3W solar garden light help.

[earton]

Hi I am new to the forum, am ok at basic electronics and just wanted a little advice on my new possibly ambitious project.

I would like to make a 3w solar led garden light to illuminate small tree. I was going to use an 18V 5W solar panel (Peak Voltage: 17.2V Peak current: 0.29A Open circuit voltage: 21.6V Short circuit current: 0.33A) to charge a 12v battery (Capacity : 4800mAh Rechargeable Li-on battery Input voltage : 12.6V Output voltage : 10.8~12.6 DC Output current : 1 - 2.4A) . I have found a charge controller which I think will do what I want (3A 6v/12v PWM solar panel light controller battery charge regulator http://www.banggood.com/3A-6V-12V-P...ry-Charge-Regulator-Intelligent-p-997571.html)
The led I was going to use is 3W Voltage: 3.4-3.6V current: 600MA.

I know I will need a voltage regulator to get me to the led forward voltage, but other than that does this look possible? Would an led driver be required? If there are any parts which someone would advise changing I am very happy to take advice, any help very gratefully appreciated.

 

[Gryd3]

Hi I am new to the forum, am ok at basic electronics and just wanted a little advice on my new possibly ambitious project.

I would like to make a 3w solar led garden light to illuminate small tree. I was going to use an 18V 5W solar panel (Peak Voltage: 17.2V Peak current: 0.29A Open circuit voltage: 21.6V Short circuit current: 0.33A) to charge a 12v battery (Capacity : 4800mAh Rechargeable Li-on battery Input voltage : 12.6V Output voltage : 10.8~12.6 DC Output current : 1 - 2.4A) . I have found a charge controller which I think will do what I want (3A 6v/12v PWM solar panel light controller battery charge regulator http://www.banggood.com/3A-6V-12V-P...ry-Charge-Regulator-Intelligent-p-997571.html)
The led I was going to use is 3W Voltage: 3.4-3.6V current: 600MA.

I know I will need a voltage regulator to get me to the led forward voltage, but other than that does this look possible? Would an led driver be required? If there are any parts which someone would advise changing I am very happy to take advice, any help very gratefully appreciated.

Consider charge / discharge times.
The 5W Panel in a perfect world will store 60Wh in a 12-hour day of sunlight.
This 60Wh will be used up in 20-hours by a 3W load... So... it looks fine so far! Lot's of head-room.

The charge controller looks decent to begin with as well.

Only thing I would correct right away is that you don't wand a 'Voltage Regulator' for your LED... you want a 'Constant Current LED Driver' .
The forward voltage on an LED is a side-affect . This is what 'usually' forms across the LED when driven at the rated current. That's why the Forward Voltage is given in a range. A constant current driver will be the best thing for the LED and will auto-adjust it's voltage to ensure it does not force too much current into the LED as the environment changes or parts warm/cool.

 

[Alec_t]

The battery is presumably a three-cells-in-series one and will need special charging/discharging control to avoid fire or explosion and to keep the cells balanced. So a dedicated charger/balancer will be required. The one in the link doesn't seem to have any call balancing ability, since there are only two terminals for battery connection. It is unclear whether it is suitable for a 3-cell Li-Ion battery.

 

[earton]

Thank you for your replies, much appreciated. A Li-ion battery seems to be the wrong choice for me, and makes things more complicated. The charge controller says its compatible with the following VRLA battery, gelled electrolyte (GEL) Battery, 3.2V x 2 iron-phosphate-based lithium batteries 3.2V x 4 iron-phosphate-based lithium batteries, 3.7V x 1 iron-phosphate-based lithium battery. Could I ask which you would recommend? Having not bought any parts yet I will get an led with a driver as suggested. The charge controller can switch the power off after a set amount of time, I would be asking for less than 4 hours after dark falls. Finally, for a little more money I can get a 18v 10w solar panel, is the 18v 5w sufficient of would I be better with 10w. Again thanks for your help this project is a non starter without your invaluable help!!

 

[Alec_t]

Personally I'd go for a small SLA (gelled electrolyte LA battery).

 

[ChosunOne]

I concur with Alec t, a Sealed Lead Acid battery. The advantage of the lithium family of batteries (and most others) is the smaller size and lighter weight of a given capacity, neither of which matter in a fixed location. One advantage of an SLA battery is that it's easy to charge--low voltage and no arcane protocol to determine state-of-charge. Another advantage is the low cost for a quality battery.

Just to put in my two cents' worth on Gyrd3's ;calculations though, you should adjust your numbers to reflect the amount of sunlight you actually get in a day, for every season you plan to use the light. He prefaced his tabulation with "In a perfect world", but you'd better figure on making it work in the world it's being designed for--this one. I don't know any place in the UK where one can count on 12 hours of sunlight every day, even in midsummer.

If you want the light to be reliable all the time, don't figure on averages for sunlight: Figure for those 3-or-4 day periods you get little or no direct sunlight, if it's like that where you live.

 

[earton]

Thanks for your replies, I will follow the advice given. As you point out there is more chance of sewing air than getting 12 hours of sun in the UK (at least where I live)