First DIY scratch build.. my "Fresnel Frower I" prototype NEW MkII pics!

LouieAtienza · 2019-01-12T00:19:46.000Z

SO after owning a BLF GT70, a GT Mini, and reading all the awesome builds on this site I decided to take the plunge and try to make my own “thrower.”

To make things simple I’ll only use stuff readily available. Parts include:

4”–3” PVC reducer coupling
3” PVC repair coupling
3” PVC end cap
3” PVC pipe
Pushbutton switch (currently only a momentary switch as it’s what I had on hand)
Buck driver (from MicroCenter)
1-Cell 5V 1A USB power bank
Round door knob
1/4”–20 x 2” thumb screw; washers

What I had to source were:

3-1/4” Aluminum heatsink
Fresnel lens (hence the name)
Osram “Flat White 1mm^2” LED on copper MCPCB

Goal:

To eventually make Enderman’s list! (Anywhere is fine for now…)

Construction was straight-forward, using lengths of 3” PVC pipe to connect the fittings. To recess the Fresnel lens into the reducer coupling I used a rabbet bit on a handheld router. I then lined the interior with black felt.

The White Flat LED was secured onto an eBay purchased heatsink with the supplied screws and thermal compound.

To make the RLT dome, I cut a round door knob in half, then cut the aperture to my best guesstimation, and polished the interior. Works decently though it’s not a perfect focus, as the shape is not 100% precisely hemispherical.

The power bank was popped open so that leads could be run to the various components.

I just used this buck driver because I had it, and didn’t want to run the LED at a full 5V because it’s only passively cooled right now I didn’t measure the current but suspect having more will give me a bit more light output.

Two holes were cut (by hand), one for the momentary switch, and one for the end of the power bank. The nice thing about this is that I can charge it in the car, AND use it still as a power bank!

I do have a lux meter but have not familiarized myself yet of it’s operation or how to calculate candela.

EDIT: Some trouble posting pics, so I’ll link my album here…

[Album] Fresnel Frower I

netprince · 2019-01-12T05:16:47.000Z

nice build! I didn’t even see the hotspot in your pictures at first it is so small…

toddcshoe · 2019-01-12T05:31:11.000Z

Very cool. Great job. I love projects that are built with stuff just laying around the house.

LouieAtienza · 2019-01-12T05:34:15.000Z

Thanks… The apartment building and trees are approximately 200 mreters away from where I stood. Battery was not fuly charged at the time…

Enderman · 2019-01-12T06:51:50.000Z

Nice job, I like the construction and final look!
Your DIY RLT dome is also very good.

Using a luxmeter is fairly simple, but you need to know the distance between the light and the luxmeter.
Then just multiply the lux that the luxmeter shows by the distance (in meters) squared.
So candela = lux * (distance^2)

I’m sure that with a fresnel lens of that size and a white flat you’ve made it on the list, looking forward to see what the final candela is

LouieAtienza · 2019-01-12T14:18:26.000Z

Enderman:

Nice job, I like the construction and final look!
Your DIY RLT dome is also very good.

Using a luxmeter is fairly simple, but you need to know the distance between the light and the luxmeter.
Then just multiply the lux that the luxmeter shows by the distance (in meters) squared.
So candela = lux * (distance^2)

I’m sure that with a fresnel lens of that size and a white flat you’ve made it on the list, looking forward to see what the final candela is

Thanks… I tried aluminum baking rounds but it seems the steel polishes to a higher finish. Could be the paricular pieces I have or not using fine enough poish. They are mirror like from a foot away but the scratches can be seen with bright enough light so I’m sure I’m losing some RLT efficiency there. But it’s significantly brighter with it on.

Question as far as reading lux. I have a laser range finder so distance measuring should be fine. But what distance is good? The practical distance limit at home is about 50ft.

Jerommel · 2019-01-12T12:58:03.000Z

Kudos for the collar ! :+1:

Enderman · 2019-01-12T21:18:10.000Z

LouieAtienza:

Thanks… I tried aluminum baking rounds but it seems the steel polishes to a higher finish. Could be the paricular pieces I have or not using fine enough poish. They are mirror like from a foot away but the scratches can be seen with bright enough light so I’m sure I’m losing some RLT efficiency there. But it’s significantly brighter with it on.

Question as far as reading lux. I have a laser range finder so distance measuring should be fine. But what distance is good? The practical distance limit at home is about 50ft.

Yup, laser rangefinders are the best option, that’s what I use.
I would recommend at least 20m, I try to test my lights at 50-100m though.
Since you have an easy focusing mechanism you could do closer distances and simply adjust the focus so that instead of being focused at infinity it is focused at your luxmeter at 50ft or whatever.
This should get you the same values as if you measured at a farther distance.

LouieAtienza · 2019-01-12T21:42:28.000Z

Jerommel:

Kudos for the collar ! :+1: :+1: :+1:

Thanks!

Enderman:

Yup, laser rangefinders are the best option, that’s what I use.
I would recommend at least 20m, I try to test my lights at 50-100m though.
Since you have an easy focusing mechanism you could do closer distances and simply adjust the focus so that instead of being focused at infinity it is focused at your luxmeter at 50ft or whatever.
This should get you the same values as if you measured at a farther distance.

Cool… I’ll give it a go tonight (in the freezing cold…)

WillyD · 2019-01-12T22:19:54.000Z

Awesome idea with the doorknob!

LouieAtienza · 2019-01-13T12:24:17.000Z

WillyD:

Awesome idea with the doorknob!

Thanks… I found some other suitable household items that would work too. Hope to feature those soon…

MRsDNF · 2019-01-13T20:25:44.000Z

netprince:

nice build! I didn’t even see the hotspot in your pictures at first it is so small…

+1 on this.
Love the build and thanks for posting up. :+1:

LouieAtienza · 2019-01-13T22:55:12.000Z

Thanks!

So tonight is slightly warmer than last night (at 30 degrees F) so I tried to take some measurements.

With the 1-cell power back I was able to achieve around 3610 lux at 45ft, or according to the online calculator, 679,144 candela.

Being that puts me somewhere near the bottom of Enderman’s list, I decided to make a tube extension (re: length of 3” PVC pipe) and use a 2S LiPo battery. The light was fluctuating, but probably because I was killing the cheap power buck I got from MicroCenter. I got readings from around 8000 to 10000, but it would settle around 9060 (before bouncing back and forth.) Also I don’t have a fan installed (yet) but this is still my test “mule” According to the calculator that equates to 1,704,405 candela! I had the light on for 5 minutes, then the scent of electronics baking started to permeate the air. Everything looks OK inside, but I turned the light off and allowed it to cool.

So using 2*sqrt(candela) I get 1648m with the power bank, and 2611m with the 2s LiPo or about 1.62mi! I’m actually quite happy with that for a first try, with no “real” LED driver and some parts fudging. Still a long way from the higher throws of the other Fresnel lens builds but those have considerably larger lenses. Back to the drawing board!

I’ll post some new beam shots once this thing cools off some… but the up in juice sure makes a difference in the hot spot intensity and beam visibility…

LouieAtienza · 2019-01-19T04:18:07.000Z

OK so here’s what happened…

The LiPo battery I used seemed to have killed the cheap buck I bought from MicroCenter. Or maybe it couldn’t handle the extra juice. Looks like a cap blew on the board, which caused my poor LED to eventually die. Anyways, this was a quick test build.

I decided to rebuild the light, using all 4” PVC pipe and fittings. I took a 3” coupler and sanded it down to fit the ID of the 4” pipe and place both heatsink and fan inside said coupling. This makes it easier to slide the entire unit for focusing. I used a 4” coupler for the head, and shaped the body end to resemble a Maglite by tapering it. I also made a much longer adjustment slot, which will allow me to swap heads with different lenses of different focal lengths, and even test out a couple aspheric lenses I have.

The LED was replaced with a White Flat 2mm^2 to give a larger, more visible beam and handle extra current. I have a few of these cheap buck/boost converters with digital readout that I use on my bench. After getting sick and tired of connecting/disconnecting it from the LED for testing, I decided to just implement it in the design! Very convenient.

Also the cooling fan is run with a separate 9V battery and switch.

I think the 2s LiPo is now the limiting factor in terms of my power output. But I manage to get around 3V and 8A. From the tests I’ve seen here on BLF there’s a bit more headroom, so I may switch to a 3s LiPo when I have some extra cash.

My lux measurement at 40ft (laser measured) was 12600 according to my lux meter. This gives me unofficially 1,872,925 candela according to the online calculator, or 2,737m (8,979ft, 1.7mi) of calculated throw! And a nice well-defined rectangular hot spot to boot!

A bit cold right now, and battling a slight cold myself, but I’ll take some beam shots tomorrow. I’ll also document everything in pics to make the numbers “official!” But for now I’m stoked, and for about $50 in parts I think it’s pretty darn amazing!

Link here:

[Album] Fresnel Frower MkII

Enderman · 2019-01-19T04:24:32.000Z

Looks great!

LouieAtienza · 2019-01-19T04:27:46.000Z

Thanks!…

A look down the tube. Still need to cut vent holes in the head and add a tail cap.

LouieAtienza · 2019-01-19T15:09:50.000Z

So modding for the 3s LiPo I managed another 1A of juice for about 27W. Thought I’d get more than that but I’ll see tonight if that extra 3W of power equates to more throw, or if a 12% power increase is significant enough…

LouieAtienza · 2019-01-22T23:42:02.000Z

OK I don’t know if it’s a problem with this buck converter or me, but I cannot seem to get more than 3V to the LED. My 3s LiPo is fully charged and I’m reading over 12V at 8A input, but only getting 3V at 8.5A. Methinks something’s amiss.

Regardless, I’m not sure how much more output I’d get from this setup. That said I have some updates and results.

First I cut vents in the head to allow airflow through the heatsink fins through the back of the light. This is so the cool air hits the heatsink first and does not have to get pulled through the light then have no easy escape out.

Reading of the output voltage and current:

Lux meter reading at X100 setting:

And some requisite beam shots. There seemed to be a bit of air traffic activity overhead, and I live about 10 miles from LaGuardia Airport, so I did not want to take too many chances…

So plugging in 9000 lux and 46ft into RapidTables gave me 1,769,245 candela! A tad bit off what I’d hope to achieve (2 million) and a little less than with the 1mm^2 White Flat, but the beam is so much more impressive. And the hot spot is a nice, well defined rectangle! Working this out equates to 2,660m throw, or 8,778ft, or 1.65 miles. I still am puzzled as to why this reading is lower than with the 2s LiPo I previously used. Being it’s 20 degrees outside, I’ll hold off till tomorrow to re-test with the 2s LiPo battery. Maybe some here has an idea as to why I cannot get this buck driver set at 5V output. I can adjust the juice, butaccording to djozz’s review and charts I’m pretty close to the current threshold, so any slight gains will come from getting more voltage to the LED - I think…

What I did change was use the LiPo for both fan and LED. So the leads from the battery go to the DPDT switch, which then feed separately the fan and buck driver. The buck driver has its own on/off button, so I can shut off the LED and have the fan still cool off the unit. A thermostat would be nice.

In any case, I think I made Enderman’s list… hope to get included at some point.

LouieAtienza · 2019-01-22T23:44:38.000Z

I just noticed the 13/16” I missed when calculating the candela… that’s probably good for another 3m of throw!

BlueSwordM · 2019-01-22T23:59:36.000Z

How about using a 4S LiPo pack?

The lower the input current draw in a buck converter, the better the efficiency.