What is the best way to mount LED strips on polycarbonate panels?

Polycarbonate panels are cheap, strong, light, durable, and easy to buy. They are perfect for constructing large scale LED strip installations. But what is the best way to secure your LED strips to the panels? I’ve done a lot of testing to find out, and the most reliable method turns out to also be one of the cheapest and easiest…

2016-03-31 11.20.43

TLDR;

Surface mounting bare strips with a bead of GE Silicone I is the best combination of cheap, long lasting, and easy for my tastes- but only for panels that will not get bonked.

About LED Strips

My personal favorites are WS2812B (aka Neopixel) RGB strips. These come in any pitch you could want. You can get them quickly from Adafruit & Amazon, or amazingly cheaply from Alibaba. You can drive them easily from an Arduino or BeagleBone.

But the findings below should apply to other types of strips as well.

Twinwall 8mm With Bare Channel Slide

2016-04-21 10.58.41.jpg

Pros:

  1. Very robust. The strips are projected inside, so you can bang panels around.
  2. Simple. No extra parts.
  3. Relatively quick assembly if you are using strips without connectors.
  4. Strips are supported along their length, but are free to expand and contract. This could theoretically improve robustness in locations with wide temperature swings.
  5. You can get these panels in easy-ship sizes from GreenhouseMegaStore.

Cons:

  1. Standard JST connectors will not fit though the channel, so you can’t use strips with connectors already soldered on both ends.
  2. The strips do not lay flat so LEDs do not always aim perfectly forward. I’ver played around with sliding different kinds of compressible strips in behind the LEDs to push them against the front surface, but have not found a fast and reliable solution.
  3. Poor heat rejection since there is no airflow over the LED. If you have a lot of LEDs and they are on a lot of the time, things are going to get hot.
  4. Options for the spacing between strips are limited to where the channels are.
  5. Higher density strips (>72 LED/meter) tend to be wider and do not fit in an 8mm channel.

Comments

While most big projects I’ve seen use this system, I don’t. Not being able to use pre-soldered connectors on a big project means the people assembling the panels need to be skilled at soldering, rather than just being about to click-and-go. I also thing the wiggling strips look ugly.

Hurricane Panel With Silicone Sheath Channel Slide

These triple-wall panels have larger channels that are just big enough to hold strips with IP67 waterproof sheathing.

2015-07-05 21.55.11.jpg

Pros:

  1. Very robust. The strips are projected inside, so you can bang panels around.
  2. Simple. No extra supplies.
  3. Very quick assembly with non-skilled labor. Just pull strips and plug the connectors.
  4. Strips are supported along their length, but are free to expand and contract. This could theoretically improve robustness in locations with wide temperature swings.
  5. You can get large panels delivered for free from HomeDepot.

Cons:

  1. The silicon sheathing likes to stick to the walls while you are pulling it though the channels. See below for tip.
  2. The strips do not perfectly lay flat, but much better than bare strips in 8mm channels.
  3. Options for the spacing between strips are limited to where the channels are.
  4. Even worse heat rejection than 8mm bare slides since there is no airflow over the LED and they are encased in silicone. If you have a lot of LEDs and they are on a lot of the time, things are going to get really hot.
  5. The sheathing acts as a bit of a diffuser, so the LEDs are not as sharp and you probably loose a bit of brightness.

Tips

To make it easier to pull the strips though the channels, I made a tool out of a coat hanger and some wire. It speeds things up a lot.

2015-05-25 14.24.04.jpg

To keep the strips from shifting horizontally, I like add a squirt of caulk or hotmelt to the ends of the channels as shown in the above photo. This makes it possible to keep the columns of LEDs lined up pretty accurately.

Comments

I don’t know how much waterproofing you’d actually get from the sheath, but it does help to hold the LEDs facing forward better than bare strips in 8mm channels. This is my preferred method for panels that need to be able to hold up to rough handling.

Bracket Clips

2016-04-21 17.53.27

Sorry, but these don’t get a full section because they don’t really work at all. They are cheap, but I think you’d basically need to install one between every LED to keep the strip flat.

Surface Mount With Double-Sided Tape

2016-03-31 11.20.05.jpg

Pros:

  1. Works with any size or thickness panels.
  2. You can use any spacing you want between strips.
  3. LEDs have direct airflow across their faces for much better cooling.
  4. LEDs are very stable and flat and aim straight forward.
  5. Relatively quick and no mess assembly.

Cons:

  1. LEDs are naked and exposed and could be shorted or damaged by things bumping against the front of the panel.
  2. For any serious project, you’ll want to order your strips without adhesive backing (see below), which is non-standard.
  3. Extra cost for tape.

Tape choices

Standard “3M” Backing

Most strips come standard with backing tape labeled “3M” or “3M 200MP”. It varies in quality, but is never good enough for serious use. It has poor adhesion to both the strip back and to the polycarbonate panel. You could maybe use this for a project that only had to last a couple of days and if you didn’t mind having to occasionally re-stick the strips back onto the panel, but otherwise I’d ignore it.

3M Hardware Store Foam Tape

This is the normal 3M Foam Tape that you might use around the house, but it works surprising well. The 1/2″ width is perfect for LED strips and is available for about $1/meter in quantity.

With this tape, it is possible to pull the strips off the panel but it is hard. I haven’t done any long term tests, but I think you’d be safe with this tape for at least a year under normal conditions.

3M 4941 VHB Tape

Wholey crap, this stuff is amazing. They use it to hold cars and buildings together, so you can be sure your LED strips will stay on for at least… well, forever. If money is no object and you want the strongest long-term mounting possible, this is the way to go.

That said, VHB tape is prohibitively expensive for most projects at about $4/meter.

Surface Mount With Liquid Applied Adhesive2016-03-27 17.40.49.jpg

Pros:

  1. Works with any size or thickness panels.
  2. You can use any spacing you want between strips.
  3. LEDs have direct airflow across their faces for much better cooling.
  4. LEDs are very stable and flat and aim straight forward.
  5. Negligible cost.
  6. Relatively quick assembly.

Cons:

  1. LEDs are naked and exposed and could be shorted or damaged by things bumping against the front of the panel.
  2. For any serious project, you’ll want to order your strips without adhesive backing which is non-standard.
  3. Slightly messy and very smelly. Probably best to assemble outdoors.

Adhesive choices

GE Silicone I

Even though it is sold as a sealant, this stuff adheres great to the back of strip PCB and to the polycarbonate.  While it is possible to pull the strips off, it takes several pounds of force. I’ve tested with 30 cycles between 0C and 120C and there is no noticeable bond degradation.  It is widely available and a single $5 tube can mount dozens of meters of strips (depending on how thin a bead you make).

This is my default choice for all strip mounting except when the strips will be exposed to rough handling.

GE Silicone II & Den Braven S7

These are more expensive than GE Silicone I and do not bond nearly as well. The only possible advantage is that they don’t smell as bad. I guess if you already had a big stock of one of these that you needed to get rid of, you’d probably be OK to use it for strip mounting, but probably better to sell what you’ve got on ebay and buy some Silicone I instead.

Tips

2016-04-21 13.24.51

I use a printmaking roller to help squish the strips into the silicone bead. You want to push hard enough to make sure that the silicone contacts both the back of the strip and the front of the panel, but not so hard that you squish all the silicone out of the interface.

I use a thin bead, maybe about 1/8″ wide  (thinner than you’d use for normal caulking), but I try to make the bead wide enough that I can see the silicone squish out the sides of the strip when I press it down. I feel like this gives a better mechanical connection at the edge, but I have not thoroughly tested this.

 

 

7 comments

  1. JD Gershan

    Hey Josh. Thank you for this. Do you have any video of finished panels in operation you would care to share? I’m curious what you are using them for: Lighting? Color effects? Signage? Thanks, J.D.

  2. Nerd Ralph

    I always used Silicone II (as a caulk, not adhesive). Did some searching, and I think I’ll be switching to Silicone I. Apparently Silicone II uses some sort of organic compound for curing while Silicone I uses acetic acid. I’m also curious about shelf life, since I’ve had unopened tubes of silicone that were useless after a few years.
    I may also try Iron Grip as well to see if it can handle temperatures high enough for soldering.
    http://nerdralph.blogspot.ca/2014/09/on-chip-decoupling-capacitors.html

    • bigjosh2

      Heat can increase bond strength when bonding to metal parts (generally this same increase is observed at
      room temperature over longer times, weeks). For plastic parts, the bond
      strength is not enhanced with the addition of heat.

      Can you link to info that says otherwise?

  3. Zhahai Stewart

    Very interesing, thanks!

    Have you tried bonding strips enclosed by silicone tubes to a polycarbonate panel surface?

    This is intermediate in handling robustness since the chips are not bare, but also not enclosed inside a polycarbonate channel. However it could be waterproof for outdoor use, a substantial advantage.

    I’m wondering if GE Silicone I or II would adhere well to the generic silicone tubing available for strips; I assume that it would continue to bond well with the polycarbonate backing as it does in the bare strip scenario. Have you tested this?

    By the way, the Silicon I may indeed work better for your strip-back bonding where it’s not making contact with wiring, but people often try to avoid using it on electronics (eg: to seal the ends of a strip after soldering wires to it) because the released vinegar (acetic acid) corrodes the exposed wire/solder/strip. (So Silicone II is preferred in direct contact with circuitry or wiring). I would still be somewhat watchful for corrosion over time in the case of bare strips glued with GE Silicone I.

    • bigjosh2

      I don’t really like the strips in the silicone. They are more expensive, and not really weatherproof because you still have the exposed connectors. I also don’t trust the globs of silicone that seal off the ends. I prefer to make a full assembly weather-tight.

      I didn’t even think about the acetic acid issue, but makes sense. So far I have not seen evidence of corrosion with Silicone I. Would you expect that be a continuing risk, or pretty much only matter during the cure?

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