Hey hot stuff! Its going to be heated underneat those sheets. Let me grab you by the hand, close your eyes and feel the cozy warmth, emanating from my XL bed. But dont touch anything! (…jet), you might get burned! No seriously, please dont touch the electronics XD
While looking up usefull things to print for my XL, I came across some great mods for cooling the print bed electronis. The XLs printbed consists of individual heating tiles, controlled/powered by a controllboard directly underneath the print bed. Looking at this board I identified some power electronics for driving the tiles. Also one IC, possibly acting as the brain and also some passive parts like diodes, resistors, capacitors and two 10A fuses.
Thinking about it, it absolutelly makes sense to me to have these electronics components cool during operation. Not neccessarily because of something getting fried, but for extending the overall service life. I mean, MOSFET drivers are getting hot while in use and more often than not, ICs are tending to like it cool in general. Also heat spots are bad for the PCB it self. This is because steep temperature gradients across material are going to cause stress (within the material) and degrade it over its life time. Temperature cycles in general are a reason for degradation too of course.
Fortunately i have a thermal camera at my disposal and so I just had a look at whats going on down there.
We are now underneat the print bed, looking up into the exposed power distribution board. On the left and right side of the picture, one can see all the cables radiating out to the tiles above. On the lower side of the picture, one can make out the low voltage power line (its connector terminal to be precise) and data connection to the rest of the printer. directly beside, two fuse holders are located. But as you can see, you see nothing. The bed is turned off and all parts are around room temperature. This makes all apear in a similar color.
After switching on the bed heating, one can imediatelly make out the position of what might be components possibly involved in driving the tiles, since they heat up first. The color gradient makes this look much more drastic than it is in reality. They heated just a couple of degrees at this point.
After some additional time passed, but before the bed reached its final temperature, i noticed something interesting. One of the fuse holders on the PCB took a lead in temperature. It quickly passed the drivers temperature, only to be the hottest thing around with roughly 66°C (See red cross hair). The power elcetronics, only seconds ago, showing as destinct bright spots, are so cold compared to the fuse holder that they barely even show anymore. At first i thought this might be an defective fuse with high internal resistance but swapping the fuses also brought no change. Still only this one holder got warm. Ok then, seems to be normal mode of operation here. Lets proceed.
As we can see, the print bed above still is heating to temperature. Not every point has reached its temperature jet and one can see the destinct tile pattern underneath the sheet. But down below of all that, somethin odd started to show. No, really. Lets have a look together because i did not expect to see, that I again basically cant see anything.
Who had guess this? A completelly different picture of the PCB reveals itself. As the heat from the bed above slowly starts to bleed through the insulating foam, and also the aluminium frame slowly gets to temperature, the PCB seemed to have reached some sort of temperature equilibrium. Basically no hotspots, no piping hot power electronis, no nothing.
So? now what?!
I think with all i can see, an active cooling actually might not really be necessary in this case. The temperatures are well within the expected operating temperatures of most electronics of this sort. I absolutelly did not expect to get to this conclusion.
Lets have a smal real world exampe in order to bring these temperatures into some context. Lets have a hot summer day for example. The inside of your car, left cooking in the sun for the day, will easily reach around 60-70°C. Nobody would waste a thought about cooling the electronics within the dashboard (I know, nowadays some cars have active air cooling there, but lets be generalists here for a moment). Even your entertainment electronics, like phones, tablets, speakers, laptops, earbuds etc. can stay there without getting damaged. They can even be used without sustaining damage in these temperature regimes. From a technical point of view, this is just not that hot.
An additional fan might be easy to implement here but if im honest, i could immagine a scenario in which cooling at this point might even be detrimental. See, all parts basically have the same moderate temperature after some minutes. no hotspots, all nice and even. Immagine having a cool stream of air now on the PCB. Suddenly we introduce a steep gradient of something 50°C or more. One side still is heated to 70-80°, the other side force cooled down to room temperature. Really not sure if this might be the best thing to have. Dont get me wrong here. I dont think that cooling these parts is a bad thing but based on what i saw, I think it is just not mandatory to have here on this exact spot.
Smal bonus fact:
Did you ever wonder if the tiles might be driven all at once or depending from the size/shape of the actual print? In fact, they seem to be heated according to the part you are going to print. Does this have any meaningfull effect on power consumption? Maybe not. Does this make your printer ready to print faster? Maybe a litte. But anyway. How cool is that?!
Please note that thermal imaging is one topic for it self. The temperatures shown here, are not representative (within 2-6°C) because this device is not calibrated to the specific material(s) probed. I set the emission coeficient to 0.85 (semi matt materials) to have a compromise from PCB, IC (resin), to aluminium frame and also the soft insulating foam. The thermal view only is a quantitive approach in order to get a feeling for what is going on there in general. Its basically for entertainment purposes only ^^
So, thats all. Just something mildly interesting i wanted to share with you.
cya
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