# Optical comparator LED Upgrade.



## dkemppai (Dec 23, 2021)

This project started out as a 'wish list' find. An 8" bench top optical comparator, which of course needed bulbs. Given that bulbs are impossible to find and expensive, an LED upgrade was eminent. 

The first step was to identify the LED. The filament in these style bulbs are designed to provide a 'flat plane' of light, in the case of this bulb the filament covered approximately 3mm by 3mm. This is an exact match with the die area of many common 5mm LED's. The Cree XM-L3 was settled on, as it has a 3mm  by 3mm die. The big thing with the XM-L is that it's a single die making, light over the whole 3mm by 3mm surface. The LED light output is overkill (70W bulb is probably a few hundred lumens, where the XM-L3 is around 1800 lumens max). These were sourced soldered on 20mm stars, from kaidomain. This image was sourced from the kaidomain web site.  



The LED Drivers were more of a pain. Most flashlight drivers are small and hard to mount. So, I sourced some of the larger DC-DC modules on line (amazon, ebay, etc). It turns out this might have been a mistake. LED's need to be powered with a constant current power supply which these supplied claimed. These DC-DC modules claimed to operate in CC mode, and they did, sort of. The plan was to mount the constant current adjustment remotely from the board, where the light bulb voltage selector was. 




Testing the power supply is where the trouble started. These did a horrible job regulating current. Being an EE by trade a good old reverse engineering was done. It turns out the implementation wasn't just bad, it was downright horrible. There are so many things done poorly, I almost threw them in the trash and started from scratch. After reverse engineering the schematic, I did what any other cheapskate would do; Modify them to work as needed. The bottom line is that after several days, a few modifications to the board (and very small parts) would allow these supplies to operate as adjustable constant current sources. They allow LED current from 250mA to the maximum 5A needed by the LED's. (I'll include details on the on the modifications below).

Next was the LED mount. For those not familiar with LED's they differ from light bulbs in one significant way; They need to run cool, where light bulbs run hot. The LED mount needs to cool the LED as much as hold it in place. LED's are typically mounted to copper based circuit boards (star) that have thin copper surface traces for power. The copper is a heat spreader that gets mounted to a heat sink. The LEDs don't need to be dead cold, but the cooler they run the better.  

The original contour light mount was removed, and a replacement aluminum mount was designed. Keep in mind, the contour light needs to be culminated, that is all of the light 'rays' should be parallel to each other. The lower focusing lens is a culminating lens that takes the 'cone of light' from the source and culminates it to parallel rays. This lens is comprised of multiple lenses (I know I had to disassemble it for cleaning!). The location of the light source is also critical. The mount was designed to reproduce the X,Y, and Z, positions as well as being square in all planes of the original filament. (This comparator allows for some X,Y, and Z adjustment, so exact duplication isn't needed but closer is better). Fortunately the bulb mount was rather large, and allowed the use of a big chunk of aluminum for heat sinking. 





The next step was to repeat the process with the surface light. The lens there doesn't appear to be a culminating lens, but alignment it probably more critical as there is no X,Y, or rotation adjustment. This location was duplicated very closely. This lens does have some ability to focus, making the LED die spot focus from very small to very large. If the die isn't in the right location focus won't help get you there. So this mount was probably more critical than the contour light. 




After all that, a quick test was done with contour and surface LED's. Once they were working the existing wiring was pulled out of the comparator, and the DC-DC modules were mounted on the original transformer mount. The 'brigtness' control potentiometer chosen was a dual ganged pot, so it adjusts brightness of both LED's at the same time. Other than an hour of wiring, the last major issue was DC power for the DC-DC drivers. Last minute the decision was made to power this off a 24V wall wart, so no AC power would exist inside the unit. The power plug was replaced with an aluminum mount holding a standard barrel connector.




Overall I'm pretty happy with the upgrade. It works well, and a check with a gauge block shows it to be very accurate. This is only a 10x comparator, and being 8" it won't work for big parts. But for small lathe cutters, or checking the torx drive features I mill into #2-56 screws it will work fine. The biggest thing was that from the outside (other than the power connector) everything is original. The same power cable was used for the surface lamp, and all the switches and knobs were reused.  I wanted to keep that 'vintage' 1980's look and feel. Other than needing a good cleaning, it appears to be in pretty good shape. Here's a couple of shots of a lathe cutter (very worn out) and the printing on that same cutter with the surface light. (FYI, It's hard to get a good shot with a cell phone. 









Hopefully this helps anyone wanting to do an LED upgrade. Other than the LED driver, it's pretty basic machining and wiring. 

Dan




P.S. For the TLDR on the LED supply upgrade, continue on. 

The modifications are relatively simple (for those unafraid to solder 0603 surface mount components). The mods basically turn this CV/CC supply
to a CC/CV supply. (Emphasis on CC mode).  See attached images for details on mods to be done. 

In the control loop for constant current there was a diode to separate CC and CV modes. That diode was moved from the CC feedback loop into the voltage feedback. After doing this the supply was not properly compensated and would tend to oscillate, so a few of the values setting loop bandwidth needed to be changed. With this done, the supply has good control over the constant current setting, but poor constant voltage. Of course being a LED driver now, we don't care. 

A new OP-AMP was used for the current sense opamp, MCP6V76UT-E/OT from microchip. This opamp is a low drift opamp, where the existing LM321 is not. Not may choices exist in this footprint in this package. (This Footprint is common in SOT-70, Not SOT-23). Note the opamp is a 5 pin part, even though there are 6 pins on the board. Pay attention to the orientation. 

Once the changes are made, Current operating point can be set with the CC potentiometer. (I wired this external to the board for hand
control, but this will tend to make the supply oscillate if that wire is long or routed poorly). 

The maximum current can be trimmed with the CV POT. Adjusting this pot with the LED Load and a Current Meter monitoring the output will
trim the feedback circuit such that the maximum current is limited. In tests done with this board, the target was shifted from 3.0A to 5.0a maximum.

Note, however the .160 Ohm resistor used is is only rated for 2W. At higher currents, a higher wattage resistor may be needed. But honestly, 5A at 1800 Lumens is just too stupid bright to be useful, especially on the contour light. The surface light might benefit from more current however. 

For the brave, the rest of the images show how to do the mods.


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## Dhal22 (Dec 23, 2021)

Over my head,  way over.   Like U2 spyplane over.


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## woodchucker (Dec 23, 2021)

NICE... the electronics is out of my league. I can solder, fairly well, but I do not know anything when it comes to electronic ckts.  Fortunately I can sometimes get my neighbor to help, He's a IEEE.

But what I would like to see is your comparitor.


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## dkemppai (Dec 24, 2021)

So, the electronics isn't super complicated. Basically just need an LED driver, and almost any LED driver will do. The big part is getting the LED where it needs to be. If anyone really wants to do a similar conversion on their own unit, I can certainly help coach you a long...

The comparator is a Shinko, and the compact bench top footprint was what drew me to it (Quickly approaching zero extra space in here!). The last cal date was 1986, so it's got some years on it. The case is case aluminum, which makes it easy to move around.

It's is still super dirty. Not grime, but just dust from sitting around.


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## woodchucker (Dec 24, 2021)

that's awesome. Thanks. Is the light up in the cone head on top?


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## dkemppai (Dec 24, 2021)

woodchucker said:


> that's awesome. Thanks. Is the light up in the cone head on top?


I should probably qualify, I'm no expert in these things...   ...but I play one on the internet!   Here's a couple shots of a homemade carbide marking tool.

The contour light is below the table, and shines past the part through a glass plate on the XY table. The light then passes through a 10x lens to a mirror mounted at the top of the cone. This mirror is at an angle, and reflects the light to a mirror in the back of the unit directly behind the screen, which reflects it to the screen. These are curved front surface mirrors. The optics in these things are really quite amazing. Everything needs to be done just right to get the exact 10x multiplication onto the screen. And, that's where the lens above the contour bulb (LED) is important, making that light as parallel as possible going past the part. 

The table cranks up and down for focus adjustment, it's a bevel gear driven lead screw.

The cross hairs are on the glass screen. You can use the X-Y table to move from point to point on the part, and by noting the micrometer position measure small distances. The micrometers are resolved in .0002" divisions, but splitting the marks you can pretty easily get to .0001". Even at 10X, you can see a tenth movement on the screen. The screen also rotates, and is marked in degrees with vernier minutes. So you can measure angles down to single digit minutes. (Is that 60deg thread cutting tool really 60deg???) The table also rotates, and is degree marked in vernier to minutes also. 

The surface light is in the box on the left. that just shines light on the part which reflects up through the objective, to the mirrors, and onto the screen.


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## brino (Dec 24, 2021)

Dan,

That looks like a fantastic bench-top unit.
Most of the ones I have seen are nearly as big as my mill, and priced in the stratosphere.

It is wonderful that you could bring it back to usefulness.

Brian


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## whitmore (Dec 25, 2021)

dkemppai said:


> I sourced some of the larger DC-DC modules on line (amazon, ebay, etc). It turns out this might have been a mistake. LED's need to be powered with a constant current power supply which these supplied claimed. These DC-DC modules claimed to operate in CC mode, and they did, sort of.



That's an amazingly nice job, and has me pondering some of the microscope illuminators that aren't working well
for me (though I have a fair stock of the right bulbs, right now).   An easier way to go, since there's a big
aluminum casting, might be just a regulated DC source (wall wart) with series resistance to the LED, and maybe
for giggles, mount the LED on a thermoelectric cooler (there's a few in my junk box...)
driven with its own limit resistor.   Any aluminum case is a great heatsink for those limit resistors...

 For the less engineering-talented of us, there's also LED-on-disk
modules with builtin current limiting available, like the ones in Ikea's JANSJO lamps,
"KTB-HLDL-06" labeled, and available online.  If you want to play with power supplies, those will
presumably not blow up much.   Though, I've managed it...

An afterthought: white light isn't the only available color in disk-mounted LEDs, and for something like a comparator, 
it might be advantageous to use a monochrome (red or yellow or green or blue) source, because 
edge definition can suffer from chromatic aberrations in lenses (even human eye lenses).


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## ub27Rocks (Dec 25, 2021)

Thank you showing the way forward for these shadowgraphs/comparators. Bulbs are indeed pricey, if available at all. Everytime I sue mine I wonder if it the last time for the bulb.

Where you use the word culminating it is actually colimating but your meaning came across.

I have a Nippon Kogaku 6 (precursor to Nikon name change). It looks like your stage is Nikon? appears to be same as mine.

Is there an off-the-shelf power supply that would do the job?


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## dkemppai (Dec 26, 2021)

brino said:


> Most of the ones I have seen are nearly as big as my mill, and priced in the stratosphere.



Yeah, having a comparator the size of my mill or lathe wasn't going to happen. This little guy still leaves me room to work. And it was small enough to sneak by the wife...  



whitmore said:


> An easier way to go, since there's a big aluminum casting, might be just a regulated DC source (wall wart) with series resistance to the LED



I thought about this too, but foreword voltage drop over temp does change the current a little. I just figured the CV/CC power supply was going to be the easiest (I was dead wrong, tho!). Knowing how much light is really needed, I might do it differently if I did this again. 

If you picked a low enough current compared to the LED maximum, I'm sure it would be just fine. 500mA on a 5A LED for example would be more than enough for a contour light. A 5V power supply and a 3.3Ohm 1Watt or 2Watt resistor would give you a dead simple driver for a CREE XM-L3. Seems like you need more for the surface light, tho. Even then 1A drive or 1.5A drive would leave a bit of headroom. 

After studying this some, I am going to swap out LED for one with a smaller die. I think that may improve things a little. I've got some XP-L2's on 20mm stars to try out. Going from 3MM to 1.75MM die may sharpen things up just a little. (although it really is pretty nice right now). 



whitmore said:


> For the less engineering-talented of us, there's also LED-on-disk
> modules with builtin current limiting available, like the ones in Ikea's JANSJO lamps,
> "KTB-HLDL-06" labeled, and available online.



Do you know the LED die size on these? Might just order a few to see how they work out. (I have a couple of the JANSJO LED desk lamps, so might even have some around) 

I actually have a measuring microscope I'd like to do a LED upgrade on next, this might be the easiest way to go. Although, it's really hard to fight the urge to over engineer things... 



whitmore said:


> An afterthought: white light isn't the only available color in disk-mounted LEDs...



I did think of other colors. Although with the white light this one is really pretty good. There are color aberrations outside of the field of view at the edge of the objective lens, etc. But those don't seem to be a problem in the field of view. Getting the contour light aligned properly seems to be the most important thing. Maybe two colors, one for surface, and the other for contour???   Hmmm....   



ub27Rocks said:


> I have a Nippon Kogaku 6 (precursor to Nikon name change). It looks like your stage is Nikon? appears to be same as mine.



It's possible this could be a Nikon stage. The micrometers are labeled NSK, and the XY is labeled Shinko. Really, everything but the micrometer heads are labeled Shinko (even the lamps), but there may have been subcontracting going on. 

Do you have any pictures of your Nippon Kogaku to share? 

Dan


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## whitmore (Dec 26, 2021)

dkemppai said:


> [about modules with onboard current/thermal limits, "KTB-HLDL-06"    ]
> 
> Do you know the LED die size on these? Might just order a few to see how they work out. (I have a couple of the JANSJO LED desk lamps, so might even have some around)


They're Luxeon Rebel model,  specs here and seem to have 3 x 4.5mm dimensions in the 700 mA size
(which is about the current limit on the JANSJO lamps, two AMC7135 in parallel).


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## dkemppai (Dec 28, 2021)

whitmore said:


> They're Luxeon Rebel model,  specs here and seem to have 3 x 4.5mm dimensions in the 700 mA size
> (which is about the current limit on the JANSJO lamps, two AMC7135 in parallel).



Quick check shows incandescent bulbs at around 12lm/w efficacy. I have no idea if the projector style bulb runs at this level, but it's probably a good guess. The stock bulb in this unit is 70W, or about 800lm give or take.  From the datasheet those Luxeon Rebels are running about 170lm at 700mA.

Anyway, I did a quick test with a JANSJO light as a surface light last night. There just isn't enough power there, even with the light head right next to the part. The optics in the actual surface light may help, but based on how much light the XM-L3 puts out, I don't think the Rebel will work as a surface light. For the surface light, the XM-L is running at a bit north of 3A, or close to 1150lm light output. Even at that level, the surface light could be brighter. The rebel isn't up it, I think...

It might be OK as a contour light, though. Compared to the Rebel a 170lm, the Cree is running pretty close at ~140lm at the 250mA minimum current I chose. Although, I'll admit things look better at ~1A to 1.5A from the Cree (~475lm to ~680lm ).

Based on the above, I think in this unit it should be getting around 800lm for contour, and some of the smaller die Cree LED's would work well. The result might be a slightly sharper image. But even then the etching on viewing screen gives some 'granularity' to the image, so sharper image may get lost hitting the screen anyway.

For bigger units, you may need double the light. It seems some of the mitutoyo bulbs are 150W, perhaps 1600lm??? The XM-L3 at 5A should do ~1800lm, so would be a pretty good match.  

Dan


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## ub27Rocks (Dec 29, 2021)

My comparator/shadowgraph uses 10v 70w bulbs, with no built in reflector. The contour bulb has variable voltage via a wirewound pot, the surface light is full on.
I was thinking of using a 110v dimmable driver and then replacing the wirewound pot with a regular dimmer (led capable). In conjunction with your suggested XM-L2 or XM-L3. My screen is 12" so more light is better. The 100x lens has a beam splitter internally and gobbles up a lot of light for surface viewing.
You can see the surface light behind the lenses, it requires using a front surface mirror to reflect light if using the 10x or 20x lenses. My unit is at eye level, on a wheeled cart.


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## dkemppai (Dec 30, 2021)

ub27Rocks said:


> My comparator/shadowgraph uses 10v 70w bulbs, with no built in reflector. The contour bulb has variable voltage via a wirewound pot, the surface light is full on.
> I was thinking of using a 110v dimmable driver and then replacing the wirewound pot with a regular dimmer (led capable). In conjunction with your suggested XM-L2 or XM-L3. My screen is 12" so more light is better. The 100x lens has a beam splitter internally and gobbles up a lot of light for surface viewing.
> You can see the surface light behind the lenses, it requires using a front surface mirror to reflect light if using the 10x or 20x lenses. My unit is at eye level, on a wheeled cart.



This looks like a pretty nice machine. Certainly the magnification from 10x to 100x could be handy at times. The X-Y stage sure looks like the one shinko was using. Is the elevation/focus changed by moving the table up/down with the nuts below the X-Y? 

The surface light being full on is a good hint of needing as much light as possible! Makes me wonder if an XHP50.3 or XHP70.3 might even be good choice there. Depending on optics, the XHP50.3 might be the better choice. The surface light driver would be simplified as dimming wouldn't really be needed. Cooling the XHP70 might be harder, although the ~5500lm might make it worth the trouble!


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## ub27Rocks (Dec 30, 2021)

dkemppai said:


> This looks like a pretty nice machine. Certainly the magnification from 10x to 100x could be handy at times. The X-Y stage sure looks like the one shinko was using. Is the elevation/focus changed by moving the table up/down with the nuts below the X-Y?


There is a handle/wheel on rh side near bottom front. It drives a bevel gear on the column that the stage mounts on. Inside the column is also the front surface mirror that brings the light for contour viewing. Needs to be replaced, when I get a break using the thing. Once you have one of these it comes into play for a lot of things, like deciphering 0.5mm diameter threaded items to determine pitch and thread angle. The usual fish tail isn't much use at that point.

What do you think about using a dimmable driver with household dimmer to avoid bad supplies?


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## dkemppai (Jan 4, 2022)

ub27Rocks said:


> Once you have one of these it comes into play for a lot of things, like deciphering 0.5mm diameter threaded items to determine pitch and thread angle. The usual fish tail isn't much use at that point.
> 
> What do you think about using a dimmable driver with household dimmer to avoid bad supplies?



Slow response. Sorry, buried in major truck repairs right now...

Yeah, I think this will be handy. Even at only 10x, it should cover a lot of things I do.  I also picked up a measurement microscope a while back, same idea, X-Y table with Mitutoyo digital micrometer heads and a cross hair (That one is 90x zoom, so really nice). It's slightly handier for small parts, only because of the digital micrometers. It is a lot handier if you're trying to measure something through glass (Like a lightbulb filiment for example). The comparator will do angles that would be more difficult on the micrscope (although with four x,y and cad, it can be done.).

I've been thinking about the dimmable driver idea. If you had a simple transformer and diodes, going to a filter cap, and fed the led through a resistor it would probably work. Dimmers are (usually) phase angle controls, that is, they just cut off part of the sine wave cycle (think 0 to 90, or 180 degrees of the sine wave.  This changes the waveform, which makes the average voltage fall (thus the dimming). 

Basically you'd make an old school analog adjustable DC supply. But then, you might as well just look for an adjustable LED driver. I'm sure they're out there, for probably not a lot of $$$. I went the cheapskate route, and picked a 5$ supply to start with.

Honestly knowing what I do now, for the contour light I might have gone this route.
http://kaidomain.com/S028637    (No affiliation, and haven't actually bought one.) 
Throw 12V into this board, and you get constant current drive to an LED. At 2.5A into an XM-L3 it ought to be similar or maybe just a bit more light than a 70W projector bulb. 

Dan


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## ub27Rocks (Jan 5, 2022)

Thank you Dean, that helps narrow down my choices. 
The first power supply you bought, and 'fixed', did it really need fixing for the average person? Or was it really really terrible. There are so many choices it has become paralyzing :-(


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## dkemppai (Jan 5, 2022)

ub27Rocks said:


> The first power supply you bought, and 'fixed', did it really need fixing for the average person? Or was it really really terrible. There are so many choices it has become paralyzing :-(



Full disclosure, I do switching power supply design professionally and for fun. The power supply I bought was absolutely horrible. There was no way to make it operate correctly out of the box. Short story is I picked it because it looked like it had all of the right parts in the right places. Upon close inspection after reverse engineering, it was absolutely unusable without rework. 

Yes, there are a lot of options. However the biggest problem with finding an LED driver for a single LED, is the LED market right now. There are basically two segments, the flashlight/headlight group (small segment) and AC powered lighting group (big segment).  

The AC lighting guys care about big lumens spread out over the area of a light bulb, T8 tube, or high bay down lighting fixture. They string A LOT of 3V LED's in series and run them at higher voltages (20V or higher) off an AC source. There you really don't want a 'point' source of light anyway, so many LED's is a good thing. 

The flashlight guys on the other hand, run one really high powered LED in a reflector. They want one point source of light, so it can be focused as needed. The problem is they do that from one or two 3.7V Li-ion  batteries, so the drivers are designed to run from low voltages (3V to 9V), and are designed for space constrained designs in a small flashlight tube. The boards are hard to hold on to, and hard to keep cool. 

For a fixed instrument lighting source like this, running from 12V or 24V is nice. But there aren't many LED drivers for the 12V-24V input range designed for single LED use. That application really falls into the 'gap' between the market segments. Thus the reason I picked these supplies. If they operated as advertised, they would have been fine. 

If you can find a fixed, single mode LED driver that runs from 12V, and drives one LED, that's the way to go. Otherwise, I think a resistor and 5V supply is the next easiest thing to try. Beyond that there are many other options, but none are neat/tidy or cheap. 

Again, if you really want to do a conversion, let me know. I'll help where I can.   

Dan


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## ub27Rocks (Jan 5, 2022)

Thanks Dan, that is an excellent explanation.

I think it best then if I just order a couple of XM-L3's and use my own variable supply for now. My brother also does analog stuff, from radar to high power servo drivers. (I'm great with digital only) Between the 2 of you I am sure there is a worakble solution. If the light output is good enough to replace my bulbs then I will go the next step, a driver.

The XM-L3 mounts with aluminum back plate is what I will go with. Machining a mount for that is not a problem for me.
Thank you for your input, it is greatly appreciated.


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## dkemppai (Jan 5, 2022)

ub27Rocks said:


> The XM-L3 mounts with aluminum back plate is what I will go with. Machining a mount for that is not a problem for me.



The XM-L3's I picked up were on a copper heat spreader, but same difference. Sounds like you have a current regulated bench supply, that's all you need to test out the concept. 

Mounting and measuring the correct position is certainly one of the more important parts. Much more important for the contour light, less so for the surface light. 

If you haven't ordered LED's yet. I'd grab an XHP-50.3 or two to test out for the surface light. I think the extra lumen output will be helpful with any magnification over 10x. The cross (or dead spot) between the dies shouldn't show up on the surface light optics.


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## ub27Rocks (Jan 5, 2022)

dkemppai said:


> The XM-L3's I picked up were on a copper heat spreader, but same difference. Sounds like you have a current regulated bench supply, that's all you need to test out the concept.
> 
> Mounting and measuring the correct position is certainly one of the more important parts. Much more important for the contour light, less so for the surface light.
> 
> If you haven't ordered LED's yet. I'd grab an XHP-50.3 or two to test out for the surface light. I think the extra lumen output will be helpful with any magnification over 10x. The cross (or dead spot) between the dies shouldn't show up on the surface light optics.


Glad I checked this thread again, was about to order  I'll get a few of each.
And now the waiting begins,,,,,

Tku


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## dkemppai (Jan 10, 2022)

ub27Rocks said:


> And now the waiting begins,,,,,



Even expedited shipping is kinda slow! 

Just for fun I lined up a bunch of leds on stars. 
The order is XHP70,  XHP50,  XM-L3,  XP-L2,  XP-G3,  and  XT-E.
	

		
			
		

		
	




On the leftmost two (XHP70 and XHP50) you can just make out the four dies, or LED chips that make up the LED. I was concerned that cross would show up in the middle of the screen (you can see it's effect in a parabolic reflector at close range). 

The third one in is the XM-L3. The active LED Die is ~3mm x 3mm. That matched the size of the filament of my bulb. 

The last two are small die format LED's (XP-G3 and XT-E) that might improve the contour light focus. With the collimated (spelled correctly auto correct!!!) lens, it might, just maybe, improve edge sharpness. I've yet to try them out. Less light output on that light probably won't hurt anything. 

In terms of light output:
XHP70.3   ~ 5500lm
XHP50.3   ~ 2300lm
XM-L3      ~ 1700lm
XP-L2       ~ 1200lm
XP-G3      ~  900lm
XT-E         ~  650lm

Even the lowly XT-E will be pretty close in total light output to a 70W projector style bulb. The XHP70's, are just plain stupid...    ...and they're awesome in a flashlight!

Anyway, If anyone is wondering what these look like side by side, this should help.


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## ub27Rocks (Mar 1, 2022)

It's been a while, but finally got my LED's installed. I had ordered XHP50.3's and XM-L3's on 5050-20 mcpcb mounts. 
To start I decided to use just the XHP's after my first test. I am using XM4016 power supplies set to 11.9vdc and .4A current limit. I think I can increase the current to >1000ma but no reason to at this point. Light output is more than adequate compared to the filament bulbs. I might not bother with making the surface light adjustable.

One unexpected problem (not yet solved) is that the copper back of the MCPCB is not isolated from the LED when power is applied. When the LED is lit, there is 5vdc between the copper back and ground. While this has little effect if you only mount 1 led, since I have 2 they both light up regardless of which one I power! (this is through the frame of the machine joining the 2 electrically)

I'll have to figure out a way to isolate the MCPCB's while still having them mechanically secured. I will probably 3D print something to separate the aluminum heatsink from its bottom mount. 
Except for that I am very very pleased with the results. Thank you for starting this process off.


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## extropic (Mar 1, 2022)

@ub27Rocks

Thanks for the update.
Can you show a picture of the original lamp/mount that you replaced with the LED?
It helps me understand when I can see the "before" state, as well as the "after" state.


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## dkemppai (Mar 1, 2022)

ub27Rocks said:


> One unexpected problem (not yet solved) is that the copper back of the MCPCB is not isolated from the LED when power is applied. When the LED is lit, there is 5vdc between the copper back and ground. While this has little effect if you only mount 1 led, since I have 2 they both light up regardless of which one I power! (this is through the frame of the machine joining the 2 electrically)



Nice! Glad it's coming along.

Now, for the 5V gnd issue. See the datasheet here:  https://cree-led.com/media/documents/ds-XHP50.pdf
The XHP50's are designed for 6V or 12V operation. The wirepads on the LED and how to board is wired configures the voltage. Sounds like you have a 12V 'star' board. If you look at the above datasheet pp30-32, you will see the two recommended layouts.  The center pad on bottom of the LED die is normally connected to the heatsink. In the 12V configuration they short that heat spreader pad the center of the diodes, setting the heatsink potential at 1/2 of the LED string voltage. 

You could try the XLM's. Or make/print a fiber or insulating spacer to hold the LED heatsink you made floating from earth ground. 

Let us know how you sort it out! 

Dan


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## ub27Rocks (Mar 1, 2022)

extropic said:


> @ub27Rocks
> 
> Thanks for the update.
> Can you show a picture of the original lamp/mount that you replaced with the LED?
> It helps me understand when I can see the "before" state, as well as the "after" state.


The third photo with glass bulb and white mount is the original mount/assembly.


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## ub27Rocks (Mar 1, 2022)

The solution was to shorten the al mounts by 15mm and place this 3D printed part under them. Everything is now as it should be.

Much more light than before, and no longer worried about burned out filaments.

Thank you again for the idea and support.


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## extropic (Mar 1, 2022)

ub27Rocks said:


> The third photo with glass bulb and white mount is the original mount/assembly.



Thank you.
More questions, please.

Regarding the lens assembly on the original lamp mount:
Is the lens assembly deleted or are you going to figure a new mount for it?
What is/was the function of the lens assembly?


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## ub27Rocks (Mar 1, 2022)

I only replaced the light bulb and its mount with an LED. The LED arrived on a 20mm diameter plate which I attached to an aluminum upright. It was designed to place the 3mm square led itself in the same place as the 3mm square filament of the bulb.
The shadowgraph/comparator has 2 lights, one for shadow/profile work, the other for surface lighting.

The lenses are still needed, they colimate the light and make it into a more focused beam. The reason for the replacement is to a) remove the worry about a US$50 bulb buring out while in use. That would cost me an extra US$35 to ship to Canada. the LED is US$6 and is not likely to burn out in my lifetime. The side benefit is that the LED generates almost no heat, the bulb heats the first lens and generally bakes dirt on to it.


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