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  1. #41
    Member TobyOneKenobi's Avatar
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    Default Re: Brushed DC spindle motor power supply

    Quote Originally Posted by RCaffin View Post
    Unexpected happenings with HQ-SXPWM-X unit. Essential reading.

    The HQ-SXPWM-X seems to be controlled by a microprocessor. Changing the various parameters is done the same way you adjust a watch: with up & down buttons. This has certain unexpected and probably undesired consequences.

    I had the system fired up and running yesterday, and the voltage on the spindle 'fluttered' at about 1 Hz. It took some thought to figure out why. Note that on the bench when driven by either the supplied pot or by my sig gen there was NO flutter. But explaining this takes us into some obscure internals of Mach3.

    Mach3 has an internal engine/update speed. By default it is 25 kHz, but that can be changed by the user to over 100 kHz. It also has a user selected base frequency for the PWM. Default seems to be 20 Hz, but again this can be changed by the user. Most users would probably not touch this. But the manual for the HQ-SXPWM-X recommends a PWM frequency of 1 kHz. There are consequences. For reference, my system is set to 100 kHz engine and 1 kHz PWM.

    Imagine you have an engine speed of 25 kHz and a PWM speed of 1 kHz. The pulse width can only be set to one of 25kHz/1 kHz values by the SW. For a top spindle speed of 3,000 RPM, this means you can only set the spindle speed in steps of 3000/25 = 120 Hz. But Mach3 allows you to specify the spindle speed to within 1 Hz. How does it do it?

    I think it dithers, swapping between the two nearest possible PWM widths at a cycle rate of about 1 Hz. Over time this averages out to give the specified spindle speed. If you are using a PWM to DC convertor with a good smoothing capacitor on the output you would probably never notice it. But I think the HQ-SXPWM-X senses the incoming width of every single PWM pulse digitally, and tries to adjust according to the latest width. As this width flutters, so does the output voltage! And so does the output current as the driver tries to vary the spindle speed.

    How to solve? Actually, dead easy. I had a pulse width to DC convertor on the input to the previous driver, with a bit of a filter on the output for smoothing. I will simply switch from the PWM input to the +5 V DC input using this existing convertor. I have already tested this on the bench and it works fine.

    What this means underneath all this is that Mach3 was meant for analog-type spindle controls. The PWM signal was a way for a computer to create the required analog signal - slowly. PCs have their limits.

    Cheers
    Roger
    Hi,

    found this forum whilst googling HQ-SXPWM-X because I have the same issue, only the 0-5V input using the 5v line with the variable resistor gives a stable motor drive, I have tried the PWM and the 0-10v inputs with the same result. I am using mach3 with a 4 axis usb motion controller. Now I think I might be just about to put a spanner in the works of your theory. I set up an Arduino with a 1khz variable duty PWM output at 5v and again got the same results, fluctuations/oscillations in speed, I'm wondering if it's actually the PWM input on the PSU that's the issue? I am going to follow your lead and purchase a PWM to analogue module and use that and hopefully that will resolve this issue, but it's food for thought?

    Chris



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    Default Re: Brushed DC spindle motor power supply

    I'm wondering if it's actually the PWM input on the PSU that's the issue?
    Interesting thought. Not impossible either. Or both?

    Actually, I think it is a general problem when you go to digital controls with (say) only 8 bit resolution. The digital stuff has to dither to get an average of what you have specified. But we can see the dither, and it is not good.

    Yeah, go analog. Since installing a PWM-to-DC convertor I have had zero problems. Runs smoothly.

    One other point. If you try to slam the supply from 0 V to 200 V across a motor, the current surge will be incredible - and way beyond what the supply can deliver. Not mention that the surge might well destroy the magnets in the motor. Anyhow, this supply is smart: it detects the over-current VERY quickly and faults out: display E1. Just what I want - really.

    But how to reset? Simple: switch the Enable input to Program and back. Actually, that input is NOT an 'enable' input at all, but a 'program' signal input.

    Cheers
    Roger



  3. #43
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    Default Re: Brushed DC spindle motor power supply

    Hi Roger,

    well I'm no expert, I'm a PC tech by trade and CNC stuff is just a hobby, but a useful tool in diagnosis is the process of elimination, by bypassing mach3 and the motion control module you eliminate that part of the process, the fact that you get a similar or exactly the same symptoms from a different source would imply that the common components left would be the issue? As to the motor control, the HQ-SXPWM-X has a soft start so I'm assuming that full current is not introduced straight away by it's default settings and my experience of this unit would confirm this as it takes a few seconds to reach the required speed. Apart from this I think its a capable little psu but the PWM side needs improvement.

    Chris



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    Default Re: Brushed DC spindle motor power supply

    Hi Toby

    Yes, the unit has a soft start (which I use), so that is not a problem by itself.

    But the unit does not live in isolation. If you have a relay on the output and you set the o/p to 200 V, then you enable the relay, THEN you get the problem I was describing.

    I have not one but two relays on the output on my CNC. One is a reversing relay so I can have both M3 and M4. I use them both. The other is an On/Off relay. It is not essential, but it does allow me to have a dump resistor for stopping the spindle quickly. So I have to sequence things carefully in the macro definitions. (The entire CNC electronics system is my design and construction.)

    Can the PWM side be improved? Not easily, as Mach3 is also digital and the PWM problem comes, at least in part, from that.

    Never mind, it is a nice unit.

    Cheers
    Roger



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    Default Re: Brushed DC spindle motor power supply

    I am going to give the DC drive another try. I ran mine with a straight DC signal (Not PWM) and also with the potentiometer. I had fluctuations in rpm especially at low speeds. Any suggestions?

    I'm considering moving the DC drive away from the control cabinet and mounting it close to the motor.



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    Default Re: Brushed DC spindle motor power supply

    How odd. Further exploration needed.

    For the record: I have run my supply at high, middle, low and very low speeds with a filtered DC input and not seen any fluctuations.

    Cheers
    Roger



  7. #47
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    Default Re: Brushed DC spindle motor power supply

    Quote Originally Posted by RCaffin View Post
    Hi Toby

    Yes, the unit has a soft start (which I use), so that is not a problem by itself.

    But the unit does not live in isolation. If you have a relay on the output and you set the o/p to 200 V, then you enable the relay, THEN you get the problem I was describing.

    I have not one but two relays on the output on my CNC. One is a reversing relay so I can have both M3 and M4. I use them both. The other is an On/Off relay. It is not essential, but it does allow me to have a dump resistor for stopping the spindle quickly. So I have to sequence things carefully in the macro definitions. (The entire CNC electronics system is my design and construction.)

    Can the PWM side be improved? Not easily, as Mach3 is also digital and the PWM problem comes, at least in part, from that.

    Never mind, it is a nice unit.

    Cheers
    Roger
    Hi Roger,

    just noticed that you also tried a signal generator and still had the same problem so that makes it even more odd. I'm not sure, with that the board that I'm using, that the PWM comes direct from Mach3, this board uses an STM32F103 processor so I'd suspect a bit of "translation" going on, the board isn't a bob it's more like a motion controller, cheap too!

    Chris



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    Default Re: Brushed DC spindle motor power supply

    also tried a signal generator and still had the same problem
    A correction I think: I tried a sig gen on the bench and did NOT have the problem.

    Yes, the STM32F103 will have the same problem with dither as it is (I presume) also digital.

    Cheers
    Roger



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    Default Re: Brushed DC spindle motor power supply

    I did some more experimenting. I shortened up some wires and improved some grounds and shielding. It now is acceptably smooth when using the potentiometer to control it. I had figured there was some RF interference. I was able to vary the motor speed by moving wires around. I now plan on mounting it close to the motor outside of the main control box. Then I'll try it again using the 0-10 VDC signal and see how it does.



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    Default Re: Brushed DC spindle motor power supply

    You could also try putting a ceramic 0.1 uF cap literally at the input terminals. It can't hurt, and may well help.

    Cheers
    Roger



  11. #51
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    Default Re: Brushed DC spindle motor power supply

    Quote Originally Posted by RCaffin View Post
    also tried a signal generator and still had the same problem
    A correction I think: I tried a sig gen on the bench and did NOT have the problem.

    Yes, the STM32F103 will have the same problem with dither as it is (I presume) also digital.

    Cheers
    Roger
    Oops, yes you're right but that's still odd, anyway I hooked up a dollatek pwm to analog converter and after realising that there were a few "limitations" with it got it working ok, no fluctuations in rpm. Going slightly off topic, I was thinking about some form of braking on the spindle as there is none provided on the spindle PSU, especially in regards to an e-stop, any ideas?

    Thanks
    Chris



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    Default Re: Brushed DC spindle motor power supply

    Quote Originally Posted by TobyOneKenobi View Post
    Going slightly off topic, I was thinking about some form of braking on the spindle as there is none provided on the spindle PSU, especially in regards to an e-stop, any ideas?

    Thanks
    Chris
    The simplest form is a relay that shunts the motor when power is removed.
    It would pick up when ever a spindle command was issued.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
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    Default Re: Brushed DC spindle motor power supply

    Quote Originally Posted by Al_The_Man View Post
    The simplest form is a relay that shunts the motor when power is removed.
    It would pick up when ever a spindle command was issued.
    Thanks, yes that was the route I was thinking about but not entirely sure of how to implement it, relay not an issue but it would need a resistor too? It would need to be something big enough able to soak up the current generated by the motor. It's a 500watt 180v motor.

    Many thanks
    Chris



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    Default Re: Brushed DC spindle motor power supply

    500wat is not that large, if you want to try a resistor, use ~ 5-10 ohm to start with.
    The relay would be picked up when the command start for the spindle is made.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
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    Default Re: Brushed DC spindle motor power supply

    Yes, a DPDT relay, wired to disconnect from the drive and to dump a 5 ohm 10 W resistor across the motor when M5 is issued. MUST disconnect from the drive! My spindle drive is also about 500 W / 180 VDC.

    You might worry about the power rating of the dump resistor - only 10 W, but if you pick a solid wire-wound R it will have the surge capacity to take the brief current spike. On my CNC the motor stops in about 1 - 2 seconds.

    Cheers
    Roger



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    Default Re: Brushed DC spindle motor power supply

    Al-The_Man & Roger, thanks!

    Chris



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    Default Re: Brushed DC spindle motor power supply

    Quote Originally Posted by RCaffin View Post

    an inexpensive laser digital optical tachometer
    Of what accuracy I wonder? That would depend on the clock inside the tacho. It may be of course that the tacho had been calibrated against a good reference. I don't know.
    Mine shows exactly the same RPM as the motor is running with. I checked using a servo motor and precise pulses, and at least between the range of 1 - 3000 RPM, the inexpensive tachometer shows exactly the same RPM as the pulses sent to the servo should result in. There are though some important things to consider. The reflective tape must be larger than the light beam hitting it, and that the rest of the axis, pulley, chuck or whatever is rotating is covered with black tape, preferably non-reflective. The ambient light should not containing any flickering red, and the red beam from the tachometer should hit the reflective tape at right angle, and also your hand should not shake too much, also you should not bee too close (or too far away, from the measured point. These units are based on one second pulses, and that is very easy to generate with high accuracy using any cheap crystals, even a cheap 32.768kHz crystal is accurate enough for this sort of application.

    https://www.youtube.com/c/AdaptingCamera/videos
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    Default Re: Brushed DC spindle motor power supply

    Update for what it is worth:
    I have been using the HQ-SXPWM-X for over a year now, as outlined in previous postings. It works, it works well, and I am very happy.
    As I mentioned earlier, the American supplies seem to be 50 years behind the times and 10x more expensive. This unit is the bee's knees.
    I put a small SPDT switch on the Enable input. In one position the unit is then in Run mode; in the other position it is in Program mode.
    If/when the unit detects a fault situation, it simply turns off and displays E1. I flick the Enable switch to program and back to Run, and the fault is cleared.

    So how did I get the supply to fault in the first place? Blush, shuffle feet, etc. I ran the tool holder into the chuck. No damage done really.

    Fwiiw, I have since ordered a second identical unit to go on the shelf as a hot spare. But unlike some of the KB units i was using before, this unit has proven to be extremely robust.

    If anyone want a copy of my version of the stock manual, pls contact me. I have converted most of the Chinglish into plain English, and added a few notes.

    Cheers
    Roger
    bushwalkingroger@gmail.com



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