ERROR: Heater heater_bed not heating at expected rate

[biiiink]

I replaced most of the printed parts on my gantry and after getting it back up and running, I've started getting this error. It always heats up nice and smoothly to about 95-100°C and then starts cooling down. I have noticed that If i have my target set at 110, and it starts cooling down at 95, if i change the target to 90, it will usually drop below 90, but eventually start heating up again. Eventually the issue happens again though and I can never get it up to 110.


I have tried switching the thermistor for the bed and have also re-crimped all of the heater wires. I haven't tried replacing the thermistor wire (I have a connector under the bed, that runs to the board), because to me, this doesn't seem like an issue with the thermistor, but I could be wrong.

Is it possible that it is an issue with the SSR? I have the Omron SSR from the BOM.

 

[NoGuru]

SSR or the bead heater itself. Looks like you have changed or tested the rest.

 

[Indeed]

In Mainsail, in the "Temperatures" section, click on "Heater Bed" and check the box "Show PWM-power in chart"

Now when the temp starts falling, you can see if the mcu thinks the heater should be on or off, and by how much.

If "PWM-power" is at 100% or so when the temp is falling then it's probably the heater or SSR.
In this case you could also measure the voltage at the connections closest to the bed heater. If heater PWM is well above 0% according to Mainsail and the heater voltage is close to 0, it's probably the SSR or wiring.

But if "PWM-power" is nowhere near 100% when the temp is falling then it's probably the thermistor or its wiring.

Or it may even be the PID config settings in printer.cfg that are off by a huge amount. Like a when a decimal point is missing or in the wrong place for one or more of the pid_K* settings. Could be that when the temp is getting close to target and it's time to back off on the PWM a bit, it backs off way too much and the PWM is set to 0%.

 

[biiiink]

In Mainsail, in the "Temperatures" section, click on "Heater Bed" and check the box "Show PWM-power in chart"

Now when the temp starts falling, you can see if the mcu thinks the heater should be on or off, and by how much.

If "PWM-power" is at 100% or so when the temp is falling then it's probably the heater or SSR.
In this case you could also measure the voltage at the connections closest to the bed heater. If heater PWM is well above 0% according to Mainsail and the heater voltage is close to 0, it's probably the SSR or wiring.

But if "PWM-power" is nowhere near 100% when the temp is falling then it's probably the thermistor or its wiring.

Or it may even be the PID config settings in printer.cfg that are off by a huge amount. Like a when a decimal point is missing or in the wrong place for one or more of the pid_K* settings. Could be that when the temp is getting close to target and it's time to back off on the PWM a bit, it backs off way too much and the PWM is set to 0%.

Tried your suggestions. Everything pointed to the SSR or the heater, so I tried a new SSR with no luck. So must be the heater

Going to order a new one

 

[Indeed]

Hmm... A new heater can be quite expensive, better make really sure the one you have is actually broken first.

You'll get the most reliable result if you can measure the voltage across the bed heater at the connections closest to the heater.
If the voltage stays high and doesn't drop when the temperature starts falling, then the heater is probably broken.
But if the voltage drops then something else is causing the temperature drops.

Does the bed "PWM-power" in mainsail go to 100% while the temperature is falling?
If it does, then the bed heater, ssr (you already tried that) or their wiring may be broken.
If not, then it's probably something else. Such as the thermistor or its wiring.

 

[biiiink]

Hmm... A new heater can be quite expensive, better make really sure the one you have is actually broken first.

You'll get the most reliable result if you can measure the voltage across the bed heater at the connections closest to the heater.
If the voltage stays high and doesn't drop when the temperature starts falling, then the heater is probably broken.
But if the voltage drops then something else is causing the temperature drops.

Does the bed "PWM-power" in mainsail go to 100% while the temperature is falling?
If it does, then the bed heater, ssr (you already tried that) or their wiring may be broken.
If not, then it's probably something else. Such as the thermistor or its wiring.

Appreciate the help. I had done most of what you recommended. Voltage stayed consistent. The PWM stayed at 100%. I even replaced to thermal fuse. Everything pointed to the heater.

I've replaced the heater and everything is working great now.

Thanks again for the help