Impregnating motors with thermal management materials to reduce hot spots

A doctoral candidate plucks a thermal management material out of LORD Corporation’s voluminous catalog, and one Ph.D. later, the EV world may have an exciting new boon for the efficiency of electric motors.

Anyone working within the corporate world has probably been battered with the word “synergy” to the point of it being rendered meaningless. However, when true synergy (interaction of two or more agents producing a combined effect greater than their separate effects) takes place in a developing market, the beneficial consequences can fan out across multiple businesses, as well as to the consumer side. 

In the developing world of electric vehicles, we often think of the driving forces as companies long entrenched in automotive, start-ups focused on electrification, academia, and certain arms of the government. Yet sometimes it just takes one enterprising operator to discover a new link in the chain of development and thus cook up a little bit of unexpected synergy. 

LORD Potted Motors PQ2

That’s what happened in 2013 when Shafigh Nategh, Ph.D., completed his doctoral thesis at KTH Royal Institute of Technology in Stockholm, Sweden, in its School of Electrical Engineering. Nategh studied the thermal management of high-performance electrical machines and had seen a talk on LORD Corporation’s highly thermally-conductive, electrically-insulating silicone material, SC-320. For his thesis, he designed an oil-cooled permanent-magnet motor and compared the performance of identical motors when they were simply varnished, impregnated with a standard epoxy called Epoxylite or impregnated with SC-320. 

In short, hot-spot temperatures for the motors using LORD Corporation’s SC-320 material were 34.8 to 40 percent lower than the motors using varnish, and 19.8 to 26.2 percent lower than the motors using Epoxylite. Those results imply far-reaching benefits for electric motors using a thermally conductive material like SC-320, including increased horsepower, smaller/lighter-weight motors, and improved motor lifetimes and efficiency. 

LORD Potted Motors PQ1

Once LORD got wind of Nategh’s findings, it noticed the opportunity to move into the electric motor market in the aerospace and automotive sectors. Now the maker of the material,which was not originally designed for electric motors, is beginning to further validate Nategh’s conclusions with its own tests, as well as courting partners in the EV world to work on even better materials that can provide greater efficiencies for the motors. 

 

LORD Potted Motors 

 

Simmering down

LORD Corporation was founded in Erie, Pennsylvania in 1924, but now has dozens of offices in many countries around the world. In its early years, LORD had much success selling engine mountings to automakers, but since then it has expanded to encompass hundreds of business-to-business products, including adhesives, coatings, motion-management technologies and magnetically responsive products. LORD Corporation’s SC-320 thermal conductivity silicone encapsulant was designed for electronic encapsulating applications, but was never targeted specifically for electric motors. 

“This material is state-of-the-art, but it’s been around for a long time,” said Jim Greig, LORD’s electronic materials global sales and marketing manager. “It’s been used in thermal management applications, such as AC-to-DC converters. We’re seeing some success in charger applications as well. It’s not a material we developed for a particular application; it’s a material that adds value to an application – anything that sees extreme temperatures, harsh environments or chemical spills.” 

LORD Potted Motors PQ3

Dan Barber, Ph.D., staff scientist in LORD Corporation’s Open Technology Innovation Group, now works on further validating Nategh’s research and finding ways to improve SC-320’s properties specifically for electric motors. “[Nategh] designed a motor that was cooled by a liquid circulating through the housing of the stator,” Barber said. “He impregnated the coils and the end windings with a vacuum-potting operation using SC-320, which acted as a bridge between the coils – which are the hot spots in the motor – and the housing, which was cooled. To ‘impregnate,’ you put a form around the motor. You evacuate that to get the air out. Then you introduce the material under vacuum, and you even apply a little bit of pressure to force it in there. But usually if you’ve got low enough viscosity, just a vacuum fill is sufficient.”

The Epoxylite that Nategh tested had a thermal conductivity of 0.9 W/m-K, while SC-320 thermal conductivity is more than three times that: 3.2 W/m-K. Nategh tested his different motors using various coolant flow rates, but Barber said that in LORD Corporation’s follow-up tests, the coolant flow rate made no statistical difference. Rather, “the potting material and current made a huge difference, so you can predict how the motor is going to perform based on this.”

LORD Potting Motors

At a current that would cause the varnish-only motor to reach its maximum temperature of 150 degrees C, the motor using Epoxylite heated to 126-132 degrees C – a 12-16 percent improvement – and the motor using SC-320 heated to 106-109 degrees C – a 27.3-29.3 percent improvement. Such heat reductions can result in a much longer lifetime for a motor.

“If you’re familiar with the motor industry,” Barber said, “they say every 10 degrees in temperature you can decrease, you get a doubling of the lifetime. The other way you can go is to ask, How much extra current can I put through this motor to reach that temperature limit? You can put about 26 percent more current through the motor before you expect to reach that temperature [150 degrees C], and current is almost directly related to horsepower for a motor. So you’d expect a 26 percent increase in horsepower with the same motor design. We’re trying to validate some of those numbers by designing our own motors and potting them with various materials in-house. We’re just at the beginning of that project.”

Rather than increased horsepower from the same motor design, a thermal management material like SC-320 could enable smaller, lighter-weight motors to achieve the same horsepower as larger, unpotted motors. In any case, decreased heat losses could lead to improved motor efficiency. 

“We’re going to test the efficiencies and some of these assumptions about current and temperature,” Barber said. “These motors won’t be oil-cooled, so we’re interested to see what will happen with a more typical motor that doesn’t have any active cooling, like liquid flowing through the stator. They’ll be more like cooling fans – just air blowing on the motor.”

Of course, if SC-320 can provide such a cornucopia of benefits for electric motors, it will be up to OEMs to mix and match the resulting efficiencies as they see fit. If cost is the biggest factor to an OEM, decreased motor sizes and cooling demands could help reduce overall motor cost. 

“We’re trying to give performance to these high-end vehicles,” Greig said, “and we’re weighing the cost. That’s important because we want to drive mass adoption. Not everybody has $120,000 they want to spend on an EV.”

 

Conductive expansion

Besides designing motors to perform their own tests to validate and expand upon Nategh’s original SC-320 findings, LORD is also in the process of developing new high thermal conductivity epoxies to match or exceed SC-320’s performance. And it’s planning on developing even higher thermal conductivity materials with lighter weight and/or lower viscosity. By the time this article is published, Barber said LORD would have a prototype of the new epoxy-based material. “Then we’ll be able to offer both a compliant silicone material – a softer elastomeric type material – that has a little bit more vibration damping, and a hard material that’s more like a traditional potting material.” 

LORD Corporation is seeking development partners and early adopters to test prototypes and validate the potential benefits of its thermal conductivity materials for electric motors. “We’ve still got a little bit of work to do in validating all of this data,” Greig said. “If SC-320 really does allow more power out of the same motor, or the same power out of a smaller motor, that would be interesting to the EV guys, because they could essentially take weight out of the car by putting in a smaller motor.” 

If all goes well, the EV industry may have a new player on its hands, one with 90 years of experience in the unglamorous yet important space of motion-management technologies. And if or when that happens, it will be due to some synergy created by a greater focus on vehicle electrification. Nategh went searching for an EV solution, and may have found it outside of the established EV industry. 

The famous (or infamous) motivator and human potential advocate Tony Robbins has an applicable saying: where focus goes, energy flows. Synergy and energy – both derive from the Greek word ergon, meaning “work.” We think the case of LORD Corporation’s SC-320 material shows that the more people who focus on the EV – or any – industry, the better that industry will work. 

 

This article originally appeared in Charged Issue 14 – June/July 2014