next topic »

[Reply #15 on:]

@focalist: Was that one of those old LanCity cable modems in that first video (were you using as a heatsink?)...

[Reply #16 on:]

Heheh yes it is.  I never throw something like that out.. it's just one Ginormous heat sink, solid aluminum, probably a good two pounds.. with those nice vanes on the back and even a hollow interior (where I am hiding much of the sloppy wires.  I see a heat sink like that, I grab it.

Remember my big old rack mount Telco power supply?  It was time to sacrifice her, she's just too big and unweildly.  But why would I do that, you ask?  Simple.  Inside of the twenty five pound steel monster is an array of Volgen industrial power supplies, each one with it's own heat sinking and case.  I need 16-18v @ 3A for the fifty watter.. and one of the PS modules is a 24v@5A model.  With the voltage adjust turned all the way down, I get 17.8v  - Perfect!  With the addition of a 2n3055 based current limiter set up for 3A- we are good to go.  One question, if anyone has used them- there's an enable on the PS, open circuit the PS is on, closed circuit the PS is off.  I am just planning to use a MOSFET like the others, but I am wondering if there's any advantage to using that enable circuit (prolly not).

         
After drilling a couple mounting holes, I soldered some leads on the 50watter and slathered it with compound, and screwed the beast right in the middle of that LanCity cable modem case.. and switched it on.  I was foolish enough to actually be looking nearly directly at the LED from a foot away when I turned it on.  I'll say this.. 3500 lumens of warm white LED is BRIGHT.  Like afterimages for a good five to ten minutes bright.  With that huge heat sink, I am able to place a finger right on the emitter and it's only comfortably warm.  The resistors in the current limiter were far hotter.  I actually have to return to that limiter circuit, because I substituted 240 ohms in the circuit for 220, and when metered out, it shows that the current actually is limiting around 2.25A while the emitter wants 2.5-3A.  Not sure how much more light I can get for another 500ma, but I plan to find out.  Since output isn't linear to input, I figure I am maybe losing a hundred lumens or so without that extra quarter to half amp.

So, I am putting together the MOSFET for this one this morning.. should be ready to start UberBlinken later today.

The current capacity of the system:

8x 3w Warm White, 200 lumens each, for a total of 1600 lumens
1x 10w Cool White, 1000 lumens
1x 50w Warm White, 3500 lumens

This gives us a total of 6100 lumens or thereabout, for a power load of 84 watts plus a little overhead for the regulators.  With this mess hooked up, I am going to try to take a photo or two with it later today, just to see how it turns out.  Overall, getting 20 lumens per watt isn't very efficient.. but I am not really looking to make this efficient.  I want it BRIGHT, and able to be switched in the range of tens of microseconds.  As I am trying to emulate a Xenon strobe in a way, I want my pulses to be at least as short.. Xenon tubes typically fire in the range of a millisecond duration.

I still have six more of the three watters, plus another thirty 1w discrete LED's, just about another 50 watts.. but I am going to hold off adding more until I play with it as built for a little bit.  If I can get a usable image with the power I have at the moment, I have possible other nefarious uses for that batch.  That being said, I originally set out for an arbitrary 10K lumens, and that mess would bring the total close..

However, I am now not powering up the system until it's facing the wall-- it's painful to look at, downright blinding...

[Reply #17 on:]

So, I took the whole rig (much to my wife's glee) downstairs and just did a simple strobe program, 2ms pulses followed by a 10ms delay.  This is only using the 50 watter.  The results are pretty typical stroboscope shots.

50mm f1.8 Canon Prime lens - light source 6" from subject
ISO 1600
2 second exposures @ f/22!!

This works out to f/1.8 exposure of 1/125 second.  That's with a dark subject.  This, simply put, is going to be at least as good at close range as a xenon strobe, but FAR more controllable-  there's no recharge time, I can set arbitrary intervals for both the pulse length as well as the interval between pulses.  I still will be adding the 3 watters and the ten, almost doubling the light.

I was just pushing the shutter release then dropping a lighter on the table.  There was a delay in dropping the lighter.
For code, I just modified the delay times in Blink.

I had far too much light to use the lens anything but stepped WAY down.

What this means is that I am going to succeed.  Now, it's a matter of seeing how short I can get the pulses and still get enough light. The 50mm goes all the way out to a Beercan f/1.8, if I want it, I can borrow a friends f/1.4 but it looks like I may not even need it.

Got some things to do this evening, then I will hook up the other MOSFET and add in the three watters, and another for the 10watt.  The ten watt is mounted on it's own heatsink, so I can use it as a synchronous strobe from another angle to give fuller illumination.

Macro is absolutely possible.  We're going to see what it does on a full backdrop later on...

[Reply #18 on:]

Sounds like you have fun! I love it when projects work out this well :-)

[Reply #19 on:]

Yeah, I'm quite happy already, this is really looking like once complete, it may be able to do what I want. 
If a project's not fun at any given moment, I'll shelve it and twiddle with another.  I have several Arduino
projects going right now... ranging from CNC to Lighting experiments.  I never stop tinkering.

Anyway, A cleaned up version, I may still get a chance tonite to rig up some more shots.



This was shot under tough conditions (f/22, ISO1600) intentionally to give a worst case view.  Going to get MUCH better...

[Reply #20 on:]

Hi , this looks very impressive. Since I plan to do something similar I would be very interested in your schematic. From your above explanations it is not clear to me how you achieved the current limiting to protect the HP LEDs. Would be great if you could post your schematic.

rudy12

[Reply #21 on:]

Rudy.

On the fifty watter, I used a current limiting circuit I'll link to below.. Though I only used that circuit because I needed three amps.  Pretty much otherwise, I am using LM317 connected as a current source set up after another LM317 set up as a voltage regulator.  In that configuration, the lm 317 circuits are the easiest and cheapest up to an amp.. Under a dollar for the whole voltage/current regulator circuit.  Granted that this isn't the most efficient circuit.. But I am not really all that worried about efficiency.

Finally have the fifty, the ten, and eight three watters all going, for a total of 84 watts. The fifty gets its own MOSFET, and the rest run from 12v and are all being switched by another one.

I'll post some test shots later, as well as do some math regarding guide numbers... But for photographers out there, here's a start:

Black field, reflective subject 25% of field, f1.4 50mm at a distance of 3 meters, illumination period (flash duration) of 1millisecond..... Heavily overexposed at ISO100.  I needed to stop down to f7.1 for a reasonable exposure.

That is a peformance level that rivals low to midpower Xenon.

[Reply #22 on:]

Paint droplet stop motion.  ISO200, f/12, 50mm, 2msec strobe duration.  Triggered with IR photogate.  More coming...



ISO200, f/10, 78mm, 1msec strobe duration