240v into a 230v machine?

I’m having trouble with the B axis servo drive on my Miyano JNC-45 with a FANUC control. It has started throwing an over-voltage alarm in rapid moves. The transformers in the machine are all labeled for 200, 220, and 230 volts, the incoming power is reading between 240 - 242 volts. Could that be causing some issues with the electronics in this machine?

Have you always had 240 ish volts to the machine, and how long has it been connected to where it is now?
It is a fairly vintage machine, and electronics and everything else in them has a limited life span, although old electrical components tended to be of much better quaity then you get these days.

Honestly having 240 volts from the power supply companies from a 230 V net is totally normal, and don't cause issues with normal 220 or 230 volt equipment.
Most of the 60 hz (US) equipment is usually rated for 240 Volts at least what we come across over here.

If the machine has been connected to the same power supply for years and years on end, then it's not whats causing the issue most likely. Unless the power supply company have installed a new transformer close to you and boosted the voltage.
Check your outcoming voltages from the transformers and start from there.
Chech your documentation and find out how your overvoltage alarm is connected to the system and how it works. A multimeter and some logic will find the answer if your somewhat competent with electronis/electrical.

Second the idea that if it is a new problem, but you have had 240V all along, then it may be a failure and not an issue of the voltage.

It seems to be true that some older CNC stuff specs very tight voltage limits. This is fairly unrealistic in the real world.

Can you describe what is being done when you get the overvoltage trip?

230v to 240v isn't that big of a jump. But we have worked on new 220v 3 phase Italian built machinery that was sensitive to 248v coming in. It was only line 3 that was so hot, so if we kept that line isolated from the single phase control circuits, the machine would work fine.

We found that the codes over there conformed to having a +/- 10% voltage variance from the power company, rather than the +/- 15% over here in the US.

The typical expectation is for +/-10% voltage from nominal. So anything labeled for 230V should be fine with anything from 207V-253V.

I've heard some servo drive manufactures say they really want +/-5%, but that's still a range from 218.5V-241.5V. And we all kind of rolled our eyes at them because we had equipment installed in China and Mexico using their drives and never had any issues. (And I guarantee that incoming voltage fluctuated more than 10%.)

Sometimes you'll get those types of alarms if the phases are too far off - I've heard of transformers in the neighborhood being a problem for CNCs before.

Check out your incoming voltage first, then the phasing if you can.

Depending on the vintage of the servos the answer is yes.

I have a JNC-45 also. It has a 0T control and the servos are DC.

Older systems with 5T and 6T seemed to be a bit fussier, than the newer.

Personally, I would start with brush maintenance if they are DC motors.
If the brushes are too short, there can be arcing that gives over voltage problems.
Also if you are running the same job all the time, the commutator bars can start to have problems at each end of the rapids.

Do you have the electrical drawings for the machine?

Bill

Thanks for the replies. Been a little tied up the last few days. After some time on the phone with Fanuc, we got down to two possible culprits. The servo motors (which are AC) and the servo amplifier board. I was able to get an electrician to come by this morning with a megger to test the motors. I got him test them all while I had him. The servo in question tested out at 70 mega-ohms. The X and Z servos didn’t test a whole lot better (200 and 500 mega-ohms). It appears I am in for some repairs if I want to continue running this machine.

Spruewell said:

Thanks for the replies. Been a little tied up the last few days. After some time on the phone with Fanuc, we got down to two possible culprits. The servo motors (which are AC) and the servo amplifier board. I was able to get an electrician to come by this morning with a megger to test the motors. I got him test them all while I had him. The servo in question tested out at 70 mega-ohms. The X and Z servos didn’t test a whole lot better (200 and 500 mega-ohms). It appears I am in for some repairs if I want to continue running this machine.

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? If your electrician used a 500 or 1000V megger. who told you those values was a issue?
None of those values are even worrying. Not that your motor might not benefit from a proper touchup.
Alot of meggers wont even measure over 550 Megaohm.
If you dont have the original test values for your motor you have nothing to compare to, and even if they are identical such variation is quite normal.

If your really think changing the servo motor because it 'only' has 70 Megaohm resistance on a megger test from a 500/1000 Volts megger will help good luck.

If the test showed somewhere in the the vincinity of 1 megaohm you could start to be worried about it.

For general electircal equipment 230/400V over here the requirement is minimum 1 Megaohm. Even if it's a 400V 1200 amp VFD driven motor. And measuring 70 Megaohm on a motor of that size even is quite normal.

So anyone that told you, that you should worry about megger tests ranging in several hundred megaohms should really not give advice to begin with.
If it was your electrician next time ask for one with some experience from automation/industry and you might get someone somewhat knowledgeable for the application.

Did your electrician also check your motor windings resistance separately and compare them?
Something witch should be mandatory.
That will also give you a easy indication on its well being.

As for the power grid in Europe here is 230 or 400 volt 50 hz, and all the equipment per specs has a max +- 10% voltage variation, according to CE etc, same as the power supply companies use.
And yes a new transformer nearby has at times caused issues for equipment because of boosted voltages, and phase issues.

I have mostly Miyano lathes so I can speak for certain on this subject. In our previous location we have about 235-238 volts coming in. So we hooked up machines directly to the breaker box. No issues for the entire 5 years we were at that location. Then we moved to a new location literally down the street. I measured the power several times before we moved in. Always 242-239 volts. Hooked up all the machines. Finally when we were ready to start up production almost all the lathes got high voltage alarms. We had to rush and get step down transformers for all the machines. Stepped down from 240ish to 225. Never had a problem since.

Sorry, I haven’t checked in on this thread in a while. Been kinda swamped and haven’t had time to work on this machine. However to answer Tor, I was told by a service tech at FANUC that 200 mega-ohms was the lower limit of what these motors should test. If this is not true, that would be awesome! Then I could put in the new servo board and not worry about frying it with a dead motor. It would also save me a lot of money. As far as the megger used to test it goes, it was able to measure up to 5.6 giga-ohms on another machine.

as the capacitors dry out they will have lower uf, less energy storage.

so when you rapidly decelerate and dump power back into the dc buss, if there is no brake resistor or if the brake resistor broke, then yes you get an overvoltage alarm but not because the supply voltage was too high.

dropping the supply voltage might solve the problem temporarily but without further investigation, almost a waste of time in the long run if the drive blows up and you can't get a new one when a repair would have doubled its life. can you slow down the deceleration and see if the problem goes away?

so for like 25$ you can buy a single channel 1Mega sample per second oscope on ebay. it won't be good enough for a lot of work but it will show you the voltage ripple on the dc buss of the servo amp, enough to tell you if the capacitors need replaced or not.


secondly, this is something that i don't think anyone would recommend but it may be possible to tie the dc buss of all 3 servo amps together, rather than replace the broken one which i presume has either failing capacitors or a failed brake resistor or brake transistor.