Experimentations with high powered LEDs for microscope illumination

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Crater Eddie
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Experimentations with high powered LEDs for microscope illumination

#1 Post by Crater Eddie » Thu May 28, 2015 6:11 pm

I have been tinkering around with some 3 watt and 10 watt LEDs, as we have touched on briefly in other threads.
Today during my lunch break at work I connected a CREE XML2 10 watt LED to this PWM controller: http://www.amazon.com/gp/product/B00C46 ... ge_o04_s00
DC power source is a 12v car battery. I used 3 large 1 ohm power resistors in series with the LED to limit the current, measured current was 2.6a at maximum setting.
Talk about wicked bright! This is so bright as to be indescribable.
This PWM controller is serious overkill, but it works well, is relatively inexpensive, and easy to hook up. The only down side is that it does not turn down to zero brightness, even at lowest setting the LED is illuminated some. It's a nuisance to have to provide the current limiting resistors, but not really that big a deal. With a little fine tuning, I think this will make a great light source for a microscope.
I'll try to take a video and link to it.
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#2 Post by billbillt » Thu May 28, 2015 6:24 pm

Yes!... This is my kind of project!... I am very interested in it and would love to see a video!..... I find the current limiting resisters just a necessary extra hassle...

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Re: Experimentations with high powered LEDs for microscope illumination

#3 Post by Crater Eddie » Thu May 28, 2015 6:37 pm



Well, heck, I can't get it to insert properly, I know I have done it before. How much of the address are you supposed to put in the brackets when using the "Youtube" insertion feature to get it to play in the message window? Let me know and I'll fix it. In the meantime you can follow the link.

(Edit: fixed thanks to 75RR)

I had to take the cover off the controller because there is a switch inside that turns it on and off. Under the cover. Kind of a bad place for an on-off switch.
Anyway, you can get an idea what's going on. I need a good heat sink for the LED, and probably some bigger power resistors, but this baby is just about ready to try out in the scope.
The PWM frequency of the controller is listed as 19khz, I don't know if this is high enough to avoid banding artifacts in the recorded video or not, that's something I'll find out.
All comments welcome.
CE
Last edited by Crater Eddie on Thu May 28, 2015 10:04 pm, edited 4 times in total.
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Re: Experimentations with high powered LEDs for microscope illumination

#4 Post by 75RR » Thu May 28, 2015 7:05 pm

This is all you need between the youtube brackets: KUyE_ZLrS1I

Seems to work very smoothly. Could not distinguish the "3 large 1 ohm power resistors in series", then again I do not know what to look for. Are they a pain to connect?

One of the customer posts in Amazon had this to say:
Bybobcoon April 5, 2015
Size: DC 12-60V 10A with ShellVerified Purchase
I like it. I used it as a dimmer for LED light. other dimmers has flicker when I recored on 720p 59FPS. But it works great. I ordered 5 of them. My LED lights work with 48V and it support up to 60V.

I take it that is a good sign?
As you say proof is in the pudding (microscope) :)
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Re: Experimentations with high powered LEDs for microscope illumination

#5 Post by Crater Eddie » Thu May 28, 2015 7:27 pm

Ah, thanks! Fixed it in the above.
Yes, I think this controller is a keeper, as long as not going to dark is not an issue for you. It's rated for 600 watts, so it's just loafing here at 10 watts.
The power resistors I used are the 3 long grey rectangular things you see connected to the controller, I have the meter leads connected across one of them reading the voltage drop (i.e. the circuit current). These are just some old surplus resistors I had, it would be better to get a higher rated one as these got fairly warm during my testing. I think they are just rated at 10 watts, 20 watt rating would be better. Yes, the proof will be in the pudding. I'll try it out in the scope tonight if I can find a suitable heat sink for the LED, it gets hot fast.
Last edited by Crater Eddie on Thu May 28, 2015 10:04 pm, edited 1 time in total.
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Re: Experimentations with high powered LEDs for microscope illumination

#6 Post by Crater Eddie » Thu May 28, 2015 8:07 pm

Image

Here you see the power resistors just twisted together. But this is just a prototype situation. I ordered a couple of 3 ohm 50 watt power resistors a while ago for pretty cheap, one of those will replace all three of the ones I used here, and will tidy things up nicely.
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#7 Post by billbillt » Thu May 28, 2015 8:35 pm

I like your PWM unit... I found some on Ebay to buy the next buying cycle I go through.... Maybe you could put a inline switch such as this on the input side?
http://www.ebay.com/itm/AC-110V-220V-6A ... 58c430b0c2

The ceramic resistors you have work fine... I have used them... I place them on top of a small ceramic tile because they can get pretty hot..

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Re: Experimentations with high powered LEDs for microscope illumination

#8 Post by Crater Eddie » Thu May 28, 2015 8:51 pm

The PWM controller does have an on/off switch on the potentiometer, so no line switch needed. The internal switch is for reversing the polarity of the output voltage, for motor direction control. Apparently it comes from the supplier with the switch in the middle position, which is OFF. You have to flip it over one way or the other to get it to operate. Once you flip it the cover can be put back on and never removed again. Actually, the switch could be operated by poking something through the air vents in the cover and flipping it that way. Of course it does not come with any instructions, I had to figure this out myself. I didn't even notice the internal switch until I had removed the cover to try and figure out why it didn't work when I hooked it up. Maybe some of the Amazon reviews contain this information, I didn't look through many of them.
Yeah, I will probably operate with these cement resistors for a while, they really should be adequate, just untidy. I like your heatsink idea for them Bill, might use that.
I'm thinking of getting another one of these controllers or two, I can think of a couple more applications where they might come in handy.
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#9 Post by 75RR » Thu May 28, 2015 11:05 pm

Thanks for the photo. Much clearer now.

There are several similar controllers on ebay, hard to find the exact one.
This one looks identical yet seems to have slightly different specs.

http://www.ebay.com/itm/Pulse-Width-DC9 ... 5d50b66af8

Would it be ok to send 10v DC from my 2v - 12v 5A AC/DC transformer:
1) to run the 12v 60w tungsten incandescent bulb as is
2) and by adding a resistor to keep the amps below 3A to run the LED ?
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Re: Experimentations with high powered LEDs for microscope illumination

#10 Post by Crater Eddie » Thu May 28, 2015 11:40 pm

That would probably work just fine. I just got home, I'll be trying this out on my scope shortly. I'll report back late tonight, hopefully with another video or two.
Yes, I found several on Ebay that look like the same thing. Some of the specs are a little different, but I'll bet they are the exact same unit.

CE


Later:

It controls the 100 watt halogen lamp perfectly, from full dark to full brightness. I didn't feel it necessary to make a video of that, but I can if anyone wants it.
It will take longer to install the LED in the scope.
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Re: Experimentations with high powered LEDs for microscope illumination

#11 Post by 75RR » Fri May 29, 2015 1:05 am

It controls the 100 watt halogen lamp perfectly, from full dark to full brightness. I didn't feel it necessary to make a video of that, but I can if anyone wants it.
It will take longer to install the LED in the scope.
Very good news.
No rush but a video to confirm absence of banding would be helpful to my peace of mind.
Very tempted to order controller right now but will hold on for the LED test.
This is looking very good.
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Re: Experimentations with high powered LEDs for microscope illumination

#12 Post by Crater Eddie » Fri May 29, 2015 2:59 am



This is a quick vid taken with the PWM controller running the 100 watt halogen lamp. Not the greatest because I was in a hurry to install the LED.
Unfortunately I'm using the old USB camera, it's not the best.
LED demo vid is still processing, I'll post it as soon as it's finished.
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#13 Post by Crater Eddie » Fri May 29, 2015 3:27 am



Here is the demo vid of the PWM controller running the 10 Watt LED using a lawnmower battery as the DC supply.
I blew up 2 LEDs trying to get it running. Suffice it to say that it is best not to have someone in the room talking to you while trying to perform a delicate operation.
Watching the vid as the light goes down to the lowest level I see a little rainbow effect as it gets near minimum. This is with the exposure on the camera set at somewhere around mid level. If I crank it up this effect goes away, so I'm not sure how much of this is due to the PWM and how much is just the cheap USB camera.
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Re: Experimentations with high powered LEDs for microscope illumination

#14 Post by Crater Eddie » Fri May 29, 2015 3:46 am

At first I didn't like the color of this LED. It's Cool White I think, and through the eyepiece it looks a little blue/green. However, the more I use it the more I like it. The images just seem crisper somehow than with the halogen bulb.
I could have uploaded these vids a little earlier, but this was such a great slide I had to spend some time looking it over. I'll post some still shots in another thread.
I should add here, that observing visually I mostly ran the LED at near minimum brightness, even with the 20x objective. Turning it to about half way up it was too bright to be comfortable.
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#15 Post by billbillt » Fri May 29, 2015 5:46 am

Looks to me you have come up with a great LED set up... You might use something like this to eliminate the battery:
http://www.ebay.com/itm/121399593874?_t ... EBIDX%3AIT

It should be plenty good, as you only need 0.833 amps to drive this 10 watt LED at 12 Volts..

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Re: Experimentations with high powered LEDs for microscope illumination

#16 Post by 75RR » Fri May 29, 2015 11:21 am

Here I was all excited to view the Halogen and I find a LED video as well!

I do not see any banding in either video and the change in light intensity looks very smooth. :):):)

This is great news.

What you call the rainbow effect (top left corner at low illumination?) is due I think to the LED being a little off-center.
Sorry to hear about your two LEDs (Any lessons there for a newbie?)


What specifications would I need in the resistors?

Looking at the LED specs again it would seem to be 3.5v max not 12v as I had thought. (Lost in translation?)

Image
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Re: Experimentations with high powered LEDs for microscope illumination

#17 Post by Crater Eddie » Fri May 29, 2015 1:01 pm

This Ebay listing is the resistors that I ordered last night: http://www.ebay.com/itm/291177401079
One of these should work just fine, and you get a spare. This is overkill, but I prefer to over-design than to live on the edge.
Yes, the LED was somewhat off center, I was running through everything pretty fast trying to get to the point of shooting vids before midnight local time. The rainbow effect I mentioned might not be visible to anyone but me... look carefully at the lower right area of the screen as the illumination dims down. I see some wide colored bands sweep across the screen diagonally as the light gets very low. I don't think anyone would try and shoot video at this low light level anyway, so I really don't see this as an issue... assuming it is really there at all.
As far as tips go, just work through the process piece by piece, don't get in a hurry, and don't have any distractions going on. The first dead LED was caused by me testing the controller with the mower battery and forgetting to put the resistors in series with them... POOF! :oops:
The second dead LED happened after I had the whole thing re-assembled, LED in the scope lamp house and all buttoned up... and again I forgot the resistors. POOF! :evil:
The 3.5v max is the forward voltage drop across the LED. You use this value along with the source voltage and desired circuit current to calculate the desired value of the current limiting resistor, which with this LED and a 12v supply works out to about 3 ohms.
Here is a quickie tutorial on this: https://www.sparkfun.com/tutorials/219
And here is a little more involved discussion: http://electronics.stackexchange.com/qu ... um-voltage
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#18 Post by 75RR » Fri May 29, 2015 1:15 pm

Wondering if this would work?
I = V / R
I = 8v / 3Ω (8v DC max output from my transformer)
I = 2.6A

Is the higher wattage that you mentioned for the resistor to handle the heat better?

Added red lines. Would this provide sufficient illumination within the LED parameters?

Image

Looks like we were posting concurrently - sorry. Will read your links now.
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Re: Experimentations with high powered LEDs for microscope illumination

#19 Post by Crater Eddie » Fri May 29, 2015 1:28 pm

I go for higher wattage resistors simply for the extra margin. They won't get as hot and will be better able to dissipate the heat that they do generate. I don't mind spending an extra dollar or two for a little bit better safety margin. It is simply good engineering practice.
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#20 Post by 75RR » Fri May 29, 2015 1:41 pm

I go for higher wattage resistors simply for the extra margin. They won't get as hot and will be better able to dissipate the heat that they do generate. I don't mind spending an extra dollar or two for a little bit better safety margin. It is simply good engineering practice
Makes good sense. Found some on ebay that will ship to Venezuela.
Are the calculations I made above ok? Awaiting your thumbs up to order controller and resistors.
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Re: Experimentations with high powered LEDs for microscope illumination

#21 Post by Crater Eddie » Fri May 29, 2015 1:46 pm

Your supply only outputs 8 volts dc? I can't guarantee that the PWM controller will operate on 8vdc, the rating says 9v to 60v I think.
I could test mine at 8vdc, but wouldn't be able to do that until next week, as it's at home now and my variable dc supply is at work.
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#22 Post by 75RR » Fri May 29, 2015 1:53 pm

The problem is that the transformer is not that precise, as in it does not follow the nominal voltage exactly.

Nominal------Actual
2v -----------2v
4v -----------5v
6v -----------8v
8v ----------10v
10v ---------13v
12v ---------16v

So not sure which to use.

10-3.35/3 = 2.2
13-3.35/3 = 3.21
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Re: Experimentations with high powered LEDs for microscope illumination

#23 Post by Crater Eddie » Fri May 29, 2015 2:03 pm

If you use the formula R=(Vcc-Vf)/If that ends up as 8-3.5/3 ((supply voltage minus LED max forward voltage) divided by max LED current) = 1.5 ohms. So if you are certain that you only get 8vdc max from your supply, then it looks like you could use a 1.5 ohm resistor, if you could find one. Most likely you would round that up to 2 ohms. Or, you could stick with the 3 ohm resistor and be happy with the extra safety margin, realizing that you are missing a few lumens.
CE
Last edited by Crater Eddie on Fri May 29, 2015 2:10 pm, edited 1 time in total.
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Re: Experimentations with high powered LEDs for microscope illumination

#24 Post by Crater Eddie » Fri May 29, 2015 2:09 pm

Oh, I see. If it was me, I would get the 3 ohm resistor and use the 10v - 13v setting, realizing that I would probably never run it at full brightness for very long anyway. I'm sure my 12v battery was outputting more like 13v, no problem. Also, I'll wager that at high loads your supply is bogging down a bit, so it probably would not produce full output voltage anyway.
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#25 Post by 75RR » Fri May 29, 2015 2:15 pm

If R =Vs - Vf / i
Using 3.5v (max) rather than 3.35v @ 3000mA
We have:
10 - 3.5 / 3 = 2.16Ω
13 - 3.5 / 3 = 3.16Ω

Which would be best? 10v with 2Ω or 13v with 3Ω

Update: Concurrent posting again!

Ok will go for the 3Ω thanks.
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Re: Experimentations with high powered LEDs for microscope illumination

#26 Post by Crater Eddie » Fri May 29, 2015 2:39 pm

Of course I'm not saying that this controller is the best one to use. It's a handy one in that it is fairly inexpensive, readily available, and easy to get working.
I'm sure there are better options, but I'm happy with it. So far. I might easily change my mind after using it for a while.
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#27 Post by Crater Eddie » Fri May 29, 2015 2:43 pm

billbillt wrote:You might use something like this to eliminate the battery:
http://www.ebay.com/itm/121399593874?_t ... EBIDX%3AIT

It should be plenty good, as you only need 0.833 amps to drive this 10 watt LED at 12 Volts..
Hey, that looks interesting! I wonder how adjustable the output is. You going to get one to play with?
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#28 Post by 75RR » Fri May 29, 2015 4:10 pm

Of course I'm not saying that this controller is the best one to use. It's a handy one in that it is fairly inexpensive, readily available, and easy to get working.
I'm sure there are better options, but I'm happy with it. So far. I might easily change my mind after using it for a while.
Talk about throwing someone off their stride.

Oh well. Will go for it anyway. As you say it will not break the bank.
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Re: Experimentations with high powered LEDs for microscope illumination

#29 Post by Crater Eddie » Fri May 29, 2015 5:56 pm

No alarm intended, just pointing out that I have used this setup a grand total of ONE time.
CE
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Re: Experimentations with high powered LEDs for microscope illumination

#30 Post by 75RR » Fri May 29, 2015 6:54 pm

No alarm intended, just pointing out that I have used this setup a grand total of ONE time.
Fair point.
Still thinking it through - there is no banding, it gives a smooth linear increase/decrease in light intensity and works with LED and incandescent bulbs.
What's not to like. The only improvement I can think of would be to find one with a 3A output (to obviate the external resistance), only then it would not work with my incandescent bulb, so I think it qualifies as a go.
Many thanks for this.
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