Re: [CAD_CAM_EDM_DRO] Re: Stepper Voltage and Current question

starcast82 wrote:

> I plan on limiting the current through transistors not resistors.
> This way when I pull 25 volts or 50 volts it will be limited to 2
> amps to the motor. I may also use FET's to keep the heat down.

If you do this linear, FETS or bipolar transistors will dissipate the same
heat as a resistor. (They will allow a faster current rise, however.)
So, don't think that without switching technology, that magically
putting FETs in the circuit will make the heat go away.
(25 -3 V) * 2 A = 66 W for each phase of each motor.

> I just
> need to know if each winding is rated for 2 amps or is it divided
> between the 4. I was just curious performance wise how much voltage I
> needed. I may add a chopper cicuit by adding a 555 timer to the
> tranistor circuit but am working on the basic circuit first and try
> to make sure what I need voltage and current wise.

A 555 timer is not a good choice for a chopper drive. You need to
allow current to rise to the setpoint, and then turn off the high-side
transistor and allow the current to circulate until it falls below a setpoint.
You can do it with other components, but eventually the 555 is just the
wrong part (I think).

> Gecko drives are nice but at $130 a piece I figure I can design my
> own a lot cheaper since this will be my first table and can always
> upgrade if the need be.

Unless you are an electrical engineer with some experience in power
circuits, I'm afraid you will smoke a lot more than $130 x 3 before you
get it right.

Jon