PCs at the space

[Jim Pugh]

Just listening to podcast 120, and Mike mentioned a glut of redundant PCs, Im sure you are all aware its doable. But I rip out the cpu coolers and make led cob ( 50 - 100watt) lamps that i run of the pc psu. just a thought, they are very bright and run very cool.Just sayin :)

[Robin James]

Jim's idea of using the parts to run cob LEDs is a great one.  Cob LEDs are quite cheap on ebay (some are less than £2 for a 50W).  However, to run one you need a DC supply and a  heatsink.  These are not cheap.  So an old PC is perfect because the parts are free.

Can you give us some more information please Jim?

Is it easy to check that the PSU will supply enough power?

Do you run at 12V?

When you say 'cooler' do you mean heatsink and fan, or something more sophisticated?

What size heatsink do you need for 50W?

Can you make do without a fan?

Thanks.

[Oliver]

Sounds like a great use case of the old junk ones! Will be interested in seeing how it goes

[Eric Rowen]

Beware running old PC power supplies without a load, some are ok but some don't like it, even fairly recently manufactured ones.  

Running without a load results in smoke and possibly a bang, followed by no volts! 

There are posts on the web explaining how to make a bench power supply from an old PC supply, some of these mention the problem and what resistance load to use, and particularly what wattage the resistor has to be.

On Sun, Apr 23, 2017 at 11:05 AM, Oliver <owil...@me.com> wrote:

Sounds like a great use case of the old junk ones! Will be interested in seeing how it goes

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[Jim Pugh]

Hi Gang.
Heres where i got my most recent chips.
http://www.ebay.co.uk/itm/252517110469?_trksid=p2057872.m2749.l2649&var=551416384853&ssPageName=STRK%3AMEBIDX%3AIT
you'll see that 10 watt can run happily off 12 volt, but its important that you add a constant current thingy like these
http://www.ebay.co.uk/itm/322322855511?_trksid=p2057872.m2749.l2649&var=511226255534&ssPageName=STRK%3AMEBIDX%3AIT
I use one for each chip.
over 10 watt you need about 21 volts and once again i use a constant current chip/ boost convertor to boost the 12 volts, you need to dial in the voltage with a cermet on board, i tend to under run them.
https://www.amazon.co.uk/gp/product/B00EYT1DWW/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
that said im not sure about the current limiting on that chip so maybe a bit more thought needed. TBH i prefer running 5 x 10 watt than 1 x 50.
Its important to have a fuse in the equation, as theres a lot of energy floating about, and i have a mantra that each chip should be easily disconnected Im told fuse rating should be 135% of running amps. I use automotive blade fuses cos you can pick them up at halfords! and theres your disconnect too.
Yes I run the fans, not tried without, but since the unit is all in one bit and theres plenty of amps to go round...my pc psus seem to be about 16 amp max, but a lot of them have 2 feeds, some of which may be slightly less.
Early experiments i drilled and screwed the leds on, but now use thermal adhesive which works a treat without the stress of getting the mounting holes a bit off. Dont forget theres usually several assorted heatsinks in a PC. 
Be very careful not to handle the emitting surface too much as they can easily be damaged. AND DONT LOOK AT THEM. in fact i tend to wear sunglasses! To this end I incorporate one of those safety switches, that you have to open before you can turn the units on to avoid any suprises. Take care to ensure cable is big enough.
I can bring them in next weds for a show and tell if you like, and share my trials and tribulations.
If theres 2 things its this- limit current, and dont look at them. !

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[Jim Pugh]

OOPS I bought the wrong board for the 50 watt, so please ignore the link, wondered why it wasnt working :). researching inexpensive boards now, cant find the ones that worked for me last time. 

[Jim Pugh]

50 watt want about 20 volts at 1500 ma, these are the ones that worked
http://www.ebay.co.uk/itm/10W-20W-30W-50W-Constant-Current-LED-Driver-For-High-Power-DC-9-24V-to-DC-30-38V-/272438075221?var=&hash=item3f6e931f55

Sorry for the duff info.