bed temperature +20º in 1 second?

Hello,

Is it possible that the bed temperature jumps from 60 degrees to 90 or from 80 to 100 in less than two seconds? I think it is not possible, and can be that something is wrong in the firmware? Can be the thermistor not working?

No a bed can't change that fast. What electronics are you using? Some have bugs where the bed heater current disturbs the thermistor reading.

---

[www.hydraraptor.blogspot.com]

I'm using "generation 6 deluxe".

Can I do anything to solve it? or it's a problem in the board?

thanks!

I am not familiar with that board.

The two mistakes I have seen are: -

1) Powering the Atmega from the USB and the thermistor bias from the 5V rail of a PC PSU. The 5V rail changes with the 12V load causing the thermistor voltage to change. The Atmega is getting its reference from the USB, so sees the change.

2) Poor power and ground routing on the PCB so the thermistor's power and ground are sharing tracks with high current devices. Analogue and digital power and ground should be kept separate and starpointed at the chip's pins.

---

[www.hydraraptor.blogspot.com]

Apart from electrical issues (and admittedly not knowing about this bed), check how close the thermistor is relative to any heat source.

example-

If you had a loose thermistor laying next to a power resistor, a 20 deg jump isn't unrealistic...

---

Hello,

The bed resistors are close to the corners and the thermistor is in the middle.

If I move the wires connected to the thermistor sometimes I can cause the temperature jump. So, I expect that is something in my wiring... I tell you when I solve it.

thanks both for your help.

The wiring seems ok. I used more kapton to make sure that there are no shortcuts and the wires does not touch the bed. But the same.

The temperature jumps from 60~65 to 90 the first time. Sometimes it comes back to 65 after some time. Then, when temperature arrives to 80, it jumps to 108. I think the real temperature is the lowest one because when I try to print the plastic is not adhering to the bed.

Moreover, the thermistor temperature is always an integer value 60.00, 61.00, etc. But the hotend temperature is a float (231.18 and values like that). Why is using the firmware different ways to calculate temperatures from identical thermistors?

Anyway, I can not achieve higher temperatures than 80 real degrees. I tell the software to reach 130 degrees (to compensate the offset) but never achieves more than 110 (about 80 real degrees).

The temperature jump happens also when cooling the bed...

B:66.00
B:65.00
B:64.00
B:96.00
B:95.00
B:94.00
B:93.00
B:60.00
B:59.00

I changed the temperature table and it works fine now. For TEMP_SENSOR_BED I'm using 1 now (100k thermistor) instead of using 3 (mendel-parts).

---

Barcelona Dynamics - [bcndynamics.com]