OLcontest, modified light: 20cm fresnel lens thrower

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djozz
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OLcontest, modified light: 20cm fresnel lens thrower

A couple of years ago I made a 36cm fresnel lens thrower, from wood, featuring a dedomed XM-L2.

It did/still does over 5Mcd, which is great, but it is rather bulky. And because of the short focal distance I think that the outer part of the lens has a lot of distortion and contributes relatively little to the center of the hotspot. So now I try to make one a bit more compact and usable (i.e. without being really water proof, it will be usable in slightly rainy conditions), with a 20cm lens, and a bit longer focal distance: also 20cm. The hotspot will be smaller, but expect also optically better. And I move on to a more modern led: a SBT90.2 .The aim is to reach 2Mcd.

I’m not sure if this build can be done within the rules of the OL handbuild competition, because, as in my former build, one of the parts is a commercial flashlight, although it is only used as switch+battery tube, with the head removed. If it complies I’m happy to join with this build.

Edit: after inquiring, this build is fitting into the modified light category, so it will enter the OL-competition as a slightly modified Yootoo SD2 Smile

These are the parts to start with. The plate is 20cm/20cm/3mm aluminium and the heatsink is a 13cm passive heatsink made for a 65W COB. I’m still waiting for a SBT90.2 on a Noctigon from Hank. And lots of wood is not on the picture either.

Edited by: djozz on 11/08/2020 - 07:49
adam7027
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Whoa, that’s something.

Do you have data about how does the previous build compare to the current (as planned) regarding LED light emitting surface and power?

djozz
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adam7027 wrote:
Whoa, that’s something.

Do you have data about how does the previous build compare to the current (as planned) regarding LED light emitting surface and power?


The SBT90.2 should have a bit higher surface brightness than the dedomed XM-L2, but I expect also a bit better optical performance from this lens, and also the larger surface area of the die may be a bit more forgiving for the poor quality of fresnel lenses. But there is a lot of guessing involved, my fuzzy conclusion is 2Mcd but it can go either way.

The output of the SBT90.2 is also much higher as the dedomed XM-L2, about 4 times, but with the smaller lens at increased distance, the amount of light exiting the lamp will not that much higher.

djozz
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After a lot of measuring (the heatsink must be centered pretty perfectly on the alu plate to get the led centered behind the lens) I made some holes in the 20cm x 20cm x 3mm aluminium plate, 4mm small holes with a drill and two bigger holes with a fretsaw (IMO the fretsaw is the ultimate handbuild tool Cool )

It fits.

That is all for today.

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Do I recognize an Amutorch Yootoo SD2? Very interested how that plan is coming together.
FWIW, I do remember a sketch of a big thrower with the batteries placed behind/around the reflector.

You are a flashaholic if you are forced to come out of the closet, to make room for more flashlights.

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Yes, an SD2, I have two of them spare because they did not fit the boost driver I was planning to mod them with Sad
Now it is a convenient 21700 battery compartment with added switch.

And yes, this is still my favorite setup for a big thrower since the first plans for the BLF-GT. Who knows it will be picked up some day by a manufacturer.

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Forgot, the tools of today:

Not shown: drill press

MRsDNF
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Nice start djozz. Looking forward to the rest of the build. Thumbs Up

 

djozz quotes, "it came with chinese lettering that is chinese to me".

                      "My man mousehole needs one too"

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

Old-Lumens. Highly admired and cherished member of Budget Light Forum. 11.5.2011 - 20.12.16. RIP.

 

djozz
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Thanks Steve!

Today small progress: a mount for the lens made from plywood. Tools: pencil, ruler, drawing compasses, drill, fretsaw, wood glue.

The effective diameter of the lens will be 196mm.

Sirstinky
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Awesome! I bet it will be a crazy thrower.

MRsDNF
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Do your students know you are building this? So the above is two pieces of wood glued together to get the step?

 

djozz quotes, "it came with chinese lettering that is chinese to me".

                      "My man mousehole needs one too"

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

Old-Lumens. Highly admired and cherished member of Budget Light Forum. 11.5.2011 - 20.12.16. RIP.

 

djozz
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No, they do not know that I build searchlights. But they do know that I build stuff myself every now and then, before summer I built a wind tunnel from wood and polycarbonate panels for physics demonstrations (to make wind I used a 10 inch 12V 80W car radiator fan from aliexpress).

Yes, two pieces glued together, I think that I will glue the lens in the slot from the outside after everything else is finished, and keep the lens clean. In fact I have two identical fresnel lenses (they are cheap), one for during the build to check the workings, and one for the finished lamp.

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Nice project and thanks for showing …..

Also nice to see “creativity hard at work …..”.

Cheers,

Martin

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I’m here for the fun Big Smile

djozz
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Welcome MB, here is some fun Smile .

To check the potential of the lens, I clamped it in with a FT03-mini (harddriven SST-40 with dome) behind it. I measured the throw at 6.99 meter from the fresnel lens and got 2.16 Mcd (at 30 seconds). So the potential is there, the domeless SBT90.2 should even do a bit better, and if it doesn’t I can always go SST-40 and have the runtime and less heat.

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djozz wrote:
Welcome MB, here is some fun Smile .

To check the potential of the lens, I clamped it in with a FT03-mini (harddriven SST-40 with dome) behind it. I measured the throw at 6.99 meter from the fresnel lens and got 2.16 Mcd. So the potential is there, the domeless SBT90.2 should even do a bit better, and if it doesn’t I can always go SST-40 and have the runtime and less heat.


That is fun indeed! Big Smile
I admire your creativity and work! An SBT will blow it, not in the “explosive” way! You’ll soon rename your city to Amster..daaaamn Shocked when that beam hits the sky Wink
djozz
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helicoil wrote:
Nice project and thanks for showing …..

Also nice to see “creativity hard at work …..”.

Cheers,

Martin


Thanks Martin, and others. The creativity was already 4 years ago, it is more of a rebuild with improvements based on what I learned back then. I like that you do not need to be a fancy flashlight manufacturer to make a superthrower, this thing will look extremely homebuilt Big Smile . But I must admit that the cost of the parts add up, I’m over 100 dollar already, the led+board+heatsink+alu plate+SD2 were 92 dollar, I can’t remember the cost of the lens, but it was about 10 dollar. Maybe 8 dollar worth of plywood, and a dollar for a handle, so maybe 120 dollar. That is what I paid for the Lumintop/BLF GT a year ago so homebuilding is fun but does not really pay off Facepalm
helicoil
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Well see it like this .... you're now or soon will be ..... the owner of (another) homebuild world exclusive ! ....

 

... and in "my eyes" that's basically priceless !

 

Also the "material cost" is probably only a fraction of what the "manual creativity" would have cost ....

 

... that is if "someone would have payed you to do it" ?

 

Cheers,

 

Martin

 

PS> Let me know when you plan to use it so I can close the curtains first ...... cool

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A really nice build djozz. Smile
Hope the judges let it in.
If no….you have good chances to win the mod category. Smile

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Cool Thumbs Up
Modified light category? Smile

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CRX wrote:
Cool Thumbs Up
Modified light category? Smile

A slightly modified SD2 Big Smile
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Its not what you spend that matters but what SWMBO knows. Silly

 

djozz quotes, "it came with chinese lettering that is chinese to me".

                      "My man mousehole needs one too"

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

Old-Lumens. Highly admired and cherished member of Budget Light Forum. 11.5.2011 - 20.12.16. RIP.

 

djozz
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MRsDNF wrote:
Its not what you spend that matters but what SWMBO knows. Silly

I’m afraid that despite me not telling all there is, she still knows everything, no idea how she does that, there is no hiding from her Facepalm

I did most of the wood cutting, using ruler, pencil, a jigsaw, a fretsaw, sand paper. It took much more time figuring the dimensions and how to do the focus adjusting than the actual work, and after some changes of design I had to re-make some of the panels.

It resulted in two new features:
*a small silent fan on low power (it is a 5V fan that runs on the single li-ion cell) blowing between lens and led will keep the lens and interior a bit cooler.
*it is going to be a zoomie! Cool

Agro
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That’s going to be one cool zoomie. Smile

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Agro wrote:
That’s going to be one cool zoomie. Smile

I hope so Smile

WIP

djozz
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Running out of clamps, I need three more. Have to wait for glue to dry to free some clamps Sad

djozz
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Most structural work is done. Everything fits and the slider that focuses the led seems to work fine. It still needs a handle and a cover for the lens. And then the cosmetic work: final touches, sanding, painting and such.

The led is still underway from China to Amsterdam, so I can not work on the electric side of the build, but it will not be before monday anyway before I have time to continue.

MRsDNF
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Nice work bench. Looks like your almost finished. Beer

 

djozz quotes, "it came with chinese lettering that is chinese to me".

                      "My man mousehole needs one too"

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

Old-Lumens. Highly admired and cherished member of Budget Light Forum. 11.5.2011 - 20.12.16. RIP.

 

Sirstinky
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Nice! Very retro looking and the use of plywood is very cool.

djozz
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It is monday and mondays bring hours of time without people telling me what to do.

Today I made the thing work!

A few days ago I received the SBT90.2 on a chunky Noctigon from Hank, so I could do the electric stuff.

First the battery carrier was adapted. The driver board of the SD2 was cleared of components using a heat gun, then handy traces (near multiple via’s) for picking up batt+ and batt- were enlarged by scraping off some extra solder mask. Then led+ and led- wires (about 15cm of 18AWG silicon wire) were soldered on the board, so this light will be uncontrolled direct drive, with the current limited a bit by the long led wires.
Initially I bypassed the driver spring (see pic), but that limited the travel of the spring so much that the battery did not fit anymore. So I removed the spring and soldered a thin brass washer instead as batt+ contact (no picture of that).

I also glued the battery tube in the hole of the aluminium plate (with arctic alumina adhesive because that is strong glue and was at hand), so that it is fixed in place. The tail section of the battery tube was sanded a bit shorter so it does not fix/makes electric contact against the aluminium plate but against the tube as it should.
I still need to saw a bit off the head of the SD2 because it hits the lens when zooming out and thus limits the flood.

Now the spot was marked on the heatsink that is exactly centered behind the fresnel lens. I already found out that the centering is not extremely critical, a few mm off is not noticable in the beam. But still…
Then I did several attempts at drilling two 2mm holes in the heatsink to make M2.5 threads for the screws that fix the ledboard in place. But I did not get that done. Not sure what type of aluminium this is but the drills kept digging in the material and then break off in the hole Facepalm . Had to sand everything flat again, twist the heatsink 90 degrees, mark new holes, and fail again. In the end I decided on using two existing M2.5 threaded holes in the heatsink with some creativity with a small steel plate. Behind the board is a thin layer of AS5 for best thermal contact with the heatsink.

The thick wires come from the battery, the thin wires go to the little fan, it is simply wired parallel to the led and the ledboard had a convenient extra set of solder pads to connect the fan.

The lens thusfar was fixed in place with two small pieces of tape, but that needed a bit more permanent solution if I wanted to check out the workings of the decice, for the time being that will be four little screws. I think eventually a new clean lens will be glued into the frame.

A handle was added. I planned aluminium, but found with how this thing looks, a wooden handle was better.

The device still looks very basic, I’m not sure if I can ever make it look fancy, but some cosmetic stuff is still in the planning for next monday.

But now it is ready for some testing!

On a 50E battery I got 15-something amps, a bit low. On a 30T I measured 17-something amps. Although I would have liked 20A, this is good enough for some intial throw measurements. I can still bypass the tail spring, although is is already a copper-alloy one.

The fan works, even with the lagging voltage caused by the led, it makes a faint humming sound as it spins quite slowly. With the light running for about 8 minutes on a 30T, the fan suddenly stopped, it appeared that the voltage had become too low for the fan to run. The battery at that point appeared to be 3.08V resting voltage, which is fine for recharging. So maybe the fan works as a sort of low voltage alarm, if it stops the battery needs recharging. Not sure yet if that works just as nice for a 50E battery.

After the draining of the 30T, the heatsink and aluminium plate were only hand-warm, maybe I could have got away with one size smaller heatsink.

A quick and dirty throw measurement at 5.5 meter (led focused at that distance) showed 3.9 Mcd. So a few things seem to be working! Cool . The beam is way better than the beam from the 36cm fresnel thrower, that, and the SBT90.2, explains why the throw number is better than you expect when you go from 36 to 20 cm (which is a 3.2 times surface reduction).

Aiming the beam on the small square where I live is fun, but making a beamshot proves a challenge. Here is one at 70 meter, I kept the background lighting as I see it in person, but then the spot is totally overexposed. When all is finished I will try some proper beamshots.

Next week the light will be dismantled again, the interior will be sprayed black, the exterior will be sanded and maybe touched up a bit, a lens cover must be fabricated, and I have not decided on an outside colour yet.

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Awesome work! Thumbs Up Thumbs Up Thumbs Up

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