On Sat, 16 Dec 2006, Jon Elson wrote: > Date: Sat, 16 Dec 2006 14:54:07 -0600 > From: Jon Elson <[EMAIL PROTECTED]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: Re: [Emc-users] Mesa m5i20 PWM frequency ? > > Peter C. Wallace wrote: > >> >> Dont your output filter inductors always have to carry full motor current, >> regardless of PWM rate? >> >> (Well at a really low PWM rate you would have more motor current ripple so >> the >> peak current would be higher) >> >> > Exactly the problem. At some DC supply voltage around 120 V the > enductor ramps > up to above 20 A in one PWM cycle (20 us). If the current limit is set > to 20 A, then > the limit is reached as the inductor is already in saturation, and it is > a tough condition > for the power transistors to turn off at that stress. > > If you slow down the PWM frequency, then the current ripple will exceed > 20 A peak > even when the average motor current is far below that - at least with > low inductance > motors. The only solution to this is to increase the inductor value. > > At 50% duty cycle into a dead short, the P-P current ripple is a couple > of amps, if you > cut the frequency almost by half, it will go up quite a bit. > > Jon
OK so for the 5I20 I can change the PWM so it will go up to ~66 KHz instead of ~33 KHz. > > ------------------------------------------------------------------------- > Take Surveys. Earn Cash. Influence the Future of IT > Join SourceForge.net's Techsay panel and you'll get the chance to share your > opinions on IT & business topics through brief surveys - and earn cash > http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
