[Brassaholic]

401 Z Servo Alarm on Spindle Start

Enshu Accu-Mill AM-1547
Fanuc 6m Model B
4 HP Spindle

10 HP American Rotary AD Series Phase Converter
6 gauge wire from my breaker box to the phase converter at 55 feet. Then 10 gauge from the phase converter to the generator and 10 gauge to the CNC machine.
The voltage going into the mill from the phase converter is:
T1 + T2 = 239v
T1 + T3 = 246v
T2 + T3 = 245v

I will start by saying that I am very new at this. I have never run a CNC machine before but I have used manual mills a little. I recently purchased this machine. The owner passed away and his grandson inherited it. It had been in the same machine shop since 1984 and was mainly used to make carbon electrodes. According to the seller it had been working 8 months ago, and based on everything else he said about the machine I tend to believe him. The mill seems to have been well cared for. It is in excellent physical condition. The power stabilizing unit in the cabinet with the main PCB was replaced in 2001. The bubble memory was also upgraded twice, once form 16 kb to 64kb, and later a 512 kb RAM board was installed (I even have the old bubble memory cards).

Problem:
I receive a 401 Z Servo Alarm when the spindle starts. I can turn the mill on and put it in jog mode. The X, Y, and Z axis move . But as soon as I turn on the spindle I get the alarm. I can turn the spindle off and back on, but I cannot move servos. The X, Y, and Z velocity boards go out of the Ready state, the green RDY LED turns off on all 3 boards. Also, the red LVAL LED is triggered on the Z-axis velocity board.

What I've Done to Correct the Problem:
I have read everything I can find online about this error. The machine came with all the manuals and I have read through them numerous times for anything that may help. I have checked the voltage everywhere the manual says...the main PCB, the transformer, voltage stability unit, the velocity boards 24v, +/-15v, 5v, everything seems to be within range. I swapped out my velocity boards to see if the Z-axis board was bad and I got the same error with both the X and Y boards as well. I have checked and cleaned the servo brushes too, but I couldn't figure out how to get to the tac to clean it, although I don't think this is the problem.

I have read that Fanuc’s are sensitive to phase converters so I was originally thinking this was where the problem lie. I’ve talked to American Rotary a few times to try to troubleshoot the problem and they have been very helpful but we’ve pretty much ruled out the converter. They had me move a wire from a capacitor to another line within the phase converter, which increased voltage on the generated line by almost 20 volts (still within the balanced range stated in the manual), but it didn’t fix it.

The amp meter on the machine redlines when then spindle starts then hovers around 4-6 amps depending on speed. An increase or decrease in speed only momentarily increases amperage by 0.5 amps or so, nothing major. When I rotate the T1, T2, T3 wires coming into the mill, the LVAL alarm follows the generated line. For example, If T1 and T2 are my single-phase lines and T3 is my generated line and I rotate them so the order going into the machine is now T3-T1-T2, then my X axis board shows the LVAL error. If I rotate again to T2-T3-T1, so that I keep the proper phase rotation, LVAL shows up on the Y-axis board. I don’t know what this means but I didn’t expect it.

The only other option I have read about that might fix the problem is to decrease the spindle’s acceleration at startup since the amp meter shows it pegged out at startup. I have tried to figure out how to do this, and if it is even possible on my mill, but I haven't been successful. I may need to be walked through this process.

Any ideas on this issue will be greatly appreciated. I have hit a brick wall with my troubleshooting.

[cjfisher]

Brass,

First off - I'm not an electrician by trade, but I have done a fair amount of equipment spec-ing in my current job so I gotten somewhat familiar with electrical supplies. Your input voltages to the mill seem awfully low and possibly incorrect. What voltage is being supplied to the phase converter? Also what voltage does the mill require? LVAL is a Low Voltage ALarm caused by the voltage sagging below the safety limit when you start the spindle motor. Looking at my wire and motor calculators... a 55 foot run of #6 wire at a full load of 90 amps (which you will never hit with your mill) should only drop the line voltage at the input of the phase converter to 204v (if running it on 208 service) or 235v (if running it on a 240 service). I would expect to see no less than 200v(for 208 volt)/230v(for 240 volt) on the output of the phase converter. The 10 gauge should support the current requirement of the mill just fine as the spindle motor is pulling 13.4amps or so leaving 14amps of capacity to operate the servos and controls. How long is the wire run from the phase converter to the mill? You mentioned that the LVAL follows the generated leg which does not surprise me. The phase converter is working correctly, but the start up current is sagging the voltage of the generated leg low enough to activate the alarm. As for pegging the amp meter on the tool, no surprise there, I peg mine every time I start the spindle and I'm on true 240v 3 phase power.

One thing you might try as a last ditch attempt... do you have a spare 5 to 10 horse power motor with a pulley on the shaft bigger will be better? Wire the motor into the output of your phase converter with a start/stop contactor. Then start the phase converter, after that is on start the 10hp motor (as it is unloaded the phase converter should start it without issues), then turn on your mill. The 10hp motor will act as a "battery" and may help you get over the momentary current requirements of the spindle motor. The extra motor will also help to smooth out the voltage differences between the phases a little.

"6 gauge wire from my breaker box to the phase converter at 55 feet. Then 10 gauge from the phase converter to the generator and 10 gauge to the CNC machine." What is the generator you mention? Is it the the phase converter (least ways I have been assuming it is)?

Charles

[Brassaholic]

Thank you for your response. I just realized the voltages I entered above are incorrect. They should have been around 240, not 140. I updated the voltages in the original post. I am supplying 240v at 30 amps to the phase converter.

The manual calls for 220v AC +/-10%, 60Hz, 3 phase, 7.2 kVA.

Do you still want me to try to connect another motor to the phase converter? I don't have one but my neighbor has a generator. I thought about removing the generated leg and connecting his generator to it.

I've also talked to American Rotary about added a start capacitor to the converter to help the starting voltage. Even though their manual says it "May be required", they have been very adamant that I don't need to do it.

[cjfisher]

Please correct me if I'm wrong, but after looking at pictures, it looks like the machine uses a mechanical speed control and therefore the motor is a line start which runs at its rated rpm all the time (aka you don't have an electronic inverter for speed control). And after rereading the last bit of your first post the motor has to be a line start. I'll bet the phase converter is momentarily dipping too low then recovering, but recovery takes just enough time that the servo drive can sense it and throw the alarm. You could try your friend's generator if it is a 3 phase generator at which point just disconnect the machine from the phase converter and hook it up to the generator. DO NOT hook a single phase generator up to the one leg as you will blow the wiring out of the mill, your building and likely the generator too. You will not be able to synchronize your 240v service with the generator or vise versa. The reason I recommended the motor is it will act as a "mechanical" capacitor. Energy stored in the spinning rotor of the extra motor can help provide a little extra current when starting the machine's spindle. Another option (may not be possible and would require help from someone who knows the servo drive units) would be to lower the threshold of the LVAL alarm. Then you would just need to make sure that the machine is not in motion when starting and stopping the spindle. Third option: go buy an inverter and wire it up to the spindle motor. Then set it up to ramp the motor up over several seconds (there will be a couple of other tweaks involved).

Charles

[zavateandu]

Try to change 2 phases on the spindle connections.

[cjfisher]

Zava,

Hmmm... I think that changing 2 of the phases will only reverse the direction of the spindle motor. If one the of the two legs is damaged the problem may move with the swapped leg, unless Brass swaps the two good legs. Brass could try switching 2 of the phases (IE phases A and B) then putting them back before switching a different pair (IE B and C or A and C) to verify if there is a problem in the motor. However, if you suspect that the motor has a fault I would just recommend taking it to a motor shop for testing. I really don't think the spindle motor is the issue, as the bad leg would continue to overload the phase converter the entire time it was running.

Any updates Brass?

Charles

[Brassaholic]

Thanks for the responses. I have been really busy the last few days and haven't had much time to mess with it. I did try to put a start capacity on the phase converter. It didn't help though. I would be surprised if the spindle motor were bad. It seems to run really quiet and smooth. I don't have any problems running the spindle, it's just taking a little too much power away from the Z-axis velocity board, the board that's connected to the generated leg.
I don't have an extra motor lying but at this point I have to wonder if there is something wrong with the phase converter. If not, maybe I need a larger one. I'm heading to Mexico for vacation tomorrow morning. When I get back I plan on calling American Rotary and seeing what my options are for returning/replacing or upgrading. They swear that it should have more than enough power to run my mill but I'm not convinced. While I may be new at this and it is a very complex machine, the error seems to be fairly straight forward... The drive on the generated leg is getting pissed off at the spindle for for briefly stealing a little too much power and it's shutting the whole thing down.

[cjfisher]

Brass,

Have a good time on vacation. I don't think there is anything wrong with your motor... or your phase converter. And if your spindle were operating on an inverter verses line starting, the phase converter would likely do fine (and it does fine getting it started.. it just that the voltage sag is just enough to trip the servo drive). When line starting a motor the inrush current at the moment the contactor closes is very high. As the motor gets spinning it begins to generate back EMF which reduces the current coming into the motor. At speed an unloaded motor's back EMF will just about cancel out the incoming current. You measured a 4 amp draw on your motor due to losses in the drive train, bearings, and friction.

Charles

[Brassaholic]

Charles,
That makes perfect sense. I appreciate your help with this issue. It sounds like I'll be educating myself a little more on inverters. I'll update this thread with my progress.

-Adam

[Brassaholic]

I believe this issue has finally been resolved!!!

It turns out the phase converter is half the size I need. When I figured out sizing I used the HP of the spindle, which was all the information I had about the machine at the time. Even after going through all the manuals 100 times I saw nothing about the total draw of the machine. So I decided to put an amp meter on the generated leg and see exactly what the machine is pulling when the spindle is turned on. It averaged 28 amps. At the time it didn't mean anything to me but when I spoke to American Rotary they informed me that a 30 amp draw at 240v is equal to about 10 HP. They said at 3 phase 240v there are about 2.8 amps for every 1 HP. So: ( 28 amp draw/2.8 = 10 HP ). This means I need at least a 20 HP rotary phase converter to run the mill, not the 10 HP I currently have.

It would have been nice if American Rotary would have asked me to check the amperage draw of the spindle on the generated leg when I first spoke to them, but my newbie ignorance puts me just at fault for not catching that sooner. However, this issue forced me to go through all the manuals thoroughly. I spent much more time reading through them and gaining a better understanding of the mill than I would have if it worked right out of the "box".

My new rotary phase converter is on the way. Consider this issue resolved. I will update this thread if the problem persists after the new converter is installed.
Thanks!

[cjfisher]

Brass,

Glad to hear that you figured it out. I wondered if the phase converter was too small. Just wondering (and I don't know if you are are on a tight budget or not).. have you looked at Phase Perfect converters? They are pricey, but they are much more efficient than the rotary phase converters. Just a thought.

Charles

[Brassaholic]

I have looked at the digital phase converters. I spoke to someone at Phase Perfect and got a lot of information and pricing. In the end I decided to go with a the rotary mainly because of the price. American Rotary had a unit with a scratch on it and they gave me a really good discount. So it was hard for me to spend more than double that for a Phase Perfect. This is a new hobby for me that I'd like turn into commercial work in the future, but that may be a long way off. I've told myself that if this turns into more than a hobby and I get another machine (I really want a lathe), I will sell the rotary phase converter to invest in the Phase Perfect.

...that's the plan anyways...we'll see what happens

[cjfisher]

Brass,

My "hobby" very quickly turned into a second job. At least for the moment. I hear you on the cost... however, something more to consider - power costs. The rotary phase converter will burn a few amps (I seen the specs, but I think the numbers are higher) just to keep itself running. The Phase Perfect uses maybe .5 amps to operate with no load (my buddy has a 20hp Phase Perfect and I think it uses less than .25 amps when it is idling)

Charles