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Author Topic: Mill Spindle Speed Control - DC Motor  (Read 2832 times)

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Re: Mill Spindle Speed Control - DC Motor
« Reply #10 on: August 20, 2017, 03:58:20 AM »
Yes you have the correct drawing of the DC motor that I am looking at. Thanks for the eBay links for the AC Allen Bradley, that's really awesome information and looks like a really good alternative. I am very impressed with the compact size of the motor. The question that I have is how this compares for torque against the DC motor. Time for some research on the net...

Keith
« Last Edit: August 20, 2017, 04:02:00 AM by ViKiNG »
Re: Mill Spindle Speed Control - DC Motor
« Reply #11 on: August 20, 2017, 06:05:25 AM »
Hi,
have a look on the label, the max sustained torque is on it. Aside from any thing else there is the power spec...power=torque x speed....easy.

The Allen Bradley MPL series are mid to low inertia.....the A in A310P stands for 230V, the 3 is the frame size, 80 mm square, the 10 refers to the length or
stack size and P refers to the speed, 5000 rpm is this case. The A310P in the first link is 730W. There is an A320P model of 1.3kW and the second motor I
linked is an A330P of 1.8kW.

The rated torque of the three models is:
1) A310P   1.58Nm
2) A320P   3.05Nm
3) A330P   4.18Nm

The motor I used is the A330H model which is rated to 3500 rpm but has a little more torque, 6Nm which suited me I want plenty of torque, but still 1.8kW.

You may note that the rated current of the small motor the A310P is just under 5A. You could use a smaller drive than the link I posted, the 2098-DSD-010
has rated current of 5A, overload 15A,(5/15A) and would run the A310P nicely.
The larger two will require more current, the 2098-DSD-020 is rated at 10/30 A. I used this to power my motor although if I could have found a 2098-DSD-030
rated at 15/30A I would've taken it. The larger the drive the more you pay. The 010 can be had for under $100 but $100-$200 is more realistic. The 020 can be
had for just over $100 but $200-$400 is more realistic. I missed out on an 030 for $280, $500-$800 is the norm.

The 730W motor and drive could be had for about $500 plus shipping. Whether you consider that good value for secondhand I don't know. Some of the
Chinese offerings are about the same but new. I ended up paying $700 NZD, about $500US for the motor, $250US for the drive and $150 for the cables,
near enuf to $1000 for a 1.8kW servo and drive. It kicks anus!!! I am happy that the value is there, the crappiest I was prepared to go was Delta and they
cost more in this power range.

Go to the Rockwell Automation site and get the MPL series drawings a see if you cant squeeze one into your machine, they are good.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mill Spindle Speed Control - DC Motor
« Reply #12 on: August 20, 2017, 03:30:30 PM »
Thanks Craig, the size in not a problem, I could go up to 110 square. The power of 700W and current at 5A is good as I need to run the complete machine off 230V 10A wall outlet. What you are suggesting looks good. The uncertainty is if the AC can deliver enough torque. I am not sure what it will delivery through the rev range. I have had a look for the performance curves and not been able to find them. The M4-2950 B DC option specification is continuous torque of 2Nm and peak of 14.9Nm. The DC option would definitely cost more, I am trying to get the best performance for around 5A current draw

Keith
Re: Mill Spindle Speed Control - DC Motor
« Reply #13 on: August 20, 2017, 05:31:59 PM »
Hi Keith,
the AC part of AC servo is a bit of a misnomer, it is really a 'brushless DC motor'. In order to spin the applied DC
has to comutate backwards and forwards, ie become AC.

The torque of a DC motor comes from a comutating current in the armature in a fixed permanent magnetic feild
provided by the pole magnets.

The torque of an 'AC' motor is a comutating current in the 3 phase field windings operating on magnetised rotor.

The upshot is 'there is no damn difference'. An AC servo typically has an overload torque of three/four times its rated
torque, same as a DC motor. The equation power=torque x speed applies to both ie a 1Nm torque motor spinning
at 100 rad/sec produces 100W...end of story..no difference between AC an DC!

Craig
My wife left with my best friend...
     and I miss him!
Re: Mill Spindle Speed Control - DC Motor
« Reply #14 on: August 20, 2017, 08:33:39 PM »
Hi Keith,
a picture being worth a thousand words....
https://www.youtube.com/watch?v=cdiZUszYLiA

Craig
My wife left with my best friend...
     and I miss him!
Re: Mill Spindle Speed Control - DC Motor
« Reply #15 on: August 20, 2017, 09:38:21 PM »
Hi Keith,
an AC servo can produce rated torque from zero rpm to rated rpm, and if your drive allows a technique called
'field weakening' steadily reducing torque at FASTER than rated speed. In terms of control flexibility they
are better than a brushed servo.

I run my drive on a single phase outlet rated at 10A also. It doesn't stop me from drawing as much as 30A
in bursts enuf to max my drive and servo....good...very good!

Craig
My wife left with my best friend...
     and I miss him!
Re: Mill Spindle Speed Control - DC Motor
« Reply #16 on: August 21, 2017, 04:37:19 AM »
Hi Craig

I get what you are saying. I see that there are plenty of motors and drives for sale on eBay for reasonable prices. This definitely looks like a good option. Am I selling myself short @ 730W, should I look at the 1.3kW? How is it that you can run your A330P which is rated at 12A continuous from a 10A outlet? Are you running all the axis drives and other electrics for the machine off the same supply?

Thanks

Keith
Re: Mill Spindle Speed Control - DC Motor
« Reply #17 on: August 21, 2017, 05:19:59 AM »
Hi Keith,
yes the whole shooting match off on 10A circuit. Don't know what its like where you are but in New Zealand its not uncommon for a 10A circuit
to be a lot more heavily loaded. I work as a technician fixing welders and even little inverter welders regularly draw 30A. I know its not ideal
but that's what happens with very few if any ill consequences. The circuit feeding my mill is 2.5mm square and I'm not uncomfortable at running at
25A continuously. As it turns out you have to be doing something pretty extreme to draw that sort of juice.

I know the name plate says 12A but that is in fact the peak, not rms. It is however 12A peak per phase, and of course there are three of them! The
full load amps (FLA) referred to the 230V input is 28A! The rms doesn't sound quite so bad, 19.8A ...LOL

Of course the reality is that I seldom get anywhere close to max current and therefore max torque. Also lets imagine I'm driving a facing tool at high
torque but often modest speed, say 1000 rpm. Under that circumstance the voltage at the motor terminals will be about 1/3 rated ie 100V. The DC link
voltage is 320V (230VAC rectified and smoothed) and consequently the effective PWM of the  link voltage to the terminals represents a transformation
of 3:1. If the phase current is 12A per phase the link current required to feed that phase is 4A. You can see where I'm going here, those occasions where
I require max torque often coincide with modest speeds and the effective transformer action of the PWM buck regulators means everythings kool.

I have three 5 phase 23 size steppers with genuine Vexta 230V drivers. According to the name plate they can draw heaps of current but in practice I've
never seen the draw more than an amp, thats roughly 230W...where could all that power go...little 23 size steppers couldn't absorb that much except briefly!
The 1/8 hp coolant pump draws more on average than one of the axis drivers.

The upshot is that I have to really bore into a piece of stainless with a 16mm tool to start drawing decent current from the plug and a that stage my mill
is 'a humming and'a jumpin' and can't really take any more, its not 250 kg but probably 150kg.

If you think I'm being a bit cavilier about it wait until you see someone plug in a single phase plasma cutter and start cutting, it makes my mill look liteweight!

Craig
My wife left with my best friend...
     and I miss him!
Re: Mill Spindle Speed Control - DC Motor
« Reply #18 on: August 21, 2017, 05:23:42 AM »
Hi,
by the way go for the biggest and most powerful you can squeeze in there and/or afford. You may not use it all often, but you will use it
and the bigger it is the easier it will do it.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mill Spindle Speed Control - DC Motor
« Reply #19 on: August 21, 2017, 05:43:41 AM »
Hi Craig

Just read your bio and I see that like myself you are also in NZ, I'm in Hamilton, what city are you in?

Keith