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Registered Member #1623
Joined: Tue Aug 05 2008, 03:31PM
Location: The Netherlands
Posts: 39
You're spot on, the only thing when using the schematic you posted is that I recommend to replace the 1N4007 diodes with some fast recovery types. Although there are freewheel diodes in the transistor package included no specifications of that diode are given so use external diodes.
You can connect the motor directly to the H-bridge with no problems, the current limiting was because I assumed you're motors have a low coil voltage. My NEMA steppers have a coil voltage of only 3,6V (bipolar) but I'm driving them with 24V for increased speed. However when you do this you need to control the current in the motor, but in your case no current limiting in needed since your input voltage doesn't exceed your coil voltage.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
I see...The motor says "Recommended 24V 1.4A power s upply" since each phase is 0.7A. But when looking at the datasheet...
It says Voltage 7.8 -- 0.7A -- 11.2ohms
Now how they can say recommended 24V PSU, I don't know. So if I want to use 24V, I'm going to have to monitor the current and use power resistors to kill it down to 0.7A? I probably will use the fullbridge schematic for my driver setup... http://www.cs.uiowa.edu/~jones/step/circuitsf/9.gif This one
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
24v supply?
It depends whether you want to work at high speed or not.
Stepper motors have a large inductance, and the current takes an eternity to build if you just apply the 7v needed to push the current through the resistance. If you use extra voltage, the current will rise faster, by the magic of V=L*dI/dt. I suspect that you won't acheive their rated steps per second unless you use at least their suggested power supply voltage.
Obviously you have to do something with this extra voltage. The cheap and cheerful way is to use a power resistor in series with each coil, the pro way is to use a switcher programmed to deliver an output current rather than voltage.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Ya, I saw this done on an instructable tutorial but instead they used 1W - 20W lamps. Same concept. So If I want to use my SMPS 24V 4A psu, I need to resistor my stepper so the phase, as the schematic says, gets 7.8V Correct? I feed it the 24, but make the coils run 7.8V?
Ordered my parts/drivers today, now that I understand how to connect them all to work with Mach 3. I thank all of those who offered to help me! Will let you know how it all goes.
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bipolar stepper help
