power supply/controller for spindle motors

[PeterT]

I'm interested in getting one of these offshore motors for a project. Not for cnc. I just want to turn a knob to vary rpms.

This one has what I think is a standard 110VAC input, DCV output power supply & a knob to vary rpms. Yes?
https://www.ebay.ca/itm/CNC-Air-Coo...502893?hash=item2cd506066d:g:pDUAAOSw3UZbC8B8

Whats the difference of this one? Is the black box 'driver controller' for a cnc setup that talks to PC? Is it still a power supply or just dedicated to controlling? If so then why does it show a similar potentiometer knob?
https://www.ebay.ca/itm/500W-Brushl...750912?hash=item285a01ac40:g:DpoAAOSw4RZbCZNc

 

[John Conroy]

Hey Peter, the first one uses a brush type motor (2 wires to the motor). The speed is varied by changing the armature voltage (12 to 100V DC in this case). The second uses a brushless 3 phase DC motor. The speed is varied by changing the output frequency to the motor. I think both motor controllers can be used to manually vary speeds with a manually rotated potentiometer or the variable speed function could be accomplished with a CNC control system providing the potentiometer function. The 3 phase motor will provide more constant torque at all speeds where the other will have low torque at low speed.

 

[PeterT]

Thanks John. So for the brushless system link I would still need to source the appropriate AC to DC power supply? Actually I just realized I pasted in the wrong link that had an identical looking motor/controller but they called it 'power supply' or something like that so I thought maybe somehow integrated. But I think that's a language barrier thing. The black box is always only the speed control unit which distributes 3p power to 3p motor but does not generate its own power, correct? I need to check the PS I have but from the look of the terminals, do you think PS DC input hooks up to (red box) terminals and the knobby control thing hooks up to (orange box)? And this knob control then over-rides what would normally be CNC input control to vary rpm?

Shows a picture of PS, but reading description I don't think included Grrrr..
https://www.ebay.ca/itm/ER11-Brushl...409576?hash=item3d90af40e8:g:XhsAAOSwW2RdR4zB
Package Included:
- 1 x Brushless Spindle
- 1 x Clamp Base
- 1 x BLDC Motor Driver Controller with Speed Adjustment Knob & Start Switch

Ali package with PS?
https://www.aliexpress.com/item/329...chweb0_0,searchweb201602_2,searchweb201603_55

 

[John Conroy]

The box is the controller. In this pic you would connect the two 120 volt AC wires to the first 2 terminals on the left. The next 3 terminals labelled U, V and W go to the 3 phase motor. The potentiometer plugs into the box on the far right 7 pin connector.

 

[Johnwa]

i think the black box requires a DC input, so yes it needs a power supply.
the brushless DC motor will run at the speed it is set at up to rated load.

The other one may or may not have actual speed regulation. It might just change the voltage applied to the motor, in which case the motor will slow as load is applied.

 

[John Conroy]

After some re-reading I think Johnwa is right.

 

[JohnW]

The controller definitely requires DC input. The really big hint on that is the + and - marked on the power terminals! Feeding 120V AC in there will extremely quickly let out the magic smoke, and probably in a very impressive way.

More specifically it requires somewhere between 24 and 50V DC on the power terminals to work. From the more detailed description I found, it can control a 3-phase motor that uses up to 500W of power, or a maximum of about 12A on the input DC power. 12A times the input voltage is the real maximum output power. More realistically this is probably built as cheaply as possible (the 12A can also be called 'marketing amps' which are more likely 6-8 real amps), so for reliable operation I would limit it to half to two thirds of that.

Since any cheap power supply you order is also likely using 'marketing' ratings, make sure you get some extra. To provide a reliable 12A, I would look at least a 15-20A power supply at whatever voltage you choose.

If the motor you use is only a 250W motor, this controller would probably be fine with a 10-12A power supply, I would not try to run a 500W motor under full load on a continuous basis. For just a few seconds it is probably OK, but you are pushing your luck to run it continuously on this controller with a 12A power supply.

The output speed of the motor is controlled by the DC voltage applied to the SV terminal (from 0 to 10V). That voltage can be applied from a potentiometer that acts as a voltage divider between the supplied 10V and ground terminals, or by some external 10V source. The 0-10V is chosen because that is a very common control scheme used in industrial controls.

Exactly what speed the motor will run at is dependant on the motor and the input voltage. Many BLDC motors have a rating called KV. That is the number of thousand RPM they will turn per input volt. That rating is commonly found on the small motors used in quad-copters. For example 1000KV means that the motor will be able to spin at 1000RPM for each volt on its input. So with 12V, the motor will be able to spin at up to 12,000RPM.

It won't spin at that speed on its own. The controller needs to generate an appropriate frequency of three-phase AC to run the motor at that speed. That is just the maximum speed at which the motor retains its torque. As the AC frequency increases beyond that point the motor rapidly loses torque since its windings cannot change quickly enough. The rate at which the winding current (and hence the magnetic field that makes the motor rotate) can change is dependant on the inductance of the windings and the voltage that is applied.

The AC frequency required will be the number of rev/sec (12,000RPM = 200 rev/sec) times the number of poles in the motor. For instance, a 4 pole motor requires 4 AC cycles for every rotation of the motor shaft. So for that 1KV motor running at 12,000RPM requires 200 x 4 = 800Hz 3-phase AC driving signal. Increasing the frequency to 1600Hz will make the motor spin faster, but at much less torque since in half the time the coils can only build to half the current, which means half the magnetic field, so half the torque. It might actually only be a quarter of the torque at twice the frequency, I don't remember the details.

Basically when the controller is at its full speed setting (10V input signal), it will drive the motor with an AC signal at the full input voltage (or nearly so), so the motor should rotate at its KV rating times the input voltage. There are some loses, so it won't be quite that. This controller has a maximum RPM of 20,000 listed, but that is probably actually the maximum AC frequency (333Hz). The motor RPM would then be dependant on the number of poles the motor has.

The controller has two ways of controlling the output frequency to the motor. With and without Hall sensors. Either way, the controller uses feedback from the physical motor rotation to control its out put frequency.

Hall effect sensors are magnetic sensors that sense the position of small magnets on the motor shaft. As the motor rotates the Hall sensors tell the controller how fast the motor is actually rotating (actually the position of the rotor) so it can output the appropriate frequency. If you are trying to speed up the motor, the controller will output a slightly higher frequency than the motor is actually running at so the motor will speed up. The idea is to keep increasing the rate of the rotating magnetic field so the motor speeds up, but not so much that the motor falls behind the field. You cannot just suddenly provide a 200Hz signal to a stopped BLDC motor and expect it to catch up. It will just stall and vibrate instead.

Without hall sensors, the controller samples what is called the back EMF from the motor windings to see how fast the motor is turning. As the motor turns it generates a voltage called the back-EMF that is proportional to its speed. Basically once the back-EMF rises to the same level as the driving voltage (EMF) the motor will go no faster.

Hall sensors give the controller better feedback so it can generate a better signal that matches the actual motor RPM, but they cost money, and the back-EMF technique works, but not as well. Especially when the motor is under heavy load like when starting or transitioning to a heavy load where it can more easily stall without the real physical feedback provided by the Hall sensors.

Hope this helps a bit.

 

[PeterT]

Thanks.
The circuit diagram in the AliExpress package is maybe more clear. They show 'external analog' (=cnc setup?) and 'potentiometer speed control' (=manual mode?) screen grab attached.
The included PS is 48DCV @ 12A so nominal 576 watts. Aside from the usual specs inflation, do you think that (576w) is sufficient overhead for this 500 watt (nominal) motor & maybe why they packaged? Its not like I need the max power, more about getting appropriate PS. I checked my own PS, its 13.5V @ 55A, so wrong configuration.

https://www.aliexpress.com/item/329...chweb0_0,searchweb201602_2,searchweb201603_55

 

[JohnW]

There is really no difference between the 'external analog' and 'potentiometer' speed connections. The point is to provide a 0-10V signal to that input of the controller. It does not matter how that voltage is created. The 0-10V signal is a very low current signal. When using a pot, (the photos in a different listing show a 10K ohm pot) the potentiometer is just sampling the voltage across a 10K ohm resistor which is only drawing 1mA from 10V, so the sample current is probably less than a tenth of that, or 0.1mA.

My usual concern with this sort of stuff is that most of the stuff on aliexpress (and e-bay, banggood, etc), is rated in what i usually call 'Chinese Amps/Volts/Watts'. Also known as 'Marketing Amps/Volts/Watts' to be fair to the Chinese. If you were buying a $1000 setup from an industrial supplier, the odds are good that the equipment would run for years at its full rated specs without any problems. That may even be true of the stuff in this AliExpress listing, but probably not.

A while back I bought a few cheapie 24V 1A power supplies. I tested them, and they started dropping below 24V at over about 800mA, so they were pushing the design a bit. I got the 1A units because I needed about 700mA, so it was all OK, but if I was counting on a full amp at 24V, my project would not have worked. It is hard to say what would happen to the power supply when over stressed. It might just sag its output voltage a bit and be happy, or it could overheat and blow something up. The bottom line is it is a bit of a crap shoot when buying cheap stuff and you usually need to pad the specs in your favour just to be sure.

If you are never going to use the full '500 watts' on the motor, it is probably all fine. The motor spec says:
Speed: 12000r/min
Torque: 0.6 N.m

If you are happy with 0.4 Newton-Meter at 12,000RPM or 0.6 N.m at maybe 9,000RPM, it all should be fine. That will draw maybe 8-10A from the rated 12A power supply, and be running at less than the 'marketing' rating of the controller, power supply, and the motor itself, which would probably stay within the real capabilities of these products. Occasionally pushing the motor to its full spec for a handful of seconds would probably be OK too, but you can't be sure without testing.

The stuff is cheap, so you are not taking a big risk, but I usually like to over-spec cheap stuff like this by at least 25% just to be sure.

On the other hand, the items may actually meet or exceed the specs listed in the ad, but that is not normally the case when dealing with prices like these.

Bottom line is that if you are not running the motor too hard it will probably be fine.