Yet another LED retrofit topic

Here you can discuss DIY adaptations to the microscope.
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daruosha
Posts: 264
Joined: Wed Oct 23, 2019 7:10 am
Location: Tehran, Iran

Yet another LED retrofit topic

#1 Post by daruosha » Mon Mar 23, 2020 12:27 pm

Hi everybody,

It is COVID-19 crises in Tehran, madness spread all over the city, it's Persian new year's eve and I quarantined myself at home.

The upside is I can finish many open projects/ideas.

Yesterday I upgraded my "thinkering" microscope to 10W Cree XML LED and comparing to the previous Halogen lamp, it's like chalk and cheese; especially when it comes to darkfield photography . May be it's placebo, but even the image quality is better. I have to update the driver board as well (max 3A at 3.4V with 600KHz PWM).

Image
Microscope with a temporary (God knows how long) power supply

Image
Cree XML 10W LED with a DIY heatsink

I have to find a way to permanently fix the heat sink in place.
Daruosh.

MicroBob
Posts: 1976
Joined: Sun Dec 25, 2016 9:11 am
Location: Northern Germany

Re: Yet another LED retrofit topic

#2 Post by MicroBob » Mon Mar 23, 2020 3:28 pm

daruosha wrote:
Mon Mar 23, 2020 12:27 pm
I have to find a way to permanently fix the heat sink in place.
Hi Daroush,

I use M3 or even better M2,5 screws for this with a plastic washer to avoid short ciruits.

Owning treading tools in these sizes is quite useful for a microscopist.

A good non-professional quality will do for aluminium and mild steel.

Bob

Hobbyst46
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Re: Yet another LED retrofit topic

#3 Post by Hobbyst46 » Mon Mar 23, 2020 4:42 pm

Please note, a really efficient heat sink is important for a 10W LED. Otherwise the microscope stand - and worse, the optics - might get damaged.
I presume the dimmer is a 600Hz PWM, not 600KHz ?
A low frequency of the PWM might cause banding in the camera images.
Stay safe and sound.
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

MicroBob
Posts: 1976
Joined: Sun Dec 25, 2016 9:11 am
Location: Northern Germany

Re: Yet another LED retrofit topic

#4 Post by MicroBob » Mon Mar 23, 2020 4:57 pm

10W are 10W - it doesn't make much difference for the microscope istself. But the LED won't last long without a good and well connected heat sink. For my 18W HPH 50 LED epi-illuminator I use a heat sink with slowly turning fan as it runs on full power most of the time. The heat sink should not exceed round about 60°C. 10W are ok without fan when there is good air circulation or a good heat transmission into a heavy microscope stand.

MichaelG.
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Location: NorthWest England

Re: Yet another LED retrofit topic

#5 Post by MichaelG. » Mon Mar 23, 2020 6:51 pm

Hobbyst46 wrote:
Mon Mar 23, 2020 4:42 pm
I presume the dimmer is a 600Hz PWM, not 600KHz ?
.

600KHz is quite feasible, it appears:

https://www.onsemi.com/products/power-m ... rs/ka7553a

MichaelG..
Too many 'projects'

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daruosha
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Location: Tehran, Iran

Re: Yet another LED retrofit topic

#6 Post by daruosha » Mon Mar 23, 2020 8:45 pm

600KHz PWM switching intermodulation is quite common.

What i mean by intermodulation is to modulate a PWM signal within another PWM signal (switch mode power supply design issues and PWM generation with built-in peripheral of a microcontroller). It's not intermodulation distortion. I'll upload the complete design with PCB Gerber files on my GitHub repository later on.

I've done my homework on heatsink size and passive cooling heat dissipation. There's even %30 overload margin. Plus i wouldn't use the LED beyond %50 of it output most of the time. So overheating is not an issue at all.

I'm very good at electronics, but i suck at mechanical design and fittings. I just jammed the heatsink by friction in to the the base and centered the LED by try and error. Now i can see a very faint white spot (wife didn't notice it, but i assume educated eyes would see it immediately) in the middle of image at 4X magnification. I assume the distance between the LED and base optiic is a bit longer than original configuration. I've to test it. But overall it's much much better than that crappy halogen lamp.
Daruosh.

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