Electronics Embedding LED's in resin. Part #2: Batteries

My goal is to illuminate a 80mm clear-solid polyester resin ball. I've seen a couple projects with LED's in a similar environment. My inital plans involve hanging the wired LEDs in the mold while pouring (cures at 70deg F). The power source (batteries) will be external.

Will this greatly reduce the life of the LED's? Or will it even work with a completely sealed environment with no airflow

My backup plan envolves inserting the LED cluster in a clear plastic tube while pouring the mold, leaving space for airflow. But this will make the rest of the design more challenging.

These balls will be attached to chains and ropes and swung around for entertainment (aka poi). These are for night practice when we're not using fire. I'm trying to make them robust enough to use as Rope Dart heads also. Rope Darts tend to take alot of impact (to the ground and FACE!) when used by amateurs

 

My LEDs have all survived 420°C for about 2 seconds, I think they'll be able to handle 100°F for a minute. I could be wrong, of course

 

I'm more worried about the LED's heating up while in use, rather than damage from the curing resin. Unless I add to much catalyst

 

The sealed environment isn't an issue for the LEDs.

On a side note, from past experience the diffusion of light through several clear resins that I have tried has been pretty poor, and many have had an index that has caused the LED to appear only as a point source completely ruining any effect I was after. I'll be interesting to see what your resin does...

 

As SteveyG said, your LEDs rely on their built in lense to distribute the light.
If you put them in resin the lens basicly doesn't exist.

They are hard to find, but if you can find a ultra-bright defused LED that would work better.

 

or roughen them up a bit may work...

 

Not really. I tried.

 

Im going to try a couple small test balls today, if I can get the stuff locally. I'll be using the high priced/low output LED's from radioshack for testing

I will be using either red, blue, or green pigment dye in the final project. I'm hoping for a bright uniform glow with a "hot spot' in the middle from the cluster. If there is not enough glow, I will try a clear ball with a polycarbonate outer casing. The polycarbonate will have a light paint coat of either color to diffuse light.

What if i make a little air pocket directly in the center with the LED's inside? If i can find a plastic shell the size of a gumball to fit the LED's in, then hang it directly in the middle with a stiff wire .. maybe that would help the light diffuse brighter and more uniform?

I will keep an eye out for ultra bright defused LED's, maybe order 1-2 and test them.


-I just found this site http://www.jamesclar.com/. His project "block head" also uses dyed resin. I wish he had more pictures of it ....

 

There is no problem fully potting an led as long as the curing temperature is kept below about 150degC. They don't get hot enough running to be a problem.

Light bulbs are actually better for diffuse lighting. Try using 6 leds soldered together at 90deg to each other to make a star. Or use some sort of transparent filter to diffuse them. Stirring air bubbles into the epoxy before it sets is good too.

All you need to create a diffused led is sandpaper.

 

....

if you scratch up an LED, and encase it in resin, the resin will fill the gaps, making no scratches.

 

Would it work if you scratched the LED, and coated it in Vaseline or something like that before casting in the resin? Just wondering...

 

If you have a layer of air around the LED, wouldn't it will act as an insulator and lead to the heat issues he's worried about?

 

There's no heat issues to worry about in this application.

 

am i just misinformed, or do led's not generate much if any heat when operated at their correct temperatures, :shiftyeyes: never heard of 'ANY' led based application how we say, catching on fire, or burning up....

 

The power dissipation of a typical 5mm LED is around 75mW, which can be dissipated through the legs of the LED. So when operating correctly you wouldn't notice an LED getting warm.

 

Where I'm at now: I'm ditching the ball idea and going for 6"-12" tubes. The test ball we made wasn't as easy as I thought It came out ok, a little rough on top. But I like this this material, it took some heavy hits with a ball peen hammer before cracking away.

I've been struggling to find a good way to mount a battery inside the tubes. I want to keep the diameter as small as possible. After much thought and a little toying around with sketchup, I've decided to embed 2x AA NiMH batteries inside the resin with an external charging system.

I have a PVC tube made up with contacts. I just have to insert the batteries and epoxy it shut.

My concerns about this:

#1 Will the batteries need some sort of ventilation? Do the emit gasses when charging/discharging?

#2 I plan to buy the best 2000+Mah NiMH I can find. But is there a big risk with defective batteries? I don't want the ipod effect to hit me.

#3 Charging. I was looking at a package with a wall charger and 4 batteries. Everything I need. But the batteries will be in series inside the mold. Will I be able to still use the charger? I will have a connecter accessible at the top of the mold, but I'm not sure how to wire it up. Should I charge in series, a - of one battery slot and a + off the other. Or just use one battery slot and charge at.. whatever a single battery charges at

 

All leds use energy, W=Forward Voltage x Current, with maybe 70% coming off as light, rest wasted as heat. That's why Luxeons need a heatsink.

Maximum junction temperature is only about 125C, so they'll fail long before they get hot enough to burn.

 

#0 Battery mounting: You can buy batteries with a solder tag from some electronics stores.

#1 They can emit gasses if charged too quickly or overcharged. They can also swell slightly during charging. In practice my brother fully potted a pack using some sort of epoxy and hasn't had any issues. Then again he is into electronics and paranoid enough not to let them get overcharged. If there is space around the battery drill a small vent hole. Interesting Fact: the pressure inside a NiCd can be over 200psi during charging.

#2 should be good for over 300 charges.

#3 Many chargers require pairs of batteries to be inserted because they are in series.

 

I have 4 additional LEDs in my mouse, running at about 10 Ma each, 2 chains of 2 in series. And my mouse is noticeably warm in that one corner even if its been sitting for a while, no big deal, just a bit warm. So yes, they do make some heat, and if you have them trapped in an air pocket (like the mouse) it can warm up. But if they are encapsulated, it shouldnt make much difference.