tag:blogger.com,1999:blog-2270124316233555550.post3248327466477298031..comments2023-01-26T20:59:29.216-08:00Comments on Porsche 914 EV Conversion: Doing Vibration ResearchTimKhttp://www.blogger.com/profile/09059780797709299125noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-2270124316233555550.post-79140126095714913562007-10-01T08:18:00.000-07:002007-10-01T08:18:00.000-07:00The VFD just skips right over it. It seems a litt...The VFD just skips right over it. It seems a little strange (and not always smooth) to go from 39Hz right to 45Hz, but if the harmonic imbalance is gone, then it is better overall.Unknownhttps://www.blogger.com/profile/14640447834642177209noreply@blogger.comtag:blogger.com,1999:blog-2270124316233555550.post-71179310477697939362007-09-30T19:48:00.000-07:002007-09-30T19:48:00.000-07:00Hi Roger, thanks for the kind words. During these...Hi Roger, thanks for the kind words. During these experiments, I'm not even spinning the tranny, just adding the weight of it to the system. I actually replaced all the bearings including the input gasket during the rebuild several months ago. I have the new tranny mounts on order from Pelican Parts, but I'm not sure those will be enough.<BR/><BR/>Hi Carlo, you're right that the DMOC doesn't support RPM skipping. I'm curious, how does one accelerate through a particular RPM if the controller skips it? I've heard other people using the transmission to maneuver the engine around a particular RPM, but the motor still has to pass through it.<BR/>Let me know if you're in the area and I'd be happy to give you a tour (and a ride if the car is drivable).<BR/><BR/>Cheers,<BR/>TimTimKhttps://www.blogger.com/profile/09059780797709299125noreply@blogger.comtag:blogger.com,1999:blog-2270124316233555550.post-79248660934812765172007-09-30T12:46:00.000-07:002007-09-30T12:46:00.000-07:00Tim, for my day job, I work with boilers and pumps...Tim, for my day job, I work with boilers and pumps (with an emphasis on controls). As I mentioned before, I work a lot with 3-phase variable frequency drives on pumps. When we get vibrations, they are often at specific hertz values or RPM values as you have noticed. Unfortunately, your controller doesn't allow you to program skip frequencies or skip RPM's. The bad news is that it is very difficult (in my experience) to eliminate these without that feature built in to the VFD. If the pump impeller is changed (akin to changing your transmission), usually the problem either goes away or changes to another frequency. <BR/><BR/>I really don't know why they didn't add that parameter. It would have been handy to have in there even if it was only used 5% of the time.<BR/><BR/>Next time I go to Portland I would love to see your car (I live in Seattle).<BR/><BR/>http://www.austinev.org/evalbum/preview.php?vid=1333Unknownhttps://www.blogger.com/profile/14640447834642177209noreply@blogger.comtag:blogger.com,1999:blog-2270124316233555550.post-55672851861462513242007-09-30T12:23:00.000-07:002007-09-30T12:23:00.000-07:00Tim: I'm sure, for an engineer, all this analysis ...Tim: I'm sure, for an engineer, all this analysis is very fun and rewarding. My gut instinct tells me that your technical evaluation are right on track. Probably you'll find the solution in several places, including firming up the motor and tranny mounts (not rigid, but firm) and also perhaps replacing some of the bearings in the tranny ... especially the input shaft bearing.Roger Daisleyhttps://www.blogger.com/profile/10752698755981213856noreply@blogger.com