3d printer heater cartridge modification with Picaxe.

Puuhaaja

Senior Member
I have build my own version of open source 3d printer. Link: https://www.ultimaker.com/pages/our-printers/ultimaker-original

I have ordered those parts all over the world and many of those parts I have done by using lathe and milling machine.
Problem(Challenge) is that Ultimaker is using 19V and my non original heater cartridge is made for 12V. I have measured that when using 19V my heating cartridges's power is about 90W. It should be around 40W. 3d printer's software controls heating power using mosfet and pwm.

I have planned that I could drop heating power from 90W to 40W using Picaxe and mosfet. Maybe I will do that using ex. 10ms cycles when Picaxe controlled mosfet is on and off. Any ideas if this would be possible? Is there any things to take in to account because now there would be two mosfets between cartridge and voltage sourge.
 

papaof2

Senior Member
Using a MOSFET with sufficient power capability and a MOSFET driver (the PICAXE can't provide enough drive for most MOSFETs at this power level), you could drive it with the PICAXE's HPWM.

However, would it not be simpler to use a separate 12 volt supply, such as this one from ICStation?
http://www.icstation.com/product_info.php?products_id=1905

The next question is whether the heater temperature needs to be adjusted for different types of filament. Is that capability already part of the printer electronics? If so, is it compatible with an external PWM of the heater power?
 

Puuhaaja

Senior Member
Is there any way in the 3D printer software to change the current going through the heater cartridge?
I haven't checked that but i'm sure it's possible because it's open source code and Ultimaker uses Arduino mega boards. I have not skills to modify that code so that's the reason why I am planning to use two mosfets. Anyways good idea.

the PICAXE can't provide enough drive for most MOSFETs at this power level
I think that mosfets are voltage controlled so controlling them will not consume much millAmps. Anyways I think that it's important to have right mosfet which is fully saturated at 5V

Ultimaker uses Cura software and you can choice the filament type that you are using and electronics will adjust right temperature for filament. Printer's electronic will adjust heating power using pwm with mosfet. My plan is to add one mosfet more which will reduce the heating power 50-60% after first mosfet. I have to do this because my heating cartridge is about two times more efficiency than Ultimaker's original. I suppose that it's compatible with external pwm. At least I will test it. Hopefully not with blue smokes.
 

marzan

Senior Member
I have built a Prusa i3 printer that uses the Arduino mega board. They are all bsically the same electronic setup. There are many tutorials on how to change the settings of the arduino software. although time consuming, it is definitely easier than what you have planned.Do a search for "Arduino mega configuration" and that should find what you are looking for.

Marz.
 

Goeytex

Senior Member
I think that mosfets are voltage controlled so controlling them will not consume much millAmps. Anyways I think that it's important to have right mosfet which is fully saturated at 5V
While MOSFETS are indeed "voltage controlled" ... try driving one with 5 volts but only 1 ma of current. It will perform terribly and overheat. Voltage is not the only consideration. There is gate capacitance to deal with. The gate capacitance of a MOSFET must first be overcome before the MOSFET will begin to turn on. This takes time. During this time the MOSFET is in its linear region where it generates a lot of heat. The time the MOSFET is in the linear region is a function of current, not voltage. The 20ma supplied by a Picaxe or (any microcontroller) pin is not enough for efficiently switching a MOSFET at anything but very slow speeds. A 2 amp MOSFET driver will over come the gate capacitance in a few nanoseconds, allowing the FET to switch rapidly and efficiently, with minimal heat dissipation.

So don't disregard the advise of experienced users too quickly when they suggest a MOSFET driver. There is a good reason. for it.
 

Puuhaaja

Senior Member
So don't disregard the advise of experienced users too quickly when they suggest a MOSFET driver. There is a good reason. for it.
Nope. I'm sorry if it sounds that because english isn't my mother tongue. The reason Why I opened this thread was to ask for you all that is there somekinds of effects that has to tako into account. Now I know that there really is. Goeytex: Your explanation about gate capacitance was very understandable I didn't know that earlier. I checked some formulas how to calculate mosfet's driving current but didn't specialize much for them because I haven't yet chosen the mosfet I will use. One othe optsion is to find enough slow switching cycle that Picaxe can handle that. So...Is there any kind rule of thumb eplanation that how fast mcu can controll basic logic level mosfet. Is it 20ms....100ms etc..

@marzan I checked some ultimaker code, but at this moment I don't have skills to do that. Later on I will search more about that because I will test some heating nozzle modification.

@papaof2 I will use normal computer atx power supply and voltage transformer. Maybe it would be possible to take one 12v line to 12->19v transformer and other line for heating cartridge but then there's too much messy power lines..
 
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