Garden solar project

I have a shed in my garden and I had the thought to put my caravan 12 volt leisure battery in the shed and use it to light the LED lights on and around it using its high energy capacity. Each LED light in its housing and strings of led lights would be connected via light twin telephone like cable to the shed. The existing solar cells and electronic circuits of the bought LED lights would be surplus to requirements.

As the project developed a wiring arrangement like that below developed.

Wiring all the LEDS to the same supply would allow for a single dark detecting circuit to switch on all the LEDS at the same time. A timer could be used to make the supply available from early afternoon and turn off the LED’s about 1 a,m, Clearly the 12 volt battery supply would be too much for the LEDS and so in addition to the 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 two items 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 barely lit up). Increasing the voltage above this forward voltage will brighten a LED. Using my multimeter on its milliamp scale and in series with each LED or LED string I raised the voltage until the LED delivered a suitable output light. I recorded the current in milliamps at this stage as well as the voltage at which it did this.

The highest voltage 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 for each LED or LED string 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 and used them to charge the leisure battery. At this mid winter time of year limited daylight meant the battery was being mildly discharged each day. The leisure battery required a recharge after about each three week period of operation which was acceptable. This discharge time extended 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.

Below a photograph taken by my son John of the bottom of our garden

I may as next winter approaches purchase a solar panel specifically for leisure batteries and wire it in parallel with the existing series panels. I can add switches, if need be so that battery charge arrangements are appropriate to the time of the year and the energy needs of the system. .

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