Reasons\u00a0 I have some small 2V solar cells that put out about 20mA when well lit.\u00a0 When I use this solar cell to charge a 1.2V Ni-MH AA cell, I need to put a diode in series with the solar cell to prevent current from the battery from going back into the solar cell.\u00a0 If I use a Schottky diode, the voltage drop should be about 1\/2 volt when charging.\u00a0 One problem I see is that the 20 mA may not xharge the cell fully during the daytime.\u00a0 I’m doing some thinking and calculations to see what may work the best.\u00a0 Right now, I’m considering putting two or maybe more solar cells in parallel to increase the current.<\/p>\n
One thing that concerns me is that when the current passes through a 1N5817 Schottky rectifier for instance, there is that half volt drop across the diode and the losses that it causes.\u00a0 One Idea I thought about is to connect the solar cell directly to a Joule Thief so that it can boost the voltage up to the required voltage, and since it will do the rectification, there will be no diode losses between the solar cell and the rest of the circuit.<\/p>\n
The output of the Joule Thief will be used to supply 4.5 to 6 volts to a wireless FM microphone near the bird feeder in a tree.\u00a0 This is why I need to have the power come from something that doesn’t require a power outlet.<\/p>\n
I built the Joule thief circuit to boost the voltage from the 1.5V AA cell to 4.5 to 5 volts to supply the FM microphone.\u00a0 It is just a joule Thief with the LED removed and replaced with a 1N4148 diode and 33 uF filter capacitor to remove the ripple.\u00a0 After the filter cap I put a 1N5231B 5.1V zener diode across the filter cap to limit the voltage should the FM mic be disconnected. The JT runs at about 87 kHz.\u00a0 I also placed two RF chokes in series with the JT’s DC output to keep the JT’s pulses from going to the FM mic and modulating the RF carrier.\u00a0 I also ran both positive and negative of the JT’s output through a ferrite bead to prevent the RF from going back into the JT.<\/p>\n
The JT puts out 4.8V to the zener diode with nothing connected.\u00a0\u00a0My problem has been that when I connect the FM mic, the voltage drops down to 4.5 volts, which is enough to make the FM mic work, but all of the JT’s output is going to the FM miic, and no current is through the zener because the voltage is below its breakdown voltage.\u00a0 I had figured that a small current, maybe 1 mA, would flow through the zener, with the remaining 4 or 5 mA going to the FM mic.\u00a0 But the FM mic was hogging all the current.\u00a0 So I replaced the FM mic’s 330 ohm emitter resistor with a higher value, 390 ohms, and it cut the current down somewhat.\u00a0 But all the current is still going to the FM mic, with none to the zener.\u00a0 I may have to reduce the 1k resistor in the JT to get it to put out more current.\u00a0 Methinks more investigation needs to be done.<\/p>\n
More experimenting later (Dec 29)…\u00a0 I found that the JT transistor was a 2N3904, which is a poor choice, so I replaced it with a PN2222A.\u00a0 The voltage is still about 4.7 volts across the zener.\u00a0 The FM mic works fine when I connect it to the power supply set at 4.5 volts.\u00a0 I can tune it in at the bottom of the FM band and blow into the mic and it’s loud and clear.\u00a0 But when I remove the power supply and connect the battery to the JT, the voltage into the FM mic is 4.7 volts, and I tune the radio to the bottom of the band ans I gt a horrible buzzing noise, like the microphone amplifier is oscillating at a few hundred Hz.\u00a0 Just what I need: a Fuzz Tone.\u00a0 The buzz seems to be caused by the Joule Thief.\u00a0 From my many past experiences this kind of problem is hard to get rid of because the RF can go back into the JT and cause problems, in addition to the JT pulses going into the FM mic.\u00a0 Once I solved this by separating the RF and power supply by ten feet of wire.\u00a0 The RF apparently radiated off the wires before it got back to the power supply.<\/p>\n
Back to experimenting…<\/p>\n","protected":false},"excerpt":{"rendered":"
Reasons\u00a0 I have some small 2V solar cells that put out about 20mA when well lit.\u00a0 When I use this solar cell to charge a 1.2V Ni-MH AA cell, I need to put a diode in series with the solar cell to prevent current from the battery from going back into the solar cell.\u00a0 If <\/p>\n (Read More…)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[],"class_list":["post-475","post","type-post","status-publish","format-standard","hentry","category-radio-frequency"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/475","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=475"}],"version-history":[{"count":9,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/475\/revisions"}],"predecessor-version":[{"id":1566,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/475\/revisions\/1566"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=475"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=475"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=475"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}