LED light for Fiji 2008 Completed

[richhagen]

A while back I had posted about building a light for small solar power systems for the expedition back to Fiji this year.  The design goal was an efficient, yet robust light which would survive for a long time in a relatively harsh environment.  

I had obtained some manufactured bulbs utilizing Cree LED's and had tested their current/power draw, and was impressed by the amount of light that they put out.  

At $30.00 U.S. a piece, however, they were not practical for this mission, and several would be needed together to light up a room.

I wound up ordering 30 boards with 3 Cree 7090XE LED's on them from a supplier in Georgia, U.S.  

Once I had the boards, I needed a circuit to drive them.  I wound up using the circuit designed by Amanda here:

http://www.fieldlines.com/story/2007/5/1/74856/25992

Next I built a test circuit on a breadboard.

Next I soldered a circuit on a proto-board and gave it a lengthy test at 18 volts.

This probably saved these geraniums from dying out as they had not been getting enough light.  You can actually see how the leaves near the light have turned towards it over time.  Once I was satisfied that the circuit was working as designed, I took over the basement kitchen and put together a batch of them for the lights.  I was originally going to etch boards for these, but I wound up just using the prototype boards instead to save precious time.

The soldering is small, so sometimes you have to get a little help with fresh eyes and smaller hands [;-)  Joel wanted to learn how to solder, so he gave it a go.  With a bit of practice it is no problem for him.  

Next it was time to make the frames.  I decided to make the frames out of aluminum so that they would basically be giant heat sinks to keep the LED's and the FET's cooler.  I made an aluminum face plate to hold 4 of the LED boards.  I measured the hole locations from the board with calipers, and put it into a computer file that I could run on my small Taig CNC mill.

 

Parts were made for 7 lights with 4 of the 3 LED boards each.  

 

There are 48 size 4 at 40 threads per inch holes on the front plate.  

I am definitely not good at tapping holes with those small taps.  I broke not one, not two, not three, but 4 of those taps making the front plate.  I think my hardware store was out of stock by the last one, but I did get a bit better at using them.  

 

I made a few other mistakes along the way, for instance, one cannot put screws in at the same location on angle stock as the screws run into each other.  

 

I have found that it is always good to make a prototype to avoid these issues when assembling a batch of items.  Once the parts were made and the bugs worked out it was time for assembly.  

This is the result:  

 

 

I powered one up.  They are annoyingly bright, but they can light up a room.

 

At 18 volts, the case gets warm over time, but can be handled at that point.  They are designed for 12V operation, they should be fine for that.  I think we will definitely need to consider adding shades to these though.  Now I just have to clean up all of the messes that I made in putting these together.  :-(  Six of these will make the trip, and one will stay here.  It will probably go up in my laundry room where I have a 12V light now.  :-)  I have saved the g-code file for the front plate as I plan to make more of these, so if anyone wants it, just ask.  Thus far I am happy with these lights.  Time will tell how well they will hold up on the island. It was a fun project, Rich  

[commanda]

Absolutely beautiful Rich. I congratulate you on your workmanship.

My only suggestion is liberal use of a conformal coating on the boards, after masking off the leds themselves. Help prevent corrosion from the humidity  and salt air.

Amanda

[Sundog]

If you have a lathe, preventing breakage of taps is easy-peasy.  If you don't have a lathe, it's nearly as easy.  

With a lathe -

  Grab a piece of 1/2" diameter brass rod about 3" long.  Chuck it up, turn the outside down true.  Now drill a hole about 1.5" deep using a chuck in the tailstock, just a hair larger than the OD of the tap shank.

Use a dremel with a grinding wheel (or a file, if you're a glutton for punishment), to put some flats on the tap, just above the cutting threads.  Make it a size that's easy to grab with either a tap wrench or a small ignition wrench.  

Without a lathe -

Very carefully clamp the brass stock in the mill vice, then drill a hole in the center of it (as close as humanly possible) just a tad larger than the tap shank.  Modify the tap the same as above.  

To use -

Drill your hole using a drill press.  Without moving the workpiece, table, or head, swap the drill bit for the tap holder.  Put the wrench on the tap and slip it into the chuck.  Hand tighten the chuck, then lower the quill, lock it in place, and start tapping!  

For holes to a specific depth, put a set collar on the drill bit shank, set the plunge depth on the drill press, and use the above procedure.  That way when you replace the tap holder with the drill bit, your depth is still correct.  Most blind tapped holes have a bit of fudge factor involved in their depth, anyway.  

The above method sounds like a royal PITA, but in actuality it isn't that bad, and once you get used to it, it becomes very fast.  You tap the holes straight, true, and best of all, you'll rarely break taps anymore.  Unless you get crazy and abuse 'em.  

The above method also works excellent for tapping holes that are drilled at an angle to the surface of the workpiece.  Drill the hole, counterbore, etc, de-burr, then swap in the tap holder and tap it before you change the position of the workpiece or head.  Works like a champ every time.  

Just my $.0134 (damn recession!)

Shad H.

[donald77777]

Very interesting. I do have to say the finished product looks very professional. Keep up the great work. Only question is did you put a piece of glass or a covering over the boards? or are the boards uncovered?

[richhagen]

Thanks, I ordered up a silicone based spray on conformal coating.  If it arrives before I have to have these dropped off for shipping then I can get them coated.  If it does not, I will likely be out of luck as I don't think I can ship that to Fiji.  Rich

[richhagen]

I might try something similar for my mini milling machine.  That way I could drill all of the holes in one step, and then change out for the tap holder design.  The machine would then line up the tap over each hole through the code, and I could pause it at each for tapping.  

I did manage an average of 84 tapped holes per broken tap, so it added about 6 cents per hole tapped for the costs of the taps that I broke, and about $20 to the project costs, so reducing that would make a difference.  Rich

[richhagen]

Right now, the boards that hold the LED's are mounted straight on the aluminum plate that was drilled and tapped for them.  There is no covering right now, although the LED's are on an aluminum based board with a vinyl type coating over all but the areas masked for soldering.  I think we will need to add some type of a shade to this primarily because of the harshness of the LED points of light in operation.  Rich

[JamesJackson]

Congradulations on your completed project! They look really nice and bright shining in the photo that you posted.

One word of caution.

Do NOT allow these to be angled down into the home(s) where the point-source is visible to the occupants - these high-intensity LEDs are considered 'laser' lights - or at least have the same warnings that are given to laser LEDs.

I have three 5-watt LED lights that have been mounted on the wall of my home - pointed downward into my living room - basically shining right into my face. I could actually see the die when lit. They are pretty durn bright!

Well... after about nine months, both me and my wife acquired uncontrollable 'twitching' of the eyes. Very annoying, and I couldn't figure out why, until it dawned on me that it might be related to the LEDs shining in our eyes every night.

I left them off for a week - the twitching subsided. I re-positioned the LEDs to shine at a different angle, and everything seems to be much better now.

So - take care. I don't think that you want to harm anyones' vision with these enormous light-sources.

Regards,

James Jackson

Oztronics

[richhagen]

I just saw your reply, Yes, I think that adding shades to these will be on the agenda.  I have one in my laundry room and the one lighting up a plant is still there.  No twitching yet, but they are bright, they are being driven at about 430ma, or about 1.6 Watts so they are probably not as bright as when driven at higher currents, but they are still very bright and can use a shade.  Some of these are already on there way to Fiji, so the shades will have to be added there now.  Rich

[richhagen]

I was able to spray them down inside and out with a silicon based conformal coating.  I put pieces of electrical tape over the LED lenses during the process.  Rich