Storing Power

Discussion in 'The Projects Forum' started by mapleman555, Mar 27, 2015.

Thread Status:
Not open for further replies.
  1. mapleman555

    Thread Starter Member

    Dec 15, 2014
    56
    0
    I have an idea for a project. I want to power an LED or two with a solar panel. I was wondering about using two (or more) capacitors for the project. The first one to set the flash speed (a typical 555 timer set up) and a second larger one or more to hold energy to keep the flow steady, say when a cloud passes over and the sunlight isn't as strong. This is the panel I am considering http://www.harborfreight.com/15-Watt-Solar-Battery-Charger-68692.html.
    Are there any projects like this on the internet? Would this even work?

    Thanks
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,984
    3,223
    You need a very large capacitor for that, depending upon the circuit current draw and how long the clouds cover the sun.
    Much better and cheaper is to use a few rechargeable NiMH batteries.
     
    cmartinez likes this.
  3. mapleman555

    Thread Starter Member

    Dec 15, 2014
    56
    0
    OK. Would four AAs work? Is there a circuit that I could build that would detect when the light is low and the batteries need to kick in? I have some photoresistors if that would work.
     
  4. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    A simple Google of Solar Garden Light Circuit will bring up dozens of circuits based on many of the Chinese imported garden lights. Batteries charge under daylight and run the LEDs in darkness. Get yourself some AA size NIMH batteries and have at it. You can get as fancy or simple as you like.

    Ron
     
  5. crutschow

    Expert

    Mar 14, 2008
    12,984
    3,223
    NiMH AA's will store about 2AH so whether that's sufficient depends upon you load and how long you need it to run from batteries.
    But for 12V, which is the rated voltage of the Harbor Freight solar panel, you will need 10 AA NiMH in series since each battery is 1.2V.

    However, if you want to operate at a lower voltage, you could use as few batteries as you like. Four would give 4.8V nominal. The solar panel is basically a current device so it will charge at a lower voltage without any problems. It will actually have a somewhat higher charge current when operated at a lower voltage but the power output will be less.

    For a simple connection just wire the batteries in parallel with the solar panel and the batteries will automatically take over when the sun goes away, no extra circuits needed.
     
  6. mapleman555

    Thread Starter Member

    Dec 15, 2014
    56
    0
    Yes, I have some thing similar on my window sill. It looks like a little lamp that's based on the same idea. You can turn it on or off. I noticed that it says it has one AAA rechargeable battery in it. I can get the garden style ones for a dollar at a local store so I might have to buy a couple, one to dissect.
    There is a local store that specializes in rechargeable batteries of all kinds. I went there once to get some cells to replace in my rechargeable camera flash battery. I think I could find some thing there if I don't use AA or AAA.

    I want it set up so that one or two bright white LEDs can run all night or say 12 hours.
     
  7. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    There is always a trade off with things like this. The brighter and brilliant the LEDs the more current they will consume, thet is a given. So we start by finding LEDs we like for our project and determining how much current they will draw in total. We look at the forward voltage and current for each LED and form a circuit. Once that is known we think about the batteries, their voltage and current. For example if our circuit current is 100 mA and we have a 2000 mAH battery in theory we should get 20 hours out of out battery but in reality we likely won't see that. Then we have the matter of charging the battery, so we need to look realistically at our solar cell. We know a few things about solar cells. To deliver their full rated current and voltage they need bright sunlight, anything less and we get less. So we start by selecting our LEDs and getting LEDs that include a good data sheet.

    Ron
     
  8. mapleman555

    Thread Starter Member

    Dec 15, 2014
    56
    0
    Thanks for the help every one. I'm new at this electronics thing and am having a lot of fun with it. It sounds like I need to do some math before I buy all the parts for this project.
     
  9. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    Yeah, every good project begins with a blank sheet of paper and a sharp pencil. Most of my sharp pencils also have good erasers too! :) As things move along just keep returning to this thread and ask questions you have. Don't hesitate to ask.

    Ron
     
  10. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    I think you might get away with two good AAs but four would be more likely to do the job. I've seen a solar light with a single AAA, with a low capacity rating, still be lit in the morning. But it's more typical for them to poop out after a few hours. Since you want two bright LEDs and a full 12 hours, you'll need the extra capacity.

    Those solar light circuits can usually light two LEDs in parallel (handle more load current) and they can work with two cells in series (handling higher voltage). I've never run one for a long time this way, but I was surprised to see they were fairly robust this way.

    Solar lights use a boost circuit partly so they can get away with using just one cell while still getting enough voltage to overcome Vf of the LED. If you can go to a higher battery voltage, the boost circuit may not be necessary. Also, it's been my observation that the PV panel's open circuit voltage is usually about double the battery's nominal voltage. This ensures that charging still occurs under less-than-full-sun conditions without impairing efficiency when the sun is at full strength.
     
  11. mapleman555

    Thread Starter Member

    Dec 15, 2014
    56
    0
    I bought some "Solar Stake Lights" on the way home today. It says they have one AAA 1.2v rechargeable battery that will last up to 8 hours fully charged. It has a single LED. I can start with these and have some fun. Fortunately it looks like the top where the solar panel and every thing is comes off with a couple of screws, less chance of breaking it when I take it apart.
     
  12. mapleman555

    Thread Starter Member

    Dec 15, 2014
    56
    0
    These are the ones I bought http://www.dollartree.com/Stainless...h-Stakes-10-frac14-/p336083/index.pro#details.

    I guess I found the volunteer light to experiment with of the 5 I bought. I looked over at the the bag of them setting next to me on the computer desk it looked like the shopping bag was light up. Sure enough one of the lights some one had taken that tag/barrier that you have to remove keeps the battery from going dead. There is little enough light at the computer to cause it to light up, until I move to the desk lamp then it goes off. So I will set this one in the window for a few days and see how it goes.
     
  13. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    Nothing like experimenting a little. The little creatures are interesting. :)

    Ron
     
  14. mapleman555

    Thread Starter Member

    Dec 15, 2014
    56
    0
    Could I disassemble a couple or three of the solar lights I just bought, take the LED off all but one, hook them together in series to increase the voltage and not use a boost circuit? Each light has a 1.2v battery.
     
    Last edited: Mar 29, 2015
  15. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    The trick is, if there is a trick is to take one apart as you are doing. Then create a schematic of what you have. Garden lights like this are all the same and all different. :)

    Once you have a good representation of what you have on paper then you can figure out what you can or can't do.

    Ron
     
  16. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    If you could do that you's just burn out the LED. You can't do it anyway as these are basically current output switchers and no two units will ever switch together.

    Here's what's inside one recent unit: http://forum.allaboutcircuits.com/threads/solar-powered-dragon-fly.101962/#post-769008

    The newest ones just use an IC for most of the functions, just needing the solar panel, battery, and a single inductor to drive the LED. Current is controlled by the value of that inductor.
     
  17. mapleman555

    Thread Starter Member

    Dec 15, 2014
    56
    0
    OK, couldn't wait any longer so I opened one of the lights up. It has a YX8018 transistor (does that mean both male and female can use it?).
    Any way, here is an image of it.
    I was thinking of cutting the wires to the solar panels and taking them off the circuits except for the one that would be the main one. I would put them is series (maybe I would have cut them all off, put them in series, then solder them back to the circuit). But as I am writing this I am thinking that the LED could handle the higher voltage but could the batteries? Would the panels to the batteries have to be hooked in parallel to increase the charge rate? Hmmmmmmmmmmm.

    100_0095.jpg
    100_0095a.jpg
     
    Last edited: Mar 30, 2015
  18. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    I'm not following what you are proposing, but as I said earlier you can probably use two panel in series, with two cells in series, and two LEDs in series. This doubles all the system voltages and in my limited testing, the circuitry can withstand it. I never waited to see how long it lasted.
     
  19. mapleman555

    Thread Starter Member

    Dec 15, 2014
    56
    0
    I reread your first post. I didn't read it thoroughly the first time. Right now I am running this all through my head trying to get a handle on it before I start chopping things up.
     
    Last edited: Mar 30, 2015
  20. mapleman555

    Thread Starter Member

    Dec 15, 2014
    56
    0
    Originally I was thinking of a flashing LED light powered by the sun that had a storage area for the less sunny moments. Now I am thinking of a light that will last all night. I think I have more than one project here.
     
    Last edited: Mar 30, 2015
Loading...
Thread Status:
Not open for further replies.