The control factor

Hubbell Industrial Controls has introduced a new DC generator-based magnet controller that protects against magnet system power spikes, and virtually eliminates controller maintenance and premature failures of generators and lifting magnets.

After more than a year of field testing, the new e-mag controller, manufactured by Hubbell, has demonstrated that it will vastly reduce maintenance demands while enabling maximum efficiency and control during operation, even in high duty-cycle lifting applications such as scrap handling.

The company announced the new controller as ready for market in co-operation with its originators, Control Services. Winkle Industries, Hubbell’s master distributor, will market the e-mag controller for use on all makes and models of mobile cranes in recycling and steel mill material handling applications.
Control Services’ John Samila explains that the e-mag DC generator controller takes a dramatically new approach to controlling all power fluctuations inherent in the duty cycles and demands of lifting magnet applications.
“The current generation of solid state DC magnet controllers are static controlled devices that are subject to speed and load variations that may negatively impact the magnet system efficiency,” says Samila.  

“These systems are generally outmatched by the job, absorbing massive voltage spikes through very sudden surges and drop-offs.”
“Our e-mag controller withstands and eliminates inherent magnet system problems by controlling the source which is the generator,” continues Samila.
Instead of reacting to magnet system failures as other units do, the e-mag controls the flow coming out of the generator before it becomes an issue. In essence, the e-mag prevents failures by protecting the magnet system and controlling the generator output for optimum efficiency.

Generator speed matched to demand for power

According to Samila, the e-mag controller is designed with a closed-loop circuit that responds to the generator’s demand for power and matches the output to the demand. He says that all other DC generator controllers do not have these dynamic features and therefore, do not have feedback mechanisms to adjust power output to the demand requirements. The e-mag controller de-energizes the generator output when the magnet is not in use. As a result, there’s no failure due to a power spike when the crane operator releases the load.
“Every magnet owner has seen the worst-case for magnet systems,” Samila says. “The generator is running full power to the magnet, the magnet goes into the pile and the output cables get cut, causing catastrophic failures on other types of controllers and magnet systems. With the new e-mag, cutting a lead will not damage the controller, the magnet or the generator.”
He adds that; typically, DC crane generators are operated at constant rpms to obtain a constant voltage.

“DC generators are proven reliable in high duty cycle operations whereas AC integrated units come with their own set of issues when combined with high duty cycle applications,” Samila says.
When using an AC integrated magnet system, there are inherent downfalls, not the least of which is a catastrophic failure. Such a failure would require removal of the entire system for repair and may require a total system replacement. The e-mag eliminates this issue, has very few components, and it can be easily maintained on-site by the user.   

The e-mag design is ideal for high demand operations such as scrap handling, is available for generators from 5 kW to as much as 50 kW, and will eliminate problems associated with maximum voltages.
 

Drop-ball application drives innovation

As America’s largest producer of magnet controllers, Hubbell is very familiar with magnet systems and the problems that inherently arise. Steve Loeck, Hubbell’s Vice President of Sales, reports that the need for a new solution became clear when one particular customer was attempting to commission a magnet system for a drop-ball application.
“This was an incredibly rigorous application,” he recalls. “The drop-ball application required a near 100 percent duty cycle. The customer was attempting to operate the generator at the required 1,800 rpm’s and 230 volts, but the on/off cycling of the application requirements caused erratic rpm spikes in the generator that effectively raised the voltage of the generator above 300 volts or more.”

“The existing open loop magnet controller was not up to handling the spikes and the variations in generator rpm’s during the loading and unloading process,” continues Loeck. “With the e-mag, the generator loading and unloading voltage spikes are effectively removed and are no longer an issue. The e-mag controls the generator output, and as a result, when power is not required, the generator is no longer producing voltage. Therefore the generator is not affected by spikes and has a much more efficient cooling cycle.”

Often, traditional controllers also rely on a crane’s compensation valve to shield them from the impact of sudden surges and drops in hydraulic pressures. According to Hubble, the e-mag controller is unaffected by hydraulic loads, and fluids can always flow freely, even in machines that aren’t equipped with a compensation valve.

Fine tuning the magnet to material

By controlling the power to the generator output, the e-mag controller also allows greater flexibility in matching the magnet to the material it is handling. It enables infinite voltage control within the speed requirements of the generator, power can be increased to the maximum for short periods without damaging the magnet, and operators have equal control over the magnet’s draw down time. For heavily saturated loads such as steel slabs, the release time can be increased to as much as 14 seconds. The maximum draw-down with any other controller is typically about 2.5 seconds.
With this added control, operators can easily set up their magnet system to pick up more material in less time, and release it more efficiently. Combined with a high-duty cycle magnet, the result can be significantly more cycles, which leads to more material being moved.

Maintenance-free for 15 months

In December, 2008, e-mag units were installed on four Liebherr 954 material handlers at SMS Mill Services yard in Indiana. There, SMS (Scrap Metal Services) owner Rick Gertler reports that all four cranes are in a 24/7 operation, equipped with 72-inch and 78-inch magnets powered by (25 or 30 kW) generators. Gertler is more than pleased with the results.
“We have had zero downtime with these units,” Gertler says. “By that I mean that over the past 15 months we have had no service or repairs to the controller, no servicing for the magnets, and no problems with the generators.”
“As one of our long-time maintenance hands said, ‘I’ve never found a maintenance-free system like this.’”

Gertler adds; “I’m pretty sure we’re stretching the life of our generators, too.”
The four cranes handle a varied mix of material and Gertler reports that with the e-mag controller, the magnets are moving their loads faster and more efficiently. Each magnet is fitted with a scale to ensure accuracy and Gertler says the cranes have no trouble lifting their loads, with no bogging down on the pick and no material falling off through the carry. “With the old controllers,” he says, “we would just run out of generator. Now we can run right up to the material and pick the load easily.”

Gertler is convinced enough that he plans to include the e-mag controllers in future upgrades to the rest of his fleet. “It’s simpler,” he says. “In this work, simpler is what you need.”
 

Easy installation, lower cost operation

Joe Schatz, president of Winkle Industries, also expects to see e-mag controllers taking a prominent place in his future business with mobile crane customers.
“These controllers will start saving our customers money before they even start to operate. They are very quick to install with no external relays and field resistors required. Because it’s controlling the DC generator, there’s no need to rectify the power to the magnet – so there’s no alternator to install or service.”
The four units at SMS Mill Services were installed in 16 hours total – just four hours each. According to Schatz, installing a conventional controller easily takes a nine hour day each, with two technicians on the job.

“The whole system is surprisingly simple,” says Schatz. “The e-mag makes setup and troubleshooting dead easy, too. Everything is easily accessible. If there’s an issue, you’ll know right where to look. And in the long run, with no spiking or overheating, our magnets are going to stay in service much longer.”
He continues; “Heat is the worst enemy of magnet coils and generators. Customers will really get the most service-life and most productivity out of all the equipment in their magnet systems with the use of the e-mag. It’s a very cool concept, in more ways than one.”

Schatz believes that by improving the control of the system’s power profile, e-mag controllers will allow cranes to use smaller generators to power their magnets.

“You’re able to run up the voltage for short periods to get extra power out of the generator when you need it,” he says. “But then the generator gets a chance to cool off through the release cycle, whereas other controllers don’t give you this flexibility.”

“You’ll see customers getting longer life from their generator, moving more material and spending less on fuel for the job.”