Mains power trip - potential damage to VFD or CNC?

[crjohnson]

Hi guys,

I am close to being able to turn on my CNC and start some testing, but the power upgrade to my shed is not going to be able to happen as planned before the machine is ready.

I believe I am ok to start testing the movements of the steppers but I was worried about what might happen if I run the spindle and the mains circuit breaker were to trip. Can this cause damage to my VFD or spindle?

I have a 2.2kw spindle (220v, 6A), a 3.7kW Fuling VFD (with the max amps set to 6) and 2 x 350W 48v power supplies for the steppers.

The current CB in the shed is 16Amp (I may be able to slightly increase depending on the supply wiring) and I know I can arc weld at 125amps for about 20seconds before it trips! Also I am in Australia so run 230/240V mains..

Cheers!

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[boydage]

In NZ I ran the same setup in my workshop with a 3hp compressor running, along with other bits and pieces off single phase with 20A D curve breakers for the larger single ph motors. In the very very rare occasions I popped a breaker my cnc router stops dead, and the spindle just winds down.

Dunno. Someone may disagree. But it never did any damage to my machine. Computed included and they don't like being "switched off".

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[CitizenOfDreams]

Loss of AC power is a normal situation, it can be expected to happen from time to time. The VFD will shut down gracefully without any damage to itself or the spindle.

[mactec54]

Hi guys,

I am close to being able to turn on my CNC and start some testing, but the power upgrade to my shed is not going to be able to happen as planned before the machine is ready.

I believe I am ok to start testing the movements of the steppers but I was worried about what might happen if I run the spindle and the mains circuit breaker were to trip. Can this cause damage to my VFD or spindle?

I have a 2.2kw spindle (220v, 6A), a 3.7kW Fuling VFD (with the max amps set to 6) and 2 x 350W 48v power supplies for the steppers.

The current CB in the shed is 16Amp (I may be able to slightly increase depending on the supply wiring) and I know I can arc weld at 125amps for about 20seconds before it trips! Also I am in Australia so run 230/240V mains..

Cheers!

Your 2.2Kw spindle can't be 6A, it will be 8.5 to 9Amps for the regular 2.2Kw spindle, it will run on 16-amps supply but don't load it in any way or it will trip the breaker

just let it run at 12,000 RPM for testing and you should be ok, yes you can damage the IGBT's if the power is cut at full speed.

[mactec54]

Loss of AC power is a normal situation, it can be expected to happen from time to time. The VFD will shut down gracefully without any damage to itself or the spindle.

Not if it is running at 24,000RPM many have been smoked from this happening, it's never a good idea to cut the power at full speed with these spindles.

[mactec54]

In NZ I ran the same setup in my workshop with a 3hp compressor running, along with other bits and pieces off single phase with 20A D curve breakers for the larger single ph motors. In the very very rare occasions I popped a breaker my cnc router stops dead, and the spindle just winds down.

Dunno. Someone may disagree. But it never did any damage to my machine. Computed included and they don't like being "switched off".

Sent from my SM-N970F using Tapatalk

Not yet, do it enough times and you can, it also depends on the VFD Drive you have also, quality VFD Drives can handle this better, than the cheap VFD Drives.

[crjohnson]

Thanks mactec, I quickly wrote 6amps as that is what is written on the nameplate, will have to go back through our discussions. This spindle is a 4 pole if that matters at all?

Anyway, I will double check what the max amps setting is that I put into the VFD before trying anything and not go near full speed. I don't plan to cut anything anytime soon, mainly practice running programs and getting my head around that stuff first. Then I might have fun breaking some tools!

[Al_The_Man]

Loss of AC power is a normal situation, it can be expected to happen from time to time. The VFD will shut down gracefully without any damage to itself or the spindle.

I agree, of all the installations I have done, power failure is usually inevitable, never had a bad result yet.
Most are designed that as soon as the HV DC collapses, they turn every thing off.

[mactec54]

I agree, of all the installations I have done, power failure is usually inevitable, never had a bad result yet.
Most are designed that as soon as the HV DC collapses, they turn every thing off.

You have never installed one of these 400Hz spindles in your life, if you had you would know, that this can happen, like these unexpected Zone users experienced.

There have been many that have had this experience.

Here is one when the Power was removed at full RPM

[mactec54]

Thanks mactec, I quickly wrote 6amps as that is what is written on the nameplate, will have to go back through our discussions. This spindle is a 4 pole if that matters at all?

Anyway, I will double check what the max amps setting is that I put into the VFD before trying anything and not go near full speed. I don't plan to cut anything anytime soon, mainly practice running programs and getting my head around that stuff first. Then I might have fun breaking some tools!

4 Pole 800Hz, does this have a tool change, or just a regular ER collet type of spindle, amps would still be the same for any 2.2Kw motor of this type 6A is what the 1.5Kw spindles are.

[crjohnson]

ER20 collet. Its a jianken JGH-105/2.2. 2.2kw, 220v, 4 pole.

Do these spindles basically turn into a high-voltage generator when the mains power is unexpectedly killed? So all that high RPM inertia/energy feeds back into the VFD?

[Al_The_Man]

You have never installed one of these 400Hz spindles in your life,

And you know this how??

,
Here is one when the Power was removed at full RPM

That damage was not caused by the period of time that a loss of power exists, as some one who ha re-wound motors, that shows the symptoms of running that high rpm motor at too low a frequency.
For all the enamel to burn off all the windings takes a period of time.

[boydage]

Mactec could you please expand on how those windings came to look like that from the input power being removed? It only happened a couple times in the 4-5 years I owned one of those, and it just coasted to a stop. Although I can't remember what the rpm was at the time. B

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[mactec54]

ER20 collet. Its a jianken JGH-105/2.2. 2.2kw, 220v, 4 pole.

Do these spindles basically turn into a high-voltage generator when the mains power is unexpectedly killed? So all that high RPM inertia/energy feeds back into the VFD?

Yes, that is how it kind of works at 24,000 RPM without the power connected the VFD Drive, can't control how the spindle slows down, so the spindle normally takes the hit sometimes the VFD Drive IGBT can be damaged also, on any low speed 50/60Hz 3Ph motors this is not a problem.

Some of the quality spindles seem to handle it, (most likely have better windings / insulation) the cheap spindles that most are using, smoke quite easy.

[mactec54]

And you know this how??



That damage was not caused by the period of time that a loss of power exists, as some one who ha re-wound motors, that shows the symptoms of running that high rpm motor at too low a frequency.
For all the enamel to burn off all the windings takes a period of time.

Yes, you have done everything we know, and you are very good at what you do, but you have no experience with these Chinese highspeed spindles.

The problem with your theory is these spindles won't run at 24,000 RPM if the Parameters are not set correct, yes, they can fail if someone does not set the parameters correctly, a similar thing can happen.

That is not the case with this spindle body in the photo, this was on a working machine before this happened, it was running at 24,000RPM and the power was cut, (Accidentally) it started to smoke almost immediately while slowing down. the windings and insolation are not that great in these cheap spindles. so, nothing to be confused about, stuff like this happens. it's just you have never experienced it.

As of late there have not been many of these smoked spindles, 5 years ago there was at least 2/3 per week that smoked them, 90% was from incorrect Parameter settings some others from stalling the spindle in a cut, VFD Drives have got better to help protect these spindles, so not so many failure's

[mactec54]

Mactec could you please expand on how those windings came to look like that from the input power being removed? It only happened a couple times in the 4-5 years I owned one of those, and it just coasted to a stop. Although I can't remember what the rpm was at the time. B

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If you read what I posted, this does not happen all the time, the quality of the spindle is when you see these spindles fail, even if they were stalled while cutting the same thing can happen, if the VFD Drive can't react to the overload problem

If the VFD can handle the shutdown (which most cheap VFD Drives have got better at this) then it is only something to be aware of that can happen, this has happened to some users, and will still happen with the low-quality spindles and VFD Drives.

Why do you think they add Breaking Resistors to VFD Drives, so they can safely take a dump when the spindle is stopping fast / slowing down.

[Milling_man]

I have had many problems on a surface grinder where the power to the frequency converter was suddenly cut off. I turned it on in this mode, hoping for a power reserve, but in the end it just burned out It survived many power outages, like 50 or more. But in the end it killed him.
After that, of course, I would have to change the scheme of the engine. But it's too complicated )))) Therefore, I installed varistors between phases directly on the motor power terminals. Since then, there have been no problems for 2 years. I'm not saying that this is the right option, but as a last resort.

[crjohnson]

So the manual for my 3.7kW Fuling DB600 VFD says units <20kW have a "built-in brake unit". I'm assuming any braking parameters you set are of no use when the mains power cuts out? You are basically in the hands of whoever built and supplied the spindle and vfd when the power trips?


Thanks for the info though guys, I will steer well clear of 20,000RPM and also get a clamp meter to monitor the mains amp draw when I turn the spindle on.

[mactec54]

So the manual for my 3.7kW Fuling DB600 VFD says units <20kW have a "built-in brake unit". I'm assuming any braking parameters you set are of no use when the mains power cuts out? You are basically in the hands of whoever built and supplied the spindle and vfd when the power trips?


Thanks for the info though guys, I will steer well clear of 20,000RPM and also get a clamp meter to monitor the mains amp draw when I turn the spindle on.

I would not go to much off what you read as far as Breaking Resistors go, most regular VFD Drives can be fitted with a Breaking Resistor, no matter what size it is.

Correct, nothing is functional in the VFD Drive once the Power is cut, the spindle motor overheats, which is what causes the failure

Just remember you won't be able to measure the output from the VFD Drive unless you have very expensive equipment, or a meter with a low pass filter built in, as the output from the VFD Drive is a regular sinusoidal waveform.

[crjohnson]

Yea I was thinking of measuring the 240V mains going into my machine and seeing what it draws. If it starts to draw too much then I'll stop whatever I am doing.

Would you recommend fitting an external brake resistor as an added safety/protection feature? Common sense says "upgrade the supply capacity", which will happen at some point. But I'm always interested in the other things here and there which can be good insurance against larger dissasters

If so could you recommend any particular resistors? Cheers