[ezland00]

2 resistors means one resistor for phase 1,2 and one for phase 3,4 right? Just did a search for some power resistors at Mouser.com. Is this the right resistor?resistor by the way what is the 1% mean

I don't know what FET's are, but i'll just use resistors.

EZ

[digiot]

If a diode is placed in series with each switched lead of the stepper, would it be appropriate to enter (in steppercalc) .6v less than the supply voltage, due to the voltage drop across the silicon junction?

TIP120's are darlingtons. What voltage drop can be expected across each transistor.....1.2v? Or is that already considered by steppercalc?

The reason I'm asking is, that the values listed in this discussion are almost exactly what I am planning to use. I have 3A, 3V, 1ohm, 191 oz-in. (Vexta PK268-03A) steppers. I have the steppers turning now using a 12v supply, a 2 ohm 25W resistor on each phase. Is this close? I'm using Kleinbauer's Piker.

The motor and 'sinked transistors get somewhat warm, but you don't want to touch the resistors! I've got the 'cement' resistors and I'm still trying to figure out the best way to mount them on a heat sink. I can line up 4 resistors over a Pentium4 heat sink/fan. Would RTV silicone conduct heat adequately, or is it an insulator?

[balsaman]

2 resistors means you are using 2 per motor. 1 resistor means you are tieing the center taps together on one resisitor.

1% means it is accurate to 1% of its rated resistance.

You controller will use transistors or FET's to switch the windings on and off. Transistors drop about 1 volt across them, fets do not, so the calc is a little different for each.

Steppercalc subtracts 1 volt from the ps voltage if you are using transistors, it ignores the voltage drop across a FET.

Eric

[MrBean]

The resistors mentioned look like wire wounds. Doesn't this increase the inductance, as it is in series with the motor winding, which defeats the object of running higher than rated voltage to improve the slew rate. The higher inductance brings the slew rate problem right back again.
I have not used power resistors, so don't know how much effect the increased inductance has.

If anyone has/ is using these. How do they perform against running with the motors at the rated voltage and no current limiting?

[balsaman]

The very small winding on the resistor causes a negligable amount of inductance.

Eric

[ezland00]

balsaman,

I decided to use one resistor. Here is the result for the calculation 1.43ohm, and 51.60watt. will 1.5ohm and 50watt power resistor work?