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[FR] Please document HEATER_0_MAXTEMP limit offset #21265

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ZhuDaHai opened this issue Mar 6, 2021 · 11 comments
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[FR] Please document HEATER_0_MAXTEMP limit offset #21265

ZhuDaHai opened this issue Mar 6, 2021 · 11 comments

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@ZhuDaHai
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ZhuDaHai commented Mar 6, 2021

Description

I stumbled upon this undocumented feature after setting HEATER_0_MAXTEMP to 245 and then not being able to set the temperature above 230. Having reset it to 275 and then finding this bug report. I understand now what is going on. However I don't understand why that is not documented in configuration.h for that setting.
#17693

Feature Workflow

This is basically just a documentation request, The existing documentation in Marlin for the HEATER_0_MAXTEMP is as follows:

// Above this temperature the heater will be switched off.
// This can protect components from overheating, but NOT from shorts and failures.
// (Use MINTEMP for thermistor short/failure protection.)

Please add addition documentation to this section, such as:
//The maximum settable temperature will be 15 degrees below this temperature

Then we know that with PTFE lined hot-ends, we need to set the HEATER_0_MAXTEMP to 265 so that we can't stupidly set the temperature above 250c and croak from toxic fumes.

Additional Information

Thank you

@ZhuDaHai ZhuDaHai added the T: Feature Request Features requested by users. label Mar 6, 2021
@ellensp
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ellensp commented Mar 6, 2021

Its not that simple... the value is not hardcoded to 15. its is what ever HOTEND_OVERSHOOT is defined as, default when not manually defined is 15.

Further the MAXTEMP is also tied to the thermistor your using

_MIN(thermalManager.heater_maxtemp[e] - HOTEND_OVERSHOOT, ui.material_preset[indh].hotend_temp)

ie it will use the minimum value between the HEATER_0_MAXTEMP-HOTEND_OVERSHOOT and the highest temperature value in the thermistor table you using.

Could all this be documented, sure, would it cause more headaches than it solves, very very likely.

@ZhuDaHai
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ZhuDaHai commented Mar 6, 2021

// The max settable hot-end temperature will be less, according to the HOTEND_OVERSHOOT parameter, 
// or the default of 15 degresss less, if not defined

@thinkyhead
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Further the MAXTEMP is also tied to the thermistor your using

Oops! You're looking at the function that starts heating based on a preset, and it is being limited to what is (now) called the max_target_temp for the given hotend.

@thinkyhead
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thinkyhead commented Mar 6, 2021

This should get their attention…

/**
 * As an operator of a 3D printer it is VITAL that you understand the concept of "overshoot."
 * If you set the target temperature right at MAXTEMP you must be trying to cause a MAXTEMP error.
 * If you have observed your printer heating, you know that it can "overshoot the target" by a
 * lot, especially before you do your PID tuning. Marlin sets reasonable OVERSHOOT values to
 * prevent accidental MAXTEMP errors. If you like MAXTEMP errors, set HOTEND_OVERSHOOT to 0.
 */

@thinkyhead
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thinkyhead commented Mar 6, 2021

Then we know that with PTFE lined hot-ends, we need to set the HEATER_0_MAXTEMP to 265 so that we can't stupidly set the temperature above 250c and croak from toxic fumes.

Sure… But the typical error would be in unintentionally setting the max too low, not too high, right?

@thisiskeithb
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Breaking out or warning about HOTEND_OVERSHOOT & BED_OVERSHOOT would be a good idea. I'm starting to add a comment on my configs with the overshoot math factored in:

#define HEATER_0_MAXTEMP 310 // 310 - 15 = 295
#define BED_MAXTEMP      132 // 132 - 10 = 122

@thinkyhead
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thinkyhead commented Mar 6, 2021

I must admit, I am slightly annoyed. In my frazzled condition I am wishing that this was a PR and not just a FR. It would have taken less typing and less of our time. The website lacks a good section about this too, and that is open source. If it's worth complaining about, it should be worth doing…. Ok, rant over. Apologies… Clearly I need sleep.

@thisiskeithb
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Extending the options are easy enough. I added the disclaimer from above as well: #21273

@thinkyhead
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Maybe I should tone it down … or go the other way: "Listen here ye bastards…!"

@thisiskeithb
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github-actions bot commented May 6, 2021

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.

@github-actions github-actions bot locked and limited conversation to collaborators May 6, 2021
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