Hydrogen, magnetics cool compact power relay

Contrary to what you may first think, hydrogen gas and electrical arcs do mix, resulting in a small, high voltage relay. Here's the why and how.

Electrical power generation is shifting from ac applications because of the rapid growth in dc systems, such as larger capacity uninterrupted power supplies (UPSes), fuel cells, motor controls, and 42V (up from 14V) vehicle applications. But designing power relays, which deliver and remove this energy, presents design engineers with a dilemma: these higher voltages require greater relay contact gaps (more distance between conductor ends) to break the arc when the device opens. "The name of the game is breaking the arc," according to Omron Electronics Product Manager Steve Massie.

But vehicle applications are space critical and cannot accommodate industrial-sized units on the order of a 4-inch cube. "A hybrid electric vehicle (HEV) requires three of these type relays," Massie notes. Full electric vehicles will require even more relays.

Omron's new compact (1.43 x 1.85 x 2.65 inches) G9EA dc power relay resolves these conflicting requirements with some clever engineering. First, the twin contacts are housed in a hermetically sealed chamber containing pressurized hydrogen (see figure). Counter to the usual thinking about the gas' flammability (i.e. Hindenburg syndrome), the pure hydrogen quenches the arc to help break it. By cutting it off, "The gas doesn't let the arc get hotter," notes Massie. As for the seal's integrity against leakage, "Life testing has shown no issues," he adds, and the sealing meets military (MIL) standards.

In addition, magnets to the side of each contact serve as "blowouts" which further extend, or pull, the arc apart to cut heat generation. And counter to intuition again, the contacts themselves are softer silver alloys than the type used in conventional industrial relays, resulting in longer contact life because they better conduct heat away. The contact gap is proprietarily small, which reduces noise because the velocity of the contacts traversing the gap cannot build over the short travel distance. Using a straight-line motion solenoid actuator, as opposed to a pivoting armature type, to break contact also cuts down size. For applications 100V and under, Massie reports just the magnetic blowouts may handle the operation.

The G9EA's rated load is 400V dc and rated current is 60A, with a power consumption around 5W. Electrical endurance is 30,000 operations, minimum, at 400V dc and 30A. Specific applications include chargers for batteries and master shut-offs in hybrid and electric vehicles.