On Sunday 02 February 2003 13:28, somebody wrote > Declan Moriarty schrieb: > > A design I am looking at has replaced a DC motor with a 3 phase AC > > motor running off the same DC voltage. > > > > Can I look at the DC motor specs, and conclude anything about the > > AC motor? > > > > At this stage, it's really total current per phase I'm interested > > in. I am aware that there will be 2 phases positive and 1 negative > > (or 2 negative and one phase positive) at any time power is > > applied. > > I am not shure, whether i understand your question right: > > You want to replace a DC Motor with a 3phase AC ? > When yes - you have to specify the 3phase motor ? > Tell me if i am correct and tell me what kind of supply is available > and what is the speed range of the motor. > i hope after that i can give you better help > > The Dc motors had running current of ~80 - 100A with stall curent limits at ~400A and the A.C ones are slightly more powerful, but I have no specs at all. I would like to know enough to specify an A.C. motor controller. Specifically, the max current per phase and current limit to equate with the figures above. That's what I need to know.
Here's my analysis: The Ac motors will have a higher applied voltage, because 1. Driving with a squarewave instead of a sinewave raises the rms value of the waveform. 2. The fact of 3 phases instead of 1 also adds to the power applied, reducing current. 3. A further increase in that many of the DC motors were series wound (ie field in series with armeture). I believe the Speed is not an issue: The DC motors were geared to suit the dynamics of the motor. It appears the A.C. motors were downgeared by comparison, as this allows higher frequency lower current operation. I can soon confirm that. These motors take load from zero speed, and at any speed, the phases will be 2 low and 1 high, or 2 high & one low, when power is applied; therefore I reckon there's no saving in total current per phase. If one can calculate a current saving, I'd like to know about it. -- Regards, Declan Moriarty. -- Author: Declan Moriarty INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
