Motor horsepower comparisons from old to new.

[ajchien]

Is there something that has changed in the HP rating for electric motors over the years?

Why does it seem that a 30 year old motor with 1/4 or 1/3 HP runs stronger than a new 1/2HP? Is this my imagination?

 

[mr-compressor]

It should be the same, physics don't change.

Horsepower = torque x rpm.

Older motors usually have lower rpm, which means higher torque (for a same hp motor).

 

[zkling]

It should be the same, physics don't change.

True, but morals and business ethics do change, or so it seems.

The thing that typically gets forgotten about in electric motor HP is the efficiency. HPmechanical=torquexrpm & HPelectrical=(watts x efficiency)/746; Where watts = volts x amps

Now the issues comes into play is how the manufacture is specifying that HP. Running, max developed, rotor locked, start up current? A few years back there was a big lawsuit to the small air compressor manufactures that were putting ridiculous claims on their consumer grade air compressors. Ex. the 7hp, 115v air compressor. I read a good article a while back in one of the online engineering journals I subscribe to. I will see if I can dig it up. It talked about this particular issue.

I'd say if you compare current (pun intended) quality made motors to older motors of applicable HP, you wouldn't see much difference. The big differences become apparent with the cheaper, more common lower end motors, that are made extremely competitively today.

zkling, off to dig for that article.

 

[justanengineer]

True, but morals and business ethics do change, or so it seems.

I'd say if you compare current (pun intended) quality made motors to older motors of applicable HP, you wouldn't see much difference. The big differences become apparent with the cheaper, more common lower end motors, that are made extremely competitively today.

Its that way with everything "consumer grade" today tho, not just electric motors. Small engines, pumps, etc....anytime you buy anything cheap you need to consider that the "rated" power, flow, whatever is just an advertising gimmick.

 

[the gypsy]

Hi zkling I am looking forward to reading that article you are searching for.

 

[Davefr]

The "bastardization" of HP ratings was spawned by our friends at Sears who's mission statement includes consumer fraud and deception.

Unfortunately many others had to follow suit or be out marketed.

What's worse it that you can't even find amp ratings anymore so there's no meaningful way to evaluate/compare motor power.

(ex: I picked up an old 6" B&D block style bench grinder recently. The nameplate says 1/4 HP, 5.1 amps. It's twice as powerful as a new HF 6" Grinder that claims it's 1/2HP!!)

 

[Wakefield]

Lawn mower HP issue lawsuit or something a few years ago?
1950 Pontiac 8 must have had bigger horses than current cars- 108 felt almost like 170 of today's
I suppose electric motor rating could be maximum continuous load the motor can carry without overheat vs. the peak it can provide without conking out under the load immediately

 

[Wakefield]

I think with an electric motor,if the cord isn't thick enough for length,such that excessive voltage drop happens in the cord,the motor won't perform as well. For instance,a 50" light 18 gauge wire extension cord trying to run a heavy amp draw motor?

 

[zkling]

Its that way with everything "consumer grade" today tho, not just electric motors. Small engines, pumps, etc....anytime you buy anything cheap you need to consider that the "rated" power, flow, whatever is just an advertising gimmick.

Yep, sad but true. My ~2002 IIRC Husky lawn mower has a briggs motor largly states something like 9.8 in big letters then below it, it reads ft*lbs. Even thought the max HP is less than that.

Well what looks more appealing to the consumer a higher or lower number in large print? And this is sadly what happened to the comsumer market. If you put two mowers next to one another and let your average consumer pick. They would most likely go for the mower that had the higher number printed on it. Not even noticing or caring if that number is torque or HP.

Another real good example is the cheaper air compressor motors that, on the nameplate under HP are maked SPL

Hi zkling I am looking forward to reading that article you are searching for.

Yea, I will have to do a thorough search for it. I save so many good articles, thinking I will go back to read them and never do. My bookmark list scrolls forever.

 

[A_Pmech]

Older induction motors had larger rotors. Although less efficient, they don't saturate as quickly. Therefore, they can provide more power, within the magnetizing limits of the stator.

 

[kamesama980]

old motors: where they could run at all day just fine
new motors: how much it made a few milliseconds before it welded itself into a lump of copper and iron.

in cars, they used to rate engines in gross hp: no accessories, exhaust, filter, etc. now they have to to do net hp with all accessories, filters, emissions, full exhaust, production tune, etc. also: better, more accurate dynos to masure with.

 

[buening]

I had a post awhile back on one of the Craftsman block grinder threads, where I had pictures of the motor plates in which some 1/4hp grinders had more amps than the 1/2hp grinders, and these were the 60s and 70s grinders.....likely before the marketing goons decided to overrate their hp ratings. Efficiency of the motor is typically the hardest thing to identify and can affect the ratings.

 

[scw1991]

After 10 years of restoring vintage woodworking machinery, the motors were near bullet-proof. HP = HP, but they had large frames to dissipate heat more effectively and we're typically an ODP design. A typical 1HP repulsion induction 1725 RPM motor weighed close to 80 lbs. The motors I had were from the 1930's through 1950's and ran very strong. I even had a few 3HP 1725 RPM motors that weighed in at 140 lbs with a 1-1/8" shaft diameter. Again, bullet-proof.