Garden solar project

I have a shed in my garden and I had the thought to use my caravan 12 volt leisure battery positioned in the shed to light the LED lights on and around it using its high energy capacity. Each LED light in its housing would be connected via light twin telephone like cable to the shed and the associated solar cells and electronic circuits would no longer be needed.

Wiring the LEDS this way would allow a single dark detecting circuit to trigger all the LEDS and would allow them to be turned off by a timer not long after midnight. The 12 volt battery supply would be too much for the LEDS and so in addition to a 12 volt timer I bought a buck converter that would take the energy from the leisure battery at 12 volt and convert it to energy at a suitable LED supply voltage. The pair cost me about £10.

These buck converters have an adjuster on them and a read out that shows the output voltage. I used it to establish for each LED its forward voltage (the voltage at which it was barely lit up. Then using my multimeter in series with each LED I raised the voltage until the LED delivered a suitable output light and recorded the current in milliamps the LED consumed at that light level and noting the voltage at which it did this.

The highest voltage and current was required by a string of 5o parallel connected LEDs. It was 2.9 volts and this became the output voltage for the “in circuit” buck converter. The other LEDS would need dropper resistors to deliver the previously established desired current. Those resistor values were calculated as follows –
R = (2.9 – Led Forward Voltage) / desired LED current

I joined several of the discarded solar panels in series and positioned them facing good light on the shed roof used them and used them to charge the leisure battery. However in mid winter the limited daylight meant the battery was being mildly discharged each day and it required a recharge after about three weeks of operation. This discharge time improved as daylight hours extended and now in April it would appear that the solar cell input is sufficient to maintain the battery in a charged state.

I may at some stage purchase a solar panel specifically for leisure batteries and wire it in parallel with the existing using switches that I can set to double the winter charge.

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