View Full Version : Need Help! Fanuc dc spindle drive alarms with RPC

04-26-2009, 07:54 PM
I recently installed a Kitamura s-12 vertical machining center in my garage. This is a 1980 vintage machine with a Fanuc 6m control and a Fanuc dc spindle and spindle drive. I worked perfectly at the shop where I bought it, no problems at all. I am powering it with a homemade rotary phase converter. It is a 15 hp idler motor with balancing capacitors.

Here is my problem. The first time I powered it up everything worked fine including spindle orientation but when i tried to run the fanuc 3 DC spindle motor it would kick out with a "field overcurrent alarm" which is led #2. It would go into alarm even with a spindle speed of "0" rpm.

I checked the motor wires, the motor brushes, removed the motor, cleaned and inspected it (it looked great) and I had a fanuc technician check out the spindle drive. He said it was fine.

I then did a better job of balancing the 3 legs of the rpc and the spindle will now start but:

I started out with s1000 command and it ran at 100 rpm only.
If I tried a higher spindle rpm it would go into alarm again.

I suspect it has to do with my house voltage, which is high. The voltages out of the phase converter with no load are AB=254, AC=268, BC=271.
The voltages to the created leg, C, are higher so that they will pull down under load. My house voltage is 258. My house is right off the transformer on the pole.

The shop it came from used 208v 3ph. The manual is not real clear but the wiring diagram shows a transformer right after the disconnect with various input voltages and 200v to the machine. My machine does not have this transformer. The manual does not specify a voltage in its specs.

So, what do I do? get a buck boost transformer? Are there adjustments that can be made on the spindle drive?

Thanks for any help you can give me!

07-29-2009, 10:57 PM
WOW! If you are lucky enough to not have done any damage, you MUST drop the voltage. You need to get as close to 200VAC as possible. This, and most CNC's are not tolerant of the voltage being high. That spindle drive in that machine is close to $12k to replace if you blow it. Fanuc is not taking exchanges at the moment for that either....at least 6 months ago they were not. Our customer decided to scrap the machine after blowing this drive!!

I can sell you a cheap transformer of you are interested. Brand new. Or you can find one local.

Good Luck.

07-30-2009, 10:48 AM
Thank you for the info.I took the spindle drive to a technician in Tampa and he said it checked out fine. I bought a buck-boost transformer and was able to reduce the voltage by 32 volts but still no luck. I pulled the motor and checked it with a 500 volt megohmmeter and found some carbon tracking on the brush holders that gave low resistance readings and fixed those. Still no luck. So I finally gave up on the rotary converter and bought a phase perfect digital converter which should arrive tomorrow. I will know if it works by monday I will post the results as soon as I find out if I have a working machine or a divorce.