I think that was my original point. Capacitors are expensive and bulky. Especially if you buy ones that have wide temperature ranges and can handle a large amount of ripple current. All which are a requirement for switching power supplies which is what the VFD really is.
A manufacturing building a VFD for use on 3phase can use a smaller capacitor than one who has to limit to the same ripple on single phase. Here's a simple explanation. http://www.electroschematics.com/7048/capacitor-input-filter-calculation/ With 3 phase there is less time between each peak to recharge the capacitor and therefore the ripple is lower with the same size capacitor. Or the same with a smaller value capacitor. If the ripple is too much then the VFD will probably fault out or become eratic. My simple and inexpensive Automation Direct VFD meant for 1HP can run a 1 HP motor on 3 phase. My South Bend lathe originally had a 3/4HP motor and it's unlikely I'd even load it at full RPM to require the 1 HP so I can get away with single phase input for a 1HP motor. The lathe headstock bearings are the limiting factor for top speed on my lathe. And as Stephan mentioned, the diodes can also be an issue if they are sized on the edge and expected to work with 3 phase. John > -----Original Message----- > From: Stephen Dubovsky [mailto:smdubov...@gmail.com] > Sent: January-07-16 3:14 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] VFD Tweaking > > > They do typ top out around 3HP 1ph. So just don't use them;) > > What John pointed out is entirely correct. The inverter runs from a > rectified DC bus. There are 2 things limiting you running a 3ph vfd on a > 1ph line. > 1) Phase loss detection. Some big inverters will fault if they detect one > of the phase inputs missing - it can usually be disabled in a software > setting though. > 2) heating and ripple in the diode rectifer and caps. There will be more > ripple current in the caps on 1ph AND it will be going though only 4 diodes > (vs 6 in a 3ph configuration.) They will be more stressed. This is why > most people recommend oversizing a 3ph vfd if running it on single phase - > to get oversized caps and diodes. But if you are using a 10hp motor to > replace a gearbox, you will never actually be drawing 10hp but only 2hp as > high torque at low speed = low hp. (if you resist the temptation to > overload the original machine and use all the avail new hp;)) There are > however easy solutions if you actually want to run a 10hp vfd *AT* 10hp. > Every one I've ever seen has the rectified DC bus available at terminals. > You can add more external caps to that bus. You can even use a BEEFY > external rectifier thats rated at your single phase ripple to feed the VFD > w/ DC directly (again, phase loss detection needs to be turned off.) > > FWIW, I have a 7hp hitachi vfd on my Sheldon R15 (5hp motor.) running from > 1ph 240V. I found the drive cheap so I simply oversized it vs building an > external rectifier/cap. > > SMD > > On Thu, Jan 7, 2016 at 5:31 PM, andy pugh <bodge...@gmail.com> wrote: > > > On 7 January 2016 at 22:10, John Kasunich <jmkasun...@fastmail.fm> > wrote: > > > > > This is rarely ever done in industry because industry doesn't want > > > to pay for the extra iron, copper, silicon, and capacitors needed > > > to build a 10HP motor and VFD when they're only going to get > > > 2HP from the shaft. But for a one-off where you find the motor > > > and/or VFD cheap on eBay or a scrap-heap, it can work very well. > > > > I am sure you are right, but that wasn't my point. 240V single-phase > > VFDs largely top-out at 3HP. > > > > > > https://www.inverterdrive.com/group/AC-Inverter-Drives- > 230V/?filter=Input%7c230Vac+1ph > > Does actually list some, I admit. But I am fairly sure that there > > weren't any over 2.2kW last time I looked a couple of years ago. > > > > -- > > atp > > If you can't fix it, you don't own it. > > http://www.ifixit.com/Manifesto > > > > > > ---------------------------------------------------------------------------- -- > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > ---------------------------------------------------------------------------- -- > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
