My Motor's Bigger Than Yours....

[Brad Kimbrell]

I have a nice old woodworker up the street that just loves to come in my shop and tell me how his 1960 model 3HP Unisaw will kick the crap out of my 2001 model 3HP $1,700 Unisaw with "that bogus 3HP motor on it"! :confused:

He claims that since his motor weighs 70# it must be much stronger. I was under the impression that a 3 HP motor was a 3 HP motor. If his had a flywheel in it or something I could see it being stronger, but is it?

I understand peak HP vs rated HP but thought that the Unisaw was a "3 HP rated motor", not a peak rating?

What gives?

[Michael Ballent]

Just go out and get something really hard like 12/4 purple heart and 2 brand new rip blades. Place a new blade in each saw and time how long it will take to rip a 3 foot piece. I think that you will get your answer pretty quick ;) At least you will have the beginnings of some table legs or some spindle blanks if you happen to have a lathe :D


I have a nice old woodworker up the street that just loves to come in my shop and tell me how his 1960 model 3HP Unisaw will kick the crap out of my 2001 model 3HP $1,700 Unisaw with "that bogus 3HP motor on it"! :confused:

He claims that since his motor weighs 70# it must be much stronger. I was under the impression that a 3 HP motor was a 3 HP motor. If his had a flywheel in it or something I could see it being stronger, but is it?

I understand peak HP vs rated HP but thought that the Unisaw was a "3 HP rated motor", not a peak rating?

What gives?

[Barry O'Mahony]

Yea, well, compare a 200 HP 1960-era autombile engine to a 200 HP engine today. The old ones were alot bigger, heavier, and more inefficient.

Motor designers today have access to computer design, simulation, and modelling tools that engineers in the 1960's could only dream about. If today's designs weren't smaller and lighter, something would be seriously wrong.

[Stu Ablett in Tokyo Japan]

I think that the problem is that we see these "3hp" motors on stuff with a little * beside it, and if you read the fine print it is the "3hp just before the motor lets all that smoke they put in at the factory escapes" rating ;)

I agree that the stuff now should be lighter and better designed, but the older stuff is often way over engineered, and that can be the rub.

Something that is built to be just stronger than it needs to be to do the job, if it is taken above that level, often, it will fail sooner, but the WAY over engineered stuff, well it has such a buffer for abuse that it can take the beating for a longer period of time.

If you go and get a good quality top of the line motor rated for continuous hard use, made today, it would out last the same kind of motor that was made in the 60's, as the machining tolerances and the quality control is a lot higher than it could possibly be, in the 60's.

All that being said, I think his motor is a good one, and I bet you motor is good too.

I'd just let the old guy have his bragging rights, what is in it for you to prove him wrong?

Cheers!

[lou sansone]

This topic comes up now and again. Even though I am a EE and have worked in a variety of industries for almost 30 years I have not actually designed and built AC motors from scratch. Maybe some creeker has that expertise and can weigh in. I can tell you from experience that some of the older motors seemed to be "stronger" than their modern day counterparts.

besides old motors vs new motors is the designed rpm of the motor


If you take a look at my 5 hp band saw motor here ( 575 rpm motor ) f

keep in mind that the band saw is 9 feet tall for scale purposes

http://www.sawmillcreek.org/showthread.php?t=24218

you will see that this is a 286t frame - a standard 30 hp motor uses the same 286T frame! the 5 hp motor weighs about 500 lbs !

what is more interesting is the actual rated torque

a 5hp motor @ 3600 rpm = 91 in lbs
a 5 hp motor @600 rpm = 525 in lbs

food for thought
lou

[Kyle Kraft]

Here again, I'm nothing but a knuckle-draggin' machine repairman, but this discussion is just like the 7hp air cooled engine in todays lawn equipment vs. the 7hp air cooled engine that was built in 1958. I believe that even though the actual horsepower output is equal, you can do more work with the old iron because of the bigger mass of the components. For instance, all the new engines (and many electric motors) use lighter flywheels (rotors). In the case of the electric motor, the current (ampere) input may be the same for todays 3hp motor and the 50 year old motor, but the old motor can drive a more robust piece of equipment and therefore accomplish more "work" (force x distance) due to an increased flywheel effect of the beefier rotating members.

How 'bout it all you mechanical engineers out there? Does this make any sense??

[Ken Fitzgerald]

I'm just waiting for Tod Evans to jump in with "my dog's bigger than your dog".....and He can prove it!:D

[Lee DeRaud]

Yea, well, compare a 200 HP 1960-era autombile engine to a 200 HP engine today. The old ones were alot bigger, heavier, and more inefficient.Not to mention that before 1970 or so, engines were rated as"SAE gross" instead of the current "SAE net", with the result that the same engine makes about 15% less power under the newer rules. The scary part is that you end up with things like 3.5L V6s making about the same real-world HP as the 327CI V8s that were in mid-60's Corvettes.

I'm ignoring anomalies like 500HP street-race engines that were deliberatedly understated to keep the insurance company lawyers from freaking out. And yes, most cars are heavier now.