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Author Topic: I burnt out my lathe motor today. So have a few questions.  (Read 282 times)

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I burnt out my lathe motor today. So have a few questions.
« on: March 01, 2019, 02:42:35 AM »
One of those days where we are busy, out cnc machinery is working in the background, the tool goes where it shouldn't on the lathe, stops the workpiece, pop goes the nice single phase motor - and it was a reversible one at that! Anyways I have had a DC treadmill motor sitting on the shelf to put into this lathe, just means I need to do it now. But a couple of quick questions if someone could please answer with a yes or no?

I know I am not supplying all info here and am just keen on hearing opinion in a general sense.

1) I plan to control the speed of this lathe DC motor with mach 3. And am actually going to use a PWM to 0-10VDC converter I bought off someone in this community. I have a speed sensor on the lathe already for threading. Does Mach 3 read this speed input and then decide what output to send to the motor controller?

2) The Chinese motor controller has the three connections for a 10k pot for the speed control. Its plausible I can plumb my PWM converter into these connections to control the speed?

3) The DC motor has CW written on it. I thought all DC motors were reversible? Wondering if this one is reversible or is there something mechanical that would make it unhappy going in the other direction. Its a 2hp treadmill motor.

Fun fun fun!

Re: I burnt out my lathe motor today. So have a few questions.
« Reply #1 on: March 01, 2019, 04:07:00 AM »
Hi,

Quote
I have a speed sensor on the lathe already for threading. Does Mach 3 read this speed input and then decide what output to send to the motor controller?

That depends on your motion controller. Mach's parallel port, despite being run in the same PC as the Mach application, is
a motion controller, and can vary its PWM under certain circumstances. There are other external controllers where that is not
the case. Indeed Mach3 always, historically, used to be an 'open loop controller', that is without feedback control.

The attached pic is from Config/Ports and Pins/Spindle Setup. I have never used this particular feature of Mach3, in fact I use
Mach4 now and wont be going back either, but I understand that Machs parallel port requires an index signal from the
spindle, that is one pulse per revolution. The PID control then adjusts the PWM signal to suit the commanded spindle speed.
Note that the control loop is pretty slow, it cannot accommodate rapid excursions in speed but is none the less an advance
on open loop control.

Quote
The Chinese motor controller has the three connections for a 10k pot for the speed control. Its plausible I can plumb my PWM converter into these connections to control the speed?
Yes it is plausible but it is not a slam dunk either. Some US made KB DC controllers can and do work that way, but not all.

Quote
The DC motor has CW written on it. I thought all DC motors were reversible? Wondering if this one is reversible or is there something mechanical that would make it unhappy going in the other direction

You are correct most DC motors are reversible. It depends on the phasing of the brushes on the commutator.
If the brushes are neutrally phased then the motor can run either way. If however you set the brushes a few degrees off neutral
then the motor will work much better one way than the other. It will still run backwards probably but you will likely
reduce the life of the brushes and/or wreck the commutator. It might be that you can adjust the position of the brushes
inside the motor. I personally am not familiar with the process. I have fiddled with and old school DC generator that had
adjustable brushes and you could tell it had a 'sweet spot', not very scientific but it worked.

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

Offline MN300

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Re: I burnt out my lathe motor today. So have a few questions.
« Reply #2 on: March 01, 2019, 07:21:03 AM »
You should address the issue of motor overload protection when the spindle jams. I don't know what features your cheap Chinese controller has for that. The max current limit may give you several seconds grace period.

Opto isolation of the PWM signal will reduce electrical noise between the motor and controller. If the speed input of the controller is off ground it would be mandatory.

Posting the model numbers of the motor controller and PWM circuit would be helpful. Also, what was the HP of the original motor?

Offline RICH

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Re: I burnt out my lathe motor today. So have a few questions.
« Reply #3 on: March 01, 2019, 06:23:40 PM »
For lathe threading use the single pulse for rpm readout and use by Mach 3, but, manually set the rpm of the motor manually and not via PWM for threading. The reason is that when threading, the PWM and Mach3 internal adjustments to thread pathing will be fighting each other.

RICH
Re: I burnt out my lathe motor today. So have a few questions.
« Reply #4 on: March 01, 2019, 09:42:13 PM »
Thanks for the words. Its why we belong to these forums huh?

The controller is from Jinan Keya Electronics P/N MMT-115/230RT10AL I dont see a PWM input on it.

The motor I burnt out was a 750w single phase reversible motor. I actually dont know what happened. I had cut several items of the same out and was using a loud machine in the background. The reason I knew something had happened was when the breaker in my shed popped. For some reason the tool decided to bury itself thus stopping the workpiece. It didnt do this on the previous runs. Also, the overcurrent device inside the lathe did nada. Ha.

I will check the motor, I reckon its reversible which is only necessary for a few operations.

The PWM to voltage converter I dont have the part number for. I bought it off one of the Gurus on one of these forums to control a spindle.

Hey so Mach 4. This is a recommended upgrade yes? I am so into keeping original working software but should look into it. Infact I still have an XP disc unused. On that subject, I am a ROV supervisor. It was only in the last few years we stopped using XP as the platform to run the very expensive ROV spread. Yep. XP.
Re: I burnt out my lathe motor today. So have a few questions.
« Reply #5 on: March 01, 2019, 11:07:09 PM »
Hi,
I found a copy of a manual for that DC controller, all in Chinese. On page 11 however there is a diagram showing a 10 kOhm
pot spanning a +12Vdc output, c ground and a analogue input.

If you can arrange for your PWM to analogue converter to output a voltage from 0 to 12V you should be able
to adapt Mach3 to the DC controller.

Quote
Hey so Mach 4. This is a recommended upgrade yes?

I've used Mach4 for 2-1/2 years and am of the opinion that its light years ahead of Mach3.
Mach4 is native to, and really requires an external motion controller like a SmoothStepper or a UC300. Be prepared
to spend a 2-3 hundred dollars on hardware to take advantage of it. If you don't want to spend the money stick with
what you've got.

Craig
« Last Edit: March 01, 2019, 11:17:03 PM by joeaverage »
My wife left with my best friend...
     and I miss him!

Offline MN300

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Re: I burnt out my lathe motor today. So have a few questions.
« Reply #6 on: March 01, 2019, 11:32:08 PM »
I found the same Chinese manual. Google translate does work on it but drops the figures.

 It is a 4 quadrant controller so you could drive the motor in either direction, if the motor handle it. The drive is limited to 7.5 amps unless you add a heat sink. If you have a 90 volt motor that's 675 watts. (1 HP = 745 watts). With a 180 volt motor you will get twice that, 1350 watts, which is more than your old motor. Of course you wouldn't want to run the drive flat out.

A problem with reversing is that the speed input takes a positive voltage for forward and a negative voltage for reverse. Your PWM circuit most likely only puts out a positive voltage. If you do want reverse additional circuitry with an OP Amp to invert the voltage could be added. It might be worth a search in case it's a product somebody sells, otherwise you would have to assemble it yourself.
As I said before it would be best to isolate the drive with relays for enables and opto isolation for the PWM.
Re: I burnt out my lathe motor today. So have a few questions.
« Reply #7 on: March 01, 2019, 11:50:57 PM »
Hi,
I could see a 10k pot and a +12VDCsupply and a -12VDC supply to provide both + and - voltages for forward
or reverse but no PWM input, the analogue input is the wiper of the pot. You cannot feed PWM straight into that.
it must previously have been converted to an analogue voltage. Uless you have a linear opto isolator in mind
I don't see how that would work.

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

Offline MN300

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Re: I burnt out my lathe motor today. So have a few questions.
« Reply #8 on: March 02, 2019, 05:47:36 AM »
The PWM to voltage converter would be connected directly to, and powered by the drive. The digital PWM signal would be isolated by an opto-isolator.
The voltage inverter, if needed for reverse operation, would be an IC like a KA358 and 2 resistors.