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solar garden light Answered

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.

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Downunder35m

2 years ago

For obvious reasons it would be best to use a LED that has a build in regulator that allows a wide input range for the voltage - but they are quite hard to find.
So you most feasable option would be to use a LED driver that gives you the 3.4V you need but will accept 10-15V as the input, a 12V max will do too.
LED drivers are easy to find on Ebay, just search for the right output voltage - if in doubt you might have to replace the LED as well and use something that works good together.
The rest of the setup should almost work as planned but you have to calculate your power requirements to get the max runtime for your light.
And double check that the charge controller has undervoltage protection so the battery won't be drained completely.
For Li-Ion batteries you will need a suitable charger, I doubt your solar controller alone will do it as they are designed for lead acid batteries.
Either change the battery type or get a charge controller that is suited for the Li-Ion batteries.
Keep in mind the panel only supplies around 250mA, some will be lost to the charge controller so you need a much longer charging time than what the LED needs to deplete your battery.
With the driver the LED will use something around 180-200mA on 12V.
In the winter months you might struggle to keep it working as planned.

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eartonDownunder35m

Reply 2 years ago

Thank you for taking the time to reply. I have checked and the solar controller says its designed for the following types of battery

More compatibility with a variety of storage batteries such as 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.
Prevent storage battery being overcharged, over discharged and back discharged at night and it also has PWM flating- charged protection.
Could I ask what type of battery you would recommend for this application? Also from what you have said I would be better finding an 18V 10W panel to give 500 mA.

Having not bought the led yet, I will follow your advice and get the led and driver together

The plan was to have the light come on at dusk and run for no more than 4 hours each night. Again thanks for your time, its much appreciated

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Downunder35mearton

Reply 2 years ago

The controller supports the batteries, so you only need to calculated if the LED can run 4 hours on them without discharging the batteries too much.
But you wanted to run on 12V, the controller won't support that from your post.
Get the mix right first so you know what voltage you want to use and select the parts accordingly.

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eartonDownunder35m

Reply 2 years ago

Sorry if I am making hard work of this and thanks for your patience. I think I have now settled on parts which should work. I dont necessarily need 12V so instead I am looking at a 3.7V 4000mAh Li-ion battery. If the led uses 200mAh this should be sufficient for 4 hours a night. The controller says that it can take up to a maximum of 18V 40A solar panel so the 18V 10W one which I was looking at should be ok. Thanks again