Single Phase Motor Control

I would imagine that I get asked several dozen times a year about a VFC for
controlling a single-phase motor. Well, here it is in writing as far as what is
available at this time:

There is not one manufacturer building a single-phase input and single-phase output variable frequency controller, Not One. The only way to control the speed of a single-phase motor is via voltage control and this only works on certain motors. Voltage control as I am describing it in this document can be best identified as a “Dimmer Switch”. The only ones that work well are the Solid State type and are limited in use to just a couple of motor applications. They will not work on the following:

     - Capacitor Start type Motors

     - Dual Winding Motors (Start and Run) with speed engaged contacts

The above-mentioned are the most common type single-phase motors and if you try to control these with variable voltage, they will definitely burn up. These are the motors mostly found on Clothes Driers, Washing Machines, Drill Presses, Band saws, Table saws, Small Lathes, Air Compressors and so on.

Capacitor Start- Capacitor Run type motors have been used on variable voltage but I still don’t believe that these are reliable on variable voltage control as eventually, the capacitors overheat and wear out due to the lack of proper voltage applied to them.

Shaded Pole motors work well on variable voltage control but understand that these motors have very little starting torque to begin with; so using them with a variable voltage source will make them very, very weak when starting. These motors are commonly found in ceiling fans and will run little else. Next time you get the chance, pay close attention to a ceiling fan starting. You will notice that it takes it some time to get up to speed. That is because of its low torque, high slip characteristics.

I wish I had something to offer but I don’t think it will ever happen in my lifetime.


Scott

Merry Christmas and Happy New Year

Here it is, December 23rd and we are here hoping all is well with you and your families this Christmas.  Hoping that it has not been too hectic as this time of year can be for most of us.  It's mid-morning and I will probably turn everyone out about noon or so to start their Christmas holiday events.

I truly appreciate all of you and hope this coming year brings us all bigger and better things in our lives.  Well, at least more satisfaction than we expect and have enjoyed over this years trials, tribulations, travels and adventures.

Everyone, have a great holiday season and I will be in touch soon; next year!

Scott

November Newsletter

Well, it is nearly the end of November.  The day before Thanksgiving, the day after a blizzard warning in which we mostly received wind.  There is currently about 3 or so new inches of fresh snow but the real news is the temperature.

It was 1 degree on the way into the office this morning and quite a fun drive in, as the roads were very slick.

We are currently working on a project that is nothing short of ambitious for us.  We are going to build and market a new product that will be sold exclusively through a Rep company.  We have been in various meetings with factories for items we will need to embark in this venture and still have some more negotiating that needs to be completed prior to an announcement. 

I will let you know as soon as things are all finalized.  Needless to say, we are all a bit excited about this.

The holidays are upon us with things kicking off tomorrow-on Thanksgiving.  It’s always a difficult time to do “business as usual” do to the fact that a number of our factories will be closing for the holidays or for “inventory”.   Every year, we face the same hurdle with our suppliers but somehow manage to pull through. 

So what I’m trying to say is, although we do our best to have as many of the items that we think we may need to fix whatever problem may arise; we may not have the part you need.  This leaves us all at the mercy of the factories.  Hopefully, this season will come and go and most of you will not have the misfortune of being down for any reason.  But if you do happen to go down, rest assured that we will do our very best to help correct the problem if called upon.

Everyone have a great Thanksgiving and enjoy this Holiday Season.

Scott

Capacitor Installation Problems

In the past few years, facilities that have capacitors installed for power factor correction have been experiencing quite a few problems with the units failing. Whether it be a few individual cells or the entire bank failing, these problems have started to show up now on a more frequent basis.



I guess if I think back, this has been happening for the past eight or more years but seem to be worse in the last two years than ever before. Most of the failures are on “fixed” bank units. That leads me to a few conclusions about what may be going on at these facilities:



- The load profile has changed either up or down

- A Main Transformer has been changed out

- More Non-Linear load has been added to the system



In any case, something has changed at these facilities that is now causing the capacitors to fail.



Let’s take the Load Profile for example:



When originally installed, the capacitor sizing is based on the kW load of the facility. What also comes into play is the Transformer size, Impedance, existing Power Factor, Site Voltage and other things that we look at such as Linear verses Non-Linear load.



Factoring in all of the above information, we calculate how many kVAR will be needed to correct the power factor. Also the placement of the capacitor bank(s) is looked at very closely. We determine where it will be best suited electrically (depending on system) for survival in the facility. We also make sure that we are not “tuning” the system to a frequency that is close to critical frequencies that are generated by most non-linear loads, such as the 5th, 7th, 11th harmonic.



In most every instance that we have had capacitor failures after a few years of service, I have found that the user has added Variable Frequency Controllers to the system or some other non-linear device(s) that are now causing harmonics that become detrimental to the existing capacitor bank. In one instance, I found that the Main Transformer had been changed out to a different size unit. This caused a rise in voltage that is bad for the power factor and also re-tuned the system close to the 5th harmonic.



In conclusion, what I am trying to say is that if you have power factor capacitors at your facility; pay close attention to changing, adding or deleting anything on the electrical system as this can cause you major headaches in the long run.



If you want more information, you know where to get it.



Scott

Our Little Salt Project

Well, here it is in original form.  A Buell Blast 500cc, 4 stroke motorcycle.  This little girl is what most call "a half a Harley".  It is perfect for what we are going after.

It will soon go on a serious diet and become a lot lighter than its current weight of 360 lbs.  I have a mess of various parts to begin doing a few things to it but the first thing is to form a game plan for the class we are determined to go after.  I know most of what we will need to make this thing into the beast we are wanting and have a preliminary budget set that is pretty tight.

I will continue to post progress pictures as we go along.

October thoughts and a goal for next year

As most of you may know, one of my pastimes is working on motorcycles. I usually have a project sitting on the lift at the house most of the time. I am currently finishing up a 1952 45-inch solo that I am preparing for an auction this January.




I have had a passion for motorcycles since the age of 11 when I was given one by my dad. Since that point, I have had numerous brands, types and sizes of them but for the past 16 years I have mainly spent my time with Harley-Davidsons. Zachary, Brandan and I built a chopper back in 2006 that I took to the Sturgis Motorcycle Rally in South Dakota. That was a memorable experience for the boys and me. Four months of solid work in the shop at home and a lot of figuring and learning along the way.



On a recent trip to Wendover, Tammy and I stayed the night at a motel on the eastern edge of the town. The parking lot was full of people there for the speed finals at Bonneville. Being me, I talked to quite a few of these folks and found that they have the same blood pumping in them as I do in me for the love of anything powered by an internal combustion engine and the want to make it not only look good but Go Fast!



So, here’s the deal. I have a motorcycle that is going to become a project/representative for the company over the next 10 months. We intend to build a machine (in our off time) that we can go after a land speed record with next year. I have set a tight budget and we are going to limit ourselves to a 500cc class.



Some of you may be saying to yourselves, “What does this have to do with E.C.T.?” Everything! We pride ourselves in being able to solve problems, be creative, and achieve greater heights than our competitors can. So why not think outside the box?



I will be posting some pictures and notes as we get started on this “Run for the Salt 2011”. All along the way, we will give progress reports and post build pictures so you can follow along. This will be fun for us and I hope for you as well.



Scott

October News

We recently took a trip out to see some folks that we have been building some panels for in the west desert of Utah. The operation is Desert Hawk Gold in Gold Hill, Utah.




This location has been mined (off and on) for over one hundred years and was primarily an arsenic mining site. At one time there were over 3000 people living and working in Gold Hill. A rail line was even run into town at the height of the operation I believe in the 40’s.



Today, there are a few residences in Gold Hill. There are only a handful of people that live there. The mill (located just a short distance from town) is being refurbished for gold recovery. Several people working there are friends that are retired from other gold operations in Nevada. We have known these folks for a long time and we are doing our part to try to help them get things together so they can start producing from a quarry they have several miles from the mill.



Prospects look good and at the price of today’s gold, it should work out to be a successful operation. Tammy took some goodies out to the mill and we were glad to be greeted as the first vendors to visit the site.



Upon leaving, we decided to come home via the old Pony Express route. I had not been across this road since I was in my teens and it was quite a trip. My youngest son and I had antelope tags for that week in the area so we did some scouting on the way. Later that week, my son and I filled our tags in the Simpson Springs area. It was a great hunt.

Scott

Harmonic Trap Filter Issue Revisited

Well, I can now report back on what we found with the Harmonic Trap Filter issue and running on a Generator.

Problem:
Multiple VFC's with attached Harmonic Trap Filters.  All connected to a back-up Generator.  The Gen-set was having trouble with the VFC's all on line but only half of them in service.

We installed Contactors in the Filters to disconnect the Capacitor Section of the Filters when the VFC is not running.

This fixed the problem.  It seems that the extra capacitance on the system was raising the voltage to a level that the voltage regulator on the Generator could not compensate for.  This was causing the Gen-set to trip out on Over Voltage.  Be aware that this is not as simple as just adding a contactor.  There is more equipment involved with this and various wiring changes that need to be made to make this work.  If you need more details, call me and we can discuss your application.

I have seen this now being asked for on several jobs that require a back-up Gen-set and the site having multiple VFC's, some that will not be in service during certain portions of the day do to the system demand.  So if you have a site that has this type of application and you are using a back-up generator, you have been informed and warned about possible problems you may experiance.

Just thought you may want to know....

Scott

This Blog thing and other stuff

I have been writing articles for this blog thing for about a year now with very little feedback from anyone. I have done this hoping to inform anyone that reads about troubles we have found on service calls, new information from our suppliers and anything else that I happen to think about and have the time to type up and post.




No feedback tells me that what I am writing is either not important, taken as gospel or just not worth the time to comment on, I wonder which if any it is.



Ran into a situation lately where a customer is having a problem running drives that have harmonic trap filters on their back-up generator. It seem that the capacitors are causing a voltage rise that the generators voltage regulator cannot compensate for. This causes the generator to shutdown on over voltage.



The factory is looking into this issue. The application engineer sent me an email stating that he was going to do a write-up on running VFC’s with HTF’s on generators but I haven’t seen anything as of today’s date. As soon as I see this, I will make sure and follow up with another post that addresses this issue.



So if you read this and are interested in the solution to this problem, keep following the post. If you are not, you probably didn’t read this to begin with. Either way it’s fine by me.



Hello, anyone out there?? Damn, nice echo! Echo, echo, echo……….



Scott

The importance of proper grounding

An interesting thing happened yesterday. I had been talking to a customer that had purchased a new VFC to replace one that had gone bad in a Motor Control Center. He told me that the 4-20mA signal was acting very erratic and that the drive would not follow the signal.




I went to the site and sure enough, the signal was all over the place from zero to maximum and everywhere in between. We looked at everything from cable routing to the shield ground connection but still didn’t see anything.



I replaced the control board at this time thinking that maybe something was wrong with it. I asked him to power the unit back up and when he did he received a small jolt. I quickly measured the potential between the VFC chassis and the ground in the panel and there was 67 volts…..No ground strap on the chassis to the panel.



Here’s the lesson, the paint on the steel chassis of the drive is a thick powder coating and it will not ground just by the mounting bolts. US Drives provides two ground terminals near the input/output connection points for not only connecting wires for incoming and outgoing but also for a connection to the equipment. There must be a solid ground for the drive and this one was floating.



Right after we ran a ground the signal worked just as it should. Lesson learned.



Just thought you should make note of this.



Scott

Elko Mining Expo

We will have our trailer with products and demo's at the Elko Mining Expo in Elko, Nevada this coming Thursday and Friday.  That's June 10th and 11th.  If you are in the area, stop by and say hello.  We will be on the north side of the expo center in the display lot.

Scott

Beginning of Summer

Here we are at the beginning of summer and the temperature will be going up. Now is the time to be thinking about making sure your electrical equipment that requires ventilation is clean and breathing well.




Here in the Salt Lake Valley we have a lot of Cottonwood Trees that produce cotton all over. I have walked into many well houses and seen vents completely plugged with the stuff. Dirt and other debris such as seeds from trees and plants get trapped in the air inlets of our drives and solid state starters.  When the temperatures go up, next thing we know is that our drives are shutting down when we need them most!



Summertime is the hardest time on our electrical equipment. Now is the time to make sure all your equipment is well ventilated and that all the fans and other cooling equipment is in good working order.



Take precaution when blowing out with compressed air as it can do as much harm as good. Most compressed air contains moisture that can be harmful to components. I personally don't like this method of cleaning but sometimes is may be necessary. Never do this with the equipment energized! A vacuum and a brush is the safest way to clean but also remember to never do this with the power on. I have see air bourn dust cause a flash in live electrical components and choose to never see this again!



Be careful in how you go about cleaning your equipment but by all means, this should be high on you current priority list.



Just a reminder for all….



Scott

Some basics on Variable Frequency Drives

Let's take a very basic look at how a VFC works:

Three phase input power enters into the drive and the first thing it arrives at are the Diode Bridge Rectifiers.  At this point, we are converting the input AC power to DC power where it then goes to a Capacitor Bank for smoothing and storage until needed.

The voltage as stored on the bus, which since rectified has gone from 480 VAC now to about 690 VDC.  The reason for this is that when you rectify AC power, you need to multiply the number by 1.414 to get the new DC value.

The Positive and Negitive legs of the Capacitor Bank are connected to Output Transistors, in simple terms "Switches" that are in-turn connected to the Output Terminals.  There is a Positive Transistor and a Negitive Transistor connect to each of the Output Terminals.

When we start the drive, it fires two positive transistors and one negitive transistor on, multiple times and for different periods of time.  Starting out very breifly and getting longer in time until the Voltage reaches desired output.  Then, more and more breifly again until reaching zero.  This is done firing one side of one transistor per phase resulting in one half of a sinewave being delivered from the DC bus to the output terminal.  Then the output changes.  One of the positives goes negitive, the one that was negitive going positive and the other staying on positive thus completing one cycle or hert. 

The above happens very quickly and can only be seen with the use of an o-scope.  The frequency of what I just explained happens at the speed of the desired output frequency.  The rate of the firing of the transistors happens at the speed of the Carrier Frequency which is thousands of times per second.

Now, one question I am always asked is "why can't I change the rotation of the motor with the input terminals?".  The answer is above.  We rectify the power as it comes in therefore we don't care what the phase rotation of the incoming power is, we just rectify it and dump it on the bus.

The above is explained in a very simplified manner but may be useful to know in the future for you.  Questions?  You can always call me and we can discuss this further.

Scott

Industry Standards for Enclosures

Just thought I would give everyone a list of Standards for Enclosure Ratings, so here goes:

NEMA 1- For indoor use.  To previent accidental contact with enclosed equipment, in areas where unusual conditions do not exist. Protects from falling dirt.

NEMA 3R- For indoor or outdoor use.  To provide protection against windblown rain, Snow, Sleet and external formation of ice.

NEMA 4- For indoor or outdoor use.  To provide protection against wind-blown rain and dust, splashing or hose directed water, and external formation of ice.

NEMA 4X- Same as NEMA 4 with the addition of Corrosion Resistant.

NEMA 12- For indoor use.  To provide protection against dust, falling dirt, dripping non-corrosive liquids, lint, fibers, external condensation of non-corrosive liquids, and light splashing of water.

This list is for the most part the ones we deal in most cases.  There is this thing called NEMA 12 Ventilated.  This is a standard NEMA 12 that has Fans and Filters cut into it that are designed to trap dirt and other foreign materials from entering the cabinet.  In other words, it is for the most part a NEMA 1.

People seem to get confused about these ratings quite a lot of the time, so I thought this may be helpful to you all.

Scott

March News

The past few weeks have been challenging.  Madhu had a mild Heart Attack (if there is such a thing) and is currently still in the hospital with an infection in his lungs.  The news we are hearing seems to be the same everyday, that he is making progress in recovering little-by-little.  We are all praying for a speedy recovery for him.

Last week we had a booth at the RWAU annual meeting at the Dixie Center in St. George.  We were very pleased with the activity we had around the booth and talked to a lot of people from various cities around the state.  There still seems to be a lot of bad information out there about single phase applications for VFC's.  There is a posting I wrote a few months back about this if you need some more information on this subject.  If that still does not answer your questions, please feel free to call me and we can discuss single phase applications.

I have had a technical sales engineer here for the past few days from Williamson IR.  These folks sell Infrared Temperature measurement devices and their products are the best product on the market.  We just finished observing various test procedures that were being preformed by Shaw Pipe Company.  They do specialized coatings for pipe that is mostly for the petrochemical market.

The William Temperature Monitor is measuring the temperature of the pipe that is preheated just prior to applying the coating material.  The temperature is very critical to insure proper application of the coating.  The tests went very well and we hope they will be standardizing on the Williamson product in all their plants across the globe.

Williamson is the leader in Temperature Measurement for the Nonferrous Metals market, Iron and Steel processing, Flame-Fired Process and Engineered Materials.  For more information on Williamson, go back to our website, go to Resources, click on Williamson.  There, you can find a link to their website.  We have lots of literature and I would be happy to come out and talk to you about your application or specific need.

It is coming up on riding weather.  That means road projects, Asphalt, Concrete, Aggregate and building in general season as well.  Lets all hope for a productive spring, summer and fall and not too high fuel prices!  And when it comes to riding.......keep the shiney side up.

Scott

Service issues

Here's one for the books.......

I get a call from a customer on Friday night.  They had just installed a new VFC and it had been running off and on for the past day and a half but was now having problems.

It seems the drive was faulting out on "Under Voltage" and would not run.  The fault would clear but the minute that they gave the unit a start command, it would trip back out on undervoltage.

I asked the customer to measure the input line and it checks out okay.

I asked them if they could hear the precharge contactor picking up when the unit was energized.  They reported to me that they could hear it.

I asked them to measure the bus voltage and watch it as they gave the unit a run command.  They report back that the bus voltage was dropping by 30 percent.
That tells me that the pre-charge contactor is not picking up and that the voltage to the bus is still running across the pre-charge resistor.

Saturday morning comes and the customer has brought the unit to our shop.  We test it and the precharge contactor is pulling in and all seems well.  Then with further inspection we find that although the pre-charge contactor is pulling in, the contacts are not changing state.  Wierd!

Just another one of those things that happen from time to time that I thought you may want to know about.  We change it out and the unit is now reinstalled at the site and working well.  I usually rely on my ear to tell me if the pre-charge is doing it's job.....this time that didn't work.

Scott