AC induction motors need to slip in order to develop torque. This means they will fall behind synchronous speed. For example, synchronous speed of a standard motor on 60 hz is 1800 RPM, but the speed at rated torque is normally 1725 RPM. This is explained better in the two references below....
Page 6 of this reference: http://www.ab.com/support/abdrives/documentation/fb/1019.pdf figure 2 of this reference http://www.ecmweb.com/mag/electric_minimizing_ac_induction/ OK, now with this as background, understand that slip is not what most people want. Normally you want it to go at the commanded speed with little speed variation despite variation in load. This is done differently in different types of AC inverter (VFD) drives. Volts/HZ: Most simple drive. The stiffness in velocity is dependent on the motor winding as noted in the graphs on the above mentioned references. The drive creates a 3 phase AC output and the motor turns proportional to frequency. The drive also reduces the voltage proportional to frequency so it does not go over current at lower speeds. (lower frequency into a fixed inductance would result in higher current unless the voltage is reduced). Expect 5% speed variation as the load changes. Sensorless Flux Vector, aka: sensorless vector: The drive senses the slip through characteristics of the electrical load and increases the frequency to adjust for the motor slip while under load. Expect 2% speed variation as load changes. Flux Vector: The drive has an encoder and knows exact motor speed as well as rotor angle. Magnetic field angle is adjusted dynamically to deliver very accurate speed or torque regulation. Expect 0.2 % speed variation or better depending on the nature of the load. I hope this helps. By the way, I have a large number of 1.5 HP VFD drives for sale if anybody needs one. These are standard volts per hz drives, new in the box, warranted for 1 year. The drives will operate on either 230 V single phase or 115 V single phase. They will operate 3 phase induction motors up to 1.5 HP and will run up to 120 hz (1725 motor will spin at 3450). Please contact me off list if you're interested, I'll send you a PDF datasheet. The drives are $165 to members of the list. Greg > -----Original Message----- > From: turbulatordude [mailto:[EMAIL PROTECTED] > Sent: Thursday, November 04, 2004 11:26 AM > To: [EMAIL PROTECTED] > Subject: [CAD_CAM_EDM_DRO] Variable speed drives > > > > > Hi all, > > I'm looking into putting a variable speed drive on my lathe and am > wondering about the different type of drives. > > I have seen ones optimized for HVAC, some constant torque, others > like sensorless vector control, flux vector.... > > > All the sales hype sound like anyone will run your motor and wash > your dishes. > > Can anybody help with what the differences are ? > > Dave > > > > > > > > Addresses: > FAQ: http://www.ktmarketing.com/faq.html > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/ > Post Messages: [EMAIL PROTECTED] > > Subscribe: [EMAIL PROTECTED] > Unsubscribe: [EMAIL PROTECTED] > List owner: [EMAIL PROTECTED], > [EMAIL PROTECTED], [EMAIL PROTECTED] > Moderator: [EMAIL PROTECTED] [EMAIL PROTECTED] > [EMAIL PROTECTED] [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 > > > > > > > > Addresses: FAQ: http://www.ktmarketing.com/faq.html FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/ Post Messages: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] List owner: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Moderator: [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED] [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: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
