LED Resistor Calculations ...

[EasyGoing1]

Re: LED Resistor Calculations ...

So the whole reason why this project even started in the first place was that I mounted a dartboard in an area that has very little light and it makes it impossible to see where the dart hit when it's close to any number border. So I figured I could just make my own light because it would be fun to do.

I designed a shroud for it in Tinkercad ... as you can see, I used the version of the panel that is NOT aluminum and I attached a 12 volt fan to the housing but to be honest, the fan doesn't move much air ... you can't really feel any air moving around the light, but it's good to have it moving air anyways in my opinion.

After leaving it running for an hour, the housing is a little warm, especially at the boarder of the two halves of the housing, but certainly not HOT by any means. And technically, this is the same panel as the aluminum PCB ... only without the aluminum so I'm not sure why this one doesn't get as hot...

Here are some pics...

[eccerr0r]

Re: LED Resistor Calculations ...

[EasyGoing1]

Re: LED Resistor Calculations ...

That first aluminum panel where I was taking temp readings from ... I had it sitting on top of a glass face down while it was running and I didn't notice until after I disconnected it and let it cool down ... that the damn thing got so hot, that it messed with the components as you can see:

[EasyGoing1]

Re: LED Resistor Calculations ...

But are the thermal via boards electrically isolated like the aluminum boards?

I suppose I could see an advantage to using the aluminum board since heat is evenly distributed throughout the aluminum, you could then attach different heat syncs to the aluminum without having to worry about placement using that CPU thermal epoxy. That would at least let you hodge podge heat syncs you have laying around or just use a few smaller and less expensive heat syncs instead of buying a large one cause they can get pricey as they get bigger.

[EasyGoing1]

Re: LED Resistor Calculations ...

But are the thermal via boards electrically isolated like the aluminum boards?

No, apparently what you do with the standard PCB boards, is you have an area on the backside of the board with an exposed pad that has vias connecting the pad on the LED where the heat is dissipated. THEN, you use a heat sync and attach it to the backside of the board.

Of course, this would make your heat sync electrically connected to the anode ... so it would be important to not have the heat sync close to anything that could cause shorting ... like a cassis cover etc.

[eccerr0r]

Re: LED Resistor Calculations ...

But are the thermal via boards electrically isolated like the aluminum boards?

[EasyGoing1]

Re: LED Resistor Calculations ...

After a little research i have found that heat affects the Vf of the LEDs in turn drawing more current, that's why the pads need to be the same size so there is no temperature differential, that trace to the resistor has to be changed to another pad.
I think a panel your size should run warm at 7.5W it's an 1/8th the size of my 60W.

I've been looking at how these kinds of PCBs are manufactured, and I've also been looking at the designs from professionals who put on youtube, their own high-powered LED custom-designed circuit boards, and I've really learned a lot from those videos.

I guess CREE makes the most popular high-powered LED that people seem to use ... one of them, in particular, can run a SEVEN AMPS, but the guy ran his at only 700 milliamps with damn good light output ... I'm thinking that doing something like that might provide me with the ability to get the same amount of light from an LED that would hardly kick out much heat at all because it's being driven WAY below its tolerance levels...

Also, I saw one video where a guy compared the actual thermal output from an aluminum PCB vs. a standard PCB and the aluminum PCB didn't perform any better really than the standard PCB ... which I found interesting ... if you click here to see the video, I set the time index to the relevant spot on the video.

I need to look into it more and look at the costs of the LEDs etc., but I might be looking at a complete re-design of this panel.

[diif]

Re: LED Resistor Calculations ...

After a little research i have found that heat affects the Vf of the LEDs in turn drawing more current, that's why the pads need to be the same size so there is no temperature differential, that trace to the resistor has to be changed to another pad.
I think a panel your size should run warm at 7.5W it's an 1/8th the size of my 60W.

[EasyGoing1]

Re: LED Resistor Calculations ...

There's no precision but it is science getting the heat out, bad deign is bad design and that will create hot spots at the base of those LEDs.

I don't know the size of your panel but I have one here 24cm square, 150 0.5W LEDs, run at 60W it's warm, not hot to the touch. It doesn't use crappy no name LEDs though, there are no traces on my panel. Just + and - pads the full width of the board with no dividers.

The final panel will be 120mm X 60mm. They had two options for the aluminum thermal conductivity. The default selection was 1.0W/mK (whatever mK is ... ) I chose the other option which is 2.0W/mK which meant to me that it can move more heat than the first option.

These boards that I've been testing with are only 90mm x 40mm with the 1.0W/kM aluminum and they simply get too damn hot. Worst-case scenario, if the final panels are too hot, I can leave out a couple of rows of LEDs ... these things are damn bright as it is ... one or two rows less won't be that noticable.

[diif]

Re: LED Resistor Calculations ...

But the actual traces were not clear in the photo. Compare your photo to the ones I've been providing ... there is no guesswork involved in my photos, your photo was clear as mud.



I would agree with that, if there were some kind of precision in the actual transferring of heat out to the aluminum backing. But the fact is, it doesn't matter which pin is producing heat, the aluminum will dissipate the heat from any pin universally throughout its entire surface area ... so additional dividers are essentially useless.

There's no precision but it is science getting the heat out, bad deign is bad design and that will create hot spots at the base of those LEDs.

I don't know the size of your panel but I have one here 24cm square, 150 0.5W LEDs, run at 60W it's warm not hot to the touch. It doesn't use crappy no name LEDs though, there are no traces on my panel. Just + and - pads the full width of the board with no dividers.

[Per Hansson]

Re: LED Resistor Calculations ...

Thanks for sharing this mate! It helped me a lot

Which part, specifically?

These kind of posts are usually by a spam bot to look legitimate and fly under the radar, but I usually wait untill he makes the actual spam post and then nuke from orbit...

[EasyGoing1]

Re: LED Resistor Calculations ...

I even included a photo to aid with the explanation.

But the actual traces were not clear in the photo. Compare your photo to the ones I've been providing ... there is no guesswork involved in my photos, your photo was clear as mud.

If you want to improve your design further, then add another couple of vertical breaks so you can remove the trace to the resistor. All anodes and cathodes with then be on large copper pads.

I would agree with that, if there were some kind of precision in the actual transferring of heat out to the aluminum backing. But the fact is, it doesn't matter which pin is producing heat, the aluminum will dissipate the heat from any pin universally throughout its entire surface area ... so additional dividers are essentially useless.

[diif]

Re: LED Resistor Calculations ...

I even included a photo to aid with the explanation.

If you want to improve your design further, then add another couple of vertical breaks so you can remove the trace to the resistor. All anodes and cathodes with then be on large copper pads.

[EasyGoing1]

Re: LED Resistor Calculations ...

NO, the PROPER way is as I showed and detailed above, definitely no large ground plane.

The problem is ... nothing you've said so far makes any sense. So your method is still a mystery.

After working with the aluminum boards, I think this layout will be the most efficient.

Dark red is power in as well as heat dissipation for the anode's of the first LEDs in each row.

Dark green is heat dissipation for the anodes of the next two LEDs in line, and the gray area is ground.

[diif]

Re: LED Resistor Calculations ...

But I'm convinced NOW that the proper design for this kind of board would be an isolated copper area for each anode, since heat transfers out to the aluminum immediately without needing to physically connect the copper with the aluminum ... I just don't know how they do it.

NO, the PROPER way is as I showed and detailed above, definitely no large ground plane.

[EasyGoing1]

Re: LED Resistor Calculations ...

Is it really 117c not 117f?
If it is that hot I wonder what the junction Temp of the LED is.
Typical 1W white LED has junction temp max of around 110c.

https://www.photonics.com/Articles/M...erature/a34316

The thing with these boards ... and I can't seem to get a straight answer from the sales reps at PCBWay ... but there is definitely some kind of layer between the pads and the aluminum so that no matter which pad I put heat on, that aluminum has to heat first before the pad will be hot enough to even put solder on. Im gonna make a video to demonstrate what I'm talking about ...

But I'm convinced NOW that the proper design for this kind of board would be an isolated copper area for each anode, since heat transfers out to the aluminum immediately without needing to physically connect the copper with the aluminum ... I just don't know how they do it.

[EasyGoing1]

Re: LED Resistor Calculations ...

Is it really 117c not 117f?

It's running a little cooler right now cause it's cooler in the room than it was earlier...

[budm]

Re: LED Resistor Calculations ...

Is it really 117c not 117f?
If it is that hot I wonder what the junction Temp of the LED is.
Typical 1W white LED has junction temp max of around 110c.

https://www.photonics.com/Articles/M...erature/a34316

[EasyGoing1]

Re: LED Resistor Calculations ...

Thanks for sharing this mate! It helped me a lot

Which part, specifically?

[BadmanRasta]

Re: LED Resistor Calculations ...

Thanks for sharing this mate! It helped me a lot