Eccentric vs Concentric Rotor Design

Which Rotor Design Delivers Better Separation in an Eddy Current Separator

An eccentric rotor design generates greater separation force than a concentric rotor design because its magnets sit off-centre, concentrating the magnetic field precisely where material leaves the belt. Concentric rotors spread the same field evenly around the full 360° of the head drum, which weakens the field at the point of throw. This is why Magnapower builds every Eddy Current Separator with an eccentric rotor as standard, it’s the design that delivers the strongest, most consistent repulsion force.

If you’re specifying or upgrading an Eddy Current Separator, the rotor design sitting inside the head drum is one of the most important, and most overlooked, decisions in the whole machine.  It determines how much separation force you get, how well you recover, and how easily ferrous contamination clears the belt. This guide breaks down the difference between eccentric and concentric rotor design and explains why it matters for your recovery rates.

What Does Rotor Design Actually Do?

Every eddy current separator works the same basic way: a magnetic rotor spins at high speed inside the head drum of a short belt conveyor. As non-ferrous metal pass over the rotor, the rapidly alternating magnetic field induces eddy currents inside them. Those currents create an opposing magnetic field, which repels the particle forward, away from the rest of the material stream and into a separate collection zone.

The strength and shape of that magnetic field is strongly influenced by where the magnets sit inside the rotor. That’s the difference between an eccentric and a concentric design, and it changes everything downstream of it.

Concentric Rotor Design

In a concentric rotor, the magnetic core sits in the centre of the shell, with an equal gap between the magnets and the outer drum surface all the way around. Because the magnets are evenly spaced from the shell across the full circumference, the field strength at the belt surface is spread out rather than concentrated.

Characteristics of concentric rotors:

• Magnetic field is distributed evenly around the full 360° of the head drum
• Field strength at the belt surface is comparatively weak, since the magnets sit further from the material at every point
• Pole position is fixed and cannot be adjusted to suit different material sizes
• Mechanically simpler, with fewer moving parts than an eccentric assembly
• Tends to hold ferrous contamination against the belt for longer before it discharges, increasing the risk of belt and rotor wear

Concentric designs can suit coarser, larger, high-conductivity material where raw separation force matters less than mechanical simplicity. But that even spread is also the design’s biggest limitation: the field is never concentrated enough in one place to maximise throw distance, and smaller or lighter particles (those that are hardest to recover) often don’t get enough force to separate cleanly.

Eccentric Rotor Design

In an eccentric rotor, the magnetic core is mounted off-centre within the shell, so it sits close to the drum surface on one side only, typically across the top quadrant, where the material actually crosses the rotor. Instead of spreading magnetic energy around the entire head, the field is concentrated into the exact zone where separation happens.

Characteristics of eccentric rotors:

• Magnetic field is concentrated over the working area, rather than spread across the full circumference
• Delivers a stronger, more focused separation force at the point where material leaves the belt
• Pole position can typically be adjusted, allowing the field to be tuned to the material being processed
• Field falls away sharply outside the working zone, so any ferrous contamination clears the belt faster, reducing wear on the belt and rotor

The trade-off is mechanical complexity. Magnapower’s view is straightforward that added engineering is worth it, because separation force and recovery rate are what actually determine plant performance and revenue.

Why Magnapower Builds Every Eddy Current Separator With an Eccentric Rotor

Every Magnapower Eddy Current Separator, from the ECS600 through to the ECS2500, is fitted with an eccentric rotor as standard. We don’t offer concentric as an alternative, because in our engineering experience it simply doesn’t compete on separation force, and separation force is what drives recovery rate, purity, and return on investment for our customers.

Pairing the eccentric rotor with our proprietary, non-deteriorating Rare Earth Neodymium magnet system means the concentrated field doesn’t just start strong, it stays strong, throw after throw, for the working life of the machine. Combined with a high-frequency rotor and variable-speed conveyor, this is what allows Magnapower ECS units to hold consistent purity across demanding streams like WEEE, shredded scrap, incinerator ash, and dry recyclables, down to particles as small as 1–2mm on our Superfines range.

If maximising non-ferrous recovery is the goal, the eccentric rotor isn’t just the better option. It’s the only one we’d put our name to.