131Views17Replies

Author Options:

Which Circuit Is Best To Use? Answered

I am trying to configure a LED circuit that allows me to charge 1.2v batteries using a solar panel. But i also want the solar panel to be used as a light sensor(detector) so during the day it charges..then at night the battery kicks in and lights up my LED strips. This is my first upgraded version using a schematic software.. Please help.

Should i add 2 indicator LED's to let me know when the battery is being charged and when the battery is in use?

I attached two images..one containing a LM317T and the other without. Just need some advice! Thanks



21 Replies

user
icengBest Answer (author)2015-03-08

First one assuming the red led fwd voltage even lets current flow. You may have to reduce the led count.

Select as Best AnswerUndo Best Answer

user
islandboii242 (author)2015-03-08

Ok what if im using a LED Strip of lights...the strip contains about 60-80 LEDS?

Select as Best AnswerUndo Best Answer

user
iceng (author)islandboii2422015-03-09

The strip uses much more current so you need a higher current transistor as the N channel MOSFET.

BUT there is no way you can expect a small solar array to charge an 80 AH battery needed to run the LED strip :-(

Select as Best AnswerUndo Best Answer

user
islandboii242 (author)iceng2015-03-09

My battery will be 1800 mAh 10 1.2v AA batteries. Sorry i didn't Mention this, and the solar array will be 1.25 - 1.5 watts

Select as Best AnswerUndo Best Answer

user
iceng (author)islandboii2422015-03-09

78 led / 3 => 26 groups x 19ma => 500ma @ 12V => 6 watts

1800 mah/ 500ma => 3.6 hours

Your solar cell needs to be bigger and stronger.

Your battery will run out in 3 hours.

Select as Best AnswerUndo Best Answer

user
islandboii242 (author)iceng2015-03-19

I sent you a message in your inbox. What i wanted to know was your schematic does this have the two most important features i need which is:

1. Using Solar Cell AS Light Detector (Photo Resistor)

2. Battery charge protection (so battery doesn't over charge or drains?)

Select as Best AnswerUndo Best Answer

user
iceng (author)islandboii2422015-03-19

As it gets dark base current begins to flow through the solar cell turned into a resistor turning on Q1 which raise the gate voltage about 10 volts which turns Q2 on to deliver heavy current to the LED strip...

Select as Best AnswerUndo Best Answer

user
islandboii242 (author)iceng2015-03-20

Will this still charge the battery?

Select as Best AnswerUndo Best Answer

user
iceng (author)islandboii2422015-03-20

Yes, study the ckt notes.

Select as Best AnswerUndo Best Answer

user
islandboii242 (author)iceng2015-03-21

Designed it in my software and here is your design on left...question about the battery being over drained.

Select as Best AnswerUndo Best Answer

user
iceng (author)islandboii2422015-03-21

Your circuit does not have a resistor to guarantee the mosfet gate is truly at zero and non-conducting discharged when going from dark to sunlight.

Select as Best AnswerUndo Best Answer

user
islandboii242 (author)iceng2015-03-21

ok understood ...if i wanted to add a feature of red and green led to indicate when battery is being charged (red & green) via solar cell and the other led (green) when the battery is now being used after the sun goes down?

Also for the mosfet should i add a heat sink also because this circuit will be running 24/7.

Select as Best AnswerUndo Best Answer

user
iceng (author)islandboii2422015-03-21

I would think the LED strip lighting up would be a good tell of Discharge.

Recommend a 20 amp TO220 transistor

http://www.ebay.com/itm/like/361225892157?lpid=82&...

If 1/2 amp LED strip makes the 20 amp FET hot, put a heatsink on it

Select as Best AnswerUndo Best Answer

user
islandboii242 (author)iceng2015-03-21

ok awesome thanks...this is the final design with pcb..top and bottom layer. Let me know what you think.

Select as Best AnswerUndo Best Answer

user
iceng (author)islandboii2422015-03-21

Could you mean over charged ??

over drained means over dis-charged..

For over charging add resistance in series with charge path.

I worry more about not turning the mosfet fully on.

Select as Best AnswerUndo Best Answer

user

Your LEDS are probably ~12W. you need more than 12 hours of light for each hour of operation.

Steve

Select as Best AnswerUndo Best Answer

user

:-( Looks like i need to redesign...What i am trying to create is a back light sign that uses solar/battery which gets charge during the day and after dark the led strips turn on. But i have a small space to work with for the solar array.

Select as Best AnswerUndo Best Answer

user

There are some changes you could make, by not using off the shelf LED strip, you can eliminate the dropper resistors and make a bunch of LEDs more efficient.

Select as Best AnswerUndo Best Answer

user
islandboii242 (author)iceng2015-03-09

should i also get a higher mah battery?

Select as Best AnswerUndo Best Answer

user
islandboii242 (author)iceng2015-03-09

Ok i will use my original solar panel instead...its a 5 Watts Solar Panel

Select as Best AnswerUndo Best Answer

user
Downunder35m (author)2015-03-08

For less than 5 bucks you can get a solar garden light that has everything you need inside.

Your images show 12V batteries but your text says 1.2V - which one is it??

For 12V you want to use a proper solar charger with automatic shut off and overcharging protection.

Only a few bucks on Fleabuy.

Select as Best AnswerUndo Best Answer