I recently found some post style solar garden lights i like a lot. They are much heavier and look mode durable then the ones i have been using for years which i am retiring.
They work with a single 2000mAh 18650 and are quite bright, however they don’t last as much as i would like. So i’m thinking of lowering a bit the output to extend their runtime by adding a resistor before the led - the easiest mod probably.
Would that work and what possible value or range (Ohm) should i try?
PS: i will also try to use higher capacity cells but that will only be of benefit if the solar panel can fully charge it over a sunny day, which i don’t know.
Its possible these have some sort of current limiting driver or resistor already installed which limits the output. If you can post a clear close up pic of the driver or pcb board that’s installed would help in finding a solution to lower the output.
I took it apart and took a couple picture, but i can’t host them right now (domain name issue). There is very little to see: a tiny PCB with an 8 pin IC that is probably dealing with the solar panel, charging and switching to night mode… and what may be a resistor, all surface mounted. I don’t want to touch at that as i haven’t the tools and the skills… and i’ll need to do the mod on possibly dozen of lights.
Could you give me a hint as to whether simply adding a resistor on the led path would work?
There’s probably a current limiting resistor already there. That’s the reason a pic would help. Do you see a resistor with a marking starting with the letter R.
Like R500 or R250. But it really does help to see the circuit to know if we are changing the right one. It could have one that limits charging current also. The old saying a picture is worth a thousnd words applies here .
Pictures will have to wait…
There is a “R1” printed on the PCB beside that component which is labeled “203”.
I don’t want to change it, just add some resistance.
The IC is labeled “JD1480” and “1806”.
100%. I tested one and it came out 1900+mAh.
What’s so odd about it? It is most certainly cheap but the solar panel is quite small and i’m not sure it can provide 2000mAh on a sunny day. The light itself is supposed to output 50 lumens which must be around 300mA - not a huge current. The light is spec’ed to run “up-to” four hours. This cell may be plenty enough. I’ll try a better one for sure.
You can try just adding a resistor in series with the led, Im not sure it will work if it already has some kind of current regulating circuit.
Its possible it could let the magic smoke out if it does. But if you want to try and see use this calculator to find the resistor to current you need. http://ledcalc.com/
A single white led should have around a 3 volt v-drop, a guess not knowing the led used.
A quick calculation for 200mA under 4V outputs 5 ohms. Now i know in what range i should test. I may even try with a pencil lead before ordering components.
Just keep in mind by using a simple resistor to limit current, as the voltage drops from the battery so does the current and the lumens.
At 3.5v battery voltage and using a 5 ohm resistor the led will see around 100ma and the lumens will decrease to about half.
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