Scanning for Ideas: A Motor Pump Built for Solar Power

Engineers at Laing Thermotech Inc., Chula Vista, Calif. (lainginc.com), anticipating a sharp spike in interest in solar-powered systems, have designed the Ecocirc DC pump, a circulation pump that can be connected directly to photovoltaic cells. The design is based on a spherical motor, a concept invented by Laing. It consists of a hemispheric rotor and impeller that sits on a hard, wear-resistant ceramic ball. There are no conventional shaft bearings or seals, which eliminates play in the bearings and the resulting noise. The ceramic ball, acting as a self-aligning bearing, is lubed and cooled by the fluid being pumped. And the ball, like all parts exposed to fluid, resists corrosion. The pump does not require regular maintenance, even after lengthy shutdowns, according to the company.

When hooked to a solar cell, the pump is programmed to wait until there is enough power, then aligns itself, turning the rotor to the start position. Then once a capacitor is fully charged, (which takes less than 1 W), the pump starts. This minimizes cycling during unsuccessful starts. Following its programming, the motor controller checks every 3 sec to see if it needs to alter its operating point on the pump’s voltage-current curve to get maximum performance. This coincides with the point at which the pump generates maximum rpm and, therefore, maximum performance.

The electronically controlled motor operates on 8 to 24 Vdc. The pump can generate up to 250 psi with a brass housing, or 50 psi with the plastic version. It can pump hot or cold water and water/glycol mixtures, and be modified for others.