Hi Rick, For good AC controllers, it is required to generate the AC waveforms not only of the correct frequency and phase, but also the right voltage. The voltage level should be high enough to generate the current (torque) to let the AC motor behave properly (a synchronous machine should never fall out of sync, so the torque generated must be high enough to match the requested change in speed (mechanical torque) or you could create situations where the motor starts skipping in the same way that a worn sprocket/chain allows a chain to skip a tooth. For asynchronous machines it is less of a problem - you simply need enough current to generate the torque or the field will turn without the motor following. When the motor voltage reaches max that is exactly what happens - you can't generate as high torque as you like so the motor power starts getting limited by the voltage (back EMF). There are intricate control methods to weaken the field even in an AC motor and even in a PM motor (Prius uses this) to allow higher top RPM than the magnetic field would otherwise allow.
But yeah - both DC and AC motors use their controller as voltage transformer during some part of their operation. Cor van de Water Chief Scientist Proxim Wireless Corporation http://www.proxim.com Email: [email protected] Private: http://www.cvandewater.info Skype: cor_van_de_water Tel: +1 408 383 7626 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Thursday, December 27, 2012 11:34 AM To: [email protected] Subject: Re: [EVDL] 9" motor Mishap Quite right, I've been following these debates for many years. I have one point (or more of a question really) that I can't really get over as to why to go with the AC over the DC. Can AC controllers function as voltage transformers in order to allow the use of a higher voltage battery pack in order to compensate for battery sag that might keep you from achieving max power and holding that power to max set RPM in your controller output. For example a modern 300V input DC controller can easily be set to an output voltage to match a lower motor voltage requirements. 250V in 170V out for a 9". The advantage here would be to reduce battery currents and keep them within their proper C ratings. This way you get every Kw of controller you paid for right up to your set RPM. Does this make any sense or have I missed something? Is there a lack of flexibility with AC or do I just have to plan better? Rick Miller In a message dated 12/26/2012 10:24:36 P.M. Central Standard Time, [email protected] writes: On 26 Dec 2012 at 18:17, Cruisin wrote: > I guess the DC [motor] people saved a nickel and now lost a dime. > lets hear from some of the DC diehards Ah, memories. This takes me back to 1996! Nothing like a good old fashioned EVDL AC vs DC debate. ;-) Maybe we can also revisit the flooded vs AGM battery battle. ;-) David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to "evpost" and "etpost" addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
