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Torque difference between 1PH and 3PH motor

Maybe missed is inertia as we talk about the output of various motors.
Rotating mass and flywheel affect on actual output to the work?
An ICE only makes power in rather brutal pops.
It is a system not just a power driver.
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Has anyone gave a number??
Normally-aspirated 8V92 has 983 ft-lbs of torque (depending on the injectors). Again, depending on tune and purpose, the turboed ones ran around 1250 ....

JST said:
Then there was the comment that there is a difference that may or may not MAKE a difference, in the way that torque is delivered (smoothness, etc).
He could put a flywheel on it if the pulses bothered him. Altho there is a theory that v-twins work better on dirt because of the uneven inputs to the torque equation :)
He could put a flywheel on it if the pulses bothered him. Altho there is a theory that v-twins work better on dirt because of the uneven inputs to the torque equation :)
there are some videos on youtube that explain why this works.
gives the rider a soft failure point where you can feel the rear tire start to slip because of the uneven torque, lets you ride the edge of the static vs dynamic friction coefficients.. since, you know, everyone wants to do that.
All things being equal power application between single and three phase motors of the same Hp/Torque/RPM can be seen in the surface finish in some situations. In lighter lathes, there are cases where repeating bands of uneven cutting show up in the work when using single phase motors that is not present when they are converted to 3 phase with the same motor operating specifications. It is not a specific resonate frequency, it shows up at different speeds/feeds and materials. It may be a rigidity issue, but it is clearly associated with single phase motors. I have seen this several times, and in all cases converting to a 3 phase motor eliminated the problem. Other solutions have been to rubber mount the single phase motor, which sometimes work. Previous discussions as to the etiology had to do with the motor pulsations.

Same pattern in aluminum and steel.
Lathe Single Phase Motor pulsations.JPG
I noted an immediate ability to get 15% to 25% more depth of cut without flat belt slippage on similar cuts when the machine was switched to a 3 phase motor of the same power.

The machine also entirely stopped throwing the flat belt off the pulleys when it slipped. Since it stopped, I am not sure what number to put on that, any comparative ratios end up multiplying or dividing by zero.

I do not know exactly how to put a number on the chatter performance either. If I had documented a maximum chatter-free DOC, feed, tool width and rpm before chatter, prior to changing motors, I could give those numbers compared to now.

But, unfortunately, I did not know back then that over a decade later Jim would want to know the weights and shoe sizes of those dancing angels.
Peak torque is the same.
Torque curve to the peak is a bit different,
so it may not replace your application perfectly.

There....Summary... Happy?

Peak torque may be different; that's what's normally called 'pull-up torque' at about 70% RPM.

Rated continuous torque at rated RPM will be identical given motors with the same rated RPM and power.
Some interesting stuff to learn here. So a curious mind wants to know, what about the “smoothness” - if you will - of the torque of a DC motor. I am thinking specifically of the planers that used a large DC motor to drive the platen. Was part of the reason that a DC motor was used was a smoother torque output = better surface finish?
Seen this single phase and three phase or even converter things spoken about a lot on surface finish.
Seems the grinding people get the most anal about this.
Am wondering if only one thing got changed?
A low cost VFD does not make exactly nice power to a grind spindle. Yes chokes but measurable improvement in finish?
The choke here maybe more to protect the wiring and spikes?
Load, power, mechanical and electrical time constants, slanted rotors. ..Oh my.
On a high speed and high response servo yes these make a difference. On a belt sander drive or small lathe?
This not a $100,000 machine tool.
For all here that do sell refits at the 50k to 200k ranges for sure this has to be in the equation.
Stand up and tell me.
Some guy here named "motion guru" has not said much.*(sad face)
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........It's not engineering if there's no numbers. Without those it's mythology.
The term you are searching desperately for is "anecdotal".

Anecdotal information is not "mythology", it is simply a limited number of what can be termed "incidental experimental observations" not confirmed by numbers. Basically, interesting things observed in the course of other activities, but for which no suitable instrumentation was set up. The numbers may confirm the "incidental observations", or the numbers may not, assuming an experiment is set up to examine the matter.

When you get enough "anecdotal" reports, it is reasonable to determine that there may be something behind the matter, and proceed to experiments.

Now, "I" am perfectly satisfied with a dozen or more years of this "anecdotal" information, I have no particular personal need to satisfy you with data. So I won't be pulling the lathe out to replace the motor and instrument it up to your satisfaction.

However, I think you likely have many motors, both single and three phase, and you are completely free to make the experiment yourself. This is more appropriate than carping about others not doing that, since you are the one who is demanding the numbers.

Who knows? Maybe Jim Rozen will be the one to prove that single phase is just as good as three phase....... You could be famous......
Who knows? Maybe Jim Rozen will be the one to prove that single phase is just as good as three phase....... You could be famous......
Lets stop this right now.
JST is right on points and Jim is right on points.
Chips in your shoes and an understating the other side and working.
But this is way amusing. One side does not get the other.
I guess this is good and actually I sort of feed it or push it in my staff.
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It's a friendly debate.... and on-topic, not much of an issue as this site goes, or I'd cut it off and do some closing and deleting.

There IS room for some number-based measurements. If I get bored, I might make some of them, although I'm definitely not disassembling a lathe to do a formal comparison.

A smooth dyno as a load, and a means of measuring either torque, or belt force, etc, would be needed. I doubt any cruder setup would find the pole-related torque ripples, but those are likely not an issue, at least in a first cut test. There should be measurable half-cycle variations, however.

Separating out the effects of straight-up vibrations from torque variations might be an issue, a bit of thought about the way the forces are applied might be needed to come up with a method. I know I have nothing that can go on a shaft for wireless reporting of shaft or coupling deflections, which would be the ideal method.

If the effects are meaningful, they should not be too hard to find, however.
"incidental experimental observations"

Translation: Journal of Non-Repeatable Results.
Translation: 'can't figure out why it's doing this'

I used a single phase motor once. A red demon with horns jumped out of it and ate my workpiece. <- Valid anectdotal observation.

Seriously though, the only single phase motor that runs in the house is the oil burner motor. Works just as good as if it was 3 phase far as I can tell.

Experiment: apply a constant load to a single phase motor. Plot angular speed vs time. You'll need a good way to apply a very constant load and a very high resolution tach. 1725 rpm you will probably need to measure one part in 10e4 or better to see an effect. If the load varies at all it won't work. Possibly a dc generator with excited field powering a resistor load.
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DC generators have pole effects, which would recur at regular intervals and may be an issue. Possible problems would depend on the pole pass frequency vs the signal frequency of interest (50 or 60 Hz and harmonics).

Discs rotating in oil might work, but may not be much of a load, and are neither easily adjustable nor particularly constant in resistance, due to heating.

A homopolar generator would probably work, if the contacts on the edge and shaft can be made to be unvarying as the disc turns.

One only really needs to check at the fundamental and first couple of harmonics of the mains frequency. That is where the effect will show up. An overall wider band signal examination is also good as a sanity check for interference, or other problems.

Instead of a tach, a more direct test would be a strain gauge or pressure sensor reading the pressure of the motor or load in place of the scale used on a Prony brake.