Just about to start putting together my lights and was thinking about the best way to ensure a route for heat to disapate away from the maxflex board. The best place to connect it to would be the back of the mounting for the led's but surely this would mean that heat would also head from the led's to the board exaserpating the problem on the board in particular. So which is likely to be hotest maxflex or led's?
Maxflex heat disapation question
- Thread starter iggs
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ok then daft question stuff
My maxflex is connected by 2 copper wires to the led's. Therefore there is significant heat conductivity available there. If the led's get hot the wires are going to conduct heat towards the maxflex. Is this a problem?
Likewise, if the led's are being cooled properly via heat being conducted to the case will this also cool the maxflex? or is it a specific part of the maxflex board that needs cooling (backside of the heat sink attachment point at a guess)
Will the temperature across the board be pretty consistant? Does it disapate heat across it well or does it have insulated hot spots?
I noticed that the heat sink attachment is wired as ground. I'm wondering if I should just wire the case as ground and run all the wiring that way. By using reasonably thick wiring will this help the heat disapation to the case and therefore to the outside air.
Am I missing something that would mean this wasn't possible/sensible?
My maxflex is connected by 2 copper wires to the led's. Therefore there is significant heat conductivity available there. If the led's get hot the wires are going to conduct heat towards the maxflex. Is this a problem?
Likewise, if the led's are being cooled properly via heat being conducted to the case will this also cool the maxflex? or is it a specific part of the maxflex board that needs cooling (backside of the heat sink attachment point at a guess)
Will the temperature across the board be pretty consistant? Does it disapate heat across it well or does it have insulated hot spots?
I noticed that the heat sink attachment is wired as ground. I'm wondering if I should just wire the case as ground and run all the wiring that way. By using reasonably thick wiring will this help the heat disapation to the case and therefore to the outside air.
Am I missing something that would mean this wasn't possible/sensible?
georges80
Flashlight Enthusiast
You need a LOT MORE than just wires to carry heat (unless you're talking transmission power line sized wiring...).
The tech section for maxFlex on my website is pretty clear about working out how many watts of heat will be generated within maxFlex based on your load and drive current.
That heat MUST BE REMOVED and that is why there is a thermal pad on maxFlex. You need to thermally epoxy or solder a heatsink/tab to that spot.
The board will get hot rapidly if you are driving 1W or more. Just get a resistor and run it at 1W or more and see if you go ouch when you touch it
There is no free lunch when it comes to driving LEDs at high power. If you have 10W going to the LEDs, even at 90% efficiency that means you'll have 1W of heat being generated by the driver - you do need to get rid of that or the driver will cook/shutdown/be damaged.
Some of you "nuts" are talking about 5 LEDs or 6 LEDs at 1A or more - now we have 20W+ to the LEDs and 2W+ being generated in the driver. 2W will cook the driver very quickly (within a minute). Oh - unlike meat, cooking a driver is not a good idea
There is a reason I put that thermal interface area on maxFlex - it is to be USED. It is the BEST place to get the heat off the board because it is thermally connected by 9 microvias to the backside of the thermal pad of the switcher IC (on the other side of the PCB). That area is THE area that will get hot fast and needs to be connected to a heatsink/tab etc.
Anyhow, hopefully this answers some of your questions...
cheers,
george.
The tech section for maxFlex on my website is pretty clear about working out how many watts of heat will be generated within maxFlex based on your load and drive current.
That heat MUST BE REMOVED and that is why there is a thermal pad on maxFlex. You need to thermally epoxy or solder a heatsink/tab to that spot.
The board will get hot rapidly if you are driving 1W or more. Just get a resistor and run it at 1W or more and see if you go ouch when you touch it
There is no free lunch when it comes to driving LEDs at high power. If you have 10W going to the LEDs, even at 90% efficiency that means you'll have 1W of heat being generated by the driver - you do need to get rid of that or the driver will cook/shutdown/be damaged.
Some of you "nuts" are talking about 5 LEDs or 6 LEDs at 1A or more - now we have 20W+ to the LEDs and 2W+ being generated in the driver. 2W will cook the driver very quickly (within a minute). Oh - unlike meat, cooking a driver is not a good idea
There is a reason I put that thermal interface area on maxFlex - it is to be USED. It is the BEST place to get the heat off the board because it is thermally connected by 9 microvias to the backside of the thermal pad of the switcher IC (on the other side of the PCB). That area is THE area that will get hot fast and needs to be connected to a heatsink/tab etc.
Anyhow, hopefully this answers some of your questions...
cheers,
george.
Thanks for the reply George, much appriciated. Thats nice and clear, exactly what I needed to know. I did say it was daft question time.
Until I've solved the issue of getting heat away from the board effectively I'm going to run the led's at 750mA max which is well under 1 watt at the board
Until I've solved the issue of getting heat away from the board effectively I'm going to run the led's at 750mA max which is well under 1 watt at the board
Though given the discussion going on elsewhere about temperature sensing in the bFlex with UIB2, exactly what does the temperature sensing current drop do? I thought the idea was to sense the temperature of the LEDs, in which case you need a good thermal path to the LEDs. Won't it be dominated by the heat generated in the driver though? Or is that a reasonable measure of how well the cooling is working anyway?
georges80
Flashlight Enthusiast
Actually, inside a metal housing I've found that the 'air' heats up pretty quickly and so you now have a HOT 'ambient' for the board. I've done a bunch of measurements with thermocouples and IR thermopiles and have a pretty good feel for what goes on.
What I see is that there is quite a fast coupling of case temperature effect to driver board temperature (due to inside ambient air temperature increase). Definitely an 'offset' or 'lag', but it is quite predictable and accurate.
What this means is if you have a specific case (like an aluminium one) and bFlex (for instance) is suspended in there (with say a plastic 'holder'), you can quite accurately set the temperature trip point and have the unit dim down when a repeatable case temperature hits.
The MAIN point is that you need to measure this 'offset' for a specific case/driver mounting scheme and set the temperature trip point appropriately - that's why the user can set the trip point...
Obviously if the driver is mounted in a housing that is separate to the LEDs then there's no magical way for it to sense the temperature.
cheers,
george.
msxtr
Newly Enlightened
Hi, so much it's hot??
Greetings - Saludos
msxtr
Greetings - Saludos
msxtr
Condition: 25 degree home temp., under Fan. MagC with copper wire soldered as above.
4x 18650 (1.7A) -> MaxFlex 1A -> 6x cree = 60min ( non-stop work smoothly )
4x 18650 (2.1A) -> MaxFlex 1.2A -> 6x cree = 7min ( MaxFlex kickback after 7min.) :thumbsup:
4x 18650 (1.7A) -> MaxFlex 1A -> 6x cree = 60min ( non-stop work smoothly )
4x 18650 (2.1A) -> MaxFlex 1.2A -> 6x cree = 7min ( MaxFlex kickback after 7min.) :thumbsup:
What do you mean by "Maxflex kickback"? Which UI are you using? There is no option I can see for any temp related settings in the UIF/UIP/UIB manual I have (downloaded from the taskled website)
Have you got a UIB2 version?
Ian
Aircraft800
Flashlight Enthusiast
Wow Nice Heatsinc Downoad!!
My New maxFlex should be here this week, and that is the only issue I haven't worked out yet. I'm a little worried about soldering the sync to the driver, maybe I'll just use the Arctic Alumina and a piece of copper strip bent to a 90deg.
I may also use a PC Heatsinc and mount it to the tube, but I'd like it to be removeable like yours.
My New maxFlex should be here this week, and that is the only issue I haven't worked out yet. I'm a little worried about soldering the sync to the driver, maybe I'll just use the Arctic Alumina and a piece of copper strip bent to a 90deg.
I may also use a PC Heatsinc and mount it to the tube, but I'd like it to be removeable like yours.
georges80
Flashlight Enthusiast
The Cutout/Cutoff is NOT in the firmware - what is being seen is the SWITCHER CHIP overheating and going into thermal shutdown/protection mode.
cheers,
george.
So the chip will actually protect itself if you don't heatsink properly? Not something I've seen with mine, so I guess I'm not driving it that hard (4xCree at 700mA, which at ~10W is just about what you start recommending heatsinking for). I have got some heatsinking planned to help extend component life - it would just get in the way of firmware development at the moment!
Aircraft800
Flashlight Enthusiast
Download,
I LOVED your idea, and had to borrow it for my MOD.
George,
You're right, the Cadillac of all drivers! Awesome!!
I LOVED your idea, and had to borrow it for my MOD.
George,
You're right, the Cadillac of all drivers! Awesome!!
Last edited:
msxtr
Newly Enlightened
Download,
I LOVED your idea, and had to borrow it for my MOD.
George,
You're right, the Cadillac of all drivers! Awesome!!
Hi, great job, I think that I will copy to you
By the way, only 2 wires?? how you have connected the leds?? :thinking:
Greetings - Saludos
msxtr
msxtr
Newly Enlightened
Aircraft800, Good job! Beautifully done!
msxtr, see this
Yes, yes, I said it by I don't see the wires of the led solders to the maxflex...
Greetings - Saludos
msxtr
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