Re: stepper driver-transformer sizing question

My application I am using these motors for is kind of a art'see one.
It is called a egg plotter. It uses 1 stepper to rotate a egg and the
other to rotate a pen around the egg. I am doing this project for my
daughter and for me to get my feet wet with steppers & controls. Long
term I am looking to convert my 3Hp Index V-mill. (when I get more
money for larger steppers and drivers)

One question I forgot to ask was what voltage should I be looking at?
Should I go as high as possible(driver limit)? My application is not
even going to have 1 of the steppers ever make a full rev. It will
just rotate back and forth about 120°. I see what you mean about
gearing to get a better torque advantage and more RPM's on the motors
but I think this little project shouldn't require any reduction.
On Ebay I found a bunch of DC power supplys (I used search words:
pyramid power supply). They put out around 15V and 10-25A depending
on which model you get. Would these be good or should I look for a
power supply at around 40V and at least 4A?

Many thanks for your reply! ;-)
Scott Riddle







--- In CAD_CAM_EDM_DRO@yahoogroups.com, Robin Szemeti <list@r...>
wrote:

> On Wednesday 31 December 2003 06:36, Scott Riddle wrote:
> > I am a little confused on sizing a transformer to drive some

small 30-

> > Oz-in bi-polar steppers. They are rated at 3 amps/phase 2.1Vdc and
> > the IMS IB462 drivers I have are good for 12-40V 0-2Amps 160Watts.
>
> yes ..and no. You would never see 160 watts, because to deliver the

40V at 2A

> the motor would have to be spinning, and that would imply that both

phases

> are not on continually ...
>
> > What I am thinking is that the motors can take 6 amps (3 per

phase).

> > But can the motors only take 12.6 watts (6A x 2.1Vdc).
>
> nope. the 2.1Vdc is the DC voltage drop, whilst in motion the

signal is AC

> and you will see more than 2.1V across the windings ..
>
> >I would like
> > to just buy 1 transformer to supply power to 2 or 3 steppers.
>
> Size the transformer at 2/3rd of the motor plate rating .. in this

case your

> stepper drives are not up to delivering the full current the motor

can draw,

> so size the power supply for that, 2/3 * 2A * 3 motors = 4A. If you

want to

> build a supply that will be able to drive the motors to their full

potential

> if you got hold of some 3A stepper drives, then build a 6A supply ..
>
> > I am
> > not looking for high speed mainly low speed high torque.
>
> are you SURE about that? .. if you are not driving your motors to

AT LEAST

> corner speed, and preferably above, you are not getting anything

like the

> amount of power out of them that you can ... if your application

needs lots

> of thrust at low speeds, gear the steppers motors down a LOT ..

contrary to

> what some people believe, stepper motors need to spin to perform,

if they are

> not spinning to at least corner speed, you have got your gearing

wrong, and

> you will be getting less thrust out of them than you could, plus

bigger steps

> and worse acceleration. For high torque output you need to gear the

motor

> down a lot!!
>
> If you have geared the motors to always run below corner speed (ie

slowly)

> then you could reduce the size of the supply too, as you will never

be able

> to operate the motors in the region where they can use the current

available.

>
> > Would I also need to run
> > resistors on series with each driver to limit the current each

driver

> > would be able to recieve?
>
> No, thats the job of the stepper driver ... that will handle the

current

> control.
>
> --
> Redpoint Consulting Limited
>
> Real Solutions for a Virtual World
> http://www.redpoint.org.uk