Hitachi VFD sizing

[Brian Holcombe]

Prognosis is that the single phase motor on my saw is dead so I’m replacing it with a 3ph motor. The replacement 1ph metric motors are fairly expensive in this size range.


Motor I found is 240v 3ph 4kw. Draws 13amps.

I’m looking at a hitachi inverter since I have installed a couple of them so far.

The inverter I’m looking at is WJ200-037LF

https://www.hitachi-iesa.com/sites/default/files/supportdocs/(WJ200)SM-E265W.pdf

My math suggests I need an inverter capable of 22.5amps on single phase input.

Thank you!

[Bill Dufour]

Your math is good but add say 10% for less then 100% efficiency. Of course you can always limit it to under the motor nameplate hp.
If you need braking you probably should add a resister to soak up the back EMF and not fry the VFD buss. A spinning bandsaw has a lot of momentum.
People add an electric oven or water heater element as a cheap brake resister.
Bill D

[Bill Dufour]

MY 10% guess is a total guess. you do some research and let us know a better answer.

[Brian Holcombe]

Spoke with Hitachi and they recommended the WJ200-075. Seems overkill for this but buying once is cheaper than twice.

On the tablesaw I used a big resister to slow it to a quick stop. For this I’m going to program it to free wheel and I’ll use the foot pedal to stop it.

[Bill Dufour]

To me that factory switch seems funky. Feel free to reuse it or repalce it with something normal. Not bad to have at least an off switch on both ends.
Since I added a big mushroom stop switch on my TS I almost never turn it off other then with my knee. A lighted switch would be nice. A foot off switch on a cord could be nice or it would be a trip hazard.
BillD

[Brian Holcombe]

That switch is going and being replaced by typical push button switches.

[Aaron Inami]

I know this is late (I was on travel when you posted). The 3-phase 4KW motor is basically a 5.5HP motor. The WJ200-037LF won't work because it's rated for 5HP output when using 3-phase input (you only have 240V single phase as a power source). You can certainly hook up single phase to a 3-phase VFD, but you will only be using 2 of the 3 input diodes for power generation. This means the 037LF will only be able to power a 2.5-3HP motor at that point.

They are recommending the larger WJ200-075 so that the single phase input will still be able to generate enough power to run a 5.5 HP motor.

There are other VFDs that are specifically engineered for single phase input. This one is a somewhat less expensive model compared to the Hitachi 075HF:

https://www.ato.com/7-5hp-single-phase-to-three-phase-vfd

I use the 5HP ATO for running my Clearvue 3-phase Baldor motor and it does perfectly fine.