Replacing with Brush or Brushless DC motor

[Steamchick]

The thyristors could not handle more than 5A safely, according to my Electrical engineer who repairs these boards. He says many are blown-up because people "mess" with settings so they apply more than 5 A. - then blow-up. So KNOW your component ratings and DO NOT exceed them. (Do not use as expensive fuses!). My expert tells me (as I have also advised) that the factory KNOW what these things can handle, so set controlled limits so they do not get overloaded and develop bad reputations for the manufacturers. (He worked for a few). - Simply bad business practice otherwise...
K2

 

[SmithDoor]

The thyristors could not handle more than 5A safely, according to my Electrical engineer who repairs these boards. He says many are blown-up because people "mess" with settings so they apply more than 5 A. - then blow-up. So KNOW your component ratings and DO NOT exceed them. (Do not use as expensive fuses!). My expert tells me (as I have also advised) that the factory KNOW what these things can handle, so set controlled limits so they do not get overloaded and develop bad reputations for the manufacturers. (He worked for a few). - Simply bad business practice otherwise...
K2

You can easily find thyristors/SCR over 50 AMPS. I do not know how big they go but price price goes up.

I first start using the thyristors when they where call SCR in 1960's. The thyristors has great surge/starting amps a 50 amp some have a surge to 1,500 amps.
They are great part for motors

(FYI non electronic members background They work differently in AC and DC circuits. )

Dave

 

[kf2qd]

With any motor you are going to need some type of "controller". For variable speed you will need a variable voltage power supply or controller. A controller will detect current and compensate, somewhat, for the load on the motor at any given speed. A DC servo could be used which will give better speed regulation because a DC servo generally has a tachometer feedback which the controller then uses to compare to the control signal and compensate for load. A BLDC or AC servo is a 3 phase motor with an encoder of some type that feeds back to the controller so the "comutation" can be precisely controlled for speed or positioning. A DC motor can have lower rpm limits that does a AC servo, so very often the gear ration can be twice what the DC servo requires which makes the end result very similar. The AC servo also has the advantage that it cam be configured digitally, and the performance can be monitored with a computer, meaning that is you have several in a similar application they can be easily setup once the first one is configured.
A brush type motor will require more power that a brushless motor as the resistance losses through the carbon brushes rise as the load and current increase. Under high loads a brush type motor requires much more maintenance that a brushless motor.

 

[SmithDoor]

With any motor you are going to need some type of "controller". For variable speed you will need a variable voltage power supply or controller. A controller will detect current and compensate, somewhat, for the load on the motor at any given speed. A DC servo could be used which will give better speed regulation because a DC servo generally has a tachometer feedback which the controller then uses to compare to the control signal and compensate for load. A BLDC or AC servo is a 3 phase motor with an encoder of some type that feeds back to the controller so the "comutation" can be precisely controlled for speed or positioning. A DC motor can have lower rpm limits that does a AC servo, so very often the gear ration can be twice what the DC servo requires which makes the end result very similar. The AC servo also has the advantage that it cam be configured digitally, and the performance can be monitored with a computer, meaning that is you have several in a similar application they can be easily setup once the first one is configured.
A brush type motor will require more power that a brushless motor as the resistance losses through the carbon brushes rise as the load and current increase. Under high loads a brush type motor requires much more maintenance that a brushless motor.

AC or brushless for 1 hp uses about 1,450 watt
A DC pm brush uses 900 watts
See charts
https://www.mcmaster.com/product/6215K76

There few more calcs on motor by time both AC an DC takes the same amount of power.
Watch out for internet data if someone sell they will L○●
In my line of work did a lot motor calcs.
Iam not happen with parts of internet sorry

Dave

 

[Steamchick]

Progress yesterday.
I fitted the motor to the existing mounting plate, after drilling 4 new mounting bolt holes, and the pulley (Straight on as I ordered the correct shaft size). But what I didn't immediately notice, there was a wider part of the shaft that protruded from the surface which fouled the mounting plate. (It simply would not sit on properly). So I needed to open out the shaft hole in the mounting plate from 14mm to 22mm to get suitable clearance.

I made a new cover plate for the space in the lathe by the main-shaft bearings, where I shall mount the new controller.

As the new controller has large plugs (20mm dia. locking rings) I needed to open out the 2 holes in the back of the space, where speed meter wires had been, to 22, 24mm. to take the plugs of the wiring from motor to controller.

Today I plan to install the wiring and bits...
Watch this space! If there is a big blue flash and I end-up crisped there will be no more posts... But "Here goes"!
K2

 

[SmithDoor]

Progress yesterday.
I fitted the motor to the existing mounting plate, after drilling 4 new mounting bolt holes, and the pulley (Straight on as I ordered the correct shaft size). But what I didn't immediately notice, there was a wider part of the shaft that protruded from the surface which fouled the mounting plate. (It simply would not sit on properly). So I needed to open out the shaft hole in the mounting plate from 14mm to 22mm to get suitable clearance.
View attachment 158408View attachment 158407
I made a new cover plate for the space in the lathe by the main-shaft bearings, where I shall mount the new controller.
View attachment 158409View attachment 158410
As the new controller has large plugs (20mm dia. locking rings) I needed to open out the 2 holes in the back of the space, where speed meter wires had been, to 22, 24mm. to take the plugs of the wiring from motor to controller.
View attachment 158411
Today I plan to install the wiring and bits...
Watch this space! If there is a big blue flash and I end-up crisped there will be no more posts... But "Here goes"!
K2

Looks great

Please take video of blue flash and post it here. Maybe live feed just incase.

Dave

 

[Steamchick]

The fan I had purchased (90mm dia, 12V. 0.25A.) does not sit well at the back of the motor, bit the small 12V blower I previously used blowing cold air into the DC motor (12V., 0.18A. for slow running cooling) has been repositioned to blow into this motor.
My wiring diagram:

To anyone else working on these Chinese machines. My experience (and others!) is that the Chinese often wire the fuse into the NEUTRAL line... Possibly if they do not differentiate between Live and Neutral at the plug? - As we DO differentiate in the UK, pre-moulded plugs have wires attached, and when they put the wires in the box-of-tricks, the wires seem to be connected at random??
Worry: (As I have experienced in 2021 when the first motor failures blew-up the Controller) - If the fuse is fitted to the neutral, and it blows, you may think it safe to investigate and forget to turn OFF the power before opening covers, etc. (I had switched OFF the supply and disconnected it). If you do so, with Neutral fused, the internals are still LIVE - as the live is not fused.. I only found out when I had connected a 12V battery to the Live and Neutral pins on the plug, to chase the circuits through all the switches to see what had blown (The mains filter neutral track on the PCB!). Somehow I had "No voltage" when I checked Fuse to neutral pin on the plug, and the polarity was "the wrong way around" after I probed the fuse holder with a new fuse.... to other wires/terminals to try and find the voltage. Not helped by the multi-coloured array of wiring... a device with 2 red wires, another with 2 black wires, Blue, red, Black and Brown all used for Live wires, Green, blue, black and red used for Neutral wires, Green brown and black used for earth, where fitted! And a couple of odd yellow wires... just between switches and components. The 180V DC to motor was "easy", red and black, or brown and blue, or red and blue!
I shall be using UK Live, neutral and earth colours and cables
this time.
So if you find a NEUTRAL fuse, without a LIVE fuse, it is safer (European standard?) to re-wire so the LIVE is fused, NOT the NEUTRAL...
Any suggestions?
K2

 

[SmithDoor]

The cost of brushless is the only downside I can see. Brushless are slightly more efficient, No need to maintain brushes and comm's, and slightly better control. The controllers for AC and Brushless more complex and more expensive.
If I was changing motors and drives on a lathe or mill I would go DC brushless - DC brushed, in order of personal choice. Otherwise it would depend on the use and frequency of use.
I personally used AC variable speed to upgrade my lathe based on overall cost. There is still some degree of gearing required this way.

Just let you the brushless aka 3 phase motor has life span upto 20,000 hours . There are some high end type will go 40,000 hour. The DC motors have about same 20,000 hours and 40,000 hours but brushes need changing ever 3,000 to 10,000 hours and some special can go higher with cost too.
The DC motor we us in mini lathes is 3,000 hour may need cleaning a few times a year.
The low end like toys maybe 100 hours, low cost drill motors maybe 500 hours.
Someone selling brushless motors will pick out the number that makes the brushless looks better.

Now there lot good things about brushless but needs size correctly for replacing from a DC motor. It not just a DC 1 hp to brushless 1 hp. It low speed is what you need look at for right motor

Dave

 

[SmithDoor]

The fan I had purchased (90mm dia, 12V. 0.25A.) does not sit well at the back of the motor, bit the small 12V blower I previously used blowing cold air into the DC motor (12V., 0.18A. for slow running cooling) has been repositioned to blow into this motor.
My wiring diagram:
View attachment 158413
To anyone else working on these Chinese machines. My experience (and others!) is that the Chinese often wire the fuse into the NEUTRAL line... Possibly if they do not differentiate between Live and Neutral at the plug? - As we DO differentiate in the UK, pre-moulded plugs have wires attached, and when they put the wires in the box-of-tricks, the wires seem to be connected at random??
Worry: (As I have experienced in 2021 when the first motor failures blew-up the Controller) - If the fuse is fitted to the neutral, and it blows, you may think it safe to investigate and forget to turn OFF the power before opening covers, etc. (I had switched OFF the supply and disconnected it). If you do so, with Neutral fused, the internals are still LIVE - as the live is not fused.. I only found out when I had connected a 12V battery to the Live and Neutral pins on the plug, to chase the circuits through all the switches to see what had blown (The mains filter neutral track on the PCB!). Somehow I had "No voltage" when I checked Fuse to neutral pin on the plug, and the polarity was "the wrong way around" after I probed the fuse holder with a new fuse.... to other wires/terminals to try and find the voltage. Not helped by the multi-coloured array of wiring... a device with 2 red wires, another with 2 black wires, Blue, red, Black and Brown all used for Live wires, Green, blue, black and red used for Neutral wires, Green brown and black used for earth, where fitted! And a couple of odd yellow wires... just between switches and components. The 180V DC to motor was "easy", red and black, or brown and blue, or red and blue!
I shall be using UK Live, neutral and earth colours and cables
this time.
So if you find a NEUTRAL fuse, without a LIVE fuse, it is safer (European standard?) to re-wire so the LIVE is fused, NOT the NEUTRAL...
Any suggestions?
K2

The voltage use UK in home is high 220 volts for kids to ply with.

I have never had a thyristors/SCR give out.

About only problem was the Varistor giving out. Now I use power strip with Varistor built in if power strip dies just get a new one off shelf and keep going

Dave

 

[Steamchick]

My use is probably below 100 hours per year? 8 hours a month? So lifetime is not an issue.
On the original DC motor, the original brushes lasted about 12 years or so. 1 worn to min (5mm wear) the other only 3mm wear. But the replacements had the same wear in 3 years use. But I have been using the lathe a bit more....
New sewing machine so type 3-phase motor is very similar numbers, but higher torque than the treadmill motor. It was the only option to fit inside the original motor space.
BRILLIANT! Min. Speed (chuck) now 55rpm and I cannot stall it by hand. Previously treadmill type DC motor was 80 rpm and stalled with 1 hand holding the chuck (just!).
I can recommend the conversion when the DC motor and controller expire... £140. = new motor and controller for the same money as a replacement motor. Saved £120! - for a bette device.
K2

 

[SmithDoor]

My use is probably below 100 hours per year? 8 hours a month? So lifetime is not an issue.
On the original DC motor, the original brushes lasted about 12 years or so. 1 worn to min (5mm wear) the other only 3mm wear. But the replacements had the same wear in 3 years use. But I have been using the lathe a bit more....
New sewing machine so type 3-phase motor is very similar numbers, but higher torque than the treadmill motor. It was the only option to fit inside the original motor space.
BRILLIANT! Min. Speed (chuck) now 55rpm and I cannot stall it by hand. Previously treadmill type DC motor was 80 rpm and stalled with 1 hand holding the chuck (just!).
I can recommend the conversion when the DC motor and controller expire... £140. = new motor and controller for the same money as a replacement motor. Saved £120! - for a bette device.
K2

That is great

I think biggest problem is doing maintenance or lack of maintenance.

Your motor should last a long time.
8hrs X 52 weeks is 416 hours a year. You need a new ball bearing in only 48 years. and brush replacement and cleaning every 7 years.

Dave

 

[Steamchick]

But 8 hours a MONTH means things should last my lifetime...
K2

 

[Steamchick]

New motor and controller fitted - and running. Some titivating to do... but I have a working lathe! - See attached, for those interested in my ham-fisted mechanicing.
K2

 

[Noitoen]

New motor and controller fitted - and running. Some titivating to do... but I have a working lathe! - See attached, for those interested in my ham-fisted mechanicing.
K2

Since it's a sewing motor, normally there is an option to automatically stop the motor with the chuck always on the same position, ready for the chuck key

 

[SmithDoor]

New motor and controller fitted - and running. Some titivating to do... but I have a working lathe! - See attached, for those interested in my ham-fisted mechanicing.
K2

Looks great.

Can post photo complete lathe with motor?

Dave

 

[Steamchick]

Dave: This shows "not a lot" - as the motor is hidden inside the lathe body (mounted on the inside of the black plate).
I need to find a user manual to understand programming the motor to do clever things like "stop-in-one-place". Otherwise I'll simply screw-up all the correct factory settings...
K2

 

[SmithDoor]

Dave: This shows "not a lot" - as the motor is hidden inside the lathe body (mounted on the inside of the black plate).
I need to find a user manual to understand programming the motor to do clever things like "stop-in-one-place". Otherwise I'll simply screw-up all the correct factory settings...
K2
View attachment 158457View attachment 158456View attachment 158455

Looks great and lathe does too.

Dave

 

[NapierDeltic]

Hi Steamchick.
Congratulations for the conversion! We will wait extended impressions upon using it (with pictures!).
Thank you for the tutorial and pertinent comments included.
You can now heat your workshop with 8hours/day 750W in winter!
Do you think 500W version is more than acceptable for the lathe? (should be if - as you say - low rev torque is higher than for DC motor).

 

[SmithDoor]

Dave: This shows "not a lot" - as the motor is hidden inside the lathe body (mounted on the inside of the black plate).
I need to find a user manual to understand programming the motor to do clever things like "stop-in-one-place". Otherwise I'll simply screw-up all the correct factory settings...
K2
View attachment 158457View attachment 158456View attachment 158455

I wish I had stop at right spot on on large lathes. Maybe it has programing for Four jaw chuck.

I like heavy aluminum motor too.

Dave

 

[TSutrina]

For the operation of a machine tool such as a lathe or milling machine. Induction motors have been the choice for a century. The reason is simple. They are robust and cheap compared to at the time brush DC motors. The machines use belts or gears to chance speed while maintaining all the power of the motor. This is an option for all motors.
But remember that the torque of a motor is related almost directly to the current. DC brush motor with only winding you need to consider both stator and rotor current. For PM, and reluctance motors only the wound stator or rotor has a current. Induction motors actually have a low frequency transformer powering the rotor which is why increase in slippage is actually increasing the frequency and the inductance loses until the magnetic field is insufficient to drive the rotor.
With the drop in cost of power electronics the option of brushless DC motor (PM) or reluctance can be considered. PM cost is similar to brush DC. Reluctance is about the cost of induction. Stepper motors can be pure reluctance or PM with the associated costs. Only the induction and stepper motor doesn't need rotor position fed to the power electronics. So this is the simplest option and the cheapest and the slippage issue is well understood but will effect the operation. For steppers the speed is limited to the rotor and load keeping up with the changing field, steps.
The used bench top mill I purchase required a three phase drive for the motor, however; to get the best performance out of it use the gears to get close and the drive to make the final adjustment, spindle speed.
High end milling machines and lathes use sensors or the drive to know the exact position of the spindle. This allows them to single point cut threads or similar features using relative position of the spindle and the cutter for a lathe and the cutter on the spindle for a milling with this use to control position of the cutter or item being cut. A hobby machine today also can achieve this.