Soft starter for lathe motor

Thread Starter

hrs

Joined Jun 13, 2014
351
Hi,

My dad has a small lathe that sometimes rips up the drive belt at start-up. So I thought maybe a soft starter can fix this. I'm aware of the following soft starters:
- Stuff like this. Starting at around EUR 150,- that's a bit too pricey.
- An NTC with a relay
- A TRIAC dimmer of some kind

A store-bought product would be nice, but a DIY project would be fine too if it's not too complex. Can a dimmer be automatic, such that it will ramp up in something like 5 seconds so you don't need to turn a dimmer knob after switch on? How would you solve this?

Thanks.

Motor specification:
Rotor: Squirl cage
Stator:
┴ (what is this?)
Voltage: 220 AC, 50 Hz
Current: 6.1 A, single phase
Speed: 2800 rpm
cos phi: 0.84
[edit]Power: 0.76 kW[/edit]
 

MaxHeadRoom

Joined Jul 18, 2013
23,918
The Triac versions cannot be used on an induction motor.
These are a little difficult to run at any other speed,
Could he come up with some kind of wheel tensioner that could be hand operated in order to bring the rpm up gradually, there would be a little belt slip at first, which may not be a problem.
 

Thread Starter

hrs

Joined Jun 13, 2014
351
It doesn't need to be speed controlled, just to reduce the starting torque so it doesn't rip the belt. Can't this be achieved by limiting the inrush current?

He was considering some mechanical solution but I said I would first inform if an electronic solution might be possible.
 

Alec_t

Joined Sep 17, 2013
12,311
You might get away with having a resistor, such as an smoothing-iron element or a kettle element, in series with the motor and bypassing the resistor with a delayed-on time switch.
 

Papabravo

Joined Feb 24, 2006
17,270
The Triac versions cannot be used on an induction motor.
These are a little difficult to run at any other speed,
Could he come up with some kind of wheel tensioner that could be hand operated in order to bring the rpm up gradually, there would be a little belt slip at first, which may not be a problem.
Machine tools used to run off of a line shaft connected to a large flywheel. Each machine had a tensioner arm to gradually engage the machine to the line shaft. It is not a completely crazy idea.
 

MaxHeadRoom

Joined Jul 18, 2013
23,918
Like this?
One of my first factory experiences was an installation in a Blanket factory like it.
The operators could engage the machine with a belt tension lever.

1635004546758.png
 

Thread Starter

hrs

Joined Jun 13, 2014
351

Alec_t

Joined Sep 17, 2013
12,311
Is swapping such an element for an NTC thermistor not going to work?
If you can find a suitably rated one it could. I may be wrong, but I think the ones you linked to have too low a resistance to have sufficient torque-reduction effect.
For your purpose, the NTC heat-up time might be a tad too short. Cheap enough to experiment though.
 

Thread Starter

hrs

Joined Jun 13, 2014
351
If you can find a suitably rated one it could. I may be wrong, but I think the ones you linked to have too low a resistance to have sufficient torque-reduction effect.
For your purpose, the NTC heat-up time might be a tad too short. Cheap enough to experiment though.
Thanks, I see. Researching this some more it seems that the NTC heat-up time is in the order of milliseconds rather than seconds. Maybe I can find a smoothing-iron in the bin of discarded devices at the city recycling center and go with post #4.
 

MaxHeadRoom

Joined Jul 18, 2013
23,918
Amazon has resistance wire for $10.00 you could experiment, the clincher is to construct it safe, also you need to switch it out when up to speed.

AC220V 3000W Resistance Wire, Kiln Furnace Heating Coils Element, Resistance Wire, Kiln Element
 

Thread Starter

hrs

Joined Jun 13, 2014
351
For switching the series load out, preferably use a small contactor or suitably sized relay for switching a 1.5HP/2HP motor.
I'm getting relay overload. There are so many and with price differences that I cannot explain. Can you suggest one that you think is suitable for this application? Does a mechanical relay need surge suppression or TVS?

What about something like this SSR and the attached circuit?
https://www.digikey.com/en/products/detail/altran-magnetics-llc/ASR-SIM240D10ZW-LQ/14553491

If anyone can recommend a better and/or easier circuit that would be great.
 

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shortbus

Joined Sep 30, 2009
8,959
As some one with 2 old lathes, one a bench top South Bend and a much older Logan that was originally driven from a overhead line shaft, my first thought on tearing up belts is that something is out of line. If pulleys aren't lined up correctly they tend to throw belts or just wear them out fast. Put a straight edge on the sides of the pulleys it needs to rest on both sides of both pulleys to show if they are in line, not just one edge of both pulleys closest to each other, doing it that way won't tell you if they are in line.
 

Thread Starter

hrs

Joined Jun 13, 2014
351
As some one with 2 old lathes, one a bench top South Bend and a much older Logan that was originally driven from a overhead line shaft, my first thought on tearing up belts is that something is out of line. If pulleys aren't lined up correctly they tend to throw belts or just wear them out fast. Put a straight edge on the sides of the pulleys it needs to rest on both sides of both pulleys to show if they are in line, not just one edge of both pulleys closest to each other, doing it that way won't tell you if they are in line.
Thanks, maybe I'll have a look this weekend.
 

Thread Starter

hrs

Joined Jun 13, 2014
351
Good one, shortbus. The pulleys are not quite in-line. He'll try to trim it out with a bushing. I'm not sure if it used to chew up the old type belts that he used, but anyway currently it throws off what he has now.

Allegedly the original motor was .37 kW / .5 HP which a previous owner has swapped for a .75 kW / 1 HP motor. This may still be a contributor.

We'll see what trimming the belt does. If this isn't sufficient another thought we is to reduce the starter capacitor size.
 

t_glover

Joined Mar 16, 2021
30
I have owned a couple small lathes and still have one.
I have never had a belt problem and have worked them quite hard
at times. Is this a flat belt or a vee belt? Fractional horsepower
and automotive vee belt have a different taper and are not interchangeable.
I suspect your problem may be an alignment, tension or mismatched
belts and pulleys.
 

shortbus

Joined Sep 30, 2009
8,959
Fractional horsepower
and automotive vee belt have a different taper and are not interchangeable.
I've never experienced any problem with the very small angle difference. The biggest difference in automotive and fraction HP belts is the cord arrangement in the belt. The cord layers differ to give a stronger outer layer in automotive belts.
 
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