Anyone know what HP this motor is?

[skiier]

I have a customer who strapped a 230V single phase motor to an old reciprocating air compressor. The nameplate is missing of course and I want to know if I can use this motor with the compressor. The customer says this motor is 230V but he doesn't remember the HP rating. There is no nameplate on the compressor either. The motor is an old "Baldor" as you can see in the photos at the link I have attached

http://f2.pg.photos.yahoo.com/ph/skiierx1/my_photos

I am only concerned with the motor. Please do not dwell on the compressor. I ran this motor the way the customer wired it and measured approximately 40A draw at 230V. I figure this corresponds to a 7-1/2 to 10 HP single phase motor and i think this is what is needed to run this compressor. The problem is that without a nameplate I do not know if this load is in fact overloading the motor. Maybe. Maybe not. I don't know. Does anyone know what this motor is?
If it helps it has 4 leads out the motor. 2 leads are connected to 230V and 2 leads are shorted. Is this a 230/460V single phase motor that is wired wrong. Also where is the start/run capacitor?
Any replys would be appreciated.

skiier

 

[skiier]

Is this a split phase motor? No capacitor needed?

 

[busbar]

baldor.com should help.

 

[advidana]

Try it an see. if it stops get a larger motor.

 

[jbartos]

Suggestion: Some motor repair/rewind shops tend to identify motors accurately or establish motor parameters accurately.

 

[SteveKW]

That looks like a pre NEMA frame. Measure the base bolt hole dimensions and shaft and see how they corresponds to a NEMA motor frame chart.

http://www.baldor.com/pdf/NEMA.pdf

This can put you close to the HP if it is NEMA.

40 amps suggests to me you have a 10HP NEMA frame motor load.

A 230/460 volt motor would be very unusual! Typically it would be a 115/230 volt motor. Having two leads shorted together for SERIES HIGH VOLTAGE (230) would hint you have the motor leads connected properly.

 

[ScottyUK]

Judging from the scale of other items such as the oil filter on the compressor and the door, the motor looks small for a 10HP 1-phase motor. Size looks nearer 5HP or so, but that might be a trick of the camera. Not to say that it isn't delivering 10HP, just that it might combust in the process.





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Get it over with.

 

[aolalde]

The motor seems to be 230/115 Volts. Actually series connected for 230 Volts.

VA = 40*230 = 9200
PF*EFF should be around 0.5
KWout=9.2*,5= 4.6 (KW)= 6.1 HP

Measure the temperature and shaft speed (rpm). If the temperature does not exceed 100°C total the motor is running normal for class A insulation. Compare the shaft rpm to the synchronous rpm (120*Freq./Poles). The slip must be <5%.

 

[SteveKW]

I wonder if you an old "repulsion" type motor with brushes in it!

 

[skiier]

thnx everyone. I don't know how I missed the obvious. 115/230 single phase is THE standard motor voltage. I really duhhed on that one.
I think the motor is undersized judging by the responses from everyone. I didnt think this was a 7-1/2 to 10 HP motor.
What I was really hoping was that someone would instantly recognise it and tell me. Not going to happen I guess.
A motor rewinder I know said the shaft size will tell me the approximate HP as well. A 1" shaft or greater belonging
being a 5HP and larger.
Thanks for the link SteveK. I will measure the motor dimensions tommorrow. I will also look at the compressor and maybe post some pics of it as well.
I will also look under the fan housing for a capacitor. I want to know what type of motor this is as well.

 

[SteveKW]

AOLALDE,
Using your formula posted, what is Baldor doing wrong here on this motor when they label it 10hp?

http://www.baldor.com/products/spec...ly=General+Purpose|vw_ACMotors_GeneralPurpose

If, for instance, he had the motor shown in that link and went up to a 7.5hp with the formula you used, he would quickly burn up that motor!

 

[jbartos]

Suggestion: The motor temperature criterion and motor rpm can be used. Gradually increase the motor terminal voltage and measure temperature and rpm. Since the power supply voltage grading is very large, e.g. from 115V to 230V to 460V, the motor voltage identification can be quick. When it comes to the motor shaft load, temperature and motor input amps should be monitor. Also, the motor amp grading is somewhat large; therefore, the motor HP could be established.

 

[aolalde]

SteveKW:

Nothing is wrong with Baldor. On the contrary they are doing a terrific motor, SINGLE PHASE with Efficiency= 0.84 and PF= 0.93!! ( I am assuming again that this is a permanent capacitor split phase motor; but may be I am wrong AGAIN).

Then for this Baldor Motor EFF*PF= 0.93*0.84 = 0.781 (I ASSUMED a poor 0.5)

HP= 41*230*0.781/746 = 9.875 HP ( not a perfect match with the current for 10 HP?)

 

[Farkel]

Get your ruler out. What is the D dimension or height of the middle of the shaft from the ground or flat plane where the motor would normally sit on the ground, and what is the diameter of the shaft. The front mounting holes are how far apart in inches, and the front to back mounting holes are what dimension? What speed would you say it operates, 1800RPM? If we know the frame size, and speed, then we can tell by NEMA what the horsepower it is if it is an AC NEMA motor. The pictures look like an TEFC machine. You said you ran it on 230VAC, single phase, so it's either a capacitor start, repulsion induction, or split phase, from looking at the picture, I'd say it was an old repulsion induction. Say a 7.5HP, but first get us some answers.

 

[jbartos]

Suggestion: I agree with the above posting suggesting empirical approach and standard motor catalog information to find the missing nameplate data.

 

[AC5DC]

This motor according to some of the older hands at Baldor is a Repulsion start/Induction run motor that hasn't been made since the 50's.

The information on this product line is sketchy because of the age of the motor. This would also put it into a pre-NEMA frame which would mean the motor is probably not rated as high for a similar motor of this size produced recently.

 

[jbartos]

Suggestion: A motor of this age is probably in deep archives. I would not be surprised if there was a fee to retrieve any info. Is not there a motor museum to offer it to?

 

[Farkel]

Pre-NEMA means that is was produced prior to 1935, and if it were produced in the 1950's this is not prior NEMA. WHAT FRAME SIZE BY MEASUREMENT HAVE YOU COME UP WITH? Then we can perhaps help you.

 

[jbartos]

Suggestion to the previous posting. The nameplate data would be better than the frame size since the latter tend to be ambiguous in full motor data determination.

 

[skiier]

Thanks everyone for the replys. I have been away for a while.
I have ascertained that the motor is a split phase type. It has no capacitor and a look thru the sidecovers on this motor shows me brushes.
I ran the motor thru a few cycles via the pressure switch and found that the motor current varied little from empty air tank to full air tank at about 110PSI. The measured current at empty tank was approx. 38A and at full tank was just under 40A. The load varies so little that I think this motor may be matched OK for the application.
The customer is a funny guy. He owns a rental shop and he "collects" things at his shop at home. Some of the damndest old odd equipment that he made money off somehow sometime. He came across this old compressor without a motor at an equipment sale where he was trying to sell equipment as well. He recognized that this was not an old "garden variety" air compressor. "This is a well made heavy duty compressor" he told me but he sensed that no one at the sale saw this. Nobody wanted to buy it so he "offered" to haul it off as junk for free. You know, doing them a favor. Hehehe. All the while he remembers he has an "old grey" motor somewhere in the back of his shop he picked up somewhere else for free and it might just fit on his compressor frame. So he gets the compressor home and mounts the Baldor motor on the compressor frame. He guesses at the pulley size (from years of experience more likely)and connects the motor and compressor with some good belts. Did a good job too. Everything spins freely and nicely by hand.
The one problem he had is that he is not an electrician. By no means. He had an old Sqaure D 1HP manual pushbutton starter c/w overloads lying around in the shop so he thought this might work. He didn't know that the overloads in the unit were way undersized for the Baldor motor but he soon found out when they tripped within 30sec of mtor startup. So a "buddy" of his told him to "jumper out" the overloads with some wire so they wouldn't trip anymore and this would fix the problem. Well it fixed the problem alright but the starter is nothing more than a switch now. So everything goes along fine for THREE years while he happily uses his compressor until one day it stopps and won't restart. So that's when he calls me.
The motor stopped because the heat developed in the #12 AWG wires feeding this 38A motor was finally sufficient enough to anneal and create bad connections in wire joints. It also melted the insulation off the wires in the starter box to the point where a good "rap" on the starter box would have made a nice spark show. I don't know how it ran like this for three years with him pushing on the starter buttons constantly. The only thing the motor had going for it in three years is that it was connected to an "undersized" 40A breaker.
So here is what I did. The motor has run 3 yrs with no problems to the motor itself. The brushes look good still and won't need service for a while. The compressor is also none the worse for wear. The motor itself doesn't get very hot at all. After running thru several cycles I could place my hand (with palm open flat) on the motor and it only felt warm to the touch. This was in a 15C room. Oh yes, a cycle takes about 8-10 minutes on an empty tank.
I installed a HP rated magnetic starter c/w overloads. I picked the largest 3PH starter for which I could install an overload with a current range of 38 to 45A. I picked the 3PH because it is "off the shelf" and half the price of a "modified 3PH" single phase stater. A quick field jumper fixes things up. I set the overloads at 42A with the reasoning that since the load varies so little (38 to 40A) at 42A we MUST have an overload. The 40A cct breaker that fed this motor never tripped in three years of use as well so this also tells me that the breaker is bad or the load never exceeded 40A ever.
I tend to think it never exceeded 40A. I also installed a new 60A bkr and refed the motor/starter combination with #6 AWG. I am probably allowed a larger bkr size for this motor but the 60A is the next standard size up and offers good protection for this motor and some half decent startup capability. The #6 also allows him to install a 7-1/2 to 10 HP motor in the future should this Baldor crapout.
As it stands the compressor is working nicely. Thanks again for all your replys.
skiier