Re: Stepper Spec , Etc

Hi,
At one point you mention "Dropping" resistor, and at another you
mention "Discharge" resistor.

A "dropping" or "ballast" resistor is used to limit the current to
the stepper motor. If you are using Geckos (or any other drive that
uses PWM to limit current) you should not need these.

On the otherhand, if you have a linear power supply with nice big
caps, you don't want the capacitors to remain charged after the main
power has been shut off. You put a discharge resistor across the PWR
(+) and GND(-) so that after power has been removed a charge will
disapate through the resistor.

PS, As long as your questions are regarding CAD, CAM, EDM, DRO, I
would guess no question would be too basic for the group.

Jeff
http://www.xylotex.com


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "irj615 <i.jones@n...>"
<i.jones@n...> wrote:

> Hi,
>
> Firstly, thanks to all who replied to my earlier post on PSU for my
> first project, especially Terry and Robert Campbell. Excellent info
> and I am ordering the parts to get started. I still can't quite
> comprehend the "dropping resistor" I need between the driver and
> stepper motor. Is there a general size used or do I need to
> calculate the exact spec for my intended setup?
>
> Also, I see on the CNCKits website they use a pre-charge circuit

for

> the power on switch in the power supply. This looks fairly
> straightforward. Are there any links on how to wire this type of
> circuit and the resistor to use ?
>
> Finally (for now :-), The engineering logic I have applied in
> specifying the Nema 34 700 oz inch motors is pretty lame, in

that "I

> think they look big enough" Is there a more scientific approach to
> calculating the torque required (without specialist equipment
> hopefully). My first step is to try and couple directly to the end
> of the old lathe leadscrew shaft, engage the carriage split nut and
> have a Y axis solution. Does this sound a bit too ambitious?
>
> Please let me know if these questions are too basic for this group.
>
> Thanks guys