“Hello” you say.

“Hi my name is Kristin with EMA”  you hear  in an almost annoyingly chipper voice

Your  head drops in disgust.  How can this person be so happy so early on a Monday morning; sickening actually.  You respond back with a terse “can I help you”; all the while thinking of an out, anything to just  get this girl off the phone.  She begins her “speech”.

“Hi Tom, I’m calling with EMA and I wanted to thank you for your recent repair business.  Our technicians recently repaired a Robicon Perfect Harmony VFD  for you.  This is just a courtesy call to make sure you were completely satisfied with the repair.”

At first you are shocked that someone isn’t trying to make you buy something.  Secondly, did she just say thank you and ask if I was happy with the service?

Unfortunately, bad customer service has become so commonplace that consumers have become desensitized to it.  I have experienced so many petulant, dispassionate customer service representatives that I’ve lost count.

Because of my experience, I make sure to treat every customer that I deal with, with the utmost respect and attention.  Treat others the way you want to be treated; it’s that simple.  Yes,  I’m actually calling to make sure that you’re happy with the service we provided to you.  Yes,  I’m calling to thank you for your business.  Shocking?  Well, it shouldn’t be.  This should be customary in all businesses.  Unfortunately, it is not.

Here at EMA, we strive to make sure each and every customer understands how important they are to our company.  With the economy fluctuating the way it has recently, we are thankful and appreciative to all of our customers for our continued success.  The reason we are still thriving is because of our loyal customers, so saying “thank you” to them seems pretty straightforward.

Not everyone who is calling you early Monday morning is that pushy salesperson trying to sell you the next best gadget.    You never know, it may just be me calling to say hi and thank you.

Kristin Burdick

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Kristin  Burdick is one of our customer service people, and many of our customers have told us how much they enjoy talking with her.  Kristin lives in upstate New York, and is a integral part of our national customer service efforts.

EMA enjoys the highest customer satisfaction rating that we know about within our industry, and Kristin and our other wonderful EMA family members are a big part of that.   Visit our ABOUT page to read more.

In general, this simply means removing the old SCR s, and replacing them with new ones,  taking care to see that the new devices are mounted properly. By mounting properly, I mean both mechanically and electrically.  Devices not mounted properly will either not fire consistently, or will over heat and fail.

Often it’s best to upgrade the voltage and current ratings of the Thyristors and this can be done at minimal additional cost. Many times, when the units were first constructed there may have been limits on what was available.  Modern SCR s are built to much higher standards.  There is a bit of technical knowledge required to be certain the new devices will fire properly, but at EMA we have over 20 years of experience doing this, so you can rest easy.

Rebuilding DC Drive power assemblies in this way can not only be cost effective, but can result in very little downtime if planned properly.  At EMA we’ve done this numerous times, and would enjoy talking with you about your specific equipment.  Contact your nearest EMA facility from  the list at the bottom of this page or just click the telephone ICON at the top right.

See our SHOP REPAIR page for further information.

When you replace the control board on ABB VFD s, there are several steps to take (some of which depend on the specific ABB VFD model). The reason for this is that most ABB VFD control boards are generic to all models, so it’s necessary to ‘tell’ the board what HP drive it is controlling.   (See our SHOP REPAIR page)

These steps involve using “secret passwords”, “3 finger salutes” and other various voodoo methods (our terms)  to access hidden parameter groups that allow you to match the control board to that particular model.  Call us at EMA, and we’ll  be happy to help you over the phone with that.  

On some ABB VFD models, like the ACH600, the power board is the same for several sizes and the only difference is the amp rating of the modules and a solder pad or burden resistor. That pad on the main power board is soldered in various places to tell the logic of the drive what current draw it is rated for. If this pad is soldered incorrectly, the control board can “think” it is a larger drive than it is and not trip properly during a true over-current condition.
On ABB VFD models such as the ACH550, the ribbon cables that connect the control board to the power board easily become detached. We’ve seen numerous repairs come in with the customer saying the  “drive doesn’t power up” when the only thing wrong with the unit was a loose ribbon cable. This is a fairly common issue on older Hitachi models as well.

Our experience tells us that if anything happens to the output section of the drive, the entire power board needs to be replaced. Almost all the new model ABB VFD s use triple-layer boards that notoriously blow traces during an output issue. If the broken trace is in the middle layer of the board, its almost impossible to track down.

This list is obviously not exhaustive, but it will, I hope, help you avoid chasing rabbits during your troubleshooting efforts. To ensure you get your drive up and running properly, send it to the experts at EMA.

We’ll give you a free evaluation and no work will be done on the unit without approval. You have nothing to lose but more frustration and downtime.

See the bottom of this page to find your closest EMA facility, and give them a call.  Or click the telephone ICON on top of this page.

We perform shop repairs and field service on ABB VFD s.  (see our FIELD SERVICE Page)

This class is oriented toward industrial drives, and not HVAC VFD s. (We do teach HVAC classes as well)   You’ll leave this class with a clear understanding of VFD s and the mechanical and electrical interactions that define the applications. You’ll learn to recognize classic drive symptoms and to quickly resolve common problems.

Who should attend?  Anyone troubleshooting, maintaining, or applying industrial VFD s.  Just one instance of reduced downtime could more than cover your cost for the class.

The cost is $695 per person, and it covers tuition, materials, and lunch.   Click HERE to download a flyer.

Visit our training page for more information on EMA Training.

Sign up by calling 770-448-4644 and asking for Kristin, or EMAIL  us.  To inquire about other training, call  your nearest EMA facility as listed below, or click the telephone  icon at the top right of the page.

The E7 has been a terrific product, enjoying the highest mean time between failure rating of any other product on the market. The new Z1000 drive incorporates all the features of the E7, plus many more.
The Z1000 Variable Speed Drive is designed for building automation applications such as fans, pumps, and cooling towers through 500 HP. Its features begin with an easy-to-read LCD operator with Hand-Off-Auto functions. An internal real-time clock with time /date stamping and timer controls allows for speed variations without the need for external controls.

A built-in 5% line impedance reduces input harmonic distortion, while a 5 kHz carrier frequency with dynamic noise control provides quiet motor operation. An on-board EMI/RFI filter compliant with IEC 61800-3 minimizes interference of surrounding equipment. All Z1000 drives also feature embedded BACnet communications (BTL certified), along with Modbus/Memobus. Applications macros are available to facilitate quick and easy setup.

Closed loop control of fans and pumps for pressure, flow, or temperature regulation is accomplished via the Z1000’s PI feature, which eliminates the need for a closed loop output signal. Independent PI is also available to control an external device in your system.

Available NEMA 1 models include ratings of 3 to 150 HP (208V) and 3 to 500 HP (480V). A sealed heatsink allows the drives to be mounted in a NEMA 12 enclosure with heatsink external. All Z1000 drives are Plenum Rated (UL 1995), Seismic Rated (March 2012), and made with RoHS compliant materials.

To download a brochure on the Z1000 click HERE.

EMA repairs and services the existing E7 VFD and will continue to do so.  Call us for all of your HVAC and Building Automation VFD needs.   See your nearest EMA facility below, or click the contact ICON at the top  right of this page.

Keith and Kristyn Getty will be live at Mountain Park First Baptist Church in Stone Mountain, GA on Sunday March 4th at 7 PM. Tickets are $15.00 and are available by calling 770-921-1452 or by visiting www.mpfbc.org/gettyconcert.

Keith and Kristyn Getty have been at the forefront of the modern hymn movement over the past decade demonstrating the ability to successfully bridge the gap between the traditional and contemporary.

Keith and Kristyn Getty are currently living in the United States where they have just finished their second album together ‘Awaken the Dawn’, a collection of hymns that takes you on a lyrical journey of grace and hope for all the nations. This follows their first collection of hymns, the successful 2006 release ‘In Christ Alone’.

The Getty’s home site is www.gettymusic.com

To begin, the design of modern variable frequency drives (VFD) takes output ampere readings very seriously.  The drive protection circuits in modern drives are excellent, which is why output device failures are very low given the fact that they routinely switch large currents.

Although its not advised, most modern VFDs can take a phase to phase or phase to ground short, and trip off in time to save the output devices.  This is only possible because the current measurements are sampled rapidly and accurately.

At EMA we’ve been applying and servicing VFDs for over two decades now, and we’ve learned to trust the drive output readings.   The measurement methods are almost always considerably more precise and reliable than external measurements.

This isn’t to say that there could not be a failure, but rather to say that all things being equal, we would trust the internal drive readings over external measurements.

There are several reasons why input currents, measured externally, can differ considerably from the drive output currents.

1. Voltage Differences

The 3 phase input voltages to a VFD are more or less static.  They may vary by a small amount, but in general, a 2300 volt input is going to be relatively stable.

However, VFDs provide not only a variable frequency output to the motor, they provide a variable voltage output as well.  In  most modern drives this is accomplished by using Pulse Width Modulation (PWM) .

Since the power being consumed by a VFD will always equal the power output of a VFD plus the internal drive losses, this means that if the output voltage is less than the input, then the amperes will be higher than the input.  (Power = Volts times Amps)

2.  Drives are non-linear loads.

VFDs do not draw sinusoidal current from a power line, they draw pulsating currents, which can appear to many measuring instruments as DC currents.   This non-linear amp draw can be mitigated somewhat by using phase shifted input bridges, which have become common in high horsepower VFD equipment, but nonetheless, it remains non-sinusoidal.   This often causes errors in external current measuring equipment.

3.  Harmonic  currents.

Due  to the non-sinusoidal currents, the input voltage can be distorted by currents flowing at frequencies other than the power line 60 hz.  The equal harmonics tend to cancel each other, but the odd harmonics do not.  Consequently, one can find significant currents flowing at the 3^rd and 5^th harmonics especially (180 hz and 300 hz) and these currents can, if unmitigated, not only cause power line and equipment problems, but can result in erroneous power and current measurements.

EMA can supply your VFDs,  we can repair your existing VFDs, and troubleshoot VFD problems..   we work on both low voltage and medium voltage VFD s.  Call your nearest EMA office as listed below, or use our contact page to email us.

EMA has been repairing DC Drives for over 20 years, so we’ve seen plenty of repair issues with DC Drives and Motors. Let’s start with DC Motors.. everyone knows that a DC motor has an armature, and in most cases, a shunt field. Although

Old BBC DC Drive

most applications use DC motors in a speed control mode, DC motors are inherently torque machines. The torque, or if you prefer, the magna-motive force of a motor is the armature flux times the field flux. Flux, in general, is the lines of magnetic force produced by current flowing through the armature and field windings.

Here’s the first point.. IF you reduce the lines of flux being produced by either the armature or the field, then overall, the magna-motive force of the motor is reduced. In other words, the motor’s ability to produce torque (turning force) will be reduced.

In a typical DC motor or DC drive application, the field flux is held constant, and as the motor load changes, the current into the armature will change.

Here’s the second point… IF the field flux is held constant, then motor torque is directly proportional to the armature current. i.e. If a motor is rated at 100 ft lbs of torque, and full load amps is 100 amps, then if the motor is drawing 50 amperes, we know that motor is producing 50 ft lbs of torque. AGAIN AS LONG AS THE FIELD IS HELD CONSTANT.. (Remember my first point) If the field flux is reduced, then that relationship is no longer valid.

Now, lets talk about DC Drives and speed.

Reliance MaxPak

The speed of a DC motor IF THE FIELD FLUX IS HELD CONSTANT is directly proportional to the armature voltage. The speed of a DC motor has no relationship to the armature current.  You can be drawing 100% full load amps on the armature, with the machine stopped.  The motor is producing 100 % torque, but not moving.   Again, the speed of the motor has no relationship to armature current, but it does to armature voltage.

This means, IF THE FIELD IS HELD CONSTANT, that a motor rated for 1800 rpm and a 500 volt armature, will be doing 900 rpm if you have 250 volts on the armature.  This is why DC drives can operate as voltage regulators, and control the speed of a DC motor.

DC Motors are inherently generators..    if we take this same motor, excite the field to its rated value, and spin it by external means to 1800 rpm, then the motor armature will have 500 volts present.   If we lower the field, the voltage on the armature will decrease; if we raise it, the voltage will increase.  (until roughly 750 -800 volts  at which point it will likely flash over)

DC Drives can also be operated as speed regulators (as opposed to a voltage regulator) and can use a tachometer mounted on the motor shaft to give tighter speed control than what can be accomplished by armature voltage regulation alone.

So, armed with that bit of information..   let’s look at a couple of real life troubleshooting examples involving DC Motors and DC Drives.

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A motor is drawing much higher armature amps than it should. You measure the 3 phase input to the drive, and the current is generally balanced.  (by the way, this is always a good first check..  if the current is severely imbalanced, you probably have SCRs not firing in the drive output.  We call this condition “single phasing” and the decreased ripple frequency can cause issues with the DC motor)

If the amps into the drive are balanced,  the DC Drive is probably fine.   In general, drives supply voltage and motors draw current.  So if the motor is drawing higher amps, it usually means that either the torque required to move the load has increased, OR, the DC motor’s ability to produce torque has decreased.

What’s the first check?   Remember my first point at the beginning of this blog..    motor torque is the armature flux times the field flux. Since we’re seeing high armature amps, we assume there’s plenty of armature flux, so, what’s left?

CHECK THE FIELD! This is a simple step that’s often overlooked, and results in a lot of un-necessary downtime and trouble.  If the field is OK, then its probably a mechanical problem with the load.

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Here’s another..

The motor will not reach top speed.   (let’s assume the  DC Drive is set up as a voltage regulator)

First check…   armature current..      are you drawing more than full load amps?  If so,  then you’re back to the situation we just discussed prior to this.   If you’re not, is the current limit setting in the drive set too low?  The drive’s current limit setting will limit the armature current.  If too low, it may prevent the motor from reaching top speed.   Usually, it will also result in an unstable speed, but not always.

If current is within ratings, and the drive is not in current limit, then check Armature Voltage..     IF it’s reading 500 volts, and your speed is too low, what could that mean?

Remember that a DC motor’s speed is directly proportional to armature voltage PROVIDING THE FIELD FLUX IS CONSTANT..  so what’s the next check?  How about the field?

IF the field is too high, and this happens, the speed will be lower for any given armature voltage.  High field amps can also cause other issues, such as motor overheating and at some point a burned field, but in the short term, it will affect speed in a voltage regulated DC Drive. (by the way.. the  motor will have INCREASED torque abilities..  at least in the short term)

EMA regularly services DC Drives..   we also sell and apply new drives and motors.   Contact us!

(Visit our SHOP REPAIR page)

But, to repair the drive usually requires the end-user to send their drive to a European manufacturer and wait a month for an expensive repair. Fortunately, there is an alternative to this; at EMA, we specialize in drive repair for all manufacturers and have trained engineers with the knowledge of complex applications.

Our 48 hour turnaround Rush service means that your drive can be repaired and back to in the time it takes to get through customs.
We recently had three Bonfiglioli VFDs here for repair that had major output damage due to a shorted motor. Parts are not available for sale for these drives so the customer had all but lost hope. Thankfully, we were able to repair all three, much to the customer’s delight because we understand how a PWM drive works and were able to fix the driver boards.

The “U” phase of the customer’s motor was bad, blowing the same driver channel on the VFD. Although the driver card uses all, unmarked surface mount components, we were able to fix because we knew the type of zener diode generally used on driver channels of this kind. This is the kind of knowledge that separates EMA from our competition. Anyone can use the “pop and swap” method of troubleshooting, but to truly understand the problem, one needs specific knowledge of how a drive works, and that’s what we have at EMA.

To contact your nearest EMA facility, see the listing at the bottom of  this page or click the telephone ICON on the top right.   In addition to shop repairs, we also provide field service (See our FIELD SERVICE page)

Trey Mayfield,  EMA