Case study

Challenge

• Kerosene lamps are still commonly used in the developing world despite the numerous financial, health, and environmental repercussions, and GravityLight is a lamp powered by the energy in a falling mass.
• Conducting a rigorous and thorough design process, GravityLight asked if Precision Microdrives could assist them in their attempts to fully characterise their prototype DC motor. After this, we worked together to optimise the performance further.

Solution

• Our team of application engineers worked with the client and performed a number of very detailed tests to characterise the DC motor used in early prototypes.
• We then redesigned the motor core and magnetic circuit, to deliver, after further dynamometer testing, an improved 32mm DC Motor which was installed in Gravity Light’s own testing equipment.

Results

• After rigorous testing, our engineering team delivered an improved motor in the same form factor, but with a higher electrical generating capacity.
• This design went into production and formed the core of their patented gravity light drive.
• With future revisions of the product, we adjusted the motor parameters yet further to support a changing load point.

STAGE 1

Designing for application

• The first step was to fully characterise the motors used in the prototype Gravity Light units.
• The industry standard for characterising electric motors is typically to take measurements at a no-load condition and a nominal loading greater than the rated load.
• However, at Precision Microdrives we have a range of in-house dynamometers with electronically controlled loads. These create dynamic torque loadings at a range of load points. Using these we were able to prepare a very detailed spec as a target starting point.

STAGE 2

Testing

• For this project, we also created a specific one-off testing jig for driving the motors in reverse at very precise speeds and powers.
• This enabled us to understand the optimal load points of maximum electrical power generation.
• We then redesigned the core of the motor, to better match the optimal load point for generation with the available power from the gearbox unit.
• We manufactured a sample run of 32mm motors with a revised core configuration and tested. They worked very well as generators, with 24% more power output.

STAGE 3

Results and relationship

• The output power of the GravityLight might be relatively low (you would need over 20 million of them on the highest power setting to produce the same amount of power as a 2MW wind turbine!) but it’s important to remember it is being used to light only a single room. It does this at a fraction of the cost of a kerosene lamp, with no harmful fumes, and with no cost of fuel. 
• That said, every little helps, and the 24% extra power our motor was able to deliver enabled the LED light to shine brighter, or for the the system to run a bit longer between re-lifting the weight.