How to use 92VAC 200Hz AC-servo as spindle motor with 240VAC/50Hz mains?

[PekkaNF]

Hello,

One good soul twisted my arm to sell me cheaply an AC servo. His description of the servo is quite literally translated as:
Panasonic 200W AC servo. Nominal values: 92v,200hz,3000rpm. There is a Panasonic encoder at backside of the motor.

My choices of voltages are pretty close to 240 VAC single phase or 400 VAC three phase and 50 Hz.

I have some old transformers I could take 100 to 120 VAC 50 Hz out, but they are pretty big compared to the rest of the stuff. That would make a frigging great filter for 110 VAC VFD.

What are my choices?

Mechanical size and power and rpm of that motor would be perfect, but I don't need (neither afford) an all dancing servo amplifier, because I don't actually need feedback. I just need to turn drill/mill somewhat controlled manner, same size squirrel gage motor would have been enough if it were equally compact for power.

Thanks,
Pekka

[John Stevenson]

Simple.

You need the servo driver to match the motor

[PekkaNF]

That would be obvious solution. But to my understanding AC servo can be driven with three phase VFD. I understand that it is not good for positioning, but I only need a spindle drive. Inverter with sensorless vector mode?

Pekka

[PekkaNF]

The reason is on the attached picture....

I need small motor with some short term grunt. Hate all types of air motors in my garage, if I can avoid them.

Need a small spotting drill motor, 90W would do, marginally, but everything else should be spot on.

These motors are not exactly similar in usable continuous power rating, but I have these at hand.

1) AC motor 0,25kW 220V 1,5A 1400rpm 6kg B3

2) PM DC-motor, Proxon BFW 40/E 250W/10min 40VDC 900-6000rpm 4,2kg

3) AC servo motor, 200W 92V 1,6A rated freq. 200Hz, rated speed 3000rpm, 0,91kg


Good old AC motor would do the work with all propability beyond WW3 and beyond but is a bit of BEHEMOTH . Would need some wrestling to set and is too big.

Brushed PM DC motor would be closer to size and bit smaller. Limited brush life and limited duty cycle probably would never come to haunt me. It's still not very elegant to fit one motor with a collet to a spindle with a belt drive.

This Panasonic AC servo is smaller and with less than kilo it would make a perfect canditate. I know that for that output this servo should have it's own drive and attached a big lump of metal, but even with encoder this screams "take me to the QCTP"

I did some reading of my old inverter manual and I think I should have a good chance to get it working with some fudge factors. I'm mainly toying with the idea of faking V/F to 400Hz/full, and to limit max F to 200 Hz to produce closer to 92V at 200 Hz RMS, Also probably will have to toy with "boost" to give enough voltage and limit the current conservatively.

Pekka

[BillTodd]

I did some reading of my old inverter manual and I think I should have a good chance to get it working with some fudge factors. I'm mainly toying with the idea of faking V/F to 400Hz/full, and to limit max F to 200 Hz to produce closer to 92V at 200 Hz RMS, Also probably will have to toy with "boost" to give enough voltage and limit the current conservatively.

Just been looking at the manual for one of my Omron inverters (3G3JV 200-250v 1ph 200w):  It has a variable VF curve that looks like it can be set to give 1- 255v output at  high (Vmax ,Fmax 400Hz, FA), mid (VC, FB) & low (Vmin Fmin) frequencies. It also has the usual motor current limiting that should prevent you frying the motor.

It certainly looks to me possible to drive your servo motor with one of these VFDs

Bill

[PekkaNF]

Bill, I can confirm that. This old inverter I have has pretty basic parameters. It basically lets me fudge VF curve with few parameters and one %current limit from full nominal current of the drive. Found only one PWM switching frequency combo that worked without vibration and over current. In the end I'm at:
Maximum-voltage frequency 450 Hz (gives nominal input voltage = 230 VAC out at that "speed")
PWM 11,7 khz and maximum frequency 960Hz
Voltage boost 10,2%
Min speed 40.2 Hz
Max speed 200 Hz
Max continuous current 80% (is actually 1.6A, same as motor plate)
5s ramps up/down, no DC inject on braking

There is some room for adjustment, but got it running fine with these. Still has to check what it is when loaded with real life load. Really quiet when running right, but when parameters are wrong it sounds like fistfull of nuts and bolts on the blender. Funny how fast you can release "ON" switch in the quiet night on tranquil garden, when servo motor starts jumping on the table.

So there is hope, but clearly this is not as easy as with normal garden rated AC motor.

Pekka

[BillTodd]

Hi Pekka,

I'm glad you've got it running

I'm not surprised the servo motor is sensitive to the VFD's adjustment, it is after all design to reacted rapidly to the driver.

I'm wondering if dropping the input voltage slightly to the minimum   (to say ~200vac using a auto-transformer ) would give you a greater range of adjustment?

Bill

[PekkaNF]

it is sensitive. Thank you for couragement. I wonder one parameter. It has current mode and voltage mode. Default is voltage mode and it says you can use current mode but has a reference to technical manual and I don't have it.

I have one BIG old British made variable transformer that I could use to check if reduced input voltage would do any good, but it is sort of pointless, because there is no way I'm going to put "huge" (relatively speaking) transformer to othervice compact design. Interesting excercise though, and I might actually try it.

I'm still wondering if there would be a VFD somewhere that is designed to give 3phase 100-110VAC 2A out....something like a aviation 400 Hz but front end up to 240VAC. This should be easy to PFC. But probably there is no need for it.

I have this "need" to check up current and voltage under load, need to borrow a true rms meter to it. I probably don't need it, but just to feel better.

Pekka

[BillTodd]

I have this "need" to check up current and voltage under load, need to borrow a true rms meter to it. I probably don't need it, but just to feel better.

If you have an oscilloscope, just check for and excessive spikes that could damage the insulation, then, to check the power, just see how hot it gets .



Bill