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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 18th Jan 2022, 4:18 pm   #1
Wendymott
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Default Bench lamp modification

Hi Peeps....... Quite a while ago I posted a mod to my circular bench lamp and magnifier.. Originally it had a circular Flu tube "without a guard". Well they do limit the light output. The problem was when using a solder sucker..the occasional lapse meant an almighty bang and a shower of glass
It was costing me.... so I decided to invest in those strips of white LEDS. I glued them into place with 3 illuminated circles. Fantastic.... the light was better than expected. It was okay for a while, then i Noticed some leds going yellow, some failing altogether...so I replaced the inner strips. Again ok for a while, then they started to fail. What I had not realised that they needed heatsinking.
I bought another reel of leds, and made an aluminium strip for the inner diameter. about 20mm wide. Enough for the leds and mounting...It was under test for 3 weeks...not a single led failed. So today "tues" I replaced the outer leds and again fitted a heatsink strip. Too early to tell, but I am quite sure its a "Yes" from me
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Old 21st Jan 2022, 8:30 am   #2
Beardyman
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Default Re: Bench lamp modification

That is what will be happening to my lamp once the tube goes & the tip about mounting the strips on a piece of aluminium to sink the heat away is not something I'd have considered. Many thanks for posting.
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Old 21st Jan 2022, 10:05 am   #3
joebog1
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Default Re: Bench lamp modification

Have a look at your $5 LED torch from the Chinese shop.
Behind the LED will be a "substantial" bit of alloy. Its the heatsink.
I have a LED torch that runs 4 D cells.
It works over about a kilometre. The head of the torch is a circular heatsink about 1/4" thick. It gets hot when the torch is on full power.
Have a look at an LED street lamp. It consists of a whacking great reflector made of THICK alloy with LOTS of fine fins.

Joe
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Old 21st Jan 2022, 9:01 pm   #4
Wendymott
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Default Re: Bench lamp modification

Hi Joe and Beardyman. I should have noted what I had read in previous articles, particularly in Electronics Weekly.... which is now "fortnightly" if ever. Led manufacturers brag about their latest "whizz bang" high output leds with acres of heatsink.... so whats different about mini leds... nothing but scale...lesson learned
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Old 21st Jan 2022, 11:52 pm   #5
Boulevardier
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Default Re: Bench lamp modification

This is very interesting. Is there any general info on heat sinking requirements for LEDs - dimensions, etc, like we would use to work out the heatsinking for output transistors?

Mike
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Old 22nd Jan 2022, 12:07 am   #6
joebog1
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Default Re: Bench lamp modification

Yes there are. BUT as "most" LED's are produced in China, the information is in Chinese.
I have some single chip 100 watt LED's they are about 1" square and have two large thick copper tabs with 5mm holes punched/drilled into them for mounting to a heatsink. It is recommended in Chinglish that a generous blob of heatsink compound is employed. I cant fathom the sizes that are recommended. The mounting tabs and the back of the chip are very carefully aligned, somewhat similar to a processor chip, so that firm contact is made with the heatsink.
But I have seen LED "hunting" torches that are fitted with a largish fan blowing through a purpose designed heatsink.

Ebay, Banggood, and Amazon all have these for sale if you need information. Technically the info is light, but you will get the idea as most of these have numerous high quality photos.

Joe
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Old 23rd Jan 2022, 8:32 pm   #7
duncanlowe
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Default Re: Bench lamp modification

Indeed some commercial lamps get this wrong. I did have a batch of ES cap LED lamps that did the same. And I created a strip lamp from TH white LEDs and veroboard. Same problem. I have even seen so called pros get it very wrong with switching devices and not considering all aspects. Yes the device might handle 30A, but if you don't calculate the power dissipation and allow for it, it will still die spectacularly. He did threaten to take ST to court for false specs.
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Old 23rd Jan 2022, 8:37 pm   #8
duncanlowe
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Default Re: Bench lamp modification

Quote:
Originally Posted by Boulevardier View Post
This is very interesting. Is there any general info on heat sinking requirements for LEDs - dimensions, etc, like we would use to work out the heatsinking for output transistors?

Mike
If you source LEDs from one of the bigger brands they have data sheets available, and typically give a suggested copper area on the PCB.
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Old 27th Jan 2022, 1:56 pm   #9
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Default Re: Bench lamp modification

I cheat a bit and have used one of these modules, they have there own built in heatsink, come in various wattages and diameter easy to fit without any problems. https://www.ebay.co.uk/itm/232486846...AAAOSwnmxfZCi~.
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