Horse Power on a motor label

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physis

Senior Member
I was working with a compressor that has a motor with a HP rating of:

SPL.00

on the label.

What in blazes does that mean? :confused:

In case it matters its 230v. single phase, 15 amps.
 

templdl

Senior Member
Location
Wisconsin
Re: Horse Power on a motor label

Probably for special. Compressor manufacturers who package compressors for home and light commercial duty play games with HP ratings which I haven't found to be true NEMA HP ratings. Just marketing.
It's about the same as those shop vacs that have HP ratings on them.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Re: Horse Power on a motor label

It's about the same as those shop vacs that have HP ratings on them.
So you mean like my 120 volt, "Craftsman 5.5 Horsepower Compressor" with a 15 amp attachment plug? After removing the cover I found the motor label did not have a HP rating. The spot on the nameplate was blank. It did say 15 amps however. This would translate to about a 1 HP at 120 volts. A 5.5 HP at 120 volts would draw over 50 amps. And advertising this as a 5.5 HP isn't illegal?
 

ramdiesel3500

Senior Member
Location
Bloomington IN
Re: Horse Power on a motor label

I think that is EXACTLY why the motor label is blank. They are saying the entire tool is 5.5 HP. Not the motor. I believe under maximum load conditions, a 1 HP motor can produce up to 5 or so horsepower for a short burst. So the manufacturers are taking advantage of that fact and advertising the peak horsepower of the appliance rather than the NEMA Hp of the motor! It's all about marketing!!!
 

tom baker

First Chief Moderator
Staff member
Re: Horse Power on a motor label

If you go to the big box, they have a "5 hp" air compressor that has a 15amp 125 volt cord.
If you look in the NEC real 5 hp motor has a FLA of 53.

[ March 01, 2006, 10:22 AM: Message edited by: tom baker ]
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: Horse Power on a motor label

Perhaps they are taking credit for the horsepower that would be generated, briefly, at the moment of starting. If you multiply 120 volts times the starting current, and do a unit conversion to horsepower, you might get their numbers. But it sounds to me like a "truth in advertising" problem.
 

templdl

Senior Member
Location
Wisconsin
Re: Horse Power on a motor label

Bingo Charlie, right on.
Just a gimmick to satisfy our quest for more power.
The only think that I use the rating for is to compare products assuming the 3hp is better than 2hp even though the rating doesn't mean a darned thing.
When they refer to peak HP or "special" by whose rules are they playing by? There are no standards that I'm aware of. Is "peak" for a nano second?
Dave
 

physis

Senior Member
Re: Horse Power on a motor label

So then I'm not crazy? SPL.00 is meaningless

If I do the math I get:

230v. x 15A. = 3450w.

3450 / 746 = 4.625 HP

I thought the nameplate was supposed to provide usefull information. :confused:
 

coulter

Senior Member
Re: Horse Power on a motor label

Originally posted by physis:
So then I'm not crazy? SPL.00 is meaningless...
Well SPL is likely meaningless, but what does that have to do with you being crazy :p

Originally posted by physis:
...If I do the math I get:
230v. x 15A. = 3450w.
3450 / 746 = 4.625 HP
As noted by TomB, single phase motors are nowhere near to 100% efficient. NEC 430 shows a 230V, 2hp motor draws 12A


Originally posted by charlieb:
Perhaps they are taking credit for the horsepower that would be generated, briefly, at the moment of starting. ...
I don't think so. I've never measured a single phase motor, but I suspect that the starting load is highly inductive. For example, at the instant of starting, the current is high, the voltage is still nominal, speed is 0rpm, it doesn't matter what the torque is, the hp output is zero.

I've never seen the speed/torque curve for a 1ph motor, but as I recall (code phrase meaning I did not look it up) 3ph, Design B motor pulls out about 225% rated torque and 90% rated rpm, This gives about 2x rated hp.

Nope, doesn't apply to vaccuum cleaners or compressors.


Originally posted by ramdiesel3500:
... They are saying the entire tool is 5.5 HP. Not the motor. I believe under maximum load conditions, a 1 HP motor can produce up to 5 or so horsepower for a short burst. ...
I don't think so. Motors run where the load/speed curve crosses the motor torque/speed curve. So vaccuums and compressors will never load the motor to the madison avenue rating.


Originally posted by templdl:
... The only think that I use the rating for is to compare products assuming the 3hp is better than 2hp even though the rating doesn't mean a darned thing. ...
I'm not even sure of that. I've got a small, light weight, industrial grade compressor I use for a framing nailer. Its 120V with a 15A cord, rated at 1hp. I don't think this particular one is lying. If I connect two nailing guns, and it runs constant, it will occassionally trip a 20A CB. I really doubt Sears best 5.5HP will keep up with it.

If I had to pick one from the "big book" (or was it "box") - (in either case, yuck, ick, wash my mouth out, Bad Dog), I'd look at the free cfm, motor amperage, and tank volume.

Originally posted by infinity:
... And advertising this as a 5.5 HP isn't illegal? ...
Well if I said it in court, the junior engineers scoutpost would take away my secret decoder ring, break my slide rule, and make me eat a raw rutabaga. The court system would just call it lying.

Madison Avenue likely calls it "Inovative, proactive, leading edge information transfer. Concept is supported by previously unknown new math techniques and computer generated fuzzy logic."

carl
 

coulter

Senior Member
Re: Horse Power on a motor label

Originally posted by physis:
Hi Carl, Good to see you again. :cool:
Thanks Sam. Its always enjoyable when I can take time to check in and read what happening - it's always a learning experience. And it's also enjoyable to add my 6.7** cents where I think I have an informed opinion. Unfortunately, other things are still calling:

The house is now painted out inside, ready for window and door trim - still working the last of domestic water plumbing.

Haven't worked on the airplane for two years now (sigh)

And MY BOSS - get this - actually expects me to work every week day AND the occasional weekend - oh the horror or it all.

I check in when I can. Right now, I'm pretty interested in Don's answer on the 725 circuits. That one has all the earmarks of a possible, previously unknown, subtlety to be understood.

carl
** inflation corrected to 1.8 cents, 1955 standard - nope, sometimes not worth the full 2 cents :roll:
 
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