Testing & Tuning the PID

for tuning i followed more or less the tutorial PID Without a PhD
from Tim Wescott
and the tutorial and video from PID Explained Team.

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)

Temperature (°C)	Resistance (Ohm)	Current (A)	Power @48V (W)
255	40	1,19	57
250	39	1,21	58
240	38	1,23	59
230	36	1,26	60,5
220	38	1,26	60,3
200	34	1,35	64,8
100	26	1,8	88,6
80	24	2	96
60	22	2,18	104
40	20,9	2,3	110
25	19,5	2,46	118

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:

Temperature (°C)	Resistance (Ohm)	Current (A)	Power @48V (W)
255	27,5	1,45	70
250	27,0	1,5	72
240	26,6	1,6	77
230	25,6	1,67	80
220	25,3	1,7	82
200	24,1	1,8	86
100	18,8	2,1	100
80	17,5	2,7	130
60	16,7
40	15,6
25	14,3

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!!

Temperature (°C)	Resistance (Ohm)	Current (A)	Power @48V (W)
255	20	2,4	115
250	19,5	2,46	118
240	19	2,52	121
230	18	2,67	128
220	17,5	2,74	132
200	17	2,82	135
100	13	3,69	177
80	12	4	192
60	11	4,36	209
40	10,45	4,59	220
25	9,75	4,92	236

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.

Tuning

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. 😉