Simplest way to control 180vDC motor with PWM

Thread Starter

BigAlscorpio

Joined Feb 5, 2015
52
Hi to all, I have been trying to control a rescued treadmill motor for use in my workshop wood lathe.

I have used PWM many times before with PIC microcontrollers and never had a problem but this 180vDC setup has me stuck. I have tried half a dozen times so far with simple 555 circuits to quite involved PIC micro circuits all with the same result, something releasing the magic smoke!

The motor is rated at 1.25Hp and is brushed DC, I have used both MosFets and IGBTs with much larger ratings like 100A and 600v to no avail. All I want is to get the motor to actually start up (soft start) at low PWM and ramp to a set speed that I select with a pot or rotary encoder. I have thought of using the salvaged controller but it has a 3 second delay and a soft start that is way too long to be anything but annoying as a lathe motor. I also note that the controller gets its power though a large choke and wondered if that has an effect on the inrush current, enough to prevent magic smoke?

I also know that I would need other features before I could safely use the motor as I would like as in feedback for speed governing and a stall limiter. There are no doubt other features that I could do with that members here will be conversant with but for now all I want is to actually get ANY control at all over this motor. Any help or suggestions will be gladly received and there is no need to worry that I will kill myself trying anything that is suggested. I am a retired Electrician who has worked in both home and industry so I always take the relevant precautions and have a lifelong respect of the invisible movement of electrons. ;) Here in the UK we are on 230vAC at 50Hz.

Thanks for reading this long tome and please help, Al
 

Thread Starter

BigAlscorpio

Joined Feb 5, 2015
52
Hi Dendad, I have used various diodes from 1n4007 to the ultra fast type scavenged from switching PSUs. As for circuits, I do all my prototyping on an old program called VeroDes, it is slow and laborious and somewhat limited but it is what I know and sadly after a hard drive death I have lost all my designs. They have been extensive and the last incarnation included a relay that only cut in after the initial turn on as I thought it may be suffering from a big surge at first. Still didn't work though. Most of my attempts have relied on gate driver ICs that could provide a fast and capacitively correct 2A drive. The only thing I can think of circuit wise is to take some pictures of the failed ones, if that would help?

Al
 

Thread Starter

BigAlscorpio

Joined Feb 5, 2015
52
If you place a power R load into H bridge instead of motor do you see it
switching properly ?

Regards, Dana.
Hi Dana, All my circuits worked ok on a 300W halogen light bulb at mains voltage and the PWM worked fine to dim that. I also tested them on a 24vDC motor ( running on 24vDC batteries)and that worked ok too on each. It's just when I try with mains voltage that the problems start.
BTW I am not using an H Bridge design, just a single FET/IGBT as I only require one way rotation. Something else I don't understand is how the original circuit works in relation to the 180v motor which would be supplied by 230vAC that comes out of a rectifier at over 300vDC. I did at one stage consider only using half wave rectification which should equate to roughly half the voltage?
Al
 

MaxHeadRoom

Joined Jul 18, 2013
28,831
I see you have used a Microprocessor?
You should easily establish soft start and PWM.
The only thing that can happen if you use too high voltage over the motor plate voltage is over-speed, this is no problem with PWM as you can limit the output, especially if you integrate feedback.
Also you could use a Pot input for analogue speed control.
Extra features are over current monitoring and shut down etc.
Is the controller a MC-60 by any chance?
Incidentally what actually 'smoked'?
Max.
 
Last edited:

Thread Starter

BigAlscorpio

Joined Feb 5, 2015
52
Hi Max, The controller is an MC3-V2.0 from 2013-08-10 and it is always the FET that dies, and they always seem to go closed circuit!
I seem to remember once reading an article about a guy that simply cuts the trace on the board that goes to the FET gate and injects a signal there from a micro, but I am certain that a micro output couldn't drive the FET correctly and even if it did it would be a massive waste of all the other features on the board and a risk to the micro. I have been driving them with gate drivers but driving those from an opto-isolator.

I have no doubt that it could all be done by coercing the original board but it is double sided and has crap loads of components on it including what I believe is a 18 pin surface mount micro, probably PIC or ATMEL but even that is unmarked.
Al
 

MaxHeadRoom

Joined Jul 18, 2013
28,831
So were you just referring to the Pic on the board in the OP or have you dabbled with pic's in any way yourself?
If building your own, you could use the P.S. from the T.M. controller.
Max.
 

cmartinez

Joined Jan 17, 2007
8,293
Hi to all, I have been trying to control a rescued treadmill motor for use in my workshop wood lathe.

I have used PWM many times before with PIC microcontrollers and never had a problem but this 180vDC setup has me stuck. I have tried half a dozen times so far with simple 555 circuits to quite involved PIC micro circuits all with the same result, something releasing the magic smoke!

The motor is rated at 1.25Hp and is brushed DC, I have used both MosFets and IGBTs with much larger ratings like 100A and 600v to no avail. All I want is to get the motor to actually start up (soft start) at low PWM and ramp to a set speed that I select with a pot or rotary encoder. I have thought of using the salvaged controller but it has a 3 second delay and a soft start that is way too long to be anything but annoying as a lathe motor. I also note that the controller gets its power though a large choke and wondered if that has an effect on the inrush current, enough to prevent magic smoke?

I also know that I would need other features before I could safely use the motor as I would like as in feedback for speed governing and a stall limiter. There are no doubt other features that I could do with that members here will be conversant with but for now all I want is to actually get ANY control at all over this motor. Any help or suggestions will be gladly received and there is no need to worry that I will kill myself trying anything that is suggested. I am a retired Electrician who has worked in both home and industry so I always take the relevant precautions and have a lifelong respect of the invisible movement of electrons. ;) Here in the UK we are on 230vAC at 50Hz.

Thanks for reading this long tome and please help, Al
I already did a project very similar to what you're planning. It's simple, but not exceedingly so. Take a look at this thread, it's kind of long but most of the useful posts are in the last six pages.
 

Thread Starter

BigAlscorpio

Joined Feb 5, 2015
52
Hi Max, yes I have been using PICs for years, from the 16F84 in fact, but I never learned anything other than basic, MelPic and Mikro basics.

I could probably narrow down the unmarked micro on the board but even then the board is complex and as you know most of the pins could be any one of half a dozen different uses, analog, digital, PWM, comparator et al so it's not so clear what they even do. Al
 

dendad

Joined Feb 20, 2016
4,503
Hi Dendad, I have used various diodes from 1n4007 to the ultra fast type scavenged from switching PSUs
The 1N400x series diodes are definitely NOT the ones to use. Ultra fast is better. But the rating of the diode will need to be increased I think. Work out the max current the motor will draw in a stall condition, and rate the diode current more than that. I'd go to twice. When designing motor drives, bigger and tougher is best. There will be lots of spikes around.
half wave rectification which should equate to roughly half the voltage?
Half wave does not give you half volts. Under no load, the peak voltage is still the same as full wave. All that is halved is the power you can draw. Consider half wave rectification as 50% PWM, sort off ;)
That link from cmartinez looks like it will be worth having a read through.
 

MaxHeadRoom

Joined Jul 18, 2013
28,831
Hi Max, yes I have been using PICs for years, from the 16F84 in fact, but I never learned anything other than basic, MelPic and Mikro basics.
I could probably narrow down the unmarked micro on the board but even then the board is complex and as you know most of the pins could be any one of half a dozen different uses, analog, digital, PWM, comparator et al so it's not so clear what they even do. Al
It would not be fruitful to try and establish the firmware in the pic, easier to start afresh, there is many examples out there, I only program in Assembly but there is most likely plenty in C etc.
Just a simple PWM output depending on pot setting.
Max.
 

MisterBill2

Joined Jan 23, 2018
19,466
I suggest that you use the power device with a rating of at least 600 volts, with a 1000 volt rating preferred, and also a fairly high current rating.. My reasoning is that a DC motor is a big inductor, especially when it is not running. Then, also, put a diode with a 100 ohm 10 watt or so resistor in series, across the motor, pointing toward the positive terminal. This will give the inductive spike someplace safe to go. And you can indeed verify that it works with a light bulb load first, that is a smart idea.
 

MaxHeadRoom

Joined Jul 18, 2013
28,831
Hi to all, I have been trying to control a rescued treadmill motor for use in my workshop wood lathe.
l
Just realized a possible problem, does the motor still have the fly wheel?
As without the soft start, the flywheel presents a very high load, especially on starting without ramping or fast acceleration.
Normally it is wise to remove it if fitted in this application.
Max.
 

Thread Starter

BigAlscorpio

Joined Feb 5, 2015
52
Hi Max, No flywheel on the motor, I removed it back in the day, when I still had hope that this would work and I would need to fit a pulley. :(

As to PWM and soft start, I have had all that working as expected when using lower voltages and when testing with the halogen bulb. I think the motor has some kind of grudge against me!

Al
 

Thread Starter

BigAlscorpio

Joined Feb 5, 2015
52
Remembering back I had the PIC wait for a short time then ramp to whatever position the pot was at. It was just a run once for next loop that when powered on ran an incremental loop from 1 to whatever the ADC value of the pot was in something like 2 seconds. I did this so the pot could be left in any particular setting and the motor could then simply be powered on and would always return to that speed. I am by no means a master of code but I can usually get by after a few rewrites and a bit of debugging. Al
 

Thread Starter

BigAlscorpio

Joined Feb 5, 2015
52
Hi Dendad, Since the crash which took all my VeroDes circuits the best I can do is find the last couple of attempts out of the fail bin and either draw them out or take a few pictures. The drawings won't be pretty but I can try. I should get some decent pics though if you like? Al
 

dendad

Joined Feb 20, 2016
4,503
Hi Dendad, Since the crash which took all my VeroDes circuits the best I can do is find the last couple of attempts out of the fail bin and either draw them out or take a few pictures. The drawings won't be pretty but I can try. I should get some decent pics though if you like? Al
Yes, actual circuits or just pictures may help us figure out what is going on.
Another thing you could try is to run the motor in series with a 240V 100W lamp for a start. It probably will not drive much mechanical load but it will see if the motor works.
 
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