OK, let me clarify what I was saying...
Stepper motors are current controlled. So a stepper motor controller tries to maintain a certain current flow through the windings. On a 3.8A motor, 1 amp will give plenty of torque without risking any damage to the motor.
The current control is normally implemented with PWM (Pulse Width Modulation) - This has the effect of producing a variable voltage. I'll explain why soon. The voltage source used for the PWM is much higher than the rating of the motor (can be up to 96 volts, 24V is typical). The reason for the high voltage is that it produces a current in the motor windings very quickly. That allows a fast PWM (approx 25KHz) which provides smoother control.
For a winding resistance of 0.33 Ohm, you only need 0.33 volts to produce 1 amp. That is when the motor is at standstill. As the motor starts to spin, the generated voltage (Back EMF) increases and opposes the power supply. So, for example, when spinning at 100RPM, the back EMF may be 20 volts, so you need 20.33 volts to produce 1 amp. It is actually mush more because the inductance has greater effect - but let's keep it simple.
So if you are just going to spin the motor very slowly, a 1.5 volt source seems reasonable, as long as it can deliver 1 amp without dropping in voltage (i.e. well regulated supply).
If you intend to spin faster, then you may find you need a higher voltage to accomodate the back EMF - trial and error will help you here.
How fast are you trying to step the motor?