Fanuc Series 3 AC Servo Amp - Failure

[eriksalo]

"You main problem is the RPC"

Why do you think this is true?

To my understanding, a rotary phase converter makes power just exactly the same way a power plant makes power, by spinning a 3 phase motor. When I got it, I measured the output from each leg. They were balanced with <1% voltage difference between all the phases and had zero reactance between the legs.

What's different about 3 phase power made from a proper RPC?

[eriksalo]

Check CH28 with oscilloscope with motor running. 0 to 10 votls is desviation from comand value. If error signal is error feedback singal, if is high for long time you will have error 2. Other option is set ARS to 0, short ARS with 0, and you will disable alarms and monitor what is wrong.

Do you happen to have a schematic of this board? It would really help!

[cjfisher]

Erik,

While I'm not sure that the RPC is the cause of what you are seeing... rotary phase converters do not create balanced power. At idle, perhaps, they get close but as soon as you hit the RPC with a load the balance will change and the generated leg will go high or low. In a true 3 phase generator you have 3 exciters that provide the "kick" to get the main coils going. The RPC does use a three phase motor, but it is not at all like the power plant. In the RPC two of the legs are attached to the 240 line voltage. As the motor spins up and the rotor becomes energized it begins to generate power in the unconnected stator winding which is where you get your 3rd leg of the 3 phase power. Internal to the RPC controls are several banks of capacitors that help "balance" the output. I have also read that the coils in an RPC differ from a true 3 phase motor as they are wound with different impedances that help balance the voltage output. The Phase Perfect unit that Mac mentioned uses specially designed inverter to create the 3rd phase. Because the Phase Perfect is "electrically" generated it provides a steady 3 phase output at all loads, whereas the 3rd phase generated by the RPC tends to wobble due to the magnetic coupling between the rotor and stator. To truly generate native 3 phase power you would need to start with a single phase motor that is then connected via the shaft to the shaft of a 3 phase generator... with which comes some limitations... as (with some minor losses) power in = power out. Aka you cannot have a 10 hp single phase motor powering a 20 Hp generator and expect to use 20 Hp on the 3 phase side.
It would be worth checking your RPC output when you spin up your spindle to verify that the output is still balanced. Just for curiosity sake... what is your RPC rated for? What is your spindle motor rate for? I have helped a couple of people on the forum that couldn't keep their machines running due to the fact that their RPCs were undersized.

Cj

[mactec54]

"You main problem is the RPC"

Why do you think this is true?

To my understanding, a rotary phase converter makes power just exactly the same way a power plant makes power, by spinning a 3 phase motor. When I got it, I measured the output from each leg. They were balanced with <1% voltage difference between all the phases and had zero reactance between the legs.

What's different about 3 phase power made from a proper RPC?

Because they have a habit of destroying CNC machines electronics

[eriksalo]

cjifisher, thanks for your detailed answer.

I have a 30hp RPC. The spindle motor is 5.5kw (7.5hp). The x/y/z axis motors are ~1hp each (Z is bigger than x/y) and there's a small 3 phase hydraulic pump.

Overall, I sized the RPC to be greater than twice the capacity of the maximum Milling machine power consumption.

My other option is to scrap the Fanuc spindle controller and use my own VFD. Problem with that is I would then have to create a spindle orient solution.

[cjfisher]

Erik,

I got lucky... as I have a native 3 phase drop to my garage (480v no less - the city inspector freaked out when he saw that back when the water company switched from tubs to a pad transformer). Personally, I have never liked RPCs - primarily due to the inconsistency in the generated leg and that they are power hungry, even just idling. Should I ever move from where I'm at now, I'll spring the extra dough and buy a Phase Perfect - but that is neither here nor there. Your setup sounds fine.. even a bit overkill on the size. One of my buddies would fire up his big lathe (I think it was a 15hp motor) while he his cnc running to help absorb the spikes when the cnc would start and stop. The generated leg doesn't do well with regenerative spindle drives when they spin down - tends to over volt them. It would be worth while to watch the voltages at the output of the RPC while your spindle motor is running and when it starts and stops. I believe there are VFDs out there capable of orienting. I seem to recall that some of the higher end Mitsubishi VFDs are capable of orienting, though I'm sure there are others out there as well.

Cj

p.s... I just re-read the beginning of this thread... you made a point that you can't run up to full speed...... your RPC is over-sized plenty - it should have no problems with that motor at full speed. I see two possibilities... one, the noise from the RPC is causing problems or two, there is still a problem in the drive's electronics. Ebay wants a fortune for these drives... Have any friends with native 3 phase power that will let you test the drive on their power?

p.p.s... looking at fleabay pictures - there are a pair a BIG filter caps in the drive.. if one of those warms up and then begins to leak current you'd see the overload and the reason for the "hunting" as the DC bus in the drive is losing power. So one more check - watch the voltage on the dc bus inside the drive (BE Careful!!) to see if it wobbles.

[mactec54]

cjifisher, thanks for your detailed answer.

I have a 30hp RPC. The spindle motor is 5.5kw (7.5hp). The x/y/z axis motors are ~1hp each (Z is bigger than x/y) and there's a small 3 phase hydraulic pump.

Overall, I sized the RPC to be greater than twice the capacity of the maximum Milling machine power consumption.

My other option is to scrap the Fanuc spindle controller and use my own VFD. Problem with that is I would then have to create a spindle orient solution.

Good luck with that I don't know of anyone that has successfully run a Faunc Spindle motor with a regular VFD there is no easy way to do this

Your 30Hp RPC should of been more than enough, but if you supply is on the light side it is not going to be working at the 30Hp rating you need at least 100A 240v single phase to run the

What is the total Amps of your whole machine you just may have been able to run it with just you single phase 240v supply

[eriksalo]

"p.p.s... looking at fleabay pictures - there are a pair a BIG filter caps in the drive.. if one of those warms up and then begins to leak current you'd see the overload and the reason for the "hunting" as the DC bus in the drive is losing power. So one more check - watch the voltage on the dc bus inside the drive (BE Careful!!) to see if it wobbles."

I've thought about replacing those big capacitors. They are 30 years old and electrolytics don't last forever.