{"id":741,"date":"2012-01-11T05:53:42","date_gmt":"2012-01-11T13:53:42","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=741"},"modified":"2012-03-14T18:55:19","modified_gmt":"2012-03-15T01:55:19","slug":"2012-01-11","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=741","title":{"rendered":"2012-01-11 Solar Joule Thief or Garden Light"},"content":{"rendered":"

\"\"<\/a>I did some experiments a few years ago with a photovoltaic solar cell charging 1 or 2 NiMH cells, and running a Joule Thief after dark.\u00a0 This is commonly known as a solar garden light.\u00a0 I tried to eliminate the drop across the isolation diode, which is about 1 volt for a 1N4148 or a half volt for a 1N5817 Schottky diode.\u00a0 My experiments were somewhat successful.\u00a0 I believe I wrote this up in my watsonseblog, but I haven’t been able to recover it. Click on the schematic a few times to enlarge it.<\/p>\n

The 2N7000 MOSFET is fun to use in a Joule Thief, but requires 2 to 3 volts to turn on the gate, so it normally requires a 2 cell supply or about 2.4V.\u00a0 For a conventional JT, a single 1.2V cell will work okay, but don’t use a 2N3904 unless you want to have reduced light output; instead use a 2N4401 or PN2222A, or BC337-25.<\/p>\n

At first I thought that I had drawn the red LEDs in Fig.1 with the wrong polarity.\u00a0 But then I read the note below, and remembered how they work.\u00a0 The red LEDs are exposed to the sunlight and act like micro solar cells; they generate a small current that puts a negative voltage on the 2N7000 gate, and keeps it turned off during the day.\u00a0 I used them similarly in the other schematics.\u00a0 A red LED is cheaper and easier to obtain than a CdS photocell, and with a transistor to boost the current, can do much of what a CdS photocell can do.\u00a0 Try it if you don’t believe me.\u00a0 It works.<\/p>\n

Back to experimenting…<\/p>\n","protected":false},"excerpt":{"rendered":"

I did some experiments a few years ago with a photovoltaic solar cell charging 1 or 2 NiMH cells, and running a Joule Thief after dark.\u00a0 This is commonly known as a solar garden light.\u00a0 I tried to eliminate the drop across the isolation diode, which is about 1 volt for a 1N4148 or a <\/p>\n

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