Just a guess is that the braking resistor is not being switched out of the circuit when the spindle is stopped. If the braking resistor is getting hot at idle, then that is an indication of a problem.
Morning everyone,
After fixing a bunch of things on this used Kia I picked up, I'm about ready to run. Whenever the spindle is stopped from 1k+ my Phase Perfect PT355 shows an amp draw of 20+ amps. Idling after reset for a while doesn't cause the draw to go away. If I hit the e-stop the current draw is removed immediately. If the spindle has been stopped, the machine is idle and drawing 20 amps, and I command any rpm m03, the amp draw returns to a normal spindle amount of <10 amps. I do not have any voltage related alarms, and the lathe runs perfectly fine other then this.
Things I've checked
- No current on ground when it does this
- Pulled the cover off the spindle motor, made sure no burnt or broken wires were present. Looked very clean actually.
- Visually checked the electrical cabinet for anything out of the ordinary, and made sure all grounds were tight.
- The way I have the phases configured is Black, Red, Blue. Where black and red are the single phase pass through, and the blue is the generated third leg. I'm fairly certain I have the legs configured in the correct way.
- The amp draw is shown on l2 and l3, but no draw on l1.
- I noticed something called a discharge resister in the electrical cabinet. Wondering if that has to do with the same system? Might take it out tomorrow and look over it.
- The hydraulic c axis brake has been removed and is capped off. It is hydraulic, but just encase it was related at all I threw this in.
I am not really an electronics guys as you guys can probably tell, but I know how to use a meter.
I am unsure how to check the parameters of the drivers in the cabinet, but I did see in the manual that there are parameters that are spindle brake related.
If you have any suggestions, I'm all ears. Thank you!
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Just a guess is that the braking resistor is not being switched out of the circuit when the spindle is stopped. If the braking resistor is getting hot at idle, then that is an indication of a problem.
Jim Dawson
Sandy, Oregon, USA
How does the braking resistor usually get signaled to shut off? Is it going to be a relay, or something of the sort? I see a k7t and a k8t attached to the resistor. Looks like they are located inside the servo amplifier.
It's normally switched by a transistor in the drive. There is an entire circuit in the drive dedicated to the braking resistor function. It reads the DC bus voltage and switches it on to prevent overvoltage, but it should turn off when that condition clears. Normally I would expect it to switch off at around 360 volts or so. At 240VAC input, the DC bus would be running about 340VDC. If your incoming voltage is > 240V then it is possible that it is right on the edge of its range.
Jim Dawson
Sandy, Oregon, USA
Incoming is right around 230V, but if it was spiking above 240V during stopping you're saying that it could prevent it from sensing that?
With the incoming voltage at 230V, I would expect the DC bus voltage to drop well below the cutoff voltage at idle. So the real question is the braking resistor getting hot at idle when in the high draw condition? If so, then the drive braking circuit might be damaged, or at least very confused.
On the other hand, I could be sending you down the wrong path here, and it could be something else entirely. The braking circuit is just my best guess based on the symptoms described.
Jim Dawson
Sandy, Oregon, USA
Yes the braking resistor is getting hot, we've measured it hitting 80 degrees f in 10 mins, didn't want to run the draw any longer then that. Could you tell me where the drive braking circuit is located?
The circuit is inside the spindle drive. It may be a seperate board, or could be built into the main board. Just depends on the drive. I have no idea what drive you have in that machine.
Jim Dawson
Sandy, Oregon, USA
Amplifier module is A06B-6111-H006#h550
Would changing any of the regen related parameters help with our situation? I'm guessing any damage to the DC system will not be obvious to the eye.
I really appreciate your help!!
If you can adjust the parameters, then yes it might help. I have seen some VFDs that had an adjustment for DC bus regen trip point. Maybe that Fanuc drive has the same type of adjustment. If you have one available, a user manual for that drive would be very helpful at this point. I really know nothing about that drive. I think Fanuc has their manuals available online.
Jim Dawson
Sandy, Oregon, USA
Didn't get anywhere messing with the control parameters, and I'm a little worried about messing up the cards parameters. For now it just looks like I will have to estop the machine whenever it is not actively cutting. I do appreciate all the help you gave though! Certainly pointed us in a solid direction at least.
Happy I could be of some help.
Jim Dawson
Sandy, Oregon, USA
Your VFD Drive has a damaged Braking Circuit and will damage a lot more if you keep running it like this, the VFD need to be repaired or replaced and yes if the hydraulic brake that was removed, this in some spindles is used to help slow down the spindle, so if this was the case then the VFD Drive would of been over loaded when Braking
Who is the manufacture of the lathe and the VFD Drive
Mactec54