Created Date: December 26,2018

Created by: bellcopter

I ordered a Chinese spindle a few years ago from ebay (2.2Kw, 230V, 2400RPM @ 400Hz), and the VFD that came with it died recently. I'm looking for a replacement, and am at a loss on what to choose. I'm down to the 3HP version of either the CFW300, or the GS2. Both meet the max load amps, but beyond that I'm not sure what to look for. It's used in a CNC gantry application. Any pointers or tips?

Created Date: December 27,2018

Created by: Alexandru

The vfd you mention is powerful. I believe your spindle motor is around 1hp. If that’s the case, maybe you overload the vfd when you begin the milling process. If the spindle gets overloaded say at a direction change or at the beginning of milling, that overload turns into an inductive backfire towards the vfd.

the spindle motor works at rated power only at rated rpm. It can not be overloaded mechanically because will backfire into the vfd.

to protect the vfd:

set the vfd max current to the load amps of the spindle motor. Then set the vfd Max speed in Hz to a value corresponding to free rotation ( no load) of the spindle. This way you can’t exceed the supply to the spindle motor. If your spindle gets overloaded ( mechanically slowed down too fast) the vfd will fault and the work is ruined, but at least you understand what caused the fault. As I said, I believe a sudden trajectory change or turn could fault, and it can be addressed in gcode.

set a thermal overload between vfd and spindle motor. Again, to protect the vfd.

set a breaker between grid and vfd. To protect the grid.

Created Date: December 28,2018

Created by: bellcopter

I believe the GS2 can be configured for 400hz use, but IDK if the CFW300 drives can.

The actual line input to the old VFD was still 50/60hz compatible though right? It didnt have a special transformer before it and use a 400hz line input?

The old VFD was 60Hz compatible. Here's the hunk-o-junk in question: https://www.amazon.com/Variable-Frequency-Regulation-Technique-Capability/dp/B00ZOR5V5I

The vfd you mention is powerful. I believe your spindle motor is around 1hp. If that’s the case, maybe you overload the vfd when you begin the milling process. If the spindle gets overloaded say at a direction change or at the beginning of milling, that overload turns into an inductive backfire towards the vfd.

the spindle motor works at rated power only at rated rpm. It can not be overloaded mechanically because will backfire into the vfd.

to protect the vfd:

set the vfd max current to the load amps of the spindle motor. Then set the vfd Max speed in Hz to a value corresponding to free rotation ( no load) of the spindle. This way you can’t exceed the supply to the spindle motor. If your spindle gets overloaded ( mechanically slowed down too fast) the vfd will fault and the work is ruined, but at least you understand what caused the fault. As I said, I believe a sudden trajectory change or turn could fault, and it can be addressed in gcode.

set a thermal overload between vfd and spindle motor. Again, to protect the vfd.

set a breaker between grid and vfd. To protect the grid.

Why do you believe it's a 1HP, and not 2.2kW/3HP like it says on the spindle?

Created Date: December 28,2018

Created by: Alexandru

I thought 1hp is usually enough for a spindle and a 3hp vfd is a bit overdimensioned, but not uncommon.

however, if the spindle was 2kw, then I would look to a 3kw vfd. Feeding one phase I guess the vfd power output decreases, I’d have that in mind too.

Is more important to me why the vfd died. If is just a bad drive, then no big deal. But I believe it could be due to variable load on the spindle, due to tool path. In this case, obviously the tool advance speed needs reduced and the turns checked.

theres one more possibility, that the spindle gets old. If the bearings inside ( could be 4) are worn, then anytime the tool hits, the motor fires back to vfd.

Created Date: January 23,2019

Created by: bellcopter

I thought 1hp is usually enough for a spindle and a 3hp vfd is a bit overdimensioned, but not uncommon.

however, if the spindle was 2kw, then I would look to a 3kw vfd. Feeding one phase I guess the vfd power output decreases, I’d have that in mind too.

Is more important to me why the vfd died. If is just a bad drive, then no big deal. But I believe it could be due to variable load on the spindle, due to tool path. In this case, obviously the tool advance speed needs reduced and the turns checked.

theres one more possibility, that the spindle gets old. If the bearings inside ( could be 4) are worn, then anytime the tool hits, the motor fires back to vfd.

Final post on this:

So I 've gone with the WEG CFW300 drive, and found the spindle to be completely functional and within tolerances. I decided to tear apart the old vfd, and found one of the drive capacitors was blown (at the bottom, which I missed at first glance), which blew a few components downstream from it.

After some more research, I discovered that if a VFD sits idle for a while (I was away for an extended period) the capacitors need to be "re-formed, " which I did not do.

Also, these WEG drives are pretty fantastic. Too bad they don't have any 7.5HP+ versions available (not sure if they 're not made, or not stocked by AutomationDirect). Cheers!