only 9V to heated bed

[pmeyer]

I have a Rostock MAX v2, the new version from fall of last year with the new PSU. I'm not happy with the heated bed ramp time (much slower than my Ultimaker). I finally had things taken apart a bit (replacing a burned out nozzle heater and making my hot-end wiring completely detachable), so I started digging a bit more.

step #1: I pulled of the heated bed to check my solder joint (it gets kind of squished in there when assembling). Looks nice and solid, no tight bend, no cracking, full pad covered.

step #2: check for PSU voltage droop when the bed is heating.
Results:
heater off: 12.24 at the PSU, 12.22 at the input to the board.
heater on: 12.18 at the PSU, 12.10 at the input to the board.
Pretty healthy, no droop that would significantly slow things

step #3: what voltage is the bed actually getting during heating?

9.2v measured at the output of the board! This is measured with a DC setting on a fluke multimeter, and it is jumping around a bit (+- .5V). The light is also flickering, quite visible to the eye. I assume that it is getting pulsed, on ~3/4 of the time. This is with the bed at 40 with a target of 100, so it should be full on.

It appears I have 30% more power potentially available.

I'm going to poke around in the settings and see if if there is any limiter I'm not aware of. I'll also poke through the calibration steps again to see if I missed something.

If not, I'll need to bypass the board and put in a separate relay or driver.





Is the driver not able to handle full on? Or do I have a PID calibration problem?

[teoman]

You can set the max output of the pid controller.

If it is set to say 200 then you will not be seeing 12v at the output of the board.

This setting is not particularly usefull when you are powering the bed with 12v but it comes in handy when you have a 20v power supply connected to it.

[pmeyer]

Interesting. Poking around, I found two things:

1) the heated bed max rate is set at 200 (presumably out of 255). This explains a lot: 12.2 * 200/255 = 9.5V, close enough for government work to what I was reading. I fixed this.

2) You can do PID Autotune for the heated bed, but the documentation doesn't mention that anywhere. I suppose they decided that the defaults where good enough. I'm running it now.

Can anyone tell me why the default heated bed max rate is 200? Was this to avoid droop with the old PSU? They really need to fix it, or at least mention in the manual that it should be updated (if they don't want to change the software default to avoid voltage droop rebooting older models)

[pmeyer]

Yup, that was it. The defaults are bad and the manual doesn't indicate to update them (that I saw, at least).

Steps I suggest for all v2max owners:

1) Run PID autotune for the bed
- preheat the bed to some reasonable temp (I did 75)
- bring up the gcode terminal in mattercontrol
- type "m303 p1 s75" (or s80 or s60 or whatever temp you chose)
- let it run, copy down the p/i/d numbers it displays
-> if it times out, make sure it was preheated all the way
- configure the EEPROM
=> adjust the bed ki/kp/kd
=> set "Bed PID max value" to 255
=> set "Bed PID Drive Max" to 255

I suspect the PID autotune is less necessary, but the setting the max values gets you the full 12V applied to the bed.

[JFettig]

Connect something to the 5v lines on the power supply, supposedly that helps significantly.

[geneb]

JFettig, he's using the new power supply which has no 5v output.

g.

[DeltaCon]

I posten a lot like this OP on an other thread few days ago, so I am quite happy with pmeyer's findings and teoman's suggestion!
Will set the higher Max value later today and check the improvement. I am not an impatient guy but 30 minutes to 90 degrees just seems not needful.
The manual indeed does not show anything about bed PID tune, only Hotend PID tune is mentioned. I know this by heart, because I have been looking for it recently. But I was able to think of the p1 setting before I needed to call in the forum troops

[teoman]

you are actually fooling the PID controller by setting the max values after the tuning.