My first LED project :D

[audioguru]

Didn't you see my post?
The solar panel is a trickle charger for a huge 13.8V car battery, not for a little 9.6V bunch of AA cells. The life of the little cells will be shortened by over-charging.

A car battery is almost always being over-charged by the alternator much more than this little solar panel.

But since the solar panel is not on the equator of earth at noon and the panel is not always pointing directly at the sun then its current is low so try it.
If the solar panel is behind a window then the battery might not ever be fully charged.

 

[mike_302]

exactly haha. nooow, its just how to setup that switch to work only at night.... Any specifc tips?

 

[audioguru]

exactly haha. nooow, its just how to setup that switch to work only at night.... Any specifc tips?

Flip the switch when you brush your teeth just before bedtime.
Flip the switch again when you wake up.

 

[mike_302]

Remember when I said "easiest method" ? When I was asking for a switch idea... Yaaaaaa... I think that might have been taken a LITTLE too literally, lol. I'm willing to mkae it slightly more difficult.. Even if not a light sensing switch, then some sort of tiny, ITTY bitty clock that switches it on at 8pm, and off at... 10pm... something like that.

 

[audioguru]

Where are you going to find a clock circuit that works with you supply voltage and that does exactly what you want?

 

[mike_302]

i c what you mean.... Ummmm, like i said? Is there a light sensing switch? Or some way that I can have the power turn on once the solar panel stops giving a certain amount of voltage?

 

[audioguru]

When the voltage from the solar panel drops because there is no enough light then a transistor can be made to turn off. Then when the first transistor turns off it allows a second transistor to turn on which turns on the LED.

 

[mike_302]

sounds good. do I need a certain type of transisotr (model number) ? where do the two transistors go?... any other thing i should know about this setup?

 

[audioguru]

You must calculate the current in the transistors then select transistors that are suitable. Then you must calculate resistor voltage dividers for the transistors.

When the output from the solar panel gets low at dark then the first transistor to turns off which causes a second transistor to turn on which turns on the LEDs. My circuit has 8 strings of LEDs at 23mA each so the total current is 184mA through the second transistor.

 

[mike_302]

haha, yikes :s I didn't understadn a single thing in the first line.. Physics tomorrow: I think I'll be askin the teach how HE would complete that circuit if he wanted to have transistors turn it on or off.. Not that your message wasn't helpful, its just that it would probably be easier to understand if I had him draw it in, or show me with the actual transistors...


thanks fo all the help today! I'll message in again later if I run into trouble.
BTW! One other question: Is it unrecommended to touch the treminals together on that trickle charger solar panel?

 

[mike_302]

I put the circuit together on a bread board using a 5V supply (its an advanced board... thats all...) And I didn't include the battery... So what I'm wondering, just to make sure: How does a battery charge? Do you connect to positive end of the power supply that charges it, to the positive end of the rechargeable battery? Just like in audioguru's previous schematic?

 

[audioguru]

DO NOT connect a battery to a power supply. It will explode!

A solar panel limits its output current. A power supply usually doesn't limit the current. Too much current makes a rechargable battery hot which makes a nice big BANG.
If the current is not too too high then the hot battery will vent and spray its chemicals around.

Some lithium rechargable batteries catch on fire if they are over-charged. The power supply will be overloaded so it also might catch on fire.

You need a charging circuit to limit the current and to switch to a low trickle-charge when the battery is fully charged.

I wouldn't short a solar panel. It might burn out.

 

[mike_302]

Helpful info but.. bak to the circuit... I guess the physics teacher is confused because, when I showed him your circuit, and asked how to place the transistors, he looked at it and said he thought that eletrons would flow from the negative of the solar panel, and so he didn't know why it would go to the negative of the batteries but... In my hardware engineeriing class, another guy told me that the physics teacher is thinking about it opposite to how it really is (he said that the way you'd get taught in physics is exact opposite of what you would do in applications like this... I don't understand that but I went with it because When we tested it out, it lit up the LED's... )

Anyways, the way I'm seeing the altered schematic with the transistor on it is this: instead of a positive going aross the top from the solar panel, across all the LEDs, the positive would go striaght across the LED's and not connect to them, but onnect to the battery (which trminal on the battery? the positive or negative?) And out of that connection, the transistor would exist that would switch the flow from Solar Panel To battries to Batteries to LED (with the negative sides of the LED's all connected like in the diagram you sent, still)

Does that work?

 

[Nigel Goodwin]

I guess the physics teacher is confused

I would be VERY surprised if a physics teacher knew anything at all about electronics - and this just proves it!.

I would certainly bet on Audioguru against 99% of physics teachers, or myself against even more!

 

[mike_302]

Oh, I'm sure he's wrong, but he raised a good question to me... Why does the positive terminal from the solar panel go to the positive of the batteries? I'm sure its correct, but I'm wondering: Is that how a battery charger works? Positive of the energy source to the positive of the battery?

 

[Nigel Goodwin]

Oh, I'm sure he's wrong, but he raised a good question to me... Why does the positive terminal from the solar panel go to the positive of the batteries? I'm sure its correct, but I'm wondering: Is that how a battery charger works? Positive of the energy source to the positive of the battery?

Yes it is - and it really shows how your teacher knows absolutely nothing about electrics, never mind electronics!.

 

[mike_302]

well.. he admitted, he didn't know how a charger worked.. HE admitted it straight away so... I'll give him that much. But, now that I know! I can go bak, tell him, and see if he can draw out where the transistors would go... I THINK I know where they would go, but im not 100% sure, or even what model of transistor id use so... If someone could make a diagram of that, or something, id greatly appreciate it! Thanks

 

[Nigel Goodwin]

You don't have your location filled in - but in the UK, never mind Physics teachers, some schools have 'electronics courses'. The only requirement to teach the electronics course is to have attended a single days course - so a school can send an English teacher, a French teacher, a Dance teacher, on a single days course and this qualifies them to teach electronics!.

I think we all probably agree who well qualified such a teacher is, and how well taught the students are going to be!.

 

[audioguru]

when I showed him your circuit, and asked how to place the transistors, ....

Which circuit has transistors? The solar garden light circuit?
The solar panel turns on the first transistor when there is light. It turns off the second transistor which turns off the LED. The diode allows charging current to flow from the solar panel to the battery.
When it is dark then the first transistor is off and the second transistor works as an oscillator and the coil steps up the voltage high enough to light the LED.

 

[Nigel Goodwin]

Which circuit has transistors? The solar garden light circuit?
The solar panel turns on the first transistor when there is light. It turns off the second transistor which turns off the LED. The diode allows charging current to flow from the solar panel to the battery.
When it is dark then the first transistor is off and the second transistor works as an oscillator and the coil steps up the voltage high enough to light the LED.

You've really got to admire the crudity of that circuit!