Rustyiron
Super Member
Could you simply replace the motor with single phase 240?
Death of a machine
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I would lose the ability to change speeds which is important in wood turning.
Right now, this has slipped to a very low priority. I've found a place that can rebuild the motor if needed. I do not know what the frame size is and will have to remove the motor to make some measurements to determine that. I suspect it is a custom motor since it is longer and skinnier than all the drawings I've seen of motor frame sizes, but have to measure first.
Right now, this has slipped to a very low priority. I've found a place that can rebuild the motor if needed. I do not know what the frame size is and will have to remove the motor to make some measurements to determine that. I suspect it is a custom motor since it is longer and skinnier than all the drawings I've seen of motor frame sizes, but have to measure first.
ponytug
Super Member
As you measure the motor, I would also keep an eye out for how big a replacement could be. Sometimes minor modifications can give you alternatives. In addition to the common US NEMA motor frame sizes, there is also an international frame series under IEC.
Years ago, I lived in a town where we had a local motor rebuilder, and motor rebuilding was cheap. Where I live now, it is way more than the cost of the motor, (local labor is pricey) and given the freight costs it isn't easy to outsource. So, here it is something I now reserve for numbers matching rebuilds of antique machine tools. Hopefully your local rebuilder doesn't cost a fortune.
All the best,
Peter
fitter1
Silver Member
Electric motors must be rated for vfd duty or they will fail prematurely.
strantor
Platinum Member
+1 the only time it's ever worth rewinding a motor is when it's double-digits HP and/or some kind of special purpise-built motor.
No disagreeing, but "prematurely" is subjective and may or may not be relevant. On a production machine that gets run at least a full shift every day I would recommend going inverter duty. But for a hobby wood lathe that someone uses (ex) once a month, an ordinary motor powered by VFD will most likely outlast the VFD and probably the owner too. Not worth the extra cost of inverter duty rating.
strantor
Platinum Member
The derating advice is golden if you're looking at 3ph input drives. There is a relatively new trend of VFDs specifically rated for single phase input and they do not need to be derated. Some are dual (single or 3ph) rated and they will typically have the ratings for both stamped right on them, so no math required.
ponytug
Super Member
"Inverter duty" motors are designed to be run by VFDs. They typically have higher temperature insulation on the motor, and typically higher volume cooling fans to cool the motor at reduced speed. A few even have insulation designed for the high voltage transients that VFDs can produce. (Worth putting in chokes on your VFDs) Some even have armature and stator designs to better tolerate different frequencies. Some have special internal grounding to reduce eddy currents. You will pay a premium for the "inverter" rating, and it is often hard to figure out what you are getting for the price. A premium might be three to ten times the price.
As @strantor said, if you aren't running it at extremes all day long, you will probably never notice. If you are planning on running it all day long, my $0.02 is to buy a reputable brand like Baldor.
All the best,
Peter
As @strantor said, if you aren't running it at extremes all day long, you will probably never notice. If you are planning on running it all day long, my $0.02 is to buy a reputable brand like Baldor.
All the best,
Peter
strantor
Platinum Member
Yep, agreed on all counts. Choke/output reactor is never a bad idea, although I must confess I don't run them (or inverter duty motors) on any of my machines in my shop. I just keep the wiring between VFD and motor as short as possible, and never had an issue. My main lathe is equipped with a 30 y/o blower motor that I pulled out of a dumpster, and I've been running it on a VFD for 8 years now, not a single issue. When it does eventually fail, hopefully it won't take the VFD with it, but if it does, no huge loss as that was also used, close enough to free, and a replacement can be had for less than the cost of taking my dog to the vet.
For industrial clients I recommend (and install) everything the "right" way. Inverter duty motors, good quality VFDs, output reactors (and input reactors when the application calls for it), shielded cables, etc. Not because I make money off it (I usually spec the parts, let the client order, and I install), but because in those settings downtime means a whole lot more than the cost of a motor or a drive. It's what they want, and I'm happy to oblige. But for the weekend warrior (myself included) most of it just doesn't make sense.
Check out VFDs from Delta and Toshiba, best bang for your buck. I have a Toshiba distributor near me and I get fully featured Toshiba drives for much less than you can find them online, just slightly more than the "dumb" Teco drives most home/hobby guys use.
ponytug
Super Member
Great tip on looking for VFDs from a local distributor. It never crossed my mind that they might be cheaper than online.
I agree with you about the difference between professional and weekend warrior use.
I have chokes on one of my VFDs that is driving an antique 3 phase motor just to save wear and tear on the motor windings. Cheap insurance if it helps keep the magic smoke inside...I don't mind losing the VFD, but I would hate to lose the motor.
All the best,
Peter
I agree with you about the difference between professional and weekend warrior use.
I have chokes on one of my VFDs that is driving an antique 3 phase motor just to save wear and tear on the motor windings. Cheap insurance if it helps keep the magic smoke inside...I don't mind losing the VFD, but I would hate to lose the motor.
All the best,
Peter
