SOFT START for Servo Motors

[Constabulary]

Just a tinkering idea....

I´m not an electrician so I wonder if it possible to add a soft start module (as on table saws) to our sewing machine servos. Will it improve the comfort and does it make sense at all?

 

Edited March 9, 2021 by Constabulary

[Gregg From Keystone Sewing]

Many positioning motors have a soft start option.  The idea is that the first couple of stitches are loose, and will give the machine time to catch up to prevent the needle thread from coming out.  It's not just for comfort.

[sbrownn]

6 hours ago, Constabulary said:

Just a tinkering idea....

I´m not an electrician so I wonder if it possible to add a soft start module (as on table saws) to our sewing machine servos. Will it improve the comfort and does it make sense at all?

 

If you are using a speed reducer you probably don't need soft start.  If not, probably not too.  I have tried it both ways and had no problems either way.

[Constabulary]

I know - I have speed reducers on all my machines.

I want to add a soft start to my table saw so this just popped up in my head... just an idea... don´t know if it is possible at all. 

[dikman]

Stop thinking so much, Constabulary, you'll give yourself a headache!

[sbrownn]

5 hours ago, Constabulary said:

I know - I have speed reducers on all my machines.

I want to add a soft start to my table saw so this just popped up in my head... just an idea... don´t know if it is possible at all. 

Does your table saw have a motor hanging off a belt that drives the blade arbor or is it direct drive?  Soft start has the advantage of lowering the starting current of a motor so if your motor has a running current that is close to the capacity of the breaker, it keeps the breaker from tripping when it starts; starting current is significantly higher than running current.

[Constabulary]

Was just a wild idea... if you don´t ask you will not know the answer

Maybe a brain fart.

[Gymnast]

Sorry, but you cannot do that to a servo motor.

If you do it on the input side to the servo motor electronics, the electronics will not get the right voltage to operate. If you do it between the servo electronics and the motor, it will create all sorts of problems. The voltage here got a lot of higher frequencies, that the slow start electronics cannot handle.

[DonInReno]

Honestly I don’t know much about motors and the only soft start motors I knew existed were three phase, but this manual popped up for a single phase motor soft start thing-a-majig.

https://www.baldor.com/Shared/manuals/834-602.pdf

[Constabulary]

Don, my original idea (or brain fart) was this thingy here which goes into single phase table saws:

https://www.ebay.de/itm/Vollmetall-Sanftanlauf-Anlaufwiderstand-12A-mit-Osen-Softstart-Soft-Start/143616841340

I´m not really following the idea for my sewing servo cause I have no need but it just popped up in my head so I asked. You never know.

Edited March 11, 2021 by Constabulary

[Gymnast]

I have seen, that the servo motors have a slow start function, that you can set by a software parameter. It controls how fast the motor should increase speed to the lowest constant speed, that it can make (typically 100 RPM or 200 RPM).

[sbrownn]

5 hours ago, Gymnast said:

I have seen, that the servo motors have a slow start function, that you can set by a software parameter. It controls how fast the motor should increase speed to the lowest constant speed, that it can make (typically 100 RPM or 200 RPM).

I hadn't realized that. Good to know.  Thanks!

[DonInReno]

20 hours ago, Constabulary said:

Don, my original idea (or brain fart) was this thingy here which goes into single phase table saws:

That’s a nice simple solution.  Let us know how it works out.   I have a portable Mikita table saw that doesn’t have soft start and it would be nice to calm it down.

[Primosand]

Constabulary I'm not clear why you are considering this "soft start" for your servo. But if it is because your servo starts and stops abruptly I had this abrupt start/stop problem on my first and second servo motor. Both were Consew 550 watt servos. To get around this issue or to get the motor to start smoothly (stopping abruptly didn't really bother me) I opened up the end of the motor and disabled the little brake. I just took the brake pads out of the first one to see if that would fix the issue. It did. On the second servo (same brand and model) I think I took the arm off and that also worked. I use a speed reducer as well but now I can start out at apostate zero and feather it up to whatever sewing speed I need without any jump or lurch. Again I'm not sure this is what were were getting at but your question reminded me I needed to do this back when I switched to servo motors.

[Constabulary]

Again - it was just a brain fart. The idea was that the above linked soft start module possibly could add some sort of acceleration ramp to a servo motor without speed reducer. I´m not meaning the lowest rpm a servo starts with I mean a slightly smoother start / rpm acceleration when you hit the pedal. I personally don´t have the need cause I´m using speed reducers. It was just an idea because I´m in process of adding this module to my table saw and thought it possibly could add some comfort to one or another servo motor.

Again - just a wild idea and I though someone else here probably had a similar brain fart or maybe has some experience with this module in general - you never know.

 

EDIT:

My idea was just a softer start of certain (not all) servo motors and not preventing from tripping fuses and so on... Just a softer start, no RPM reduction...

So boobies can explain it better than I (different module - but same effect I was thinking to achieve)

https://www.youtube.com/watch?v=oSrz3GaaDO8

This was the table saw soft start module (or similar) I was thinking of:

https://www.youtube.com/watch?v=iWr0B2U-QT8

Note the difference when the motor starts.

 

 

 

 

Edited March 14, 2021 by Constabulary

[Kcstott]

13 hours ago, Constabulary said:

Again - it was just a brain fart. The idea was that the above linked soft start module possibly could add some sort of acceleration ramp to a servo motor without speed reducer. I´m not meaning the lowest rpm a servo starts with I mean a slightly smoother start / rpm acceleration when you hit the pedal. I personally don´t have the need cause I´m using speed reducers. It was just an idea because I´m in process of adding this module to my table saw and thought it possibly could add some comfort to one or another servo motor.

Again - just a wild idea and I though someone else here probably had a similar brain fart or maybe has some experience with this module in general - you never know.

 

EDIT:

My idea was just a softer start of certain (not all) servo motors and not preventing from tripping fuses and so on... Just a softer start, no RPM reduction...

So boobies can explain it better than I (different module - but same effect I was thinking to achieve)

https://www.youtube.com/watch?v=oSrz3GaaDO8

This was the table saw soft start module (or similar) I was thinking of:

https://www.youtube.com/watch?v=iWr0B2U-QT8

Note the difference when the motor starts.

1. Soft starts are garbage. They create far to much start up heat on a single phase squirrel cage motor. 
2. As mentioned above a servo motor is designed to have a servo speed control connected to it and appropriate throttle control. 
So that said what is needed to give a servo motor better start up control is a better speed control. Servo speed control units, A good one can cost $500 and up and require a separate DC power supply. The fact that we have an AC compatible servo motor with no external power supply for $300 is pretty amazing. 
What we need is analog input for control say a 0-10V from a potentiometer control. but now you need a second power supply a potentiometer and a new control. all that equals is not cheep. 

As to your table saw. I'd recommend a VFD and three phase motor. Then you can program ramp time and starting torque. far more robust then a soft start but also far more expensive too. installing a soft start to prevent breakers or fuses from popping is treating a symptom. You need to upgrade the service to the saw. 

 

 

 

 

Edited March 14, 2021 by Kcstott

[dikman]

I thought the "soft-start" modules were designed to work with universal brush-type motors? Squirrel cage induction motors are notoriously difficult to use with any form of speed control, which is why people change their lathes, belt grinders etc to 3-phase motors + VFD.

[Kcstott]

1 hour ago, dikman said:

I thought the "soft-start" modules were designed to work with universal brush-type motors? Squirrel cage induction motors are notoriously difficult to use with any form of speed control, which is why people change their lathes, belt grinders etc to 3-phase motors + VFD.

I've never seen a table saw with a brushed motor. The Universal brushed motors I've dealt with were fractional HP as in 1/10 HP. 
 

[Frodo]

Is this what you are  looking for?

German made soft start

ATS01N206QN

Model Type: Altistart 01

Altistart 01 Soft Starter Module

---

Manufacturers
Schneider, Telemecanique

[dikman]

That's for 3-phase motors. If that youtube video is working on a single phase induction motor I'm curious how it does it. The instructions with my VFD's give connection details for using with single phase induction motors to vary their speed. I thought this would be great for my grinder but I did some research and yes, it will work BUT it isn't recommended! The motor won't develop much torque and it may overheat. Hence the need to go to 3-phase motors.

I just finished digging around for more soft-start info and Don's post about the Baldor unit is the key. That unit is intended to work on single-phase induction motors and the link explains how. The one that Constabulary linked to is doubtless the same type of unit, so I've learned something new. The Baldor information indicates that the soft-start unit needs to be matched to the power rating of the motor, so buying one at random could be a problem.

Edited March 15, 2021 by dikman
more info.

[Gymnast]

On 3/15/2021 at 12:01 AM, Kcstott said:

I've never seen a table saw with a brushed motor. The Universal brushed motors I've dealt with were fractional HP as in 1/10 HP. 
 

I think most of the smaller table saws are made with a brushed universal motor. Universal motors are used for most of the vintage household sewing machines and in a power input range of 50-250 W. A lot of Universal motors are used in tools, vacuum cleaners and other household equipment. They are good small motors with a high power, but with a limited operating time due to wear on brushes. They typically can run at high speed, so they will make more noise. A vacuum cleaner typically runs 25,000 RPM and can have an input power of 2000 W. Induction motors are very silent in operation, because their speed will be below 3,600 RPM and they got no brushes.

Both universal motors and induction motors got a higher inrush current, which can be reduced by a soft starter.

Edited March 16, 2021 by Gymnast

[Kcstott]

43 minutes ago, Gymnast said:

I think most of the smaller table saws are made with a brushed universal motor. Universal motors are used for most of the vintage household sewing machines and in a power input range of 50-250 W. A lot of Universal motors are used in tools, vacuum cleaners and other household equipment. They are good small motors with a high power, but with a limited operating time due to wear on brushes. They typically can run at high speed, so they will make more noise. A vacuum cleaner typically runs 25,000 RPM and can have an input power of 2000 W. Induction motors are very silent in operation, because their speed will be below 3,600 RPM and they got no brushes.

Both universal motors and induction motors got a higher inrush current, which can be reduced by a soft starter.

I don't know what size table saw you run but the one in my garage is a 10" blade and 2HP motor and it's far from small. 

[Gymnast]

On 3/15/2021 at 12:01 AM, Kcstott said:

I've never seen a table saw with a brushed motor. The Universal brushed motors I've dealt with were fractional HP as in 1/10 HP. 
 

 

On 3/16/2021 at 10:35 PM, Kcstott said:

I don't know what size table saw you run but the one in my garage is a 10" blade and 2HP motor and it's far from small. 

Your garage table saw may be with an induction motor. I argue that most smaller table saws at about 1800 W for home use or craftsmen got universal motors. This is three examples of that:

This is a link to a small Metabo 1700 W table saw. The small size of motor and gearing to motor clearly indicate, that it is a universal motor. The gear ratio is above 3 and no load saw speed is 4200 RPM, so the no load motor speed is about 12000 RPM.
https://youtu.be/2kVjOW-VMrk 

This is a 2000 W Dewalt DWE7491-QS. I can hear on the noise, that this is a high RPM motor.
https://youtu.be/I_uLAz7ferE?t=334

This is a Bosch GTS 10J table saw. In this video you can see the sparks for the brushes of the universal motor. An induction motor got no brushes. And you can hear the high speed of motor.
https://youtu.be/RDMBiUF80Gc?t=142

 

Saws in this size becomes cheaper and lighter, when you use universal motors. I guess that bigger and more industrial table saws may use induction motors. Perhaps older table saws for craftsmen got induction motors and you may have an example of that.

Edited March 17, 2021 by Gymnast

[Kcstott]

22 minutes ago, Gymnast said:

 

Your garage table saw may be with an induction motor. I argue that most smaller table saws at about 1800 W for home use or craftsmen got universal motors. This is three examples of that:

This is a link to a small Metabo 1700 W table saw. The small size of motor and gearing to motor clearly indicate, that it is a universal motor. The gear ratio is above 3 and no load saw speed is 4200 RPM, so the no load motor speed is about 12000 RPM.
https://youtu.be/2kVjOW-VMrk 

This is a 2000 W Dewalt DWE7491-QS. I can hear on the noise, that this is a high RPM motor.
https://youtu.be/I_uLAz7ferE?t=334

This is a Bosch GTS 10J table saw. In this video you can see the sparks for the brushes of the universal motor. An induction motor got no brushes. And you can hear the high speed of motor.
https://youtu.be/RDMBiUF80Gc?t=142

 

Saws in this size becomes cheaper and lighter, when you use universal motors. I guess that bigger and more industrial table saws may use induction motors. Perhaps older table saws for craftsmen got induction motors and you may have an example of that.

I would consider those portable saws and not a true table saw, light weight hobby stuff. My saw is a 1980's Craftsman, Cast iron and weighs about 400 pounds. 

 

[dikman]

I agree with Gymnast. You refer to them as hobby saws. Maybe, but by definition they are a table saw (a table with a saw mounted in it), there is no rule that states a table saw must be large and have an induction motor. And these smaller table saws inevitably have universal motors, which lend themselves to easy speed control.