Best option to improve lathe motor

[Itsacon]

My lathe (a European Atlas 618 copy) is powered by an old (50+ years) single-phase PSC AC motor. 370W, 0.5 HP, ~1400 rpm.

It works fine and provides enough power for what I've been doing so far.

However, the inrush current is huge. It causes a lot of noise on the AC line, to the point that other devices on the same breaker are affected.

Also, the wiring is old, the switch is not properly mounted in anything and insulated with ducttape, and it's not properly grounded.

All these things make the electrical engineer in me a bit itchy, so I'm looking to improve matters.

Rewiring the switch, mounting it in a proper housing, together with an emergency kill switch I can do.

But I'm looking at improving the startup spike problems as well, as I'd like the CD player to keep working when I turn the lathe on.

So far, I've been looking a couple of options:

- There is an ample supply of simple three-wire soft-start modules for table saws available on the interwebs. I have no idea if that would work if I wired one into the primary winding of the motor. At the price they're going for, I could just try it, but I can't find anything on how they work. If they limit voltage, they might cause an increased current that could damage the motor.

- Alternatively I could spend a bit more on an inrush current limiter. That would probably work a bit better, but also not sure on the compatibility with an old motor like this.

- I've been looking at 1-phase VFDs as well, but putting a multimeter on my motor, it looks like the primary and secondary windings are not identical, so I'm not sure how it will like being run as a 'real' 2-phase motor, without the capacitor in line with the secondary.

- The last option is simply replacing the motor completely, possibly with a DC model. That would probably make the whole thing a lot quieter as well, but is obviously the most expensive option. And in this category, there's of course the choice between a relatively cheap chinese motor, or going straight for something from a known brand (what are known brands in the DC-motor business? Not really my area of expertise).


So my question: Do you guys have any thoughts on which option would probably be best? Does anyone have experience with those soft-starters and/or inrush limiters? Are DC motors really better? Will any of this make me a better machinist?

 

[Jake M]

First let me say that your electrical distribution is different than ours here, so if something doesn't sound right.... It might not be.

If I saw that issue with my tool, and house wiring, the first thing I would need to do is evaluate the circuit that the lathe receives it's power from. A half horse motor, as is, should not draw "that" much, and shouldn't bother other things on the circuit. Vacuum cleaners draw as much as this, and often more on the inrush. I would want to know WHERE the voltage drop is occurring, and why. Of course it's the inrush, but WHERE is the system being loaded too high? Does the voltage drop in a box, connections, circuit breakers, does the whole building have the lights dim? Is there simply too many things plugged into outlets fed by the same circuit?

And honestly, if this were in my house, I'd have that on a dedicated (or semi-dedicated) circuit. For example, my lathe does not plug directly in. The lathe bench is "wired". One plug from the lathe bench goes into the dedicated circuit, so I can unplug everything. But that lathe bench has the lathe hard wired, with outlets for a drill press, shop vac, lights, and anything else I'm using. This keeps "motor noise" on just the one circuit, such that A, I'm probably only using one thing at a time, B, I'm one person, so I don't start a machine and the vacuum at the same instant, and C, all the electronic stuff (radio, tablet, television, battery chargers, and all) is on the "wall outlets" where they don't see interference from the motors starting. Although I've got to say that starting a motor (dust collector, table saw, belt sander) on that same circuit where the wall outlets are powered, they really don't act up if I plug in and turn on something big...

Bottom line, it "might?) be normal, depending on how your electrical codes/rules are done? But I don't think so. And so I would want to measure, quantify, and identify where exactly the deficiency in power delivery is happening. Too much inrush can cause voltage drops, but on the other hand, undersized or overused circuits can cause low voltage, which will cause increased inrush current... Is it the chicken or the egg?


That said...
A simple soft starter or current limiter is probably the easiest and most straight forward way to reduce that inrush, but it's obviously limited to only that function. All three of your options are going to help with that situation, an quite likely are going to solve the symptom, and maybe or maybe not solve the whole problem. The question is, which one is going to serve you best. Does speed control matter "that much" to you? Of course it's always nice, but for me (not everybody, but for me), I have no problem moving belts. I might end up on a slightly slower speed than I need to be at, but how much of my day do I spend in production, and what would I actually get back on that? Well, for me, I'm not seeing any return on that. Do you do longer, involved projects where "exact" speed settings might save you some time during the day? Then this would be the opportunity to upgrade.

One last thought- You said that the switch is sketchy and not done right- I might, were it mine, take on that project first. Make that switch "right", or replace it with a more suitable one that is "right", or whatever you intend to do. I can think of a couple of ways somebody could screw up a switch to the point that it might have some undesirable side effects...

 

[markba633csi]

Not clear on which type of motor you have- PSC or permanent split cap motors have a small run capacitor which is always in the circuit when motor runs. Capacitor start type motors have a larger capacitor which is only used for starting; a switch inside the motor opens the circuit as the motor reaches full speed. Trying to limit the inrush with a device may interfere with the ability of the motor to start normally.


Running a separate dedicated branch circuit for power is the best idea as mentioned above
You want your heavy electrical loads to be fed from a central hub or breaker box directly
The problem seems to be the power distribution
not the motor itself

 

[Ulma Doctor]

Consider a replacement motor or increase the starting capacitance.
Soft starters are for use with 3 phase motors, not compatible with a single phase motor.
modifications can be made to operate the single phase motor with a VFD, but it requires the elimination of the starting circuit.
The motor will not have the same starting torque and most likely have a reduced service life as the run windings are asked to start the motor without the start winding to add additional electromotive force.
Great experiment, but hardly practical- the time and expense could easily be wasted.

Is the motor rated for 60Hz or 50Hz? A 60Hz motor will run slower and pull more power on 50Hz.