Heater heater_bed not heating at expected rate

[frairsan]

Printer Model

V2.40 350mm LDO kit

Extruder Type

Clockwork 2

Cooling Type

Stealthburner

Hi,

I own a voron V2.40 350mm LDO kit. Since the start I'm having heating issues with the bed. I have checked the wires three times already, unmounted and remounted the bed, and I keep having the same issues.
Lately I started to preheat the bed by steps to avoid the issue (up to 50, then 70, then 90 and finally 100C), but even like this it fails frequently. I'm adding a picture with the latest error requiring firmware restart (big drop in the picture). As you can see, the heating is not constant, the temperature goes up and down. Once it reaches the print temperature it remains stable.
Any idea on what to check?


Here's the printer.cfg

[heater_bed]
## SSR Pin - HE1
## Thermistor - TB
heater_pin: PA2
## Validate the following thermistor type to make sure it is correct
## Keenovo branded bed heaters should use Generic 3950
## LDO branded bed heaters will have the sensor type labelled on the heater
## See https://www.klipper3d.org/Config_Reference.html#common-thermistors for additional options
sensor_type: Generic 3950
sensor_pin: PF3
## Adjust Max Power so your heater doesn't warp your bed. Rule of thumb is 0.4 watts / cm^2 .
max_power: 0.6
min_temp: 0
max_temp: 120

I'm using a Phaetus Rapido Plus and an Octopus 1.1, so I followed LDO guide to wire the Hotend to the bed_out port and the SSR to the PA2

 

[bythorsthunder]

This is certainly a thermistor issue. Either the wiring from the mcu to the thermistor or the thermistor itself. If you have already tried replacing all connectors and wiring to the thermistor the next step would be to add a new thermistor to the bed and use that one instead.

 

[NoGuru]

Agreed, this is a thermistor issue. Does this only happen while printing or even just heating up?

 

[frairsan]

Agreed, this is a thermistor issue. Does this only happen while printing or even just heating up?

thanks, I'll check with a new one. It just happens when heating up

 

[frairsan]

This is certainly a thermistor issue. Either the wiring from the mcu to the thermistor or the thermistor itself. If you have already tried replacing all connectors and wiring to the thermistor the next step would be to add a new thermistor to the bed and use that one instead.

I have checked the connections, but didn't try to replace them yet. Maybe it's just the JST? I'll take a look and I might replace the thermistor too

 

[Phreakhcker]

I have checked the connections, but didn't try to replace them yet. Maybe it's just the JST? I'll take a look and I might replace the thermistor too

If replacing the bed thermistor (I've had to replace one of mine a while back) follow these simple instructions. Just don't try and remove or cut into the heater mat is the main thing. Here is instructions from Keenovo.


1) Cut the two small red PTFE sensor wires( usually 22AWG), some Keenovo Digital Controller has them in a white sleeve, cut the white sleeve in this case.
Cut close to the thermistor bulge. Never Try to open the patch/bulge or cut into the heater surface.

2) Connect the new thermistor( NTC100K Thermistor B 3950-1%) to the two red wires. There is no polarity here.

3) Attach the thermistor to the heater surface. High temperature silicone RTV cement is recommended for a permanent installation.

 

[frairsan]

Thanks everyone for your answers. I finally found some time to replace the thermistor. The heating curves are smooth now, no more spikes, but I still run into errors (Heater heater_bed not heating at expected rate). The only way I found to avoid them is to heat the bed by steps (ambient to 60, then 80, then 90 and finally 100)

 

[Laserbea4k43]

How's your SSR holding up?
Does your power outlet provide enough current?
I have so many gadgets in my garage that I have to run a surge protector into the next room or my breakers will trip.