PDA

View Full Version : LED filament blade?



profezorn
04-18-2016, 10:05 PM
Ebay is full of LED filaments nowadays.
Has anybody tried building a blade out of them? It should be possible to get about 25 of those in a blade, which means about 3000 lumens.
Unfortunately they require 50-60 volts, so it will definitely need some boost converters, and could possibly get a bit hot since the battery and voltage booster will have to put out 25 watts of power. Still, a good booster can be ~90 efficient, so we'd only put out 2.5W of heat in the booster.

I was thinking of designing a 12" by ~1/2" circuit board for holding the led filaments, then put as many as those as I need together. The power draw on the 60 volt side is only 0.35A, so it doesn't need any bulky cables. (Power draw on the battery would be around 5A though, assuming a 7.3-volt battery pack.)

I've ordered some LED filaments, and I found a boost converter that might be powerful enough (if it doesn't overheat) I'll post pictures and stuff here as I go.
If anybody has recommendations efficient boster ICs/circuit designs, that would be cool. I can build my own circuit boards, but I'm not terribly experienced at it.

In the meantime I'll be reading up on how to construct the rest of the blade and diffuser.

/Profezzorn (1st post)

Silver Serpent
04-19-2016, 07:04 AM
Sounds like you'll have an interesting time powering those filaments. It's definitely not going to be compatible with the regular lightsaber tech.

Good luck, and keep us informed of your results, good or bad.

profezorn
04-19-2016, 10:41 AM
I think I just figured out the easiest way to get the required power: A stack of 20 CR2032 coin cells. With a power draw of ~0.35A, the coin cells won't last that long, perhaps half an hour or so, but apparently you can buy these in packs of a hundred for $30 bucks.

If there is enough space, I could double the stack of batteries, double the voltage to 120 and connect two filaments in serial. This would reduce power losses and double the battery life. The stack of batteries would be 128mm tall, and I don't have my hilt yet, so I'm not sure how much space I'm going to have.

The coin cells probably drop some voltage under load, so it's possible that I'll need more than 20/40, . I'll have to experiment and see.

FenixFire
04-19-2016, 11:30 AM
LED Filaments are essentially a series of smd type LEDs on a flexible circuit board with a translucent elastomeric. OK so technically they are a series of blue with a few red SMD LEDs and the elatomeric is coated with Phosphor coating. Though some china companies are simply using white leds and translucent yellow plastic dip type material, you can usually see ech individual dot of lite on this type. With some patients and experimentation you could fabricate a string blade using current string blade wiring methods. Just build each of the series wired segments for approximately 7.4v. That way you can use a readily available power supply. You could make your own board using copper clad and etching, or simply have one printed by any of several places offering custom boards. Then wire each of the segments in parallel, heat shrink the whole assembly and now diffuse and insert it into a blade like a standard string blade.

Either way keep in mind heat is the enemy of any LED, and all high intensity LEDs need to have some way to dissipate the heat. I know there is a white paper on the construction and evolution of the filaments I'll dig it up for you. It might be an opportunity for some of the new thermally conductive polymers that are on the market...I bet there is someone working on that as we speak;)

Edit: here is the link http://www.ledinside.com/knowledge/2015/2/the_next_generation_of_led_filament_bulbs

FenixFire
04-19-2016, 11:42 AM
If you are looking at the extremely cheep, low end $.90 ones on eBay the flexible board is simple the thin metal strips you see exposed on the ends.

Here is the link to the actual manufactures spec sheet. http://www.runlite.cn/userfiles/5cjerp755q19k1413258994.pdf Also, keep in mind that filaments like these are designed to be installed in pressurized bulbs filled with a cooling gas. The opposite of the traditional incandescent that are in vacuum bulbs. I cant remember it is is this or one of the Philips products that list the recommended gas and pressure composition.

profezorn
04-19-2016, 02:36 PM
I'm not sure how you would wire things up to run at 7.4 volts without getting custom LED filaments where some of the LEDs are wired in parallel. If such a thing exists, I have not yet found it. However, I don't see a problem with either using a boost converter or a stack of coin cells and then controlling the high-voltage circuit with a FET. The FET can be wired directly to the sound board (with an appropriate resistor) to let the sound board control sparks and on/off. If I go with a boost converter, they usually have an "enable" pin, which would eliminate the need for a FET. I found a tool called wbench which can automate the boost converter design, but it is currently giving me designs that include non-existing inductors. :(

I've already ordered some led filaments to start testing with, I'll be interested to see how hot they get. If they get too hot I'll have to put a fan in the hilt and create an air hole in the tip of the blade.
Another option would be to replace the traditional foam diffuser with some sort of epoxy or silicone, which could carry the heat away better. That would make the blade pretty heavy though.

FenixFire
04-19-2016, 03:01 PM
You would be creating your own pseudo filament, essentially using smd LEDs instead of standard dome or top hat LEDs.

The problem you will run into with using the OEM filaments you mention is heat. High intensity LEDs are not like the normal 20mA kind. They all require some form of heatsink either copper, aluminum, THERMA-TECH™ polymer, or various coolant gasses. In the case of the Filaments they were developed as a way to aesthetically replicate the classic Edison bulbs, thus utilizing the principles of the inverse of the vacuum they use a pressurized cooling gas within the glass or acrylic bulbs they are installed into. You can run them for a short period out of the cooling chamber as shown in various youtube videos, though they will not last if exposed to long run times.

Though I have not seen or tested how long they would last outside of the chamber. After all the rebels and crees are being pushed beyond what they were designed per one of the Cree engineers I know, though he credits it to the fact that the heatsink and LED holder are effectively transferring heat to the entire hilt. Since the filaments will be in the PolyCarb blade assembly and any direct metal contact would short it out, this is not possible with the filaments.

As for the Fan solution:
High-intensity LEDs heat up instantly and do not allow time for a fan to cool them before the magic smoke is released. Fans can assist in cooling the heatsinks, but the LEDs have to be cooled through contact. Ideally with either a copper, Aluminum, or THERMA-TECH™. Look at the heatsinks used on the single CREE LEDs in the shop. The filaments are basically 10 of those leds at a 1608 smd size, with no heatsink attached.

BTW:
Silicone and Epoxy(clear 2 part not JB Weld) are thermal insulators not thermal conductors. They would actually hold the heat to the LEDs not dissipate it. Thats why they make silicone oven mitts.

profezorn
04-19-2016, 03:24 PM
> High-intensity LEDs heat up instantly and do not allow time for a fan to cool them before the magic smoke is released. Fans can assist in cooling the heatsinks, but the LEDs have to be cooled through contact. Ideally with either a copper, Aluminum, or THERMA-TECH™ heatsink.

All true, but as you say, the filament don't immediately die when you run them in air. However, in an enclosed space, the air heats up and will eventually kill the LEDs (or melt the surrounding plastic). Even a fairly modest flow of air can prevent this from happening.

Also, I just realized I have some 4- and 7-watt led filament bulbs at home, I should check out how hot they get.

FenixFire
04-19-2016, 03:38 PM
An led will never get hot enough to melt the plastic around it, before it pops.

FenixFire
04-19-2016, 03:45 PM
Good luck with your trials, here is a link to an article that will help explain some of the heat issues. http://www.electronics-cooling.com/2006/11/thermal-challenges-in-led-cooling/ It's not the one I was looking for but it should help out. Even Crees and rebels will work for a few minutes without a heatsink...but then it's too late.

For the bulbs you mention ther is the thermal conductive gas and the internal assembly transf0er the heat to the therma-thech plastic. You'll need to calculate the surface area and the surface temperature above ambient to calculate the required thermal loading.

profezorn
04-19-2016, 04:36 PM
Interestingly, the surface area of a lightbulb (~100-120 cm^2 if my google-fu is working) is pretty similar to the surface area of the blade, which would be 4 cm (length of filament) * 4 (number of filaments in a lightbulb) * 1.185 (blade diamater in cm) * PI = 94.245. However, the gas in the lightbulb is probably a decent thermal conductor, while the diffuser in the blade, is decidedly not. Using a standard diffuser will lead to a lot of thermal compression... Either way, I'm just going to have to do some experimentation to figure out how hot it really gets.

FenixFire
04-19-2016, 07:20 PM
Also the plastic section of the bulb is therma-tech which has almost the same thermal conductance of aluminum. Polycarbonate is an insulator.

profezorn
04-21-2016, 02:23 PM
I think "polycarbonate is an insulator" is too black and white. Polycarbonate, Epoxy and many other plastics have poor thermal conductivity, but it still conducts heat 10x better than air, and slightly better than helium. (Which is partially what's in the filament light bulbs.) Of course, light bulbs also have the added benefit of convection, which plastics do not have. Thus, encapsulating LEDs in epoxy should improve their thermal properties, but not nearly as as much as a proper heat sink. (copper conducts heat nearly 3000x better than epoxy.)

Anyways, I'm currently thinking that active cooling is the way to go. Basically, I want to mount the filament to a very narrow circuit board, cram the circuit board into an inner tube, which should leave some space above and below the circuit board. The inner tube then goes into the diffuser, which goes into the polycarbonate tube. The tip of the blade will have a drilled hole which connects to the inner tube, and the hilt will have a centrifugal fan which pulls air though the blade. It's a bit complicated, especially since I want to keep the blade removable but I'm hopeful that it will keep the filament cool enough. Also, the inner tube can do double-duty as a color filter for the LEDs, as I want my blade to be light blue.

The drawback of this approach is that the filaments will not be directly supported by the diffuser, potentially making them more susceptible to mechanical damage. I might be able to fix that by wrapping the circuit board in something, like thread or mesh.

FenixFire
04-21-2016, 07:32 PM
Don't get me wrong, I am very interested in you experiments, as I am also actively working professionally on trying to find better ways to disapate the heat generated from High intensity led for commercial and residential purposes. LED filament bulb at least the ones from the leading MFG that is sister company to the one I work for now, use a mixture of primarily Xenon and Argon. BTW I work for the largest polymer company in the world...so I am familiar with the properties of especially PCs and Acrylics as well as a half dozen specialty plastics designed exclusively for disapating heat off high intensity LEDs. Hence why I was helping out letting you know in advance that a fan and airflow alone will not be enough to cool the LEDs. I like the general idea you have, I just think it could be more effective if you skipped the filaments and made your own, then you could use blue or royal blue LEDs instead of being stuck with warm white...even with filters you would probably get a greenish cyan color.

profezorn
04-22-2016, 01:33 AM
I'm not sure I see any advantage (thermally) to making my own strips. I mean, if I put 25W worth of SMD leds in the blade, I'm still going to have roughly the same amount of heat to dissipate.

Pros/cons of using SMD LEDs:
+ no filters needed as I can select whatever mix of colors I want
+ can design for any voltage (with the usual constraints)
+ can easily space LEDs farther apart to reduce heat issues
- a lot more work
- you loose a little bit of efficiency since I don't have transparent circuit boards / led modules

FenixFire
04-22-2016, 07:03 AM
Just finished up a call with the LED lighting engineers from France, and had a few moments to ask them about these lower current filaments in particular. Sounds like if run at the 10-15 mA range they are designed for heat mitigation may not be a significant deterrent. The thermal issues we have is that the specific SMDs we are mounting are in the 700-800 mA range so the heat is significantly higher.

profezorn
04-22-2016, 12:46 PM
That's encouraging, means it *might* work. :)

PS: 700mA? Holy Sh*t, 40W in one filament? Lemme see, 25 of those in one blade would be 1000W, which would give off something like 130,000 lumens. That would almost be a real light saber!

PSS: I assume you guys are doing fewer LEDs than the low-power ones, but I couldn't resist some outrageous extrapolation. :)

FenixFire
04-22-2016, 01:05 PM
Depends on the specific application, strip, flood, area, or the hottest is a spotlight application with 28+ Cree XP-D on a 8" disk. It had to use an actual glass optic because...Well lets say it gets insanely hot!

profezorn
04-30-2016, 05:21 PM
So I finally got my el-cheap-o LED filaments that I ordered from ebay. Well, the ones I ordered said 50-60 volts, but the ones I got say 70-80 volts... Oh well, that's what I get for ordering from ebay.
Anyways, I have also ordered a pile of coin cells to use for experimentation, so changing the voltage is pretty easy. The good news is that while the filaments get hot, they don't seem to *mind* being hot. I wrapped one up in several layers of tape to emulate some thermal insulation and ran it for about an hour with no problem. (Apart from getting hot enough to be uncomfortable to touch.)

The usable voltage range is a lot narrower than I expected though, the leds don't even turn on until you hit 70 volt, and the light output is pretty low below 75 volt. To really get to full brightness, 80 volts is required. This means that running these directly from a stack of coin cells is not practical, as even a modest drop in battery charge will result in a lot less light. I definitely need something that can boost the output of a few li-ion cells to 80 volts. Texas Instruments has some ICs that can do that, so I'll probably just make my own board for it.

13880

profezorn
05-09-2016, 08:07 PM
I think I'm going to give up on the LED filaments for now, and build an LED string out of APA106 LEDs instead.
The biggest problem with the LED filaments is that I would need to design some circuit boards (one for holding the LED filaments and one for the voltage booster), and frankly I really really hate all circuit board cad software I've tried so far. Eagle seems to be the least bad, and it is horrible.

I might re-visit this later if I can find some way to design circuit boards which is less painful than a razor-eating contest.

FenixFire
05-10-2016, 07:07 AM
I think I'm going to give up on the LED filaments for now, and build an LED string out of APA106 LEDs instead.
The biggest problem with the LED filaments is that I would need to design some circuit boards (one for holding the LED filaments and one for the voltage booster), and frankly I really really hate all circuit board cad software I've tried so far. Eagle seems to be the least bad, and it is horrible.

I might re-visit this later if I can find some way to design circuit boards which is less painful than a razor-eating contest.

Yeah, without spending a ridiculous amount of cash on the software and annual renewal they are pretty bad...he User interface of the high-end software is still overly complicated and hard to use without the "Recomended" training. The only people I have ever encountered who enjoy or can understand the interface are EEs who choose to work in it daily.