Is there a standard setting for the microstep jumpers?
Originally shared by James Kasper - CBWP
Coming along…
What is the “standard” voltage for the ramps? All the reprap stuff says 12-35
Pololu says 8-35 is ok for their board. I am using basic nema 17 steppers, one is from adafruit, the other 4 are from sparkfun. They are the standard 200 steps/rev and the coils ring out to about 33.5 ohms each.
Do most people use 12v because pc power supplies are common or is the higher voltage better. I have been doing some reading about the .707 (rms basically)something something. Darn it I can’t remember if that was amps or voltage now. I think reducing amps reduced torque a little, but heat like twice that.
I noticed the only thing that 11a circuit fed was D8 fet, seems like that is the extruder heater. If my supply can feed 20a, I can just bridge them.
I also read about not feeding more than 12v to the mega…
So is 12v the standard or is 24 or something better?
The Pololu drivers do not change voltage, they put out the full input voltage, and they limit the duty cycle in order to control current.
Now, the stepper phases are inductors, and putting an inductor in series will have a similar effect to putting a capacitor in parallel, smoothing out the voltage so that it will look more like a lower constant voltage, but that’s not what the driver is putting out.
That’s exactly what the second paragraph of my last comment was addressing.
The reason you need a higher voltage is so that you run at no more than a 20-33% duty cycle for normal holding. The other 67-80% is held in reserve for spiking the duty cycle higher so that you can overcome that smoothing effect and change the average voltage faster.
That depends on the rated voltage (which is actually just the product of the rated current and phase resistance) of the motor. If you use a 12V-rated motor, running it off a 12V supply doesn’t give you any duty cycle reserve. If, however, you’re running a motor rated for 2.4V, you will probably have to have a pretty high step rate to see any benefit from increasing the voltage over 12V.
Of course, phase inductance and phase resistance both affect how fast a phase will energize at a given voltage, but these factors are all tied together, so you won’t find two motor with very different phase inductances where all the other specs are similar.
I read the other post.
I guess I will wait till I get my drivers to see how they go and look for something with more volts in my collection… I am not sure what I have with decent amperage. Pretty sure I would have ordered the 12v heater. I will have to check when I get home.
When I ran on 18v the motors were fine, but the fet for the bed heater burned out and damaged my controller board (using teensylu) that’s one of the reasons I want to design a new controller.
I know it’s rude to laugh, but I have had some components do that. It is cool if you ever get to be lucky enough to see a heavy solder trace become molten right before it goes black and opens somewhere lol
I have found a few pc power supplies that only have 6a on the 12v (little 200w units) but I have more to open. I did find an old hp inline block that is 19v 4740mA if the motor current limits are set near 1a that could drive the motors and the 12v could do the rest.
Does that sound doable? in theory each motor winding was about 33.6 ohms and I just measured the supply and it is @21v so that would be .625 amps and if all 8 halves of the 4 motors were at 0 hz or steady on whatever, they may be pulling 5a. That doesn’t happen though right? and with pwm or multistepping, they are not at 100% duty right?
I still have to find something for the bed I know.
I have a larger power supply, but I am kind of using it to drive an amp and some kickers.
I thought Two windings are always powered at once.
Current usage in stepper motors is weird, because of how the controllers work. Only at peak usage will it see maximum current, but i think it was like 90 degrees out of phase. You can check the Allegro datasheets if you’re really interested. Most firmware disables the steppers if they’re not moving, which really saves on current and keeps them from overheating. There is also a sleep mode for the drivers, but I’ve never seen it used.
Don’t worry about the voltage you’re giving the motors, just worry about the current. The stepper drivers are current controlled, and not voltage. However, at a higher voltage the stepper drivers may run hotter.
Or I might be completely wrong…
I dont know how the multistepping works because it cheats somehow. I have read about it before. it’s not phase angle fired like the inverters at my work are, but they get portions of the normal current or something.
I remember way back when, programming the arduino to drive it directly. (in whole steps)
I just looked it up. This is from the arduino stepper example…
The sequence of control signals for 4 control wires is as follows:
@John_Ridley That’s the general idea, though if those 1/16 and 15/16 numbers were correct, you would be approximating a sawtooth wave instead of a sine wave.
That’s why I said approximate. Its actually a square wave, but it’s modulated to approximate a sine wave. Approximating a sawtooth wave would result in the microsteps not turning the motor the same amount.
The driver produces a square wave, but the phase inductance in series will smooth it the same way a parallel capacitor would. You should not try to run the driver without the motor connected.
