1.5 volt Solar cell to charge capacitor so it can be use

[edwardo]

I have an application For a 1.5 solar cell that can charge a capacitor so it can be used as a 1.5 volt AAA battery Has anyone done anything like this . If you have please tell me what components I would have to use.

[myp71]

You would need a big cap for this and then it still will not last as long as a 1.5v aaa would.
If you are going to use a L.E.D it might last a hour or so depends on the load your using and uf of the cap<p>parts would be a small load (led) resistor and one big capacitor<p>what are you going to run on this cap?

[sundancer87]

Hey Edwardo, if the 1.5volts from the solar cell is the output when it is the 'open output' state you won't get 1.5 volts when you connect it to your capacitor.<p>Your cap will only accept what the loaded output of the solar cell is. This loaded output is considerably lower than when open.

[russlk]

If you get one of those Panasonic "gold" capacitors (1 farad at 2.5 volts), it will last 20 or 30 seconds after the sun goes behind a cloud at 10 mA load.

[jollyrgr]

Edwardo,<p>I'm not sure of your application but in simple terms, yes, you can charge a capacitor with a solar cell. The type of cap Russ Kincaid suggests is available from All Electronics Corp. at http://www.allelectronics.com. See their Catalog # CBC125.<p>It is not as simple as connecting the capacitor, load, and solar cell in parallel. As a minimum you would want to put a blocking diode in series with the solar cell. This will prevent the energy from the capacitor from back flowing through the solar cell when the light stops shining. Since a diode has about a 0.7 vold drop you will want a slightly higher voltage solar cell arrangement if you want the full 1.5 volts.<p>Depending on what you are doing with this setup will determine how long the capacitor will supply a useful amount of energy. In playing with one farad 5.5 volt capacitors I have been able to light three paralleled LEDs for as long as eight minutes. The first four minutes the light was bright enough to read by. But gradually the light dimmed. Unless you are dealing with a REAL small load such as an LCD clock/watch, the capacitor won't last long. Yes, you can parallel more capacitors in order to get longer run times. But it WILL take longer to charge them. I have a suggestion for you that might be more useful.<p>I have several solar "Malibu" lights in my yard that run off of a single NiCad AA cell (1.2 volts). They are charged by a solar cell that is about 1.5 inches square. Some models of solar lights have one battery, others have two. At night the LED lights and provides enough light to illuminate a pathway or see that it is the neighbor's cat on the deck. This setup works great, especially during the summer. On cloudy days in winter when the days are shorter I get about three hours of light out of these per night. But this is significantly longer than what you would get out of a one farad capacitor. In summer easily ten or more hours; but they are quite dim at this extreme.<p>Should you be concerned about size, the entire electronics easily hides under the solar cell. Depending on the brand and model will determine the number of batteries used. The ones I have use a single 900mA-hour battery. Fully charged this will (in theory) provide ten hours of 90mA current. If you are concerned about battery life expectancy, mine are still going strong and are about to see their third winter; over 800 charge/dischage cycles. (Yes, I know that they probably won't make it the entire winter as they are nearing the end of their life.)<p>[ November 02, 2003: Message edited by: Jolly Roger ]</p>

[edwardo]

Thanks for all the help. I am going to have to use a 3 volt solarcell and I am Going to order some of the 1 Farad 2,5 volt supercapacitors from Allelectronics . They are only $1.00 each. I will let you know how it all turns out. If it dousn't work I can always go to Solar cell and nicad batterys. Thanks again you guys are a great help. Edwardo

[desterline]

Watch out with those super caps. They are not the least bit tolerant of overvoltage. <p>A solar cell rated at 3 volts could put out quite a bit higher (5-6 volts not unheard of) in bright light and little load. That's enough to damage a supercap, even through a blocking diode.<p>While a solar cell probably (realy huge ones could, but I don't think your using those) can't put out enough current to boil the electrolyte and explode the cap, supercaps break down internaly. <p>Expose a 1 farad 2.5 volt supercap to 3 volts for a few seconds and it's useable capacity drops to less than half! <p>Whatever works in your application, but you might consider adding a 2.5V zener diode accross the cap to prevent overvoltage.<p>-Denny

[JMaster84]

What are you planing to drive with the capacitor??