Powerlolu - Powerful 10A Stepper Motor Driver
by fluidfred, published
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.
* 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
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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.
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