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« Reply #210 on: August 08, 2018, 01:31:38 AM »
Cheers Craig will have a look.

Hi All

Is this motor worth looking at?


On single-phase up to 1500 rpm has 9.9nm then drops to 7 as opposed to the DDM's 7.9nm at 2000rpm. Over that, it drops significantly.

It also has a lot higher peak torque of around 32nm.

If it proved to struggle around 2000rpm or I needed more rpm, I could change the drive to a three-phase 440v giving higher torque values than the DDM that I think we have suggested will be sufficient.


« Reply #211 on: August 08, 2018, 03:45:26 AM »
what are you trying to achieve? If I understand correctly you have a working three phase asynchronous spindle motor of 5kW.
Is that correct?

What are you hoping to achieve by replacing it? You mentioned the desirability of having it operate from a single phase supply.
Hood and I chimed in and we agree that the potential for a single phase servo is in the region of 2.2 to 3kW. Even that will put significant
demands on your supply and still be well short of power compared to the original spindle motor. I recall that you thought that operation
from a single phase supply would be a favourable selling point, and I imagine it is....but are you planning on selling it?

You will have noted that the higher the input voltage to the drive the faster the servo can run before the torque diminishes. That would lean you to
a three phase input servo drive, but that really is contrary to the idea of running it from a single phase supply.

I understand that you are going to buy a couple of 750W servos and drives for the axis drives. I commend that idea to you, it will give your lathe a new
lease of life. May I suggest that at least for the time being that you retain the existing three phase spindle motor while you get your axis drives and
controller on line. I suspect that the experience you gain with programming and handling the smaller servos will give you good insight to the potential
performance of a larger servo for a spindle and also maybe an appreciation of it problems also.

If you are dead set on having a servo as a spindle motor, and as you know I have done just exactly that for my mill and delighted with it, then you will want
the most capable motor you can afford and/or your electrical installation handle. That would tend to favour 400V drives, the servo being run with such a drive
goes that much faster and retains its torque that much longer. I would think that the exemplary torque characteristics of a servo would mean that a 4kW servo
would hold its own handily with a 5kW induction motor, if not absolute power, but the handling characteristics would be favourable. Below about 4kW
and I suspect that you would start to notice the lack of power.

A 400V servo and drive capable of 4kW is not going to be cheap, even at the discount your wife can secure. Also a large servo like that is going to place
real demands on your supply and you would have to allow some budget to improve that situation as best you can, I'd think line reactors as a minimum.

My wife left with my best friend...
     and I miss him!
« Reply #212 on: August 08, 2018, 09:54:47 AM »
Hi Craig

I am trying to achieve two things. One was to have everything running off single phase and two was to turn the spindle axis into a controllable C axis. The lathe can potentially do a lot more with a C axis.

No, I am not thinking of selling it but if and when I do it would be more saleable.

I think its clear that using single phase is not going to be an option for the spindle and after further thoughts and following all your comments, it makes sense to use a larger motor and not restrict what the machine is capable of.  

I have ordered the 750w motors and drives for the X and Z axis, absolute bargain at £718.00 with all the cables. Delivery is 16th August.

Thanks for your input on this again.

« Reply #213 on: August 09, 2018, 03:15:01 AM »
Hi Mick,
had a few days to review the discussion to this point.

It seems to me that the critical choice to make if you are to re-power your spindle with a servo is not the servo so much as the drive.
As you have seen their are a number of servos which can be driven by a particular drive but largely it is the drive that determines how well
any of those servos perform.

As a result of that I conclude to have a good as possible solution will require a three phase input drive and any servo driven by such a drive (400V)
will achieve its best or very near to it.

The drive input characteristics are particularly important as your phase converter must supply its input current.
I have attached the spec page and have highlighted the salient figures of the LX32 D30N4 being a three phase input drive with nominal input of 400V
and nominal output of 3kW.

Note the data for the drive in ABSENCE of a line reactor:
nom input 8.2A per phase
nom output 3kW

indicated input power= 8.2 x 230 x 3

The effective power factor is
power factor =3000 / 5658
Note this is somewhat better than I had predicted in an earlier post,but not that much better.
Given that your phase converter is limited to 5kW output  your drive could supply no more than 2.6kW to a servo before it starts to overload the converter by virtue
of its poor power factor.

nom input current=11.1 A per phase
nom output power=5.6kW

indicated input power=11.1 x 230 x 3
                              =7659 W

effective power factor= 5600 / 7695

Notice how the power factor has improved markedly with the addition of 1mH line reactors.
Your phase converter could now deliver 3.65kW to your drive without overload, a substantial gain over the 2.6 kW without reactors.

Simply put, the poor power factor of servo drive limits the shaft power developed by the servo, not because of any inefficiency of the servo but the poor
power factor of the drive stresses the supply. Even simple line reactors improve the situation markedly. An even more sophisticated input filter could achieve
an even better result although there will come a point of diminishing returns.

This is an area you need to explore if you wish to re-power your lathe spindle with a servo. With a good combination of line reactors and filter elements you might
achieve power outputs to match the existing induction motor WITHOUT ANY EXTRA SUPPLY STRESS. I feel sure that Schneider technical sales reps would help and
I imagine would also be able to supply the required components. Downside is that the cost could be a significant fraction of the servo and drive.

My wife left with my best friend...
     and I miss him!
« Reply #214 on: August 09, 2018, 04:24:13 PM »
Thanks Craig

That's a huge jump by just fitting a Line Reactor. Never heard of one but just been reading up on improving power factor. Interesting stuff, wished I fully understood it.

By the way, the phase converter is 5.5kw. Max single motor size 7.5hp.

There is an Amp meter built into the line side of the converter. Not sure if you noticed.

« Reply #215 on: August 09, 2018, 05:25:01 PM »
Hi Mick,

There is an Amp meter built into the line side of the converter. Not sure if you noticed.
No, I didn't see that.

In the area I live there has been an explosion in the number of farmers irragating land with 100-300kW
down-hole pumps powered by VFD's. These are all rurally sited and the degradation of the power supply is so accute
that rural residents are having TV's and computers etc blow up. The power companies are insisting that farmers
fit power factor/distortion mitigation equipment, and its expensive....and they hate it.

I suppose, they seem happy enough to pollute the environment, so polluting the power supply doesn't seem that big a deal.

The upshot is that whether you understand or not, by virtue of being constrained by your converter you will have
to come familiar with and use the techniques and equipment available.

My wife left with my best friend...
     and I miss him!
« Reply #216 on: August 13, 2018, 03:03:36 AM »
Hi All
Need to get a EMI filter for the drives I've ordered.
The motors are BCH2LF073
The spec say 4amp continuous and 13amp rms.
What ampage does the filter need to be?
Can I use one filter for the two drives?

Cheers Again
« Reply #217 on: August 13, 2018, 03:17:19 AM »
what does the manual say?

What does the Schneider rep recommend, you can bet your bottom dollar they will have all that stuff and would love to sell
it to you.

My general understanding is that because of PWM of the output you DO NOT USE CAPACITIVE FILTERS (on the output) WITHOUT SPECIFIC ADVICE to do so
from the manufacturer. The capacitive current will give the MOSFETs/IGBTs a real toweling at switch on/switch off. If there is capacitance recommended on the output
I would expect a few nF at most.

On the input side you want line reactors. You can use T section filters also but still you don't want to show excess capacitance to the drive.


My wife left with my best friend...
     and I miss him!
« Reply #218 on: August 16, 2018, 01:20:49 PM »
Drives and Servos arrived. Bit concerned they are half the size if the old Dc Motors. Modern technology I hope. Lol
« Reply #219 on: August 16, 2018, 02:47:05 PM »
remember one of those two figures of merit, one in particular Ka, the torque constant. Your 200V servos are likely to have a Ka
of about 1 Nm/A whereas your DC servos might, on a good day, have a Ka of 0.5 Nm/A.

So for the same current the new AC servo will produce twice the torque.

My wife left with my best friend...
     and I miss him!