My first LED project :D

[HarveyH42]

Unfortunatly, I'm not sure where else to get this thing :s . I guess I could always check to see if some place like PartsSource or Candian Tire had it, seeing as how it's for trickle charging batteries but... If they don't I will have to go with ebay , in which case I'd like to be sure that the one I linked to is exactly the right specs adn all which... It looks like it is.

Again, about solderign to styrofoam-- that should be fine right? The solder won't ignite the foam or anything will it?

You can't be serious. Not sure if it will burst into flame, but some chance that it will. You'll find it will melt quite easily, and the fumes are toxic. Figured somebody ought to say something, before anyone gets the wrong idea. It's a very bad, and potentially dangerous idea.

Something else that might be a problem, do you plan on making this automatically turn on at night. There was a recent thread about a dark activated switch. If you plan to just use a manuel switch, and only use the light as needed, you might risk over-overcharging the batteries (might take several days). The solar yard lights seldom fully charge the batteries in one day, but completely drain them every night. Just something to consider. I don't know if a solar panel could damage the batteries in your setup, or what would happen if does. All my little solar toys are automatic...

 

[mike_302]

OK.. scrap the foam idea for now... Haha, I'm still trying to put this together in my head...
solar cell cathode ---> resistor (to take 12V down to whatever)---> batteries connected how?(series, parallel?) ---> batteires connected to 6 pairs of LED's, each pair connected in series, the 6 pairs connected together from the battery in parallel ---> anodes of the 6 LED pairs connected to ?????

I'm going to try to draw this up on paper to see if htat helps me.

 

[audioguru]

The solar panel is for a "12V" battery that is really 13.8V. 8 AA Ni-MH cells is only 9.6V. It doesn't matter and the extra voltage will be good for a charger circuit.

The solar panel has a max current output of 150mA. The AA rechargable cells are recommended to have the charging turned off when the cells are fully charged. So you need a charger circuit.

The LEDs have a max voltage of 3.6V so 3 in series need more than the battery can supply. Two in series is a max voltage of 7.2V and a current-limiting resistor of 120 ohms will allow a current of 20mA.
That is one string with two LEDs in series and in series with a resistor.
Connect a few strings in parallel across the battery.

 

[mike_302]

**broken link removed**

That's how I see it going together... But I'm PROBABLY wrong... how wrong am I? Can anyone edit this with paint or something to fix it up?

 

[audioguru]

Your battery is connected as 2.4V.
It is in series with the LEDs which are connected as 7.2V.
They are all in series with a current-limiting resistor.
They are all in series with the solar panel.

The LEDs will glow only when the sun is shining on the solar panel and the battery will never power the LEDs.


You need two LEDs in series and in series with a current-limiting resistor. Make a few strings like that.i They are connected to the battery which is 8 cells in series so they make 9.6V.

Then a charger circuit connects between the solar panel and the battery.

 

[mike_302]

sorry... Where is this 1.2V per cell coming from? I thought they were 1.5v per cell? meaning 8 in series would make 12V if connected in series... Or 3V if connected in 4 series (2 parallel).... ?

 

[audioguru]

Don't just guess, look at the datasheets of AA Ni-MH rechargable cells at www.energizer.com. They are 1.2V over most of a charge.

 

[mike_302]

Haha, I am VERY sorry about all of this... It's probably such a simple circuit and I just haven't done much with circuits in so long that I'm forgetting basic stuff... But I don't want that to stop me.

I'm sorry to ask someone for so much work, so I don't know if anyone would do it but... Could someone take the picture that is below, copy it to a simple program like Paint, and crudely fill in the blanks along my circuit so that it will work properly? I know there wil be resistors, but I'm not sure where, and in this scenario, I upped the number of batteries to 3x 3x1.2v in series in this schematic, making 3.6v series which the ebay page says the LED can handle, but I guess it's up to you guys if you edit this image to add another resistor . Anywyas, if you DO export to paint to help me out, I can't thank you enough... If you just want to describe what would go where, I still can't thank you enough for your patience you have shown so far. Thanks to all!

 

[audioguru]

If you use a solar panel that is designed to charge a 13.8V battery then you shouldn't use a battery of only 3.6V.

The battery voltage drops a little as it is discharged. The LED voltage could be 3.2V or 3.6V or anything in between. You need to have some extra voltage to allow for the changes.

Make it like this:

 

[mike_302]

Ok, I understadn how to wire it that way... The diagram makes sense to me and all, and I shouldn't haev a problem following that BUT... Is there a smal circuit I can purchase to insert in the setup that will automatically stop cahrging hte battery when it is fully charged? Either that or switch the light on automatically when it's dark? If so, where in the line would it go?

See, I can trust your word and build that circuit, but to ME when I read that diagram, I think that what the solar panel is doing (because it's connected to all the LED's before the battery) is that it's turnign hte LED's on AND charging hte battery a tthe same time... I don't doubt you at all, but with my limited experience with circuits, that's what I see that circuit doing... Could you explain to me what it is REEALLY doing? Thanks!

BTW: I'm on my way now to pick up a 1.5 W, 12V "trickle charger" from princess auto. From waht the lady said on the phone, it sounds EXACTLY like the one at Canadian Tire, except she quoted 1.5W... But comes with the same stuff as the canadian tire one so.... We'll see

 

[audioguru]

Hi Mike,
You are correct. My circuit has the solar panel lighting the LEDs then the battery doesn't get charged.

It needs to have another circuit to turn off the LEDs during the day when the battery is charging and turn on the LEDs when it is dark. Use a switch.

It needs another circuit that is an automatic battery charger that stops the charging when the battery is fully charged. Use another switch to disconnect the solar panel when the battery becomes warm from being fully charged.

 

[HarveyH42]

Are 2 watt resistors really needed? (just curious) I've never been to canada, but hear it's just lovely... I figured the 12 volt panel would be relatively cheap, easy to obtain, and flexiable starting point. I wouldn't expect it to reach it's maximum ratings, and unlikely to fully recharge the 9.6 batteries in a single day, if they are drained nightly. Trying to keep it simple. A manuel switch to bypass charging isn't the best solution, too easy to forget to flip the switch to prevent over-charging, if the lights aren't used.

 

[Krumlink]

Here is a solar battery charger

 

[audioguru]

Hi Krumlink,
Your solar charger looks good for a lead-acid battery. This project has a Ni-MH battery that needs its charging current turned off or reduced to a trickle current when it is fully charged.

Maxim-IC have some battery charger ICs that detect a full charge then reduce the current to a trickle.

My new electric RC airplane came with a wall-wart charger for its Ni-MH battery. Boy oh boy did they both get extremely hot when the battery became over-charged. So I added an LM317 current source then when I feel the battery becoming warm I disconnect the charger. The LM317 creates a voltage loss that reduces the max voltage so the battery and wall-wart do not burn up like before. But It is bad for a Ni-MH battery to be continuously over-charging.

 

[mike_302]

Got the Panel: It's the exact same as the Canadian tire one, and the one we've all been talking about.. For $2 less... but the trip to princess auto was worth it! Anyways: Don't know if this means anything, but the package for this solar panel says that it doesn't overcahrge batteries... Don't know if that is true but... If so, it made my life that much easier. If not then...

I can easily add the switch to turn the lights on and off when I want at night, and maybe The Source (canadian Radioshack) has light sensign switches... Otherwise I'll do it manually with a basic switch. But what I STILL have no idea about is "another switch to disconnect the solar panel when the battery becomes warm from being fully charged." Sorry guys but.. I understand what you MEAN, but i dont know what that switch would be called, where to start looking for it, or how to make it if I need to.... Once that part is explained, then I should be good to go!

 

[mike_302]

actually, I'm now reading that a Ni-MH battery is able to dissipate 10% of the energy it's recieving, so--- Assuming the solar panel is giving MAX output (which it wont be but... for hte sake of easier math) of 150mah, And the batteries have a capacity for 1700mah, am I correct in believing that it shouldbe able to dissipate the excess charge if it ever did reach full capacity?

 

[Nigel Goodwin]

Got the Panel: It's the exact same as the Canadian tire one, and the one we've all been talking about.. For $2 less... but the trip to princess auto was worth it! Anyways: Don't know if this means anything, but the package for this solar panel says that it doesn't overcahrge batteries... Don't know if that is true but... If so, it made my life that much easier. If not then...

That's probably because it doesn't provide enough power to overcharge a battery!.

 

[mike_302]

thank you nigel... hence the post I made after.... So, if you're confirming that I won't need something to prevent overharging (because the excess power just dissipates as heat), then maybe I an go back to my other problem about turning on in the dark. How would I make that work? Are there "light sensing switches" that I an easily purhase? Or is there an easier way someone sees going about doing this (other than manually flicking the switch) ?

 

[audioguru]

The package says it won't overcharge a huge car battery.
Energizer, Panasonic and a few other Ni-MH battey manufacturers say that overcharging shortens the life of their batteries and recommend switching to a low trickle charge current when their battery is fully charged.

There are light sensing and switching circuits in these forums. Some work and some don't.
There are websites full of schematics of solar garden lights. Your circuit is different and they would need modification.

 

[mike_302]

I'm assuming though that since my panel IS a trikle charger, I should be fine... To be completely honest, I doubt my panel will charge the battery for more than half a day, and almost never at full power (150mah) So I think it wil be fine, now tht I'm more aware of the subject...

About the swithes for turning it on and off, since you say some work and some don't and even then I'll need to modify it, how am I to go about doing this? Can you point me in the direction of the easiest one?