Lathe repowering

[Ironman]

My lathe has been underpowered since I got it as it was used for machining MDF patterns and never had to work for its meals. Now the 2 hp motor has been popping the 30 amp breaker occasionally so it was time. Being hidden in the pedestal was no help. Here's the old one. And the "new" one. I just replaced the bearings in it because that sucker sure is heavy.

 

[Ironman]

It took two old guys in their 70's a good 3 days to change it out. One day to remove, and gravity was my friend. But now came this ugly monster. Free motor indeed, probably got rid of it cause it was so heavy. Lifting and blocking and come along work finally got us to this point at end of day 2. And now comes the part of attaching it to the sliding plate that does belt tensioning. It is a 184T frame so has the same general dimensions as the 2 hp, but they managed to make it so rotund that you can't get at the mounting bolts. One of us is a lefty and one is a righty so without that I don't know what I'd have done. I had to use some redirod and thread through and put nuts on the moter feet, because we were working by feel on the back end.. Put a bit of chain on and used the comalong to slide the plate up and slip the belts on.

 

[YYCHM]

What HP did you upgrade to?

 

[Ironman]

Now comes the fun part. I found a chinese box to hide the VFD in, and keep chips out so I got the handy dandy hole punch and made vent holes and cable holes. Mounting and trimming and connecting is a slow but satisfying part, and although I still have to wire in the remote controls and brake resistor, it is in working condition by 3:30 today. I happened to have a 3 phase toggle switch laying around and so I mounted it in a spare box and used that for an on/off for the VFD. I like to have my cabling neat but I also have to look at the event of moving the lathe around and having to pull out the 3 ph wire to disconnect and move, so I decided to leave it as is.

 

[Ironman]

What HP did you upgrade to?

It's a 5hp. I have overloaded the 2hp so many times and run it down to the start winding, hear it clicking the switch and then back off the cut, that I think the switch contacts are starting to weld together. I may take it apart and clean up the switch points and it may be ok, At one time I used an amp clamp and saw it pulling 25 amps, or equivalent to 5 hp single phase.

 

[Ironman]

Today I took a second 5hp motor in To Drayton Valley to have the motor Repair guys check it, because some of the numbers are worn off the wires and I want to have it correct in case I use it or for trading stock. While there I questioned the guy because the monster motor that I put in the lathe had a very large diameter rotor, 5" across, compared to the one I took there for a health checkup. So I asked him about that, and logically to me it would mean a higher torque motor. His response was "Nah, 5hp is 5hp and that's that."
He never charged a penny for looking at it, but I'm an electrical dummy and I figure from the mechanical point, the greater leverage you have on a shaft the more torque your snipe produces.
Does anyone have a better explanation for larger and smaller rotors with a 4 pole, 1750 motor?

 

[DPittman]

Nah, 5hp is 5hp and that's that."

Yes hp is hp but torque is another thing and a larger 5hp motor is very likely to produce more torque than a small 5hp. (My shop vacuum is supposed to be a 5hp motor and it wouldn't do the torque work that a half horse motor would do.)

A YouTube video that explains some of the crazy hp ratings of treadmill motors is found here:

 

[Susquatch]

Nah, 5hp is 5hp and that's that."

5hp really is 5hp. Also, torque and horsepower are mathematically related to each other. You cannot change one without changing the other.

Horsepower = Torque x RPM / 5,252. However......

Like so many other things today, the marketing guys lie. Not all so called 5HP motors are really 5HP.

Also, both Torque and HP are ratings that specify what the motor can do at maximum output. Few motors really produce their full potential on a lathe (except at startup) and virtually never on a mill. A mill or a lathe pushed to its limits might be another story.

HP is a measure of work done. For a metal working machine, I like to say that the power a motor produces is equal to the work needed to keep the gear train going plus the rate of metal removal (how many pounds of metal are removed per unit time).

On the other hand, Torque is a leveraged force. It is independent of time. Torque is the leveraged force applied to the gears to make them turn and to the cutter to make it cut.

The motors on most machines are sized so that the machine can keep cutting and removing metal at a reasonable rate without stalling.

 

[Ironman]

So if torque is involved in hp calculation and rpm are equal, then a motor with higher torque would produce the 5hp with less current being consumed than one with a lower torque...it seems. Maybe that's why the label says 'Toshiba High Efficiency' on the label.
I have a stationary diesel engine rated 6 hp with 47ftlb of torque, and then there are 6hp Chonda's with 6.4 ft.lb.

 

[Ian Moss]

I need a box like you have for my VFD. Can you tell me where you got it and what numbers or names specify that box please.

 

[Susquatch]

So if torque is involved in hp calculation and rpm are equal, then a motor with higher torque would produce the 5hp with less current being consumed than one with a lower torque...it seems.

Not really. There may be some differences (usually minor) in efficiency between different brands, but for all motors running at their design speed increasing the torque increases the horsepower.

Maybe that's why the label says 'Toshiba High Efficiency' on the label.

The typical efficiency of almost all electric motors is very high. But it is possible to waste less energy within limits to produce a given HP. The difference is in how much energy is wasted generating heat and overcoming internal friction. For any given rpm, there is no tradeoff between hp and torque. They are mathematically related - one defines the other.

I have a stationary diesel engine rated 6 hp with 47ftlb of torque, and then there are 6hp Chonda's with 6.4 ft.lb.

I'm not familiar with those examples. However, there are only two possible explanations for that.

1. Most likely they are each rated at vastly different rpms. Even for a given motor, manufactures will often rate HP at a different RPM than the torque rating.

2. Marketing exaggeration.

Just to clarify the first explanation a bit. Electric motors usually turn at a fixed rpm. So both torque and hp are rated at that same fixed design rpm. Fueled engines on the other hand run at many speeds. So most fueled engine manufacturers rate the torque at whatever speed it is highest, and the hp at whatever speed it is highest. It's mostly marketing.

 

[Ironman]

I need a box like you have for my VFD. Can you tell me where you got it and what numbers or names specify that box please.

I was surprised and as I was expecting chinese junk, but this is good quality.

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[Mcgyver]

So if torque is involved in hp calculation and rpm are equal, then a motor with higher torque would produce the 5hp with less current being consumed than one with a lower torque...it seems. .

No, HP is a measure of power, its Torque x rpm. Watts is also a measure power, just a different unit, its amps x volts. 1HP=745 watts.

For a give HP (any equal product of rpm x torque), the watts will be the same. With the watts the same, the the amps can be varied by changing the voltage (yes you can vary the frequency, but then the watts aren't the same). The power (HP) of AC electric motor is stated at is normal operating speed and the torque curve is flat. i.e. torque stays the same, half the speed you halve the HP, its linear.



That doesn't compare well to IC engines which have anything but a flat torque curve. Coming at from an IC engine understanding, it might hurt one's brain trying to compare, but the key is power (HP, Watts) is always the product of RPM and Torque.

I have a stationary diesel engine rated 6 hp with 47ftlb of torque, and then there are 6hp Chonda's with 6.4 ft.lb.

Because IC engine's torque curve is so curved, the HP is stated at the max, where rpm x torque is the greatest. The torque and rpm for each each engine woul reveal all, but basically if they were both 6HP, the Honda would be delivering its 6HP at a much higher RPM (and lower torque). With gearing (assuming zero power loss with it) you could create a shaft from each engine rotating at the same speed and torque, i.e. both at 6HP

 

[Susquatch]

For a give HP (any equal product of rpm x torque), the watts will be the same.

Excellent comprehensive explanation.

Only one teeny tiny quibble. Watts is usually measured as an input. Hp is usually measured as an output. Of course, there is no real difference as these are both only units of power. With 100% efficiency, input and output are the same. But it is entirely normal to have a very slight efficiency loss that shows up as a warm motor, and slightly higher input power than output. Few if any motor manufacturers own up to this.

 

[trevj]

Excellent comprehensive explanation.

Only one teeny tiny quibble. Watts is usually an input. Hp is usually an output. With 100% efficiency, input and output are the same. But it is entirely normal to have a very slight efficiency loss that shows up as a warm motor, and slightly higher input power than output. Few if any motor manufacturers own up to this.

Seen too too many examples of power output being defined in Watts or Kilowatts, to suggest that you are correct on this one Susquatch. Metric mumbo jumbo, eh!

But as long as everyone uses more or less the same measuring Standard (even in "Sears Horsepower" Shop Vac motors!) then at least, a direct comparison can be made.

A quick re-check online tells me that they call 746 Watts equal to one HP output. 750 is a nice round number to use when looking at Euro power output ratings in W or KW, for the conversion, anyways.

 

[PeterT]

Only one teeny tiny quibble. Watts is usually an input. Hp is usually an output.

Do you mean customarily to motors or in general? There are many examples of watt based dimensions relating to both input or output depending on the application.

 

[trevj]

Do you mean customarily to motors or in general? There are many examples of watt based dimensions relating to both input or output depending on the application.

Ayup. Watts as a power output, are (by admittedly shady memory!) calculated about the same way as HP, ie: Torque Value and Revs. Watts (or is it watts?) as an electrical power term, is calculated from Amperage times Voltage, iirc (P=I*E).

Given the way of things, it should not surprise me if you cannot look up the Watts output of the nice green tractor out in the shed, eh?

 

[Susquatch]

@trevj & @PeterT.

The best way to look at this is to ask yourself how they are measured.

In the case of watts, they measure the peak current multiply by Volts and calculate watts. In the case of hp, they use a brake and measure hp.

Having said that, I am certain that there are companies who measure hp and calculate equivalent watts as well as those who measure watts and calculate hp (prolly the majority). The wonders of marketing.

We all know that there is no such thing as 100% efficiency in a motor. If you agree with that, then hp out cannot equal watts in.

Furthermore, if the motor gets warm or hot then watts in must be greater than hp out.

Except in the case of really crappy motors like described by others earlier in this thread, none of this is really significant because you can stick the difference in your eye. I was only explaining why a really crappy motor can be worse than a good one and in that case hp is not necessarily hp.

 

[PeterT]

I forgot to include a Wiki link. Ctrl-F the word 'output' & there are many examples across various industries, even among motors & engines. No debate about Output vs Input (efficiency), I'm just saying I see many examples of watts referenced on the output side. Its actually quite common in compressors where input relates to gross heating value of NG mass (or whatever fuel) which derives back to Joules over time, but the equivalent imperial units are ultimately interchangeable. I agree, the nameplate specs on many of our machine motors are largely ambiguous. Doesn't 'brake' (output power term) date back to the handle / engagement mechanism on the output shaft from back in the day? Might even come rom locomotive days pre ICE days? Where is AI when you need it haha.

Watt - Wikipedia

en.wikipedia.org

 

[trevj]

@trevj & @PeterT.

The best way to look at this is to ask yourself how they are measured.

In the case of watts, they measure the peak current multiply by Volts and calculate watts. In the case of hp, they use a brake and measure hp.

Having said that, I am certain that there are companies who measure hp and calculate equivalent watts as well as those who measure watts and calculate hp (prolly the majority). The wonders of marketing.

We all know that there is no such thing as 100% efficiency in a motor. If you agree with that, then hp out cannot equal watts in.

Furthermore, if the motor gets warm or hot then watts in must be greater than hp out.

Except in the case of really crappy motors like described by others earlier in this thread, none of this is really significant because you can stick the difference in your eye. I was only explaining why a really crappy motor can be worse than a good one and in that case hp is not necessarily hp.

John Deere lists the outputs of their tractors in both Watts (OK, kiloWatts) as well as HP as representing the same measure. Not the first time in history that the same unit name has been co-opted into several different and varied meanings, making the context in which it is used, fairly much key to understanding what folks are ACTUALLY talking about.

https://www.deere.com/assets/publications/index.html?id=b8f9dab8#14

Engine power, PTO outputs, etc. I kinda lean away from the idea that they are in any way doing jiggery-pokery with the math, to try to define the output power via electric motor equivalents.

FWIW, when I last had some instructor droning on about Horsepower, it was defined fairly well as a measurement of the ability to do work over time, same as wattage of electric systems. Just measured in different units, supposedly to provide some semblance of universality (which it pretty much failed at, IMO, else there would not be fun convo's like this one happening!