Shop Floor Talk  

Go Back   Shop Floor Talk > Welding and Metalworking Forums > Mechanical & Electrical

SFT Search:   
Reply
 
Thread Tools Display Modes
  #1  
Old 12-20-2009, 11:11 AM
Porthos's Avatar
Porthos Porthos is offline
Senior Member
 
Join Date: Jul 2007
Location: Texas
Posts: 863
Default I have a question about electric motors.

HF has a 60 gallon 2 stage compressor on sale right now. It's 5HP. In my local HF they have two of them. The tanks, pumps, and everything but the motor is the same. Both of the them have A.O. Smith (made in Mexico) motors. Both are advertised at 5HP. One motor on the data plate shows 5HP and the motor has three capacitor humps on it. The other motor on the data plate shows SPL for the HP rating and it has an enclosed square metal box on top. What is the difference?

Thanks,

Steve
Reply With Quote
  #2  
Old 12-20-2009, 12:04 PM
moe1942's Avatar
moe1942 moe1942 is offline
Voice of Experience
 
Join Date: Jun 2004
Location: Alexandria, Louisiana
Posts: 10,897
Default

Probably just the cap covers. Mine has a large square cover. Most have the individual covers (humps).

As far as SPL I don't know for sure.Maybe single phase line. If they are both 2 stage pumps they will both have a minimum of 5 HP motors.

Not sure what your air requirements are but an 80 gal tank would cut down on the pump cycles. The start cycle is the hardest on everything. The fewer cycles the longer things last.

A comp with a 80 gal tank won't cost that much more.
__________________
Don't pick a fight with an old man. If he is too old to fight, he'll just kill you... John Steinbeck

"If we ever forget that we're one nation under God, then we will
be a nation gone under". ~Ronald Reagan

We should have picked our own cotton...

I love my women hot and my beer ice cold..
Reply With Quote
  #3  
Old 12-20-2009, 12:04 PM
hardtail
Guest
 
Posts: n/a
Default

Thats the next misinformation and pitfall that your going to face is this new term "peak hp", basically many compressor duty motors now run 3450 rpm and severly overate their work duty, they are way closer to a real 3hp in actual work, you might even see some that are advertised as 6.5 hp.......They need 3 capacitors to get the thing up to speed for starting because they're so underated, the one with the box will likely require you purchase a seperate starter which is the proper way to go for true motor protection.

You will be hard pressed to find a real oldworld setup in the less than $12-1500 range, but you will get a real motor than turns 1740 and runs a cast iron pump at a slow speed for decades of service.......also look for an unloader of some sort on the compressor which greatly reduces the effort on startup.
Reply With Quote
  #4  
Old 12-20-2009, 12:18 PM
moe1942's Avatar
moe1942 moe1942 is offline
Voice of Experience
 
Join Date: Jun 2004
Location: Alexandria, Louisiana
Posts: 10,897
Default

HT I think all the current underpowered comps have unloaders. They wouldn't be able to start without one. That's why I'm gently nudging Steve towards a Black Max. The only one I could find with "old world" features at HF price. Well close. I think mine was 800 plus out the door.

Mine came with start cont, unloader, press switch and 1725 5 HP motor and 80 gal tank. It doesn't hesitate when it kicks in. I don't remember the CFM but it handles all the air tools I have with no problem.
__________________
Don't pick a fight with an old man. If he is too old to fight, he'll just kill you... John Steinbeck

"If we ever forget that we're one nation under God, then we will
be a nation gone under". ~Ronald Reagan

We should have picked our own cotton...

I love my women hot and my beer ice cold..
Reply With Quote
  #5  
Old 12-20-2009, 12:54 PM
Mild Steel's Avatar
Mild Steel Mild Steel is offline
Senior Member
 
Join Date: Oct 2008
Location: Utah
Posts: 612
Default

Quote:
The other motor on the data plate shows SPL
SPL stands for "Special". What this means is that the compressor manufacturer has requested a different set of specifications and therefore it must be made special for that application. Unfortunately this leaves the consumer in the dark as to what is special about the motor or what the real rating of it is.


I have attached a link that describes many of the different factors that an electric motor is rated for:

http://ecmweb.com/mag/electric_under...duction_motor/

You may find that article interesting.
__________________
Still trying to be the man my dog thinks I am.

Last edited by Mild Steel; 12-20-2009 at 01:21 PM. Reason: Added link to motor rating article
Reply With Quote
  #6  
Old 12-20-2009, 01:12 PM
Charlie C's Avatar
Charlie C Charlie C is offline
More STEAM!!
 
Join Date: Dec 2006
Location: Southern Oregon
Posts: 6,036
Default

On the name plate there should be a stamping that says AMPs. The number that is stamped there will give you an idea of the HP.

If I remember right 6 amps is equal to one HP. 12 amps is equal to 2 HP.ect. Now this is running amps not starting amps. Starting amps is the current required to bring the unit up to operating speed but usually starting amps is a short lived thing.

Sears use to advertise their motors as a 2 HP but develops say 3 horse power. They were right but to get that 3 horse power you had to over load the motor and doing that long enough let the smoke out.
Reply With Quote
  #7  
Old 12-20-2009, 02:28 PM
GWIZ's Avatar
GWIZ GWIZ is offline
SFT Historian
 
Join Date: Feb 2006
Location: USA
Posts: 6,735
Default

Out of the UGLY"S book,
Full-Load Alternating Current motors.
230 volts.
1hp = 8 amps
2hp = 12a
3hp = 17
5hp = 28 amps.

As Mild Steel stated the SPL is more then likely 5 peek horse power, and not continuous.
__________________
*
*
The factory of the future will have only two employees, a man and a dog. The man will be there to feed the dog. The dog will be there to keep the man from touching the equipment. ~Warren G. Bennis
Reply With Quote
  #8  
Old 12-20-2009, 05:33 PM
Photomask's Avatar
Photomask Photomask is offline
Big Stone
 
Join Date: Jul 2006
Location: Deepinahearta Texas
Posts: 3,371
Default

With SPL listed on the motor data plate, it means all bets are off. There is no HP listed so they can list it anyway they want. That usually means using a 3450rpm motor and listing the HP rating on the compressor at the HP required to use a 1725rpm motor. Yes, that's right, about twice the actual HP rating of the real motor's capability. As previously mentioned, amperage has to be listed on the motor data plate and is part of the only real way to determine HP. They use a 3450rpm motor with a smaller pulley and drive the compressor head at the same RPM as a 1725rpm motor. 1725rpm motors used to be the way to go because the bearings would last twice as long, but with good quality bearings, it is really no longer an advantage. This all started at a time when compressor manufacturers were making the switch from 1725rpm motors to 3450rpm motors as a way to try and make the apearant performance of the compressor's output equal. This was done for those people that were buying a compressor based on HP rating instead of the CFM rating which is the only real way to determine if a compressor will meet your needs. And that is another game with different manufacturers rating there compressor's output with their own set of parameters and standards. Not to mention that some manufacturers will use the best of their available parts to rate their compressor at burnout with parts that are better than you are going to get on the compressor that you buy. It ain't fair, but that's the way it is.

My compressor runs a 7.5hp Baldor motor that is listed on the data plate as 7.5hp and 32amps at 230volts, for about 4.27amps @ 230vac per hp. That would equate to about 8.54amps @ 115vac per hp. And that start current is much, much higher. Baldor is a high quality name in electric motors and they would not risk their reputation by overrating their motors. Depending on who you talk to, the quality of their motor, the duty cycle of the motor, the rated rpm and it's efficiency rating, the amperage requirement per hp could easily fall anywhere between 3 and 9amps @ 230vac or 6 and 18 amps at 115vac.

So for the three Baldor motors that I can get to easily:
7.5hp, 3450rpm, 32amps @ 230vac for an equivalent of 64amps @ 230vac or 4.27amps per hp @ 230vac and 8.54amps per hp @ 115vac.

1.5hp, 1725rpm, 10amps @ 230vac, 20amps @ 115vac or 6.7amps per hp @ 230vac or 13.4amps per hp @ 115vac.

1.5hp, 3450rpm, 7.5amps @ 230vac, 15amps @ 115vac or 5amps per hp @ 230vac or 10amps per hp @ 115vac.
(Except RPM, the two 1.5hp motors are identical in every respect, including year of manufacture and the current requirement is different to reach the same hp rating....)

Yes, that's right, rpm does figure into the calculation as hp is the rated ability to perform a given amount of work over a given amount of time.

(Sorry... My computer started acting flaky and I wanted to save this before I had to start all over...)

It's a very complicated subject convoluted by the honor, parameters, specification and claims of varied manufacturers. For example: If you compare the ratings of a Baldor motor to a ChiCom motor with the data plates showing the same hp, the Baldor will use less current and provide more real hp than the ChiCom motor could even think of... The same holds true with compressors as well, considering the CFM rating of different manufacturers. Another factor to consider is how long you expect it to last.... And again, the same holds true. Buy good equipment now and you will only buy it once. Buy cheap and you are destined to replace it.

Last edited by Photomask; 12-20-2009 at 05:58 PM.
Reply With Quote
  #9  
Old 12-20-2009, 07:05 PM
Porthos's Avatar
Porthos Porthos is offline
Senior Member
 
Join Date: Jul 2007
Location: Texas
Posts: 863
Default

All righty then....I went to Sam's and had no luck finding any compressors (2 stores). Apparently the people who made the Black Max, Sanborn, were taken over by Coleman Powermate and they killed the line.

I also went to HF and took some pictures with my phone (poor quality). Both motors show 22 amps. The SPL shows a 208v-220v on the motor plate and the 5hp motor shows 230v on the motor plate.

I did confirm with the HF manager that they will honor the 25% off coupon on New Years day on this compressor and it's already listed at $50 off. That would make it around $650.

Steve
Attached Thumbnails
Click image for larger version

Name:	3 capacitor motor.jpg
Views:	187
Size:	66.0 KB
ID:	54394   Click image for larger version

Name:	3 capacitor plate.jpg
Views:	227
Size:	58.4 KB
ID:	54395   Click image for larger version

Name:	Single cover motor plate.jpg
Views:	197
Size:	70.3 KB
ID:	54396   Click image for larger version

Name:	Single cover.jpg
Views:	176
Size:	60.1 KB
ID:	54397  
Reply With Quote
  #10  
Old 12-20-2009, 08:20 PM
cutter's Avatar
cutter cutter is offline
Curmudgeon
 
Join Date: Jun 2004
Location: Lubbock,Texas
Posts: 32,667
Default

Quote:
Originally Posted by Steve V. View Post
I did confirm with the HF manager that they will honor the 25% off coupon on New Years day on this compressor and it's already listed at $50 off. That would make it around $650.

Steve
Both motors are 3450 rpm & made as cheaply as possible.
Sorry, but you're getting about what you're paying for and that's what you should expect.
A good motor would cost about half what you're expecting to pay for the entire Chinese compressor.
It's the silk purse/sow's ear principle.
If you seriously expect to beat the system then your best hope is to be patient and find a good deal on a solid used American made older compressor.
I cannot believe they don't exist in the Houston area.
__________________
cutter
Housekeeping Staff: the Gatekeeper
Director of Policy, Syntax and Grammar (by appointment)

"Dr. Chandran, will I dream?"

Just Keep Walking

"Passionate hatred can give meaning and purpose to an empty life. Thus people haunted by the purposelessness of their lives try to find a new content not only by dedicating themselves to a holy cause but also by nursing a fanatical grievance. A mass movement offers them unlimited opportunities for both."
Eric Hoffer The True Believer 1951
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Web Search:

All times are GMT -5. The time now is 02:43 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.