Thus: 1 Farad is 1 Ampere second per Volt.Īllowing for hours and milliamps: 1 Farad = 0.2777 mAh/V (ie. So therefore, a farad represents the capacitance that would hold one amp flowing for one second. A coulomb is equal to the amount of charge (electrons) produced by a current of one ampere (A) flowing for one second. One farad is defined as the capacitance of a capacitor across which, when charged with one coulomb of electricity, there is a potential difference of one volt. Now based on Farad - Wikipedia (and other web sites I found): I was trying to find the "equivalent" capacitor to a certain size battery (say, 1200 mAh), so that it could run with a certain current drain for a certain time. Let me tell you about my thought processes, so you can tell me where I went wrong. Not too keen on this sentence, for several reasons. I've seen more complex circuits involving transistors, boost converters, buck-boost converters, voltage regulators and so on, but is there anything fundamentally wrong with the above? Testing seems to show that it works OK, in fact in direct sunlight the voltage at the processor 5V pin was getting up to 5.2V. (The reverse current through D1 was quite high at 5V). T = 0.0275 / 0.000006 * 5 (6 ♚ current at 5V)Ī test shows that after 916 seconds (15.3 minutes) the voltage had dropped from 5V to 2.5V which is rather better than predicted, quite possibly because consumption went down as the voltage dropped.ĭ2 limits reverse current flow back from the capacitor through D1 or the solar panel, when there is not enough sunlight. This should power the processor for: Time = E / IV 5.6V is a bit too much for the processor, however the output goes through D2 which would have a forward voltage drop of 0.7V, thus giving the processor around 4.9V.Ĭ1 is a 4400 ♟ capacitor, which can store 0.0275 coulombs of energy. R1 (220 ohm) is designed to current limit the current through D1.ĭ1 is a 5.6V zener diode. My plan is to run my low-power Atmega328P board from it. I have a 6V 1W solar panel from Adafruit: Flexible 6V 1W Solar Panel : ID 1485 : $24.95 : Adafruit Industries, Unique & fun DIY electronics and kitsįor an initial test I am charging a 4400♟ capacitor. It is simple, it seems to work, but have I overlooked something? I've asked about this before, I'm sorry, but I've come up with a new circuit this time.
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