RE: [CAD_CAM_EDM_DRO] stepper driver-transformer sizing question

The capacitors of interest are those on the stepper drives themselves. They
will be more critical and suffer first from an insufficient power supply.

Missing steps can be created by a very large number of things. A better
quantifier of the power supply design is the bus voltage. If your
transformer is undersized you can see bus voltage drops even with a standard
voltmeter. My 73 volt bus never dropped below 70.5 volts. From that I
concluded that the transformer is was bigger than necessary. About a 4 to 6
volt drop is probably acceptable under full load. You can also size the bus
capacitor by looking at bus voltage, but for that you will need a decent
oscilloscope, not a volt meter, since the problems will occur at the
switching frequency of the drives which is much faster than a voltmeter can
react.

Greg

-----Original Message-----
From: Les Newell [mailto:lesnewell@...]
Sent: Wednesday, December 31, 2003 10:24 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] stepper driver-transformer sizing
question


I would agree with this. My tests were not a scientific as yours but I
came to the same conclusion.
My Bridgeport has 3x steppers running at 65V,7A using Gecko G201
drivers. Using the 2/3 rule my power supply should have been about
900VA. The power supply has a 500VA(not rectifier rated) toroidal
transformer with 3x 10000uF smoothing caps.
During testing I had the machine running really complicated 3D moves as
fast as possible to find how fast I could run it without losing steps.
The moves included lots of sudden changes of direction so the machine
spent a lot of it's time at max acceleration. After a day of testing the
steppers were hot to the touch but the transformer and caps were only
marginally above ambient.

Les