How To Change The Speed Of A Motor

Posted on: June 23rd, 2014 by admin 17 Comments

It seems that everyone these days wants to change the speed of their motor. Whether it is because they want more air from their fan on a hot day or they want to reduce the cost of operating a motor, it has become nearly standard practice to change or vary the speed of electric motors.

From the time the three phase induction motor was invented (circa 1889) it was a foregone conclusion that it would run at a speed dictated by the frequency of the power supply. If a different speed was needed a device was attached to the output shaft of the motor to accomplish the task. Pulleys, gears, gear reducers – all were used to obtain the desired speed at the driven shaft. Some of us old timers remember devices like vari-drives and eddy current clutches that would allow the speed to vary with the demands of the application.

Sometime in the ‘70s the term Variable Frequency Drive (VFD) crept into our lexicon. The early units were very crude by today’s standards but they got the job done. It was then possible to operate a motor at virtually any speed from 0 to nameplate rpm with the twist of a dial. Next came the ability to operate above name plate rpm, follow an electrical signal for “automatic” speed adjustment to maintain system settings, and set up PID loops. Then vector drives, steppers and servos. Whoa… my head’s spinning.

Speed changes today can be as simple as adding an electronic drive or as invasive as rewinding the motor for a different speed. Like anything else, each method has its up side and down side.

Some (not all) small single phase motors can be operated at various speeds through the addition of a resistor(s). It should be pointed out that the resultant speed is dependent on the load placed on the motor. What is actually being done is the weakening of the motor by reducing the voltage across the winding (the resistor acts as a voltage divider). The “lost” voltage is converted into heat which, for all practical purposes, is wasted into the atmosphere.

Most large single phase motors can’t (or, more correctly, shouldn’t) be operated at reduced speeds. These motors often utilize a centrifugal mechanism to disconnect the start winding. If the speed of the motor is reduced too far the centrifugal switch recloses, allowing the high starting current to flow in the smaller start winding. The end result is a motor winding failure.

There are a number of different types of single phase motors: universal, shaded pole, permanent split capacitor, capacitor start, capacitor start/capacitor run, repulsion-induction. If you are not sure what type of motor you have, give the motor experts at Gem State Electric a call at 208-344-5461. We’ll help you figure it out.

Three phase induction motors are a different story. All three phase induction motors can be run at variable speeds with the help of a properly sized VFD. Some three phase motors are much better suited to variable speed operation than others but all can run on a VFD. A number of factors must be considered to determine a specific motor’s suitability however, so give us a call to discuss your specifics.

As stated above, for decades the three phase motor was designed for a specific rpm based on the frequency of the incoming line. Only rarely were devices employed to change the frequency of the incoming power; many of these rotary frequency changers are still in use however.

With the growing popularity of VFD electronic drives a whole new industry was opened. Companies now marketed the devices as a great way to save energy, particularly in variable torque applications such as pumps and fans.

By using a 60 Hz. input to create an easily variable frequency output the speed of the motor is now adjustable. By changing voltage and frequency with a constant ratio the output torque is consistent from nearly zero to full line voltage.

Various types of electronic drives, utilizing a dizzying assortment of bells and whistles, are now available. Your motor can do things now that its ancestors could only dream of!

Another way to (permanently) change the speed of a motor is to redesign the winding during the winding process. The speed choices are much more limited however. There are, for example, no speed choices between 1800 and 3600 rpm when redesigning the winding.

There are some practical limitations in doing so, not the least of which is the diameter of the rotor. The centrifugal forces on the rotor increase dramatically as the rpm goes up. In most cases a manufacturer will use a smaller diameter rotor in a 2 pole (3600 rpm) rated motor than they do in their 1800 rpm (and lower rpm). If the larger rotor is now spun at twice the rpm because of a winding redesign, the rotor is suddenly required to handle 4 times the centrifugal force it was designed to experience (force is increased by the square of the increase in speed).

I had a customer back in the ‘70s that did not consider this when adjusting his brand new VFD. The drive was capable of outputting frequencies up to 300 Hz. His motor did not make it past 120 Hz before the rotor literally exploded!

Other considerations are the amount of torque required by the load at increased or decreased speeds, the bar/slot combination of the original motor, decreased cooling effect at lower speeds, core saturation at the new output levels, etc. Like many other things, just because you can change the speed of a winding design doesn’t mean you should do so. Before considering a change like this, consult a motor expert, like the experts at Gem State Electric, for example. (Now tell the truth – you were expecting that commercial weren’t you?)

If you do not have access to three phase power but need to change the speed of your motor you are still in the game. A customer recently came to us with a challenge. He needed more water to irrigate his field but the utility would only allow single phase power to be brought to his meter location. Single phase motors are, for all practical purposes, available up through 15 HP, but he needed a 20 HP motor/pump to move enough water for his crops. We were able to find a three phase motor/pump that we ran off of a VFD, and powered it from a single phase line – with the blessing of the utility!

With any such application it is always a good idea to consult the motor/pump/control experts at Gem State Electric (did you see that one coming?)

We are never further away than your phone, at 208-344-5461, to discuss your electric needs.

Motor Connections

Posted on: June 17th, 2014 by admin No Comments

One of the most important, yet most frequently misunderstood, parts of placing an electric motor in service is connecting the motor leads correctly. One would think it would be easy, but in fact it can be easy to get it wrong. Over the last 45 years I have seen literally scores of different connections used in electric motors. Let me say up front that, if you have any question about how to properly connect your motor, give the motor experts at Gem State Electric a call. We’ve gotten pretty good at figuring these things out over the phone. The major challenge in figuring out the proper connection for a given motor is the shear variety and the (sometimes) lack of standards. Color coding, NEMA numbering, IEC numbering and non-standard systems exist in both single phase and three phase motors. Single voltage, dual voltage, tri-voltage, wye-delta start, part winding start, two speed single winding, two speed two winding , constant torque, variable torque, constant horsepower, even two phase – we’ve seen just about everything. Then there is the occasional 18 lead motor with no markings on the leads! The point is – if you can’t figure it out don’t feel bad. Just give us a call at 208-344-5461. Some standards, of course, do exist. It’s just that some standards are more standard than other standards. So let’s look at some of the more common connections, keeping in mind that there can be variations on all of these diagrams.

SINGLE PHASE: It would be nice if all single phase motors could be reduced to two leads but that will never happen. We can however reduce the noise to a few groups that will handle most motors – single voltage, multi-voltage, set rotation and reversible. The single voltage and set rotation connections are typically a simplification of the multi-voltage reversible connections with some of the connections made internally, leaving fewer choices for the installer. Take a look at a few sample wiring diagrams, (right click on the link below to open in a new tab.)

NA Single-Phase1 connections

Some common modifications to this connection scheme: The use of colors instead of numbers (no standard between manufacturers is known to exist for colors) Some manufacturers interchange leads 2 and 3 GE made some larger single phase motors in the 1970s that used a 10 lead connection Some manufacturers use four leads for the start winding, adding lead numbers 6 and 7

THREE PHASE: Most three phase connections are either a “wye” (sometimes referred to as a “Y” or “star” connection) or Delta. There are a number of combinations that utilize both a wye and a delta connection but these connections are best left for another discussion. Let’s take a look at some of the more common three phase connections. You should note when comparing the wye and delta dual voltage (nine lead) connections that the external high voltage connections are identical. This means that when connecting a nine lead three phase dual voltage motor for 460 volts it is not necessary to know the internal configuration of the winding. However, if it is 230 volts that you wish to connect to your three phase motor you must first determine what the internal connection was used. The easiest way to do this is to look at the low voltage wiring diagram. If there is no diagram, you must take continuity readings. In order to do this you must disconnect any leads that are already connected. Caution: It is always best, before disconnecting an existing connection, to notice two things: 1) Are the leads identified (alpha numeric or color coded) 2) What leads are currently connected to each other? If the leads are not identified in any manner, stop before it is too late and call the motor experts at Gem State Electric. We can help you figure out what steps to take before it is too late! If you don’t stop at this point you may be taking a minor challenge into a major project (also spelled m-a-j-o-r-e-x-p-e-n-s-e). If the leads are identified and currently connected together in some configuration right down which leads are connected before disconnecting anything. This way, if you get in over your head you can still go back to the start instead of launching that major project to which we were just referring. With all leads disconnected and not touching each other, check for continuity (a circuit) between leads 7, 8 and 9 with your ohm meter or continuity tester. If a circuit exists between all three leads, you have an internal wye connected motor. If no circuit exists, and you know the winding to be good, you have a delta connected motor. Using the appropriate connection diagram it is now an easy matter to reconnect your motor for the lower voltage.

Why your electrician may not be the best person to call with your motor problems

Posted on: December 18th, 2013 by admin No Comments

Why your electrician may not be the best person to call with your motor problems

If your lights won’t come on you’d call an electrician, right? You wouldn’t call a plumber, a roofer or, in all likelihood, a motor technician. So why, if you have a motor problem, would you call an electrician?

Only a few electricians understand the electric motor. If you need a piece of conduit bent, they’re your best bet. Don’t know what size and type of wire is needed for your 15 amp receptacle within 3 feet of a water faucet? Call your friendly neighborhood electrician!

But when the motor doesn’t start on your air compressor, or the return air fan is making noises that it has never made before you need to rely on the person who has the experience and knowledge dealing with problems similar to yours.

I’m sure that if you are a licensed electrician your blood pressure just went up. You may know the difference between a Wye/Delta connection and a PWS connection but, odds are, you don’t. I could not count the number of times an electrician has checked a three phase motor suspected of being single phased by measuring the voltage to ground at the load side of the contactor. (Hint – that won’t find the problem. If you don’t know why, you just proved my point). Does the average electrician, or even an above average one for that matter, understand the ramifications of using a Design C motor to replace a Design D motor? Let me give you an example to demonstrate.

A customer has a 60HP Lincoln motor on a Return Air Fan. One morning, after replacing filters and doing the usual preventative maintenance on the system, the staff maintenance personnel note that the fan did not start when they flipped the switch. So they call their electrician.

The electrician comes to the job site, opens the cover on the disconnect switch and sees a six pole knife switch. The leads across the top are color coded with tape, with three colors used, left to right and then repeated. The six leads coming off the bottom of the switch contacts are not color coded, but they are numbered. The electrician places the leads of his multi-meter across the different combination of motor leads and declares the motor winding to be bad – it is “open”. The motor should be pulled and sent to a motor shop.

The customer looks at the application. In order to enter the space where the motor is mounted he must boost himself about four feet into the air and crawl on his hands and knees into a space that is not tall enough to stand up. Then he is faced with a motor that is mounted vertically, shaft up, belt-driven to the shaft that supports the fan. There is no means of supporting the 500 pound motor while the mounting bolts are removed. In service man parlance – “It ain’t going to be pretty!”

The unanimous decision of the maintenance staff was “We want a second opinion”.

A second licensed electrician was called to the job site and asked to analyze the situation. It didn’t take long for the diagnosis – the motor has an open winding and has to be pulled. There is no continuity through any of the phases (it was a three phase motor).

Still hoping for a better result the customer called us; “We need you to come and check out a motor on our air handler” was their plea. The maintenance man told me “all I want to hear you say is that I don’t have to pull that motor out”.

We always try to get the background before we begin a diagnosis. We learned that the unit had been running until it was shut down for PM. The disconnect switch had been thrown to the “OFF” position, the work done inside the air handler, and the switch turned back on. The control for the system was remotely mounted so it was necessary to walk down to the control room and reset the control. Much to their chagrin, the motor would not restart.

This information in itself would lead one to think it was not a motor issue as the motor was running fine when it was shut down. A quick continuity check confirmed that the winding appeared to be completely open. This also would usually be incongruous with a motor that was running fine upon de-energizing. So what’s up?

A simple explanation comes from an understanding of how an electric motor works and, in a related discussion, how a generator works.

When a voltage is present across a closed electrical circuit an electric current is passed through the circuit. When that current is flowing through the circuit it sets up a magnetic field. If a conductor (an element capable of conducting electricity) is moved through the magnetic field a voltage is induced across the conductor, the polarity of which is opposite in polarity to the polarity of the original applied voltage. The magnitude of the opposing voltage is dependent on the strength of the magnetic field and the direction and velocity of the motion of the conductor. What we have is a very basic generator.

An electrical meter, in order to measure resistance/continuity, must supply a voltage across a closed circuit. The magnitude of the current flow is monitored and interpreted by the meter in units of resistance (ohms). A known DC voltage across an unknown resistance will produce a known current flow, according to Ohm’s Law (E=IR). Most meters operate on a relatively low voltage (typically 9 volts DC). Even this low a voltage is sufficient to set up a small magnetic field in the motor’s stator (field winding). So the potential exists to generate electricity. Now all we need is relative motion between a conductor (like the cast aluminum rotor bars in the motor’s rotor) and our small magnetic field!

Because the fan is a Return Air fan it typically takes air from the space it services and “returns” it to the system. Because the Supply Fan was still running the air was being pushed into the room, building static pressure and creating air flow across the fan, creating rotation of the fan and therefore the motor’s rotor.

VOILÀ! We have a generator! Not a large generator. Not large enough to power your TV while watching Soap Operas all day, but a generator none the less; sufficient in output to overcome the small voltage of your meter and give a false reading. We had only to stop the rotation of the fan blade to confirm our suspicions. The motor winding was fine.

“You don’t have to pull that motor out” I told the customer.

Following a round of applause from the maintenance staff we were able to find a defective disconnect switch – one that had eluded the detection of two electricians. (Not to point fingers, but they had also missed the fact that the phasing tape was also misapplied, causing the power leads to be misidentified).

I am not asserting that we have never made a mistake. But the fact is that a license from the state does not, in and of itself, make someone qualified to troubleshoot. Go with the experience – Go with Gem State Electric!

Where Were You When They Shot JFK?

Posted on: November 15th, 2013 by admin 2 Comments

Where Were You When They Shot JFK?

Every generation, it seems, witnesses an “earth shattering” event in their lifetime to which, regardless of the age obtained, they can answer the question “Where were you when….”

I have only queried one member of the Greatest Generation that was unable to answer the question “Where were you when you heard about the bombing of Pearl Harbor?” For that generation the world was shaken (literally) by the events of a seemingly average Sunday morning in a far-off paradise known as Hawaii. The events of that day had a profound effect on the future of an entire generation of not only Americans, but the entire human race. We are barely three weeks away from the blackened anniversary of that event, yet every year for the past seventy two, we hear and see reminders of how the world as we know it was molded by the tragedy as well as the world’s response to it.

For my generation (currently referred to as “old farts”) that event was the assassination of President Kennedy. Most “boomers” were too young to have fully comprehended the sordid affairs of world politics back then. But we knew that the youngest President in our history had replaced the oldest President in our history. His rhetoric, more than his actions, drew us in to a belief that our lives held promise unimagined prior to the election.

My parents, staunch Republicans for as long as I could remember, were mightily disappointed in the election results that slowly trickled in over night in November of 1960. They had made no secret of their support for Richard Nixon and were open about their misgivings over the actions, or inactions, of a wet-behind-the-ears Democrat, despite his being a Navy Veteran and a fellow Catholic none the less.

President Kennedy, from my point of view, was solely responsible for my eventual withdrawal from under my desk at school with the defusing of the Cuban Missile Crisis. His proposed Peace Corp resonated with the youth of my time, opening our eyes to the possibilities we held in our hands and how the world could be influenced by the actions of those willing to step outside of their comfort zones and “do” instead of talking about doing. I did not observe his reluctance to enter into the Civil Rights confrontations of his time, but saw the results when he finally acted to quell the discord in Alabama with the support of Federal Troops. The cascade of events that blossomed into Civil Rights legislation in the coming years was directed by his movement from rhetoric to decisive action.

I vividly remember sitting in Mr. Reichart’s World Civ classroom, having just returned from lunch in the cafeteria, while waiting for the bell to signal the commencement of the afternoon routine. One of my classmates ran in the door and stunned the room with the news she had heard while returning to school from her lunch at home. The President had been shot!

Surely she had not heard correctly. Kennedy was too young, too well known, too popular, too well protected to have been felled by an assassin’s bullet. Communications, being what they were at the time, were creating more questions than they were answering. The next four days were spent, sitting in front of radios and TVs. With the internet today it is difficult to imagine rumors and facts emerging with equal veracity. We still didn’t know who Lee Harvey Oswald was when we saw what was probably the first murder ever carried live on TV unfold in front of our innocent eyes. From a crowd of reporters stepped Jack Ruby, his single gun shot unleashing a fury of activity, and launching generations of investigation, rumor and conspiracy theorists. Our entire world was thrown into chaos; events taking place faster than their consequences could be comprehended. The world seemed to be spinning out of control at a dizzying pace.

Then, as if a grand conductor had orchestrated it, the world screeched to a halt.

 

The televising of a funeral procession would not be the type of activity that would draw an audience in ordinary times. But this procession brought the entire country to a halt. For what seemed like an eternity, hundreds of thousands of people sat motionless in front of television sets while a horse-drawn caisson marched from the White House to the Capitol Rotunda. There was not a sound from the crowd of people gathered along the route, only the haunting notes of horse-shoes on pavement, accompanied by military drummers.

A line of people, hundreds of thousands of people, filed past the flag draped coffin that lay in state in the Capitol Rotunda. The line stretched as far as the eye, and TV camera, could see. It is little wonder that my world had seemed to halt in its tracks. The line had no discernable end from my position in front of our black and white television set. NBC broadcast uninterrupted coverage of the throng filing continuously past both sides of the casket all night long. I probably fell asleep in front of the television that night, there being no sign-off and test pattern to indicate bed-time.

The next morning I, and nearly every American who had access to a TV, watched in silence as the horse-drawn caisson marched across the bridge to ArlingtonCemetery for the funeral. The low, nearly mono-toned voice of Walter Cronkite narrated an event that was still beyond belief to most of us.

Fifty years ago this month, my world, if not the entire world, was re-shaped by the events in Dallas. A lone gunman, if the Warren Commission is to be believed, erased the future and it’s vantage point of observation, and re-wrote the historical references to the Kennedy Administration in a hue of speculation. Events that took root in the fertile ground of President Kennedys’ speeches went on to change the face of history and the mind set of a generation. The promises of a future full of hope were painted in words that still ring true today. Hope guides us. Hope moves us. Action trumps words every time. If we are to survive in a world unlimited by borders we need to take a humanitarian view of our place on this earth.

Politicians must recognize that action, and only actions, direct our future. The rift that separates the aisles of congress is surely smaller than the chasm that stood between the US and USSR during the Cuban Missile Crisis. President Kennedy found a bridge across the abyss that allowed us to back away from the edge of nuclear destruction. Congress need only to look to our recent history for hope that a solution exists that will allow our government at the Federal level to flow back from the edge of shutdowns and dysfunction. Stalemates, divisiveness, and party lines must give way to co-operation and compromise for this country to attain the greatness first hinted at by a young president that lit the imagination and optimism of a generation of wide-eyed kids over fifty years ago. Do they remember?

Do you remember? Where were you when they shot JFK? I’d like to hear from you at jerryf@gemstateelectric.com

A Basic Discussion of Torque

Posted on: November 5th, 2013 by admin No Comments

A Basic discussion of Torque

 

First of all let me be up front about this – I am not an engineer (although I have owned a few pocket protectors in my day). But if there is one thing I’ve learned in over 45 years in the motor service industry it is this: You need to be able to speak on the same level as your customer or they won’t understand your explanation. One of my pet peeves is technicians (or business owners!) that speak in acronyms and buzz words, as if their audience had any idea what they were saying.

I have met some very well educated people that know a lot more than I do about a lot of subjects. However, by the time they finish impressing you with their knowledge level you still don’t know what the answer to your question was.

 

A customer asked me recently what the comparison was between the torque of a 20HP motor and a 15HP motor. The easiest answer is that…. it depends. Let’s see if we can come up with a relatively simple answer and leave the caveats standing in the wings to amuse the engineers.

Before we answer the question we need to confirm a number of issues and before we get into those issues we’ll take a look at a definition of torque. Many people mistakenly interchange the terms “torque”, “horsepower” and “power”. So let’s look at the definitions to discern the differences:

 

Torque – “A twisting force that tends to cause rotation”.

Horsepower – “A unit of power equal to 745.7 watts (electrical) or 33,000 foot-pounds per minute (mechanical)”.

Power – “The rate of doing work”. In electrical terms, this is measured in watts.

 

Given the three definitions we can say that electrical power and horsepower in an electrical system are interchangeable. They both are (or can be) measured in watts. In the case of an electric motor there is a direct mathematical relationship between horsepower and power – one horsepower is equal to 745.7 watts (typically rounded to 746 for ease of calculation). The European standard for measuring power output of an electric motor is, in fact, the watt. We prefer to measure power in horsepower because we like horses. Someone, many years ago, decided that his horse could lift 33,000 pounds one foot in one minute and declared it a standard of “one horsepower”. Someone in France heard about this and responded “Watt?”

The one thing we need to note about our definitions is that horsepower and power both include a time factor in their calculation. They are the measurement of power over a period of time. Torque, on the other hand, does not contain an element of time. This then tells us that torque measured over time is, indeed, horsepower.

The mathematical formula that defines the relationship is:

Torque = Horsepower x 5252

           RPM

where torque is measured in lb-ft and 5252 is a mathematical constant used to accurately convert the units involved in the calculation.

 

We don’t have to be a math major to see that, as horsepower increases, torque increases; as speed increases, torque decreases.

So now we can go back to the original question – what is the comparison between the torque of a 20HP motor and a 15HP motor?

In order to answer this question we need to make some basic assumptions, namely that other than horsepower all other factors remain the same. They won’t be*, but we’ll keep it simple. Therefore the relationship between the torque of a 20 HP motor and a 15HP motor of the same speed is simply: 20/15 or, put another way, you can expect approximately 33% more torque from a 20HP motor when compared to the output torque of a 15HP motor.

A rule of thumb used when calculating torque of an electric motor is that you can get approximately 3 lb.-ft of torque per horsepower from an 1800 rpm motor. From the formula we can see a higher speed motor will reduce the available torque, a lower speed motor will increase torque. It is important to understand these relationships before changing speeds. The resultant change in available torque may catch you off guard. You may not need an engineer, but it may be wise to talk to the motor experts at Gem State Electric (I did warn you that this was a basic discussion). We are always happy to assist you.

 

*other factors that may change will be the power sources ability to provide sufficient power to the system to run a higher horsepower motor, losses in the system when using a higher horsepower motor, the efficiency level of the two motors, inertia of the two rotors and even the rpm. The actual rpm that an electric motor runs at is dependent on its ability to produce the needed torque. Given the same load on both motors a larger motor will run at a (marginally) higher rpm. This change in speed may be negligible, but in certain situations it may not be. Call Gem State Electric at 208-344-5461 if you need to discuss your application.

Why repair an electric motor?

Posted on: January 24th, 2013 by admin No Comments

Why repair an electric motor?

The largest segment of the Electric Utilities market is the power consumed by electric motors. Electric motors drive everything from the electric screwdriver in your tool kit to the large refrigeration compressors that provide air conditioning for our largest buildings and plants.
Although the average electric motor will see a usable life of twenty years or more, many will see an early demise due to their operating conditions, lack of maintenance, improper application, improper repair or defects. When this happens the owner/operator must decide whether to replace or repair the motor.
Many factors have to be considered when deciding between repair and replacement. Certainly the cost to replace a motor is important. Often, however, the availability of a suitable replacement and the cost of repairing the “old” motor are just as important. With rising utility cost, the efficiency rating of the “old” motor and it’s replacement often out weigh repair/replacement cost. A large motor can cost an industrial user more to operate than he invested to purchase the motor in the first place. Looking closely at operational cost can sometimes yield tremendous savings when replacing a motor.
When a motor fails, a professional repair facility can help with the decision-making process. Often, a quick “bench test” (usually at no cost to the owner) can often help the motor repair shop determine whether or not a repair is economically feasible. If the decision is made to further examine the motor, a complete disassembly and assessment is typical. This in-depth examination often will disclose the root-cause of the failure. For example, if a motor winding has failed, an in-depth examination may disclose the reason for the failure. The professional repair shop can often determine the cause of a winding or bearing failure, thus avoiding a repeat failure.
Many in-house maintenance personnel are interested in one thing – getting the machine back “on-line” to avoid expensive down-time. They may not be capable of determining that a loss of voltage on one of three phases caused a winding failure. If a replacement motor is installed without determining and “curing” the root-cause of the failure the new motor may fail before anyone realizes that the motor failure was the “effect” and not the cause of the failure.
By the same token, a home-owner may know that the capacitor on his irrigation pump has failed. He may not be able to determine why it failed. If the owner replaces the capacitor it may not last more than a few seconds.
Repairing electric motors is more than replacing bearings. It requires the use of sometimes sophisticated diagnostic equipment as well as relying on years of knowledge to determine why a failure occurred, then repairing the motor to suit the owner and the application. Finally, testing of the motor under controlled in-shop conditions can assure the owner/operator that his motor is once again capable of doing the job for which it was designed.

If we have the technology…

Posted on: December 13th, 2012 by admin No Comments

If we have the technology, are we obligated to use it?

The question has been around since man invented the wheel.

There is a saying in the RV business – Man invented the wheel 5,000 years ago, the next week his trailer lights stopped working.

Technology has been improving in our industry for nearly one hundred years, with motors becoming so efficient that efficiency levels have risen into the mid-90% range. You can now buy an electric motor that, coupled with the proper electronic drive and programmed properly, will perform just about any task you demand of it.

However, the fact that we have the technology to do something does not always justify its existence. We can couple an electric motor to a drive that will allow us to rotate the shaft 3,786.145 revolutions, then stop and hold the shaft in that position all day without overheating the motor. But if you’re interested only in running your air compressor in the garage would the cost of extra bells and whistles be justified?

If you have ever used a GPS you likely know this situation all too well. I recently used my Smart Phones GPS Navigator to locate a street address. A problem arose when the GPS was unaware that the street it had directed me onto did not go from where I was to where I wanted to go. Between points A and B was a large valley, with a creek at the bottom, and no bridge forming a navigable link. I had to drive back nine miles to where I had spotted a sign (you remember what those are don’t you?) that directed me to the other end of the same road.

Another foray into the unknown with my GPS found me at the dead end of a street, staring across a railroad yard at my objective, visible but just as unobtainable as if I’d gone east bound onto the west bound lane of the Highway to Heaven.

Often it boils down to an “old” term that was invented to explain the failure of technology – G.I.G.O. Garbage In, Garbage Out. We didn’t have G.I.G.O. when I was growing up in Wisconsin. If you stopped at a service station (remember those?) to ask directions you could be sure that at least three of the four guys that were sitting out front on up-ended Pepsi cases would know how to get you from wherever you were to wherever you wanted to go. If they didn’t know where Ma & Pa’s Drug Store was they’d look it up in the Yellow Pages. The only Yellow Pages in town (and usually the only YP in the four surrounding towns too)!

Now we have three Yellow Pages in town and, if that’s not High Tech enough, there are thirty seven on-line Yellow Pages, each one extolling their services over the others. But what if none of them can “get it right”?

We moved into a larger building in March of 2011, to better serve our customers. In December of 2011 the new phone books came out and, despite having been notified of the address change, two of the three YP have our listing wrong. It turns out that all three print information from the same source. They’re not about to reprint thousands of phone books so that our customers can locate us (read the fine print inside the cover) so we’re stuck with G.I.G.O. for the next year.

Luckily, no one uses the printed phone book anymore. “Everyone looks up information on-line” I am told by the thirty seven companies who call us every other week to try to sell us advertising space in their on-line service. The problem here is that no one is responsible for the information contained in their listings. We spent hours sending notices to the plethora of on-line folks who claim to be the best at what they do. If we are successful in getting them to update our listing we seem to magically regress to G.I.G.O again if we don’t pay for their services. Even GoogleMaps and MapQuest had trouble keeping the updated information on their service sites. After a couple of tries, we seem to have straightened that out now but heaven only knows what will show up on the next “search”.

For the record, Gem State Electric Motors and Pumps is located at 112 E. 45th Street, Boise, Idaho 83714 (we’re actually in Garden City, but if I told you that you would still be trying to figure out where Garden City is). Our phone number is now, and has been for many years: (208) 344-5461. See our web-site for our toll-free number, fax number, e-mail address and even my cell phone number!

Call me and we’ll send you a list of twelve things you can do with your phone book. Now that’s service!

 

 

Wake Island Remembered

Posted on: December 10th, 2012 by admin No Comments

Remember Wake Island

While the nation recognized the 71st anniversary of the attack on Pearl Harbor on December 7th, we honor all veterans for their sacrifices.

The surprise attack was an act of war against a country that still had not entered the conflict, although the US had begun to ramp up preparations for doing so, while still facing divergent opinions at home regarding US involvement.

Simultaneous with the attack on Pearl Harbor was the beginning of the Battle of Wake Island, 2300 miles to the west ofHawaii. Within 4 hours of the first bombs dropped on Pearl Harbor (it was December 8th on Wake by virtue of the fact that it lies just across the International Date Line) the Japanese began their invasion of Wake Island, occupied at the time by about 250 US Marines and about 1200 civilians, many of whom were from the Boise area and worked for a large construction company named Morrison-Knudsen. Morrison-Knudsen was a member of a group of approximately eight large construction companies that had been awarded a government contract for improvements on islands in the Pacific. The M-K workers didn’t know it when they signed on for the project, but the “luck of the draw” had placed them directly in harms way.

Some of the Morrison Knudsen workers were killed during the 15 day siege, many more were taken prisoner when the island fell to the Japanese invasion and were held as prisoners of war until 1945 (despite being non-military). Only half of the POW’s survived the war.

Approximately 96 M-K workers were kept on Wake to complete their construction project, the building of an air strip. When the air strip, which would be used by the Japanese throughout the war, was completed, the Morrison Knudsen workers were lined up and murdered. There were many heroes during WWII. These workers, as well as the Rosie the Riveters and other civilians who answered the call to duty are among that group.

My father served during WWII. He had to lie about his age and arrange to enlist in the Canadian Air Corp before the U.S. Navy would agree that he should be allowed to serve his country. My mother was a “Rosie”, working in a machine shop doing light machine work and lacing cables on aircraft electronics.

If you would like to show your support for the heroes of WWII, check out the following web-site:

VetsRoll.org    or make a tax-deductable donation by calling toll-free (800) 383-2267

 

It’s anIRS501(C)(3), started by my brothers, that has provided all expense paid trips for Wisconsin’s WWII Vets to Washington D.C. to see their Memorial. Time is running out for these Veterans. It would be great if more of them could receive just one more show of recognition for the sacrifices they made for the generations of Americans to come.

 

The Average Key Length Standard

Posted on: December 4th, 2012 by admin No Comments

The Average Key Length Standard

Manufacturers, end-users (and even many motor shops) seem to be unfamiliar with the Average Key Length standard as it relates to imbalance. There are a number of factors that can minimize the impact of not understanding this principal, but everyone who is responsible for the extended operation of rotating equipment should be familiar with it. Let’s take a quick look at a real-world example.

A couple of years ago a customer called up to have us check a large motor on a belt-driven air compressor. When I arrived at the job-site I found two air compressors sitting alongside each other. Each had a 150HPLincolnmotor belted to the large shaft of a high speed compressor.

One of the motors had experienced a winding failure and needed to be pulled. As I was about to find out, it was only the symptom of the failure.

As we discussed what would be needed to remove this 1500 pound motor from its base five feet above the floor, the other compressor suddenly turned on. The whole building seemed to shake as the compressor came to pressure then, just as suddenly, shut off. I asked the customer how long the compressor had been shaking that violently.

“Ever since it was installed. This one’s just as bad” he said as he pointed toward the unit we had been discussing. “We have to come in every so often and re-weld the supports ‘cause it breaks ‘em” he added.

While in the shop we set the rotor up in the balance stand to check the balance condition. The problem was soon apparent.

The motor shaft was 3.375” in diameter. The keyway was 7/8” wide x 8.375” long. The pulley that had been mounted on the shaft by the compressor manufacturer had a bore that was approximately 2.5” long.

The problem related to the “Average Key Length Standard”. More on that below, but first –

Let’s take a look at the manufacturing process to understand where this situation takes root.

When an electric motor is produced the piece of shaft material starts out very nearly perfectly balanced. As the material is machined, the various steps and shoulders appear as the result of material removed from the shaft. As these changes are virtually concentric (nothing is perfect) very little change is made to the balance condition of the shaft. However, two of the final steps introduce large changes to the concentricity of the rotor assembly.

When the rotor is pressed onto the shaft it brings with it a greater degree of eccentricity. The cast aluminum rotors used today throughout the industry can never be absolutely concentric. Air pockets and non-concentric shaping cause imbalance. The addition of a large non-concentric mass at a greater diameter than the shaft has a large influence on the overall balance of the rotating mass.

The final change is the cutting of a keyway on one side of the shaft. Material is removed to produce a large trough to accommodate the shaft key. As the material is removed, weight is removed and imbalance is introduced to the assembly.

To meet industry standards the final assembly is then dynamically balanced. To do so the machinist mounts the assembly in a balance stand and spins it. But the problem they face is as follows:

The motor manufacturer does not know what will be mounted on the shaft when the motor is placed into service. From a balance point of view the material that was removed when the keyway was machined must be compensated for.

By convention, one half (approximately) of the height of the key is considered to be material in the shaft, the other half is considered to be part of the attachment (the coupling or pulley that mounts on the shaft). When the rotor is balanced a weight equal to roughly 50% of the weight of the key that will be shipped with the motor is placed in the keyway. The assembly is spun and any necessary final adjustment to the balance is made by adding or subtracting weight at the proper position.

Simple enough – right?

But what about the “attachment” manufacturer? When the keyway is cut in the bore of his assembly it must be compensated for in the balance procedure. But they do not know what shaft their piece will be mounted on. The pulley and coupling makers must also supply a key, half of which is considered the material of their assembly, the other half is the compensation for the keyway to which it mounts.

Do you see the problem yet?

In the case of the air compressor motor mentioned above the pulley manufacturer supplied a key that matched the length of the bore of the pulley (approximately 2.5”). Their key weighed approximately 250 grams, half of which was to keep the balance of the pulley within specifications.

But the poor motor manufacturer had balanced the rotor assuming that their key would be used (7/8”x7/8”x8.375”). Their key weighed a whopping 837.5 grams. So when the pulley was mounted on the shaft an imbalance of 293.75 grams was immediately introduced into the rotating system at a distance of approximately 1.68” from the center of the shaft. The influence on balance increases with both the weight of the key and the distance from the center of the shaft. The imbalance is magnified by speed.

So how do you work around this situation?

 The Average Key Length Standard

 

Measure the full length of both keyways, add the two dimensions together, and divide by two. In the discussion above we have 8.375” + 2.5”/2 = 5.43”

Cut a piece of key stock as close as possible to the calculated length and you will have corrected the majority of your imbalance in many cases. It is important to know that the motor manufacturer supplies a full length key with every motor. It is the customer’s responsibility to use the correct portion of that key, whether the customer is an O.E.M. or an end user.

In this specific case, the imbalance dropped form 6.0 mils to 1.0 mils displacement. Even if you have never had to balance a rotating piece of equipment, you can probably deduce that this is quite an improvement.

 Epilogue

 After returning to the job site with the freshly rewound and rebuilt motor I examined the pulley/shaft and key size on the driven shaft. The same condition existed there with one additional factor thrown in. The pulley ratios were such that the compressor shaft was rotating even faster and the keyway in the shaft was even longer, magnifying the effect on the driven end.

Instead of the manufacturer’s representative having to re-balance the compressor and motor, a change of keys was all that was needed to stop breaking steel supports and their welds. The customer was happy and is now fully aware that when replacing a motor or the shaft attachment, care should be taken to cut the new key to the appropriate length, instead of simply using the full length of the supplied key.

Pied Piper of Poop

Posted on: October 29th, 2012 by admin No Comments

Pied Piper of Poop?

I have been asked by several people in recent years where the moniker “Pied Piper of Poop” comes from, and why I embrace it, rather than trying to stomp it out.

When “stuff” happens (to steal a phrase from Forrest Gump) it usually collects somewhere, and that somewhere is seldom where it should collect. In order to move “it” from where “it” is to where “it” should be, individuals, companies and municipalities often employ the use of electric submersible sewage pumps.

I have been repairing electric motors and pumps for more than 44 years now. Over that period of time I have worked for 6 different repair facilities. It seems that, regardless of where I have worked, I have been called upon to repair submersible sewage pumps. As a by-product (if we can forgive the use of that term) of my years of experience I have been generally regarded as an authority on the rebuilding of Poop Pumps.

Over time, each of my employers has leaned on my reputation and experience to create a faithful following – a group of loyal customers that come to rely on this capability. It’s something that most people don’t want to spend a lot of time thinking about so, when I move from one place of employment to another, the Poop Pumps follow.

When I came to Gem State Electric in 2005 my merry band of faithful customers followed. GSE quickly became specialists in the rebuild and replacement of submersible sewage pumps. In the years that followed, our reputation has grown and our circle of friends has expanded to include many of the municipal waste treatment plants inSouthern Idaho(and as far north as Orofino).

This loyal following has resulted in my adopting the moniker “The Pied Piper of Poop”.

I don’t mind, seriously. In fact, I invite you to join the crowd and follow me to affordable quality pump repair. It won’t be a song and dance routine, just honest old fashion service.