For some time now my car charger has been linked to my solar panels so that it automatically turned on when enough surplus solar power was available enabling me to charge my electric car for free. This has helped me get up to an average of 70% of my generated electricity being used my me rather than export to the grid.

The latest refinement is intended to help me increase that beyond 70% while charging the car more quickly and reducing my use of bought electricity.

Variable rate charger

The new refinement allows the charger to switch between 0, 6, 10 and 16 Amps rather than simply off/on between 0 and 6 Amps. I needed a new case to get all the bits in, but the main technical difference is the use of a Programmable Logic Controller (PLC) to determine the desired charge rate.

The PLC is programmed from a laptop via a USB lead to create a programme in ladder logic which combines inputs (currently export threshold and contactor closed) with timers to switch on one of four different outputs corresponding to the four different charge currents (0, 6, 10 and 16 Amps).

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