this morning i did a last test-run with the tweaked Felder ISO-Cream profile:
yeah… at the top i thought it is in the cooling step already and opened the window – with ~3°C cold air from outside it dropped fast.. then i found it is in the middle of the reflow – sorry… and closed the window again – until it really switched to cooling..
the old left-over pcb i use for these is done now.. i comes from my LEDBoard_4x4_16bit project – and if i remember correctly i backed it with the assembled board in the oven multiple times back then.. now grilled it again ~4-7 times. it smells very bad – is super dark discolored.. i think that is ok with about ~12 times solder cycles..
and then started to assemble a simple board to really test the profile 🙂
i added a paper-lid to have stable air inside..
reflow was successful 🙂 my profile is just a little bit to long for my right angle touch switches:
they melted away 🙁 – lesson learned – have a look in the datasheet and you know that they are very heat sensitive!
in general i have the feeling that my heating elements get a little bit to hot – the pcb also slightly discolored at on place… so will keep an eye on this and improve it..
i would like to have class at the top for a good view what is happening inside..
first i just checked with low temperatures of 20..40°C as i went on and tested up to 260°C i noticed that the current did decrease. and the temperature did not increase any more. i could see this in my graph as the heating got slower and slower with the rising temperature… (also the pid already saturated at the output..)
so i measured the resistance during the cool down of the heating elements to get some insights: (4x in series → 48V/4=~12V/Module)
Power @48V (W)
Temperature / Resistance – 4 Modules in Series – 12V/Module
result: the ~57W is not enough to get to more than 255°C…
i rearranged the Modules into 3-in-series connection. this means ~16V/Module – and tested again:
Power @48V (W)
Temperature / Resistance 3 Modules in Series – 16V/Module
with this i found that i can go above 255°C.
i then tested the profile for the Felder ISO-Cream “Clear” and found that in the reflow stage the heat-up is a little to slow:
in the *my setup* picture is a temporary cardboard thing with a 80mm 12V fan (connected to 5V) to cool down faster between tests. for the final setup i think i will buy 1 or two 5V and PWM capable fans…. and also exchange the *chamotte* ston with some metal frame. this way i also can cool the bottom side..
so i again switch the configuration – now i have a 2-in-series config: 24V/Module CURRENTLY THIS TABLE IS ONLY CALCULATED VALUES!!
Power @48V (W)
CURRENTLY ONLY CALCULATED VALUES!!!! Temperature / Resistance – 2 Modules in Series – 24V/Module
i also tested this with the Felder profile:
this time the heat-up is fast enough! 🙂 the nice and working pid tuning i had for the 4-in-series arrangement is now out of tune… so i will have to re-tune it to get less overshoot / swing.
while having a break i thought about the maximal power in this configuration – and found that this way i only be able to power 2×2 modules with my 250W power supply. for now i leave it this way. in the long run i hope with the other frame concept i get more heat to the pcb and less into the stone and this way be able to use the 3S config.
after a day of mostly waiting til the system cooled down again – one test cycle <=60°C needs 400s → 6:40min – i just rebuild my hw mounting setup.
this way i can warm up quicker and cool down much quicker as i do not store heat in the stone. – at least that is what i hope..
hmmm – does not seem to change much..
i then tested the actual Felder Profile:
seems i have a working profile. i will add a little more time for the prepare phase. so the pcb is really fully at the 50°C. at the top i have a little bit of a mis-match – i saw on my temp sensor directly connected to the heating elements at the top ~265°C – so that is hot… the pcb seems to increase its temperature resistance at higher temperatures… at the peak i have 230°C to 245°C error. and to the heating this results in ~35°C difference…
i will report when i solder the first real board. 😉