HP/amps

[Paul Saffold]

I was looking and lusting at the info on the new Jet lathe (1221VS) and they list the motor as 1 HP and 6 amps. I have a '80s Sears with a 1/2 (B) HP and 8.8 amps. I don't know what the "B" is regarding the HP but the listed amps confuses me. It doesn't take much most days, but anyhow, is there an explanation for the difference in the amps/HP? One that doesn't require an electrical engineers degree. Thanks.
Paul

[Michael Mills]

I did some research a few years back and this article puts it into layman’s terms.
http://www.kevinsbrady.net/motors.pdf
Did the ad have the normal disclaimer terminology? Peak, Max, Achieves, ect.
So the Jet has 1hp at 6 amp and the Deltas has 1hp at 8 amp? At least Delta does say Max. Oh, and the Rikon states 1/2 hp at 6.6 amps, now that I believe.

Now you know as much as I do.
I did lookup the B and it means Brake HP. You can google it for an explanation. Seems one is measured at the shaft (HP or BHP) and one is measured under normal load (maybe at the spindle in this case?)

[Joe Kaufman]

This is pure speculation as to the new Jet, however most lathes in this class use 90VDC motors with simple voltage control and current limits. (The Penn State Industries 12” lathe advertises an induction motor which I would assume to mean 3 phase with VFD Control.) I have not seen the PSI lathe, would like to.
Specifications and operating characteristics of DC motors can be hard to compare since there are different types of field excitation such as permanent magnet field or wound field and other design features – brushless technology. The short of this is DC motor performance is difficult to compare with AC induction motor performance, lack of torque RPM Current curves and throw in off shore design and manufacturing. Evaluating theoretical performance from advertised Amps to Watts to HP is questionable.

[Jason Roehl]

I was looking and lusting at the info on the new Jet lathe (1221VS) and they list the motor as 1 HP and 6 amps. I have a '80s Sears with a 1/2 (B) HP and 8.8 amps. I don't know what the "B" is regarding the HP but the listed amps confuses me. It doesn't take much most days, but anyhow, is there an explanation for the difference in the amps/HP? One that doesn't require an electrical engineers degree. Thanks.
Paul

I would guess you're looking at input vs. output numbers. Amps are always listed in terms of use--there's no way to fudge that number. At 120V, a device that is drawing 6A is using the equivalent of about 1 HP worth of electricity (720W, which is just shy of 1 HP, or 746W). That doesn't mean that there is 1 HP output at the shaft--there's some frictional loss in bearings, some energy lost to the magnetic field, and some energy lost to heat. I would agree that the 1/2 HP rating is probably a brake rating, meaning that's what you're getting at the shaft AFTER all those losses. Perhaps the newer motor is slightly more efficient, but I suspect the ratings on the old are more upfront.

[Paul Saffold]

Thanks for all the info. I didn't realize I was comparing AC to DC. I do know that companies can be creative at making their product look as good as possible.

[Harry Robinette]

I talk to our Jet PM rep yesterday and he said they we're told that the motor in a full 1hp Universal Motor. Which I don't know anything about so someone will chime maybe and tell all of us what that is.

[Josh Bowman]

Ah, but there's more! I'm not certain of this, but I believe manufacturers have to list amps accurately. But HP is another thing. Sears has for years listed Peak HP. This means the maximum amps converted to HP that the power line drew as the shaft is slowed due to friction until the motor stalls. That's why a Baldor 5 HP motor is much larger than say a Sears 5 Peak HP motor. Usually when I shop for equipment, I look for the amps not the HP. Unfortunately they don't always list the amps, so it takes some research just to compare apples with apples.

[robert baccus]

I'm stuck on stupid but I know that amps for a given horsepower depends on voltage requiring larger motors to go to 220v ect. Chime in Dennis Ford. He actually understand ecectrithicy.

[Leo Van Der Loo]

Here's a chart that gives the amp ratings and HP produced, with a 10% margin of error + or -

AC and DC, 120 and 220V, HTH

Service Tech Info, Hvac Forum.jpg

[Dennis Ford]

Here is a link to the "standard" definition of horsepower.
http://en.wikipedia.org/wiki/Horsepower

The term has been misused for longer than any of us have been alive. My grandfather would have explained it this way: "Figures don't lie but liars will figure"

[Scott Conners]

The first thing that came to mind was that the newer lathe has a more efficient motor. Horsepower is a measure of power output, while current (amps) is a measure of power input. The amount of power that goes in and is not used to generate torque varies by motor design and condition, as well as torque load.

My advice: don't sweat the figures if you are comparing similar lathes. Trust the manufacturer to use an adequate motor for the lathe size. At the 12" size, there isn't going to be a large variation in motor performance between the major brands. I think there are far more important design features and manufacturing quality to make the decision by. Having excessive power on a frame not designed for it it just asking to break stuff anyway.

[Jeff Nicol]

On most older motors the insulation may not have been what it is today, which can cause more heat, which is loss of power for HP rating. Most all AC single phase motors are "INDUCTION" motors made to be run at the RPMs stamped on the nameplate of each motor and if you try to run these motors at slower rpms you stand the chance of burning them up. There are AC motors that are rated for variable speed operations, so if you plan of trying to use an AC motor for variable speed look into that more. Also "Universal" motors can use either AC or DC power and mostly are used in small appliances that have high speed/torque start speeds and are only used for short periods of time.

On DC motors most all of them are able to be be run at slow speeds, reversed and generally have full torque at low RPMs which make them very useful in many operations and on these small lathes they are great. For variable speed AC the best way is to use 3PHASE power input and that is what is used on most of the larger commercially available lathes being controlled with a VFD.

On the AMP draw, some rate the motor for max amps at start, max draw at full load or normal amp draw at the perfect effiiciency rating of the motor with Single phase drawing higher amps than 3 phase due to more hot leads. This is also the same for 110V compared to 220V because the 220 has 2 hot leads thus twice the current meaning half the amp draw. With DC motors draw amperage the same as AC it is just the amount of electrons passing through the wire. So with a DC motor the power is direct without the switching back and forth of the Alternating current of AC and depending on wire size, winding type etc the AMP draw may be different.

Hope you are all now completely confused but learning about Electricity can be fun, but very, very time consuming when attempting to know all of what there is to know!

Have fun and buy lots of lathes,

Jeff