The following information has been supplied to us by KB Electronics, giving an insight into the concept behind their range of plug-in horsepower resistors for DC drives.
KB Electronics is unique with our usage of a Plug-In Horsepower Resistor® (PHR) in most models of our DC Drives to sense motor current. Most of our competitors use a fixed soldered-in resistor. This technical note explains why KB Drives require a PHR when the competition uses a fixed resistor, and the advantage to the customer of the Plug-in Horsepower Resistor®.
First let’s consider the time and effort necessary for KB to manufacture the PHR. If you look closely at one, you will discover it consists of a small printed circuit board, two male standoff pins and a soldered current sensing resistor. In addition, the speed control circuit board must have two female pins staked, soldered and properly aligned. Competitors solder the resistor to the board and they are finished. You don’t have to be an accountant to figure out which method is easier, and less expensive to build.
Ask yourself, why does KB insist on using the PHR when the competition doesn’t. The answer can be found in the KB slogan, “The Right Control For Your Application.” We do it because we believe our customers have more important things to do then calibrate DC Drives. We believe our customers deserve a control which is factory calibrated. The fact of the matter is, most customers don’t take the time to calibrate DC Drives. Unfortunately, they run the risk of demagnetizing a PM motor or cause it to burn up due to overload. They may even cause damage to their machinery by having the CL setting of the DC Drive greater than the motors rating. Read on to find out why.
The purpose of the PHR is to sense the motor’s load current and provide a feedback signal to the drive. The signal is used by the Current Limit and IR Compensation circuits. The CL and IR are preset at the factory, based on the signal from the PHR. The current limit circuit is very important. Its job is to limit the maximum current that the DC motor can draw. If the current is too high (as stated above), it may cause machine damage, motor over-heating or demagnetization of the motor’s permanent magnet fields which will cause the motor to lose torque. When properly calibrated, the CL circuit limits the motor current to 150% of the motor’s full load rating. The IR Compensation circuit calibrates the motor’s load regulation abilities, helping it to maintain proper speed regulation under changing load conditions. These characteristics vary according to the size of the motor.
So why does KB use the PHR rather than a fixed resistor? All DC Drive motor speed controls are capable of operating a wide range of motor sizes. In the case of a control with a fixed sensing resistor, the resistor must be sized according to the largest motor with which the control can be used. One of our competitors offers a ½ HP DC Drive but says it can be used on motors up to 1.0 HP if they attach it to an auxiliary heatsink. The question is, what is the control calibrated for? If it is calibrated for ½ HP and it is used on a ½ HP DC motor all is well. If he uses it on a 1.0 HP motor, the motor will not develop its rated torque and the IR circuit will be over compensated. What if the drive is calibrated for 1.0 HP and he uses it on a 1.0 HP motor all is well but if he uses it on a ½ HP motor there will be a good chance of putting more than 1 HP worth of current (the control’s capacity) through the ½ HP motor, causing a burned out motor, possible machine damage and unnecessary downtime.
If this same machine had a KB DC Drive, the Plug-in Horsepower Resistor would have been correctly sized for the motor. The result is that the CL and IR compensation circuits would be factory calibrated for the motor’s characteristics. No matter how it was adjusted, the CL trimpot would not allow more than 200% of the motor’s full load current, providing adequate protection for the motor and machine.
Although the customer must remember to install an individual Plug-in Horsepower Resistor with each KB speed control, its use provides a benefit for the customer. The resistor is correctly selected once the motor’s HP, voltage rating and full load current are known. A PHR reference chart is shown in the beginning or our catalog. Please note that a separate section of the chart is provided for SCR and PWM DC Drives, as well as SCR and PWM rated motors.
ComInTec is displaying its wares at Hannover Messe 2013 MDA, which is on now. The Motors, Drives and Automation show brings out the latest in technological prowess from the industry’s top manufacturers, and ComInTec is no exception as it displays the state of the art in machine protection technology.
With an emphasis on torque limiters, clutches and couplings, ComInTec’s display is both interactive and informative, ably manned by Export Sales Director Alan Johnson, among others.
All Torque Transmissions has had a long relationship with ComInTec, dealing with both Alan and Fabio, and representing the Italian manufacturer in the Australian marketplace for over a decade.
Hannover Messe 2013 runs from April 8-12 and you can check out the full range of exhibitors by clicking here.
MEPS, an acronym for Minimum Energy Performance Standards, were introduced at the turn of the 21st century by the Australian and New Zealand governments to cover a wide range of electrical equipment. For electric motors, a rating of MEPS 1 came into effect in October 2001, whilst the higher efficiency MEPS 2 superseded MEPS 1 in 2006. Internationally, IEC 60034 is a set of standards by the International Electrotechnical Commission that roughly mirrors MEPS.
All three phase electric motors ranging from 0.73kW to 185kW in 2, 4, 6 and 8 pole configuration that are either made in or imported into Australia must comply with the minimum efficiencies as set out by the MEPS ratings. There are some exceptions to the MEPS rule; MEPS doesn’t apply to submersible motors, integral motor-gear systems – like the Bonfiglioli compact range – variable and multi-speed motors or motors rated less than continuous duty (S1). Motors that have been rewound are also not required to comply with MEPS.
Motor manufacturers have not shied away from the responsibilities of meeting efficiency standards around the world. The standard measure for increasing efficiency has been to use larger, lower-resistance winding wire and higher quality steel for laminations. When coupled with total motor re-designs, the efficiency standards have been able to be met on a consistent basis.
One of the benefits of the new, high-efficiency motor range is that they also have improved performance at part load, making them extremely suitable for variable speed drive service. Many major manufacturers are taking advantage of this fact by matching motors and drives in their product offerings.
All Torque Transmissions took delivery of new mobile phones this week, having persevered with our existing ones for long enough. The new technology is quite impressive, with things like ‘the cloud’, ‘facetime’ and ‘retina display’ no longer mere existential undertakings, but now actually with us. I say most people were impressed… enter Sales Engineer Ernie Baker.
A renowned stalwart of using only proven technology, Mr Baker was taken aback at the new phone’s interface (and lack of actual buttons on the front), whilst the size of the handset was also surely going to cause problems. All Torque management was going to have to come up with a quick answer if it was going to keep its top salesman happy.
Quick thinking saw the introduction of the Maxwell Smart Suitcase Phone – Ernie Baker Edition. Fashioned from the original handsets of telephones from Australia’s Post Master General circa 1971, the special limited-edition model features an extremely loud earpiece, with the microphone turned down to its lowest setting by the factory.
Seriously, though, our new mobiles run Windows 8 and are a real powerhouse of technology. They enable our Sales Engineers to do the job both in the office and on the road.
Due to customer demand and some recent project-based orders, WEG Australia is standardising its CFW11 range of variable speed drives to include a safety stop relay as standard – with no increase in pricing levels. The safety stop relay is one component of the safety control system of a machine and/or process, and is increasingly required to comply with standards and legislation.
The CFW11 range of variable speed drives is still operable without the need to use the safety stop relay if the application doesn’t require it, although all new stock coming to Australia will have it fitted at no extra cost.
All Torque Transmissions handles the complete range of WEG drives and soft starters out of both Braeside and Preston.