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

>I have yet to find a good paper on transformer sizing. I think that the 2/3
>rule yields a transformer which is far bigger than necessary. It also
>ignores the fact that basically the same power motor can be wound for low
>current with high induction or high current with low induction. Real power
>delivered through a motor is not a function of motor current. I'll relate a
>recent test:
>
>Running 4 each size 34 motors at 6 amps per phase. These were 1240 oz in
>motors, pretty big ones. I loaded the motors by direct coupling to 4 other
>motors which had all leads shorted in order to create as much load as
>possible. I adjusted the motor speeds while watching the AC current into
>the transformer in order to achieve the highest possible power load. While
>running 4 bipolar motors at 6 amps, that's 12 amps per motor or 48 amps
>current delivered by the system. At the 70 volt bus, one might expect 3,360
>watts if regeneration were not part of the equation. In fact, the highest
>power I recorded into the transformer was 300 watts. I ran this test until
>everything came up to temperature. The motors were running around 180 F
>even with a fan on them. The stepper drivers were around 130 F, but the
>capacitor on the stepper drivers was up to 180 F (bad news). The dc
>rectifier was about 209 F and the 640 VA transformer was barely 10 F over
>room temperature. The temperatures suggest that the system was running
>plenty hard, yet the transformer was the least taxed of anything in the
>system.
>
>Mariss suggests that the most a large stepper can deliver is about 100 W of
>power. I think this is a very reasonable way of looking at things and
>probably better than motor current. My feeling is that, if using larger
>steppers, 110 VA of "rectifier rated" transformer or 125 VA of standard
>transformer per motor is probably plenty. In the context of the test above,
>I was driving 4 motors using 300 watts. Given a better load system I might
>have be able to suck up 400 watts. A 440 watt (VA) transformer would
>probably have been fine.
>
>I have not done any similar testing with any motors under 500 oz inch so I
>cannot provide any direct references there, but one might suppose that the
>system dynamics scale in a linear fashion. If anyone has references to a
>technical discussion that is a little more specific than the 2/3 rule, I
>would certainly like to know about it.
>
>Greg
>
>
>-----Original Message-----
>From: Scott Riddle [mailto:sariddle@...]
>Sent: Wednesday, December 31, 2003 12:37 AM
>To: CAD_CAM_EDM_DRO@yahoogroups.com
>Subject: [CAD_CAM_EDM_DRO] stepper driver-transformer sizing question
>
>
>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.
>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). I would like
>to just buy 1 transformer to supply power to 2 or 3 steppers. I am
>not looking for high speed mainly low speed high torque. Can someone
>help me on sizing the transformer required? Would I also need to run
>resistors on series with each driver to limit the current each driver
>would be able to recieve?
>
>Thanks
>Scott Riddle
>
>
>Addresses:
>FAQ: http://www.ktmarketing.com/faq.html
>FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
>Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
>Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@...,
>timg@...
>Moderator: pentam@... indigo_red@... davemucha@...
>[Moderators]
>URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
>OFF Topic POSTS: General Machining
>If you wish to post on unlimited OT subjects goto:
>aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
>you have trouble.
>http://www.metalworking.com/news_servers.html
>
>http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
>sister site to the CCED group, as many of the same members are there, for OT
>subjects, that are not allowed on the CCED list.
>
>NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
>DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
>bill
>List Mom
>List Owner
>
>
>
>Yahoo! Groups Links
>
>To visit your group on the web, go to:
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/
>
>To unsubscribe from this group, send an email to:
> CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>
>Your use of Yahoo! Groups is subject to:
> http://docs.yahoo.com/info/terms/
>
>
>
>
>Addresses:
>FAQ: http://www.ktmarketing.com/faq.html
>FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
>Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
>Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@..., timg@...
>Moderator: pentam@... indigo_red@... davemucha@... [Moderators]
>URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
>OFF Topic POSTS: General Machining
>If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble.
>http://www.metalworking.com/news_servers.html
>
>http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list.
>
>NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
>bill
>List Mom
>List Owner
>
>
>
>Yahoo! Groups Links
>
>To visit your group on the web, go to:
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/
>
>To unsubscribe from this group, send an email to:
> CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>
>Your use of Yahoo! Groups is subject to:
> http://docs.yahoo.com/info/terms/
>
>
>
>
>
>