Steppers How Hot Is Too Hot At 24 Volts

[Pyropainter]

I have recently added a 24 volt power supply to my Rostock Max. The heated bed and motors are supplied by the 24 volt power supply. The Logic, Heaters and Fans are supplied by a DC to DC transformer set at 12 volts. I can put my hand on the steppers for about 8 seconds before becoming too hot, although I have never given them the touch test at 12 volts. Know a few questions if you don't mind.

1. How hot is too hot (Celsius or Fahrenheit)?
2. Where are the changes to be made (I understand that they need to be made in Repetier firmware line 701)?
3. Can these changes be made thru the EEProm (avoiding the need to reload the firmware)?
4. I have Kysan steppers and the "define motor current settings" are as follows 155,155,155,165,0. Can you tell me what each set of digits represents?
I assume x,y,z axis and extruder in that order. what about the last number"
5. How do I calculate the changes that need to be made. If you can offer a good web site please let me know. I will try to figure it out myself. If you are willing to explain I am eager to learn.

Your answers are much appreciated.
Thank you.

[Eric]

1. The motors themselves are typically rated for an 80C temperature rise, so they're not even close to failing. Warm like you describe is acceptable, but you can probably turn down the current a bit so they run cooler. So long as they still do the job, it's fine.
2. "configuration.h", about the line number you mentioned.
3. No. (It's technically possible, but not something that's implemented.)
4. In order: X motor, Y motor, Z motor, Ext0, Ext1. XYZ should all be the same. Extruder motors usually need a bit more power to push filament. The second extruder is 0 by default because most people don't have one installed. Range is 0-255. 135=0.75A, 185=1A, extrapolate from there.
5. Experiment? You may not need to make any changes. Stepper motor drivers control current...the higher voltage isn't a massive factor like it is with the heated bed.

[jlmccuan]

The only thing I would add is to watch the extruder motor temp. It can conduct enough heat to the drive gear to soften filament and cause you trouble. We've had to cut the current back even on 12VDC on some machines.

[Pyropainter]

Thank you for all of your help. It probably won't be the last time you seem me here. Hopefully one day I will be answering some questions asked by fellow members.