I will most likely just repeat what you already know, sorry about that :)
I think that with a higher voltage input to the fans a higher torque is being produced within each coil, as opposed to 12V. So the fan requires more force to 'switch' from one coil to the next.
So with an incorrect (I am not sure what that would entail) starting frequency the transition happens too fast (or uneven) and you end up with a 'stuck' fan. Once the fans turns it will spin at lower frequencies because of inertia.
So at least you know that this seems to be the problem.
With respect to the #define: are you using the " Conditionals_LulzBot.h" file in your Marlin FW? If there is no comment '//' symbol before the #define then it will be used within the FW.
To be honest I am not sure how the LulzBot FW setup works. In fact, I have no idea. But I would suggest to simply add the following line in your Configuration.h file (somewhere close to the "Extra Features" section):
Just make sure it is above the following code:
Having said that I should probably never have replied to you comment in the first place. But maybe simply adding the suggested code solves the problem (if implementing the FAST_PWM_FAN is the solution).
Do note that there are standard settings in the Configuration.h files (in bold) that you could play around with, in which case you may not need to use the LuzlBot file(?):
I think that with a higher voltage input to the fans a higher torque is being produced within each coil, as opposed to 12V. So the fan requires more force to 'switch' from one coil to the next.
So with an incorrect (I am not sure what that would entail) starting frequency the transition happens too fast (or uneven) and you end up with a 'stuck' fan. Once the fans turns it will spin at lower frequencies because of inertia.
So at least you know that this seems to be the problem.
With respect to the #define: are you using the " Conditionals_LulzBot.h" file in your Marlin FW? If there is no comment '//' symbol before the #define then it will be used within the FW.
To be honest I am not sure how the LulzBot FW setup works. In fact, I have no idea. But I would suggest to simply add the following line in your Configuration.h file (somewhere close to the "Extra Features" section):
#define LULZBOT_FAST_PWM_FAN
Just make sure it is above the following code:
// Increase the FAN PWM frequency. Removes the PWM noise but increases heating in the FET/Arduino #if defined(LULZBOT_FAST_PWM_FAN) #define FAST_PWM_FAN #endifIf this is defined then, as far as your Configuration.h file is concerned, the PWM changes will be implemented. It may affect the normal operation... I don't know, as I do not know how the code is implemented into the Marlin FW.
Having said that I should probably never have replied to you comment in the first place. But maybe simply adding the suggested code solves the problem (if implementing the FAST_PWM_FAN is the solution).
Do note that there are standard settings in the Configuration.h files (in bold) that you could play around with, in which case you may not need to use the LuzlBot file(?):
// Increase the FAN PWM frequency. Removes the PWM noise but increases heating in the FET/Arduino //#define FAST_PWM_FAN // Use software PWM to drive the fan, as for the heaters. This uses a very low frequency // which is not as annoying as with the hardware PWM. On the other hand, if this frequency // is too low, you should also increment SOFT_PWM_SCALE. //#define FAN_SOFT_PWM // Incrementing this by 1 will double the software PWM frequency, // affecting heaters, and the fan if FAN_SOFT_PWM is enabled. // However, control resolution will be halved for each increment; // at zero value, there are 128 effective control positions. #define SOFT_PWM_SCALE 0