Been carrying some interesting researches into the possibilities of using solar cells and/or rechargables with our Noise Machines the last few weeks. This was sparked off by chatting in one of our Focus Groups at Brighter Sound with Caro C who explained she had previously lived off grid in a bus and ran everything of solar rechargable batteries. We’d begun to use solar cells as both sonic inputs as a light directed battery drains on chips, so as was suggested it seemed like it would be a fairly simple leap to expand this into supplying stable power via solar!
A little bit of initial research showed it was super and pleasingly simple! At its most simple; connect the positive leg of the solar cell to a battery with a diode inbetween, connect the grounds and off you go. The diode is to ensure that the solar cell doesn’t drain power back from the battery once its in the dark. Voltmeter connected up so you can double check the battery is in fact filling up. The only tricky thing here is that the rate of energy generated by the sun in Salford where the Noise Orchestra studio is located is not much more than a trickle on a grey day! (Just as an example: on 15/11/16 battery voltage at 13:21 was 7.5 Volts by 15:25 (2 hours!) it had gone up to 8.2 Volts. This was on a particularily grey day) Interesting though when the sun does peak out the flow of energy does really increase; you could also experiment with brightness of different artificial lights but this obviously defeats a little the SOLAR not drawing from the grid vibe.
One of the more fiddly bits of getting this to work was making sure the Voltage and Amps outputs of the solar cells were matched correctly for 9 volt batteries. The highish voltage for a battery of 9 Voltage is set off against a fairly low ampage of 200mAh. From what I could tell from research the charge up rate from a solar cell would need to be 10% of the total mAh rating. So this meant a pretty low rating of around 20mAh would be needed to correctly supply the 9 volt battery with charge. I went through a whole range of cells of different values staked up (3 x 3 volt with 30mAh, 2 x 4 volt with 40mAH) before finding a 9 volt cell with a low enough mAh rating. In the end the thing that helped was that our splendid Salford weather ensured the amps outputs on the solar cells stayed low enough to supply the 10% rate to the battery. This might well need to be reassessed in British summertime or if the units are to be used in a sunny country!
After this initial success I got excited and on various travels began to design an intergrated circuit in which solar cell chargable battery input and direct solar cell to circuit connection could be switched between both with our now classic potentiometer battery drain available before the final voltage reached the circuit.
Only parts of this have worked in the iterations I’ve tried so far so this continues to be a future development. Below is our first fully working Noise Orchestra 9 Volt battery recharge unit! Housed in a nice old answer phone box. Waiting on the arrival of some zener diodes so then I can add an “hello I am full” LED to them!