LED Resistor Calculations ...

[EasyGoing1]

Re: LED Resistor Calculations ...

Do you have specsheet of the LED?

Couldn't find it

[EasyGoing1]

Re: LED Resistor Calculations ...

I thought most substrate pads should be cathode, but yes, depends on the manufacturer. Datasheet should clearly indicate this, and if not, that's a datasheet error.

So this begs the question ... let's take a hypothetical situation ... let's pretend I could submerge these LEDs in liquid nitrogen ... could I push them well past their rated amperage without destroying them?

[diif]

Re: LED Resistor Calculations ...

The datasheet.
Why not use aluminium like everyone else instead of liquid nitrogen ? look at quantum boards on Ali

[EasyGoing1]

Re: LED Resistor Calculations ...

By the way, I figured out how to drill out the via's without removing the LEDs that they installed on the boards ... and the panels work perfectly after the vias are drilled out. Even with the 6.8 ohm resistors on the ends of each line, the panel only pulls 540ma at a straight 19.00 volts... I have to push it to 19.97 volts to get it to 745ma ... 750 would be the max for this array.

Still an issue with heat though ... but I'm not sure what would happen to the LEDs if left running for a long period of time. The power supply says they're kicking out close to 10 watts...

And I had another thought ... what if, instead of vias at the center of each LED, we just had a decent sized hole, then got a big assed heat sync and used heat sync epoxy - like what they use to attach heat syncs to CPUs, and put a good dab of that stuff in each hole then attached the big assed heat sync... the epoxy wouldn't conduct but it should pass the heat or at least some of it out to the heat sync... no?

[EasyGoing1]

Re: LED Resistor Calculations ...

The datasheet.
Why not use aluminium like everyone else instead of liquid nitrogen ? look at quantum boards on Ali

OK, now where does it say on that datasheet that the center pin is equivalent to the anode or the cathode?

[eccerr0r]

Re: LED Resistor Calculations ...

Crap datasheet should have warned that the center tab must be kept isolated (unless it's in chinese). I would have to assume that, at least check, since it's not bonded to one of the main terminals.

I guess it's annoying that DRC and LVS don't technically pass on this board, which is easy to slip through the cracks when the models are wrong and you're only using software checks... Oh well, live and learn?

And BTW yes technically liquid nitrogen could help dissipation ... up until the thermal resistance and this will limit the watts you can dump into them. Usually this theoretical number is written in the datasheet too, but tends to be to typical ambient temperature like 25°C, which has no correlation to boiling nitrogen.

[diif]

Re: LED Resistor Calculations ...

OK, now where does it say on that datasheet that the center pin is equivalent to the anode or the cathode?

It's indicated on page 2.

[EasyGoing1]

Re: LED Resistor Calculations ...

It's indicated on page 2.

Is it now .... well, Here's Page 2 ... kindly tell me which words indicate that the center pad and the anode are electrically equivalent...

[EasyGoing1]

Re: LED Resistor Calculations ...

Crap datasheet should have warned that the center tab must be kept isolated (unless it's in chinese). I would have to assume that, at least check, since it's not bonded to one of the main terminals.

I guess it's annoying that DRC and LVS don't technically pass on this board, which is easy to slip through the cracks when the models are wrong and you're only using software checks... Oh well, live and learn?

And BTW yes technically liquid nitrogen could help dissipation ... up until the thermal resistance and this will limit the watts you can dump into them. Usually this theoretical number is written in the datasheet too, but tends to be to typical ambient temperature like 25°C, which has no correlation to boiling nitrogen.

I ran this panel for the last 12 hours on 18 volts ... drawing only 380ma and the temp of the panel has been steady at around 36C ... and it still kicks out a ton of light ... not the blistering sun I was hoping for ... but certainly very useful ... if it had a diffuser and was hanging in the center of the room at the ceiling ... it would certainly be all that a room would need for light ... and only pulling 6.8 watts ... that's not bad ... considering back in the day, it was common place to have 60 - 100 watt bulbs in every fixture.

[EasyGoing1]

Re: LED Resistor Calculations ...

I have a bag of these LEDS as well ... and I just checked and the center pad is NOT connected to either the anode nor the cathode ... strictly heat dissipation... albeit its a much larger LED and a hell of a lot brighter too.

[eccerr0r]

Re: LED Resistor Calculations ...

Yeah I have a couple of those round ones whose pad seems to not be connected. I've not tried sending 1W into these either, so not sure how much heatsinking is needed.

At this point I wonder... I can buy $1 800lm LED modules, just need to figure out how to feed 120V into it.

[EasyGoing1]

Re: LED Resistor Calculations ...

Yeah I have a couple of those round ones whose pad seems to not be connected. I've not tried sending 1W into these either, so not sure how much heatsinking is needed.

At this point I wonder... I can buy $1 800lm LED modules, just need to figure out how to feed 120V into it.

Bridge Rectifier and large caps?

[EasyGoing1]

Re: LED Resistor Calculations ...

Yeah I have a couple of those round ones whose pad seems to not be connected. I've not tried sending 1W into these either, so not sure how much heatsinking is needed.

At this point I wonder... I can buy $1 800lm LED modules, just need to figure out how to feed 120V into it.

I just pushed one of those bigger ones at 280ma and according to my Fluke, that center pad was 70C ... YIKES! that's friggin hot.

[eccerr0r]

Re: LED Resistor Calculations ...

Bridge Rectifier and large caps?

Yes it comes with a bridge rectifier, heatsink, and diffuser. It gets quite hot too but it's expected.

[EasyGoing1]

Re: LED Resistor Calculations ...

Yes it comes with a bridge rectifier, heatsink, and diffuser. It gets quite hot too but it's expected.

But 800 lumens ... for a dollar? That's just bliss ... where did you score that?

[Agent24]

Re: LED Resistor Calculations ...

Is it now .... well, Here's Page 2 ... kindly tell me which words indicate that the center pad and the anode are electrically equivalent...

The side view drawing shows the right pad and lower pad as the same physical piece.

They could have stated it specifically, but dealing with vague datasheets is another joy of design! If in doubt - test!

[EasyGoing1]

Re: LED Resistor Calculations ...

The side view drawing shows the right pad and lower pad as the same physical piece.

They could have stated it specifically, but dealing with vague datasheets is another joy of design! If in doubt - test!

ok wait ... you're talking about THIS ... RIGHT HERE???

THIS DRAWING ...



Cause there isn't a court in any country on the planet who would acquit them for that shit right there! Hieroglyphics are clearer and more specific ... I mean I'm staring at the drawing TRYING to find some connection that I could in some way see where the two pins are connected ... but man ... I just cant make that connection with whats on that paper right there.

[diif]

Re: LED Resistor Calculations ...

It's a little crude as I did it in paint.

Aliexpress is awash in cheap LED COBs. https://www.aliexpress.com/item/4000932468693.html

[eccerr0r]

Re: LED Resistor Calculations ...

That's a very poor indication that they're connected, it could also imply the plastic fill too. If it didn't draw a line through the tabs it'd be more convincing but then it'd be wrong because you can't connect to the plastic.

The footprint model should have marked that node to be a DNC node so it would show up as a DRC or LVS error.

[EasyGoing1]

Re: LED Resistor Calculations ...

It's a little crude as I did it in paint.https://www.aliexpress.com/item/4000932468693.html

ummmm ... yeah ...

Unless you're in the LED manufacturing industry and are completely aware that those shitty drawings indicate where the connections are ... ain't no one on the planet going to see it ... whoever thought that was good idea, should be demoted.