Difference between extruder MAXTEMP variable and temp you can set the hotend to

Just a quick question about the maxtemp variable. When this is set to a given value, when I heat up my hotend manually it can only reach a value 15 degrees below the MAXTEMP setting. I just wanted to make sure this is an intended feature in Marlin and not a bug where it's displaying the incorrect temperature or something. Looking into the documentation on the MAXTEMP variable I'm guessing it is an intended feature since it shuts down the machine after reaching MAXTEMP, which would be very impractical if you'd just set the printer to that temperature.

I've just installed an E3D Titan Aero with a V6 hotend and the documentation said to set the MAXTEMP to 285 in the marlin firmware setup guide. However, earlier on in the installation guide it says to set the extruder temperature to 285 in order to hot tighten the hotend, but with this 15 degree difference it can't reach that, hence my confusion. This 15 degree difference is something which should probably be updated on the E3D guide page, but it would also probably help if that was mentioned in the Marlin documentation on MAXTEMP values.

Yes I think with any pid controller if you want to reach the desired output quickly and not wait for ages you will have to overshoot it first, so it makes sense to have a 15 degree so that the machine doesn't halt when trying to heat the head. I didn't check the documentations yet but this makes sense to me.

It's entirely possible to design a PID controller that doesn't overshoot significantly. However the PID constants you need to do that are not optimum for maintaining the temperature once it has been reached. That's why RepRapFirmware calculates two different sets of PID parameters from a model of your heater, and switches from one to the other when the temperature is close to the target.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

This discussion answered my question. Thank You. I wanted to add in my case I am installing a e3d V6 gold edition hot end.
I am using The RAMP_14_EFB firmware on my 2018 gold edition Tevo Tornado printer. This printer uses the mks_Gen_L 1.0 board.
I have noticed 2 things... First the fan (and I think the Hotend) is wired up backwards. YES, Backwards.
I replaced my fans with 2 new fans. One blower fan and one regular fan for cooling the Heatsink. I could not get the square fan
To work at all. The blower fan I rewired through the BNC connector not directly to the board. I notice that the red and black leads
Are reversed. Once I rewired the fan it worked. I have my heatsink fan connected to the 12/24v always on fan connector.
I am getting to the point of the conversation. Continuing on; 2: I hooked my e3d Hot end to the E0 connection on my main board.
My printer says E1... at start up. My hotend heats just find, though. I noticed that adjusting the Temp on the printer, the printer was not
limiting the temp. I tried to set the printer to 285c the max temp for (the e3d hotend). My printer kept giving me a MAXTEMP
Error message. I was not sure whether this firmware just starts as E1 as the first extruder instead of E0. It just occurred to me to try changing
The connections for the hotend. So I tried connecting my extruder to the E1 connection on the board directly. Now my printer, at start, displays the
Name of the printer but does not display E1 in the printer name. Also, when I adjust the Temp it is now limited to 270c not 285c as
Set in the firmware. This confirms the theory you guys are saying. This is 15c lower than MAXTEMP. I am next going to try changing
MAXTEMP to 300c and see if the max temp is then set to 285c. As a test, I am going to set MAXTEMP to 300c to see if maxtermp on the printer can
Reach 285c.

I just verified the results. I uploaded the firmware with 300c as the MAXTEMP. And Yes, the Max value I can set my printer to is 285c