How to step down stepper motor voltage?

Question

So recently I started building a 3D printer out of old DVD disc drive steppers, because they are complete with rods and steppers. To drive them, I plan on using a Geeetech Printr Board clone ( http://www.geeetech.com/new-version-reprap-printerboard-reprap-electronics-sets-p-653.html ) but the only problem is that the board drives 12v steppers, while I have 5v steppers. Is there any way I can step down the voltage coming from the board to the steppers? I will be using a 12v stepper motor for the Bowden extruder so I would only need to step down the X,Y, and Z to 5 volts.

My idea of the project was this: http://www.instructables.com/id/eWaste-60-3DPrinter/ But I already had this Geeetech board lying around so I want to use it.

Thanks!

D_Hersey · Accepted Answer

You can. Measure your coil resistance(s) and insert resistors 7/5ths as large in series with each.

bradnorwood · Answer

Are you sure it's 12 volts? Did you put a meter on it? My Printrbot board looks identical. Its 5volts and they cost around the same price. Mine has potentiometers for each motor which should allow some voltage control. I know, I had to step my extruder down some to prevent over heating and skipping. If you ever look to build a bigger system, that board will power it if it's 12v from the stepper drives. I'm interested in one now if that's the case for another printer later. Kysan electronics has a nice inventory of stepper motors for bigger projects but a $100 minimun...

D_Hersey · Answer

Most modern stepper drivers are current-sourcing chopper drives. They should allow for a fairly wide range of adjustment.

To digress, the coils of stepper motors have two params which characterize them to a first-order model. Resistance. The copper in the winding is long and thin. Positive reactance. The coiling of the coil, and the proximity of a magnetic core increase the effects of the magnetic field, we have an inductor. The resistance x coil current leads to heating (ustda say 'conduction, convection, radiation') and IR emission. In fact, if we heat the motor past the Curie point of the magnetics in the motor, the game is on hold. The inductance makes the impedance of the coil look larger when we attempt to change the current going through it. It sinks and sources potentials in an attempt to resist changes in current. 'til the energy in the magnetic field is depleted, if we are looking at things in a classical sense.

So, if we want our stepping motor to apace a republican at a buffet, we need to provide a supervoltage which we initially apply to the load, which we monitor. When the current required to get things rolling is established, we switch to a LV which is intended to help the motor rotor keep from moving under mechanically reactive load (enhance 'detent torque') or we cease the energization. Or some piece-wise linear approximation of the appropriate antilog. Anyway, the driver (if it is a feedback chopper) acts more off of current, time, R and L. The V (Russian: B) on the label of the motor is helpful in inferring the desired I by dividing by coil resistance.

The state of a motor coil has to do with the orientation of the constituent magnetic domains in its associated core. Whether they are just randomly hanging out, or if there is a bulk tendency. This has to do with the amount of current established in the coil a moment ago. V is the effort parameter. I is the flow parameter.