Powerlolu - Powerful 10A Stepper Motor Driver
Description
The existing Pololu boards found in common RepRap 3D printers are at their limits when driving the 2 Nema17 z-axis stepper motors in parallel. Continuous z-axis movement can cause the board to overheat. These boards hardly drive stepper motors bigger than a Nema17. To avoid overheating or to drive larger motors a more powerful driver board is needed.
The Powerlolu board enables the use of bigger stepper motors for a wide range of uses. This could be the conversion of manual milling machines into computer controlled milling machines (CNC-Machines) using the affordable electronics such as Arduino and RAMPS. Building 3D printers with a larger print volume or with larger extruders would be possible.
Tested the design by connecting a Nema43 stepper motor by Nanotec Electronic (capable of 6.6 Amps per coil, Torque 2000Ncm, Weight 8,4kg) to a Powerlolu attached to a 3D printer's RAMPS X-port.
A short video of the new driver can be seen on YouTube at youtube.com/watch?v=G9FWvhZI7rs .
After two hours of motor usage the Powerlolu board only got luke warm.
The schematics for the Powerlolu driver are freely available at github.com/fluidfred/powerlolu.
Technical specifications:
* 3-wire control with DIR, STEP, Enable-signal, compatible to the Pololu board
* Supply voltage of the stepper motor from 12V to 50V
* Adjustable stepping via SMD-jumper, 1, 1/2, 1/4, 1/16 (default) steps
*Precision pot to adjust the current limiter
no extra heat sink required due to passive cooling
* Molex snap-on connector for connecting the RAMPS board to the Powerlolu
* Dimensions PCB: 75.5mm x 65mm
Instructions
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I also noted a 470k resistors between G and S. It seems unnecessary to have them, but would indeed require a bigger bootstrap cap, because it will discharge through the resistor.
I took the input gate capacitance and multiplied by 20: Ciss * 20 = 480 pF*20= 9600 pF. I take 10nF because its more available but 6n8 should suffice already. Using gate charge is perhaps the more elegant way to calculate, but there is a problem in your formula, since C = Q / U. however the results seem almost correct. 12nF. I don;t understand 3V though. I would assume at least 12V (VREG) for Ugs. Maybe it's not all that critical.
I calculated it as follows . Qgs=3.7nC, Cgs=Q*Ugs = 37nC*3V = ~11nF * 10 = 110nF. I used 100nF. I tested it and it works for a voltage from 12V-48V. Please let me know if your calcualtion is different.
the datasheet of the A4989 suggests a value for the bootstrap caps of 10-20 times the total gate capacitance of the MOSFETs. With the used IRLR024N I calculate 10nF but schematic says 100nF. Any particular reason for it?
What is the IC being used here? Looked on github but can't see anything, that shows what the chip actually is?
powerlolu driving two Nema 23 stepper motors connected to a PRotos. http://www.youtube.com/watch?v...
thinking of a board for power servomotors as well. Gives 3D-Printing a new dimension - e.g. printing houses made out of concrete. ;-)
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If you try it with a 10nF cap, please let me know whether it works.