1/3 hp rated at 6A (120v), how/why?

[ching0n]

Forget about the marketing that manufacturers engage in,

I'm looking at a belt sander (craftsman) of some vintage rated at 1/3 hp w/a 6A rating and another I want to guess newer mode rated 2/3 hp w/a 4.3 A rating. As far as I know, AC motor efficiency hasn't progressed much in maybe 50 yrs+ (bearing vs bushing?) so doubt that's where my hp went.

6A*120= 720 W x .9eff ~ 648w / 0.87 hp (thinking older model)
4.3A*120= 516w x.9eff ~ 516 W / 0.69 hp ~ 2/3 (thinking newer "horsepower" model)

The 2/3 manual does say "peak" so running is likely less, so maybe 1/2 hp? The 1/3 hp doesn't make sense for the older one, but looking at full load amps is in the ball park, while running amps is also in the ball park. Why is running amps not closer to the 2/3, 4.3A load? Did manufacturers use to severely underate motor hp (would not make sense looking at load tables right now). Service factor?

Electrical Motors - Full Load Amps

Full load amps for single and 3-phase 460 volts, 230 volts and 115 volts electric motors.

www.engineeringtoolbox.com

 

[wyliesdiesels]

That chart is misleading. The values listed are NOT FLAs. Theyre FLCs- full load current, derived from 430.248.

There is no such chart for FLAs because they vary by manufacturer and motor model.

FLCs (max possible amps for all motors in that HP size, used for sizing motor circuit wire) will always be higher than FLAs (load amps for that particular motor).

 

[ching0n]

That chart is misleading. The values listed are NOT FLAs. Theyre FLCs- full load current, derived from 430.248.

There is no such chart for FLAs because they vary by manufacturer and motor model.

FLCs (max possible amps for all motors in that HP size, used for sizing motor circuit wire) will always be higher than FLAs (load amps for that particular motor).

That makes more sense. There is no reason craftsman (or other) would print amperage for the electrician sizing as opposed to spec a machine would they? How would you interpret these two?

 

[ching0n]

"1/3, 6A model"



"2/3 4.2A" , eh, maybe I shoul've looked the size from the get-go:


"

 

[walta]

Marketing propaganda is full of lies. Comparing old lies to new lies is not likely to provide any useful data.

The first photo looks like an induction motor. The second motor not so much it may well be a universal type motor they tend to make much more torque and live shorter lives.

Walta

 

[rooster59]

Might be-

current with a fully locked rotor = 4.2 amps
power = 4.2 amps x 120 volts = 504 watts
horsepower = 504 watts / (746 watts / hp) = 0.676 or about 2/3 hp

lots of exaggeration, not a real world number

 

[ching0n]

Marketing propaganda is full of lies. Comparing old lies to new lies is not likely to provide any useful data.

The first photo looks like an induction motor. The second motor not so much it may well be a universal type motor they tend to make much more torque and live shorter lives.

Walta

that might be it, I know the above 6A is a 2 shaft but the 1 shaft also shows a similar motor frame:

Efficiency​

[edit]
Even when used with AC power these types of motors are able to run at a rotation frequency well above that of the mains supply, and because most electric motor properties improve with speed, this means they can be lightweight and powerful.[5] However, universal motors are usually relatively inefficient: around 30% for smaller motors and up to 70–75% for larger ones.[5]>>>>245W (1/3 hp)/720w (6A*120v) ~ 34%



photo of 1 shaft (don't see amp draw tags anywhere for this machine):

 

[pancho400cid]

The key thing to note is the "MAX DEVELOPED" HP rating of 2/3 HP.

If you have a running motor and the jolly green giant reaches out and grabs the shaft and stops it, the motor is now making max developed HP..... that is with full rated voltage and at locked rotor current. As said, it is a completely BS rating so the manufacturer can put a "big" HP number on the nameplate. The motor is nothing but a heater with a low power factor (highly inductive load) in that case and is doing literally ZERO useful work.

 

[walta]

In my opinion both of the sanders are more toy than tool. If you need a wood eraser spend the money for a Delta 6x48 and fit it with a 1.5 horse motor and watch it make wood disappear.

If I had to chouse between the options you listed. I would select the older cast iron unit. Most because it will likely be quieter. Generally, I think older tools were better made than newer tool absent a technological jump.

Walta

 

[ching0n]

In my opinion both of the sanders are more toy than tool. If you need a wood eraser spend the money for a Delta 6x48 and fit it with a 1.5 horse motor and watch it make wood disappear.

If I had to chouse between the options you listed. I would select the older cast iron unit. Most because it will likely be quieter. Generally, I think older tools were better made than newer tool absent a technological jump.

Walta

it's mostly brainstorming for a tool mod. The more horses the better idea I get for a starting point.

 

[tool_scrounge]

One thing to note is the AC power equation is:

power = volts X current X power factor.

Power factor is between 0 and 1. For a resistive load like a space heater, the power factor is 1. For inductive loads like motors, it is less than 1.

I have seen tiny unloaded fractional horsepower motors use 10A. But they are cold to the touch. This is because the power factor is almost zero. So the real power used is also almost zero. So there is little heat.