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

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.

LouieAtienza · 2019-01-23T00:04:00.000Z

BlueSwordM:

How about using a 4S LiPo pack?

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

Thanks for the input! Have to try that. I don’t have a 4s LiPo, nor a 4s balanced charger, so I’ll have to see if the local hobby store has any in stock…

BlueSwordM · 2019-01-23T00:06:02.000Z

The one thing you can do is build up a 6S battery pack if the buck converter supports up.

You can do this just by connecting up 2 3S battery packs in series

LouieAtienza · 2019-01-23T00:12:09.000Z

BlueSwordM:

The one thing you can do is build up a 6S battery pack if the buck converter supports up.

You can do this just by connecting up 2 3S battery packs in series

Hmmm… The buck converter supports up to 40V input… I do have two 2s LiPo batteries but they don’t have XT60 connector so I’d have to hobble up an adapter to use those. Will try the hobby store tomorrow…

Enderman · 2019-01-23T00:13:35.000Z

A buck driver should have no problem running off a 3S battery to buck down to 3V.
The issue is that that regulator can’t handle more than ~8 amps, you need something more powerful.
https://www.amazon.com/Yeeco-Converter-Regulator-Transformer-Inverter/dp/B011UBLZK6/ref=sr_1_6?ie=UTF8&qid=1548202313&sr=8-6&keywords=buck+converter
You can see it says that it’s 8 amps max.

LouieAtienza · 2019-01-23T00:23:37.000Z

Enderman:

A buck driver should have no problem running off a 3S battery to buck down to 3V.
The issue is that that regulator can’t handle more than ~8 amps, you need something more powerful.
Amazon.com
You can see it says that it’s 8 amps max.

I’ve taken it to over 9 and the converter seems to have no problem with it. It’s that I cannot raise the voltage up any more. It’s rated at 120W, so I should be able to get 5V no?

BlueSwordM · 2019-01-23T00:29:05.000Z

You can’t up the current anymore because the voltage is starting to be a bit too low.

If you want something a bit overkill, I would actually recommend this monster:
https://www.ebay.com/itm/DC-DC-Converter-20A-300W-Step-Up-Step-Down-Buck-Boost-Power-Adjustable-Charger/392164184788

I’ve bought it myself, and it does work up to 15A passively.

I would not run it at higher levels without higher input voltage above say 18V and actively cooling it.

Still, if you want to push the 2mm2 LED to say 10A, you can, but you will need the best heatsinking possible, high clamping force, and perhaps, liquid metal for maximum performance

LouieAtienza · 2019-01-23T01:57:00.000Z

The one I have is rated to 12A max with cooling… at least according to this which I copied off Amazon when I bought the thing:

Admittedly, the air leaving the fan is warm, but the heatsink of the buck does not feel like it’s getting hot at all.