Maybe I should look more closely, as I said, no manual for those lights.

Do you say that, given the forward voltage on different colored LEDs, ports on the distributor supply different voltages ? I should try and measure those somehow, I do have a multimeter, but the board is so small, don't know if I can do it. So far, strips work in any port and those are not labeled.

Edited September 11, 2019 by phaenius

[MAB]

Is this a lighting it that you have bought, where they have pre-cut the strips and made up their own connector plugs and so on? Looking closely I cannot see lego logos on them.

It wouldn't surprise me if the voltages on the distributor are the same, unless there are specific instructions not to place certain strips in certain connectors. You can usually get away with going (slightly) over the recommended voltages and of course you can go under and in this case the LEDs will just not be at their brightest. So I imagine they just supply the same voltage to all strips without caring too much about the different forward voltages for the different colour strips.

[phaenius]

Light set came with the kit (5 strips - 2 white, 2 red and one yellow - and one power distributor). It's not LEGO (not a LEGO clone either), I stated earlier. I didn't got instructions for the lights, just for the car. I assume that as well, power is the same on all ports, despite different colors requiring different voltages. It doesn't bother me if the voltage is too low for some strips, if it's too high on others bothers me, lamps may burn in time.

Edited September 11, 2019 by phaenius

[MAB]

22 minutes ago, phaenius said:

It doesn't bother me if the voltage is too low for some strips, if it's too high on others bothers me, lamps may burn in time.

You should be fine longer term if they glow without blowing out now. LEDs tend to blow instantly if you apply a voltage that is too high, as the current flowing through it (which is actually what determines the brightness, not the voltage itself) will rapidly increase beyond the operating limit. LEDs are very non-linear in terms of voltage and current - their resistance is not fixed.

 

[phaenius]

Good to know. They work fine now. But I remember I blew out one LED lamp on my TV keeping backlighting at 100%. Now I keep it at 80%. LG didn't bother to tell consumers not to set backlighting too high. Other people had similar problems like me with the same model and contacted LG and they said keeping the LEDs at full power will not cause them to burn. Liars...

Edited September 11, 2019 by phaenius

[Thierry-GearsManiac]

A few posts before, about the question if the output ports do generate different voltages : they are identical, then they don't do it by themselves :

• on ports where no load (one of our LED strips) is connected, the expected voltage is the supply voltage = 9V, because the circuit is open <=> no current flows through the resistor <=> the voltage at its terminals is 0V
• on ports where a LED strip is connected, the expected voltage will be the LED's forward voltage because the LEDs clamp the supply voltage down to their forward voltage, forcing current to flow through the resistor, which "sees" the difference between the supply voltage and the LEDs' forward voltage. Therefore, with white LEDs, you can expect 3V approximately on the port, and with red and yellow LEDs, you can expect 1.8-2.0V approximately ==> the resistor will then see either 6V or 7.2-7.0V, which results (according to Ohm's law) in a slightly higher current for the red  and yellow LEDs than in the white ones.

For measuring the voltage on the LED strips, if you don't want to do it on the surface-mount leads of the connectors (they are very close to each other), you may be able to do it on the strips themselves, either on the cables' '+' and '-' solders, or on the '+' and '-' pads between the LEDs.

 

(and for the blown TV's LED, it's the thermal aspect that has not been studied/tested enough by the engineers : when dealing with higher power LEDs, even when operating them below their maximum current, one can destroy them by overheating if not enough heatsinking is provided for draining their heat away)

[phaenius]

Thanks, Thierry for explanation. I will measure the voltages on the led strips, it's easier, especially I already mounted the power distributor on the car. But it's accessible on the LED strips. Anyway, what I should read on the multimeter is the value obtained from the respective port the strip is plugged in. But, if I understand it correctly, all resistors on the distributor are the same, so it doesn't matter where you plug the strips. This kit is generic I believe, I'm sure it wasn't tailored for this car in particular, manufacturer just bundled the kit to add value to the product and it's owner's job to fit the lights as good as he (she) can. So, basically, I'm OK with either port, LEDs should be fine long term and it was a good thing I didn't cut them. Thank-you all for the support.