A British inventor has patented the design of a form of switched reluctance motor which, he claims, will have an efficiency of more that 100% - thus apparently defying the laws of physics.

The inventor, Dr. Harold Aspden, has not built his machine but asserts that several similar motors have been constructed elsewhere in the world and that one, built by a New Zealand engineer, has demonstrated efficiencies of more that 600%.

Dr. Aspden an F.I.E.E. and electromagnetism scientist, spent twenty-three years years working as a patents expert for IBM before taking early retirement to become a senior research fellow in Southampton University's electrical engineering department. He submitted his patent application in 1989 and it was granted this April.

Aspden says the main reason he has not built a practical example of his motor is that he has been concentrating on another invention, a highly efficient form of thermoelectric generator (see below). Now retired from his University post, he is looking for a commercial partner to help build the motor. He thinks a prototype will cost up to UK30,000pounds to construct.

Aspden describes his machine as an "over-excited" switched reluctance motor. It operates in a region of the B-H magnetisation curve beyond the "knee" (see diagram). This area is usually avoided by motor designers because, being close to that saturation point, it is traditionally associated with heavy losses.

But Aspden claims that when operating in this region, the intrinsic power of the ferromagnetism in the motor's core laminations supplies an amount of energy B&H for every unit of energy H&B fed in by the power supply. " If the reluctance motor takes the energy off mechanically as the poles come together with B increasing, and the magnetisation is then switched off before the poles separate, the energy B&H is not returned from work done by the poles and there must be cooling, " Aspden explains.

The apparent extra energy comes from tapping into the ambient heat energy, says Aspden. According to his interpretation of the B-H curve, the "free" energy represented by B&H can be seven times the energy H&B.

He points to the work of New Zealand engineer Robert Adams, who claims to have built several machines operating on a similar principle in the past twenty years. Adams, a former Chairman of the New Zealand branch of the I.E.E.E., asserts that his "pulsed electric motor generator" has achieved an electrical efficiency of 690%. and a mechanical efficiency of 620%. Moreover, unlike a conventional motor, it does not become hot while running, he claims.

Earlier this year, Adams published an article on his motor, including do-it-yourself constructional details, in an Australian magazine. According to Aspden, some - but not all - experimenters who have built an Adams machine from these plans have replicated his results.

Aspden claims that his machine is a more rigorously engineered version of the Adams motor, and can operate as a motor or a generator.

Although Aspden says his machine does not contravene the First Law of Thermodynamics - that power output must balance the amount of heat input - it does defy the Second Law - that heat must flow from a hotter to a cooler body. "Sadly, this law has had its day" he asserts, "because one can conceive of a self-acting machine that, operating continuously, can take heat from a cold source and convert that heat into mechanical work which one can cause to go to waste at a higher temperature."

*A switched reluctance expert has told Electrical Review that Dr. Aspden's claim of more than 100% is "clearly not on". He believes that the Aspden machine may work in a similar way to a heat pump to obtain a greater mechanical output than the electrical input. "He may be taking energy from the surrounding ambient or some other source," the expert suggests. "It would be a tremendous benefit if you could get a machine to cool itself as it works." He adds that reluctance motor designers do have experience of operating "beyond the knee" and that Aspden does not appear to consider I²R or eddy current losses.