Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Outdoor solar Project

Status
Not open for further replies.

T805

Newbie level 6
Joined
Aug 11, 2010
Messages
12
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,394
I have a small project I'm working on. I want to use a solar cell to charge a 1.2V 1000mAh battery. My project will work something like a garden light. But instead of a light, it will output an electric current straight from the battery and work during the day. My Question is, What size solar cell should I use to charge this battery? And I'm not sure what blocking diode to use. Below is a replica of the schematic I want to use for the day time.





I also want to make another one that will work at night. Below is another schematic that includes a photo transistor. Again what size solar cell should i use? And do you think adding another battery would provide a longer cycle without dying?





These are the only questions I can think of for now. Oh, and if you can't tell, I'm completely new to electronics :roll:
 
Last edited:

You may copy the schematics used in garden lamps, see the diagrams attached.

For this type of photo cell peak voltage up to 3.1-3.2V (no load).
Using indirect light the photo cell peak current up to 6-8 mA/1.55-1.6V.
Direct light sun, photo cell current increase up to 40-50mA /1.6-1.7V.
The NiCd element charged at 1.25V-1.3V.
 

Attachments

  • SL7.JPG
    SL7.JPG
    37.2 KB · Views: 53
  • SL6.jpg
    SL6.jpg
    51.1 KB · Views: 41
  • Sl5.jpg
    Sl5.jpg
    38.3 KB · Views: 43
  • SL4.jpg
    SL4.jpg
    30.3 KB · Views: 42
  • SL3.jpg
    SL3.jpg
    15.2 KB · Views: 41
  • SL2.jpg
    SL2.jpg
    60.9 KB · Views: 42
  • SL1.jpg
    SL1.jpg
    79.6 KB · Views: 45

It's a complicated problem. The size of PV cell depends on many things, including how many hours of light and the intensity of the light that falls on it. You are asking for a system that can charge the battery at the same time as produce power for something else, all I can suggest is you carefully analyze all the parameters first, then make a decision afterwards.

I'm guessing here, I don't think there is an math formula to give an accurate result:

1. Work out the load current.
2. Add the battery charging current
3. Multiply by the number of hours per day you need this power. The result will be the number of Watt hours you need from the PV.

Now multiply this by a factor to adjust for the number of daylight hours in the day. This depends greatly on where in the World you are. It can be as short as a few hours up to several months.

Lastly, multiply by a factor to take into accout the efficiency of the system, from experience I would suggest at least 3.

That will give you the size of PV panel you need. It is always best to use a bigger size if possible.

If you are planning to use this for LED lighting, the voltage will be too low, either add another battery or something like "Joule Thief" to make better use of the single 1.2V cell.

The blocking diode is essential, particularly if you use the second schematic. Try to use a Schottky type as it has a lower voltage drop, the current rating should be at least as high as the total current from the PV cell.

Brian.
 

You'll need 4 solar cells (based on the amount I see in my solar-charged garden lights). This is to provide sufficient voltage to overcome the battery, and push a sufficient charging current through the battery.

You may get by with 3 cells. It wouldn't hurt to experiment.

The string of cells should put out enough current to charge your battery during daylight. 150 mA is a reasonable amount for a 1000 mA battery.

In round figures each cell will be about 1x2 inch.

A blocking diode is not installed in my lights. Maybe it depends on the type of cell. You can experiment to make sure whether current flows out of the battery when you don't want it to.

As to needing a second battery, it depends on what load you wish to power. Does it need more than 1.2 V? Then you need two batteries in series.

Adding a battery in parallel will extend 'on' time. To find out if you need to do so, you can make rough calculations based on what current the load draws, and what length of time you want to run it.

By the way, your second schematic has a PNP transistor. Is that where you mean to put a phototransistor?
 

New version schematic for the garden lamps. This time they use a simplified circuit, photo cell missing. We can adapt this schematics to be modified from standard ''Night = ON Lamp’’ to ''Daylight = ON Lamp’’ by removing T2 and some resistors.
 

Attachments

  • SL9a.JPG
    SL9a.JPG
    29.9 KB · Views: 51
  • SL9b.JPG
    SL9b.JPG
    26.5 KB · Views: 52
  • SL9c.jpg
    SL9c.jpg
    49.7 KB · Views: 49
  • SL9d.jpg
    SL9d.jpg
    61.7 KB · Views: 41
  • SL9e.jpg
    SL9e.jpg
    48.4 KB · Views: 49

BradtheRad - in the second schematic, the idea is that during daylight, the voltage dropped across the diode holds the transistor non-conducting. The voltage on the PV cell is higher than the battery voltage when light falls on it. After dark, this 'hold-off' voltage is removed and the transistor conducts. Ideally there should be a resistor between the transistor base pin and the negative rail so it doesn't have to rely on leakage through the PV panel to bias it.

Brian.
 

BradtheRad - in the second schematic, the idea is that during daylight, the voltage dropped across the diode holds the transistor non-conducting. The voltage on the PV cell is higher than the battery voltage when light falls on it. After dark, this 'hold-off' voltage is removed and the transistor conducts. Ideally there should be a resistor between the transistor base pin and the negative rail so it doesn't have to rely on leakage through the PV panel to bias it.

Brian.

Hmmm, I believe you're right.

When the OP said 'photo transistor' I supposed he meant a lamp would shine on it at night, activating power to the load.
 

Thanks for the replies. I had written my post but my internet crashed before i got the chance to post it. So I'm writing this from memory.

@Betwixt - I want the workout load to be about 260mA. According to the manufacturers website, the charging current of the batteries is 200mA x 16h. I would like the circuit to be able to run 10 - 14 hours a day. 12 hours would be ideal.


@BradtheRad - You say add more panels, what if I used a panel big enough to power the batteries? About the PNP transistor, I actually just reread the DIY, I'll include a quote.
"...we use a PNP transistor that is controlled by the voltage output from the solar panel. When it's sunny, the output of the panel is high, which turns off the transistor, but when it gets dark, the transistor lets current flow..."

I should mention the odd thing about this circuit. The circuit won't be powering any type of electronic. The outlet of the batteries will run from wires out to two metal probes (For now the "probes" will be two 9" nails). One negative probe and one positive. But since they can't draw energy by themselves, I figured adding a resistor to the positive terminal of the battery, I could draw 300mA to the probes. Do you guy think this could work? I'm including "upgraded" schematics with my idea of adding another resistor

Sorry if this post is a little confusing. My brain is almost asleep now and like I said before, my internet crashed before I could post this. Thank you guys for your time. Feel free to ask questions if I confuse anyone.

 

@Betwixt - I want the workout load to be about 260mA. According to the manufacturers website, the charging current of the batteries is 200mA x 16h. I would like the circuit to be able to run 10 - 14 hours a day. 12 hours would be ideal.


@BradtheRad - You say add more panels, what if I used a panel big enough to power the batteries? About the PNP transistor, I actually just reread the DIY, I'll include a quote.
"...we use a PNP transistor that is controlled by the voltage output from the solar panel. When it's sunny, the output of the panel is high, which turns off the transistor, but when it gets dark, the transistor lets current flow..."

There are photovoltaic cells...
and there are photovoltaic panels which are made up of a number of PV cells.

You can obtain a panel if you wish. Usually these are listed as putting out a certain voltage and amperage.

Maybe the description will say it is able to charge such-and-such a size battery pack.

The panel you choose should have the right amount of cells in series, which will add up to sufficient voltage, in order to push current into your 1.2V battery.

Then each cell must be large enough, to put out sufficient amperage (say 150 mA), in order to fill up your battery capacity by the end of a day's charging.

If you like to experiment, consider getting the Edmund Scientific Solar Cell grab bag. (Link below) It contains various pieces of crystalline photovoltaic cells. I got one and found several cells that were almost whole and produced a couple hundred mA each. Connecting them is not easy, since they don't take solder well. I attached wires to the tops and bottoms of cells, using either conductive epoxy, or a conductive liquid pen.

Solar Cell Grab Bag | Edmund Scientific
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top