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### Topic: Solar charging 18650 (Read 1 time)previous topic - next topic

#### tjones9163

##### Aug 17, 2019, 04:46 pmLast Edit: Aug 17, 2019, 04:47 pm by tjones9163
Hello, I am trying to learn about charging time and what equations used to calculate how long it takes for a solar panel to charge 18650 batteries.
Right now I have a 6v 2w battery, which at most I have been able to get 30ma at 6 v, so not great.

1) How do I calculate MAh with my 6v 30MA panel or current over time.

2) When I go to conduct my experiment what is the best way to tackle it? Should I start with a discharged 18650 at 3.2v and record the time, and after an hour record the voltage? I have a tp4056 charger with a blocking diode to keep the battery from discharging through the solar panel and allow current in one direction.

Below I have pics of my setup, but I plan to use the circular 6v 2w panel with the tp4056 setup from the other picture.

#### slipstick

#1
##### Aug 17, 2019, 05:25 pm
30mA @ 6V is less than 0.2W. Perhaps you need a brighter sun.

mAh means mA times hours. So with 30mA you're would be getting 30mAh in an hour. But how reliable that 30mA is in real life conditions is anybody's guess.

And then how long it will take to charge a battery will depend on what the capacity of the battery is in mAh and how efficient the charger is. But it is likely to be so long that the sun will have gone in (several times). If you're actually relying on the sun then I'd guess between 5 and 10 DAYS from a typical 18650.

Steve

#### tjones9163

#2
##### Aug 17, 2019, 06:31 pm
30mA @ 6V is less than 0.2W. Perhaps you need a brighter sun.

mAh means mA times hours. So with 30mA you're would be getting 30mAh in an hour. But how reliable that 30mA is in real life conditions is anybody's guess.

And then how long it will take to charge a battery will depend on what the capacity of the battery is in mAh and how efficient the charger is. But it is likely to be so long that the sun will have gone in (several times). If you're actually relying on the sun then I'd guess between 5 and 10 DAYS from a typical 18650.

Steve
You are correct they are nowhere near as good as advertised. I bought them  here

Does anyone know where I can get good quality solar panels that are the smaller that are meant for charging phones, any brands, links?

#### polymorph

#3
##### Aug 19, 2019, 03:48 am
Most solar cells are the same efficiency, so there is no such thing as a small panel that will effectively charge a cell phone. I'm presuming you don't want to wait a week for a full charge.

There are a lot of junk solar charging power packs out there. The cells inside are probably fine, but the solar panels are so small, they simply cannot do more than a slow trickle charge.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8

#### tjones9163

#4
##### Aug 19, 2019, 04:23 am
Most solar cells are the same efficiency, so there is no such thing as a small panel that will effectively charge a cell phone. I'm presuming you don't want to wait a week for a full charge.

There are a lot of junk solar charging power packs out there. The cells inside are probably fine, but the solar panels are so small, they simply cannot do more than a slow trickle charge.
Well, my small panel is a polycrystalline and i read that monocrystalline are better and more efficient.

#### mauried

#5
##### Aug 20, 2019, 12:17 am
A typical 18650 cell can be anywhere from 2000 mah to 3400 mah if you have a decent one.
Charging one at 30 mah will take at least 66 hours for a 2000 mah battery, and thats only for the time of the day that the sun is at its maximum which is only for a few hours per day.
So many days to charge one battery.
Only way to charge the battery faster is a much bigger solar panel.
Theres very little differances between Mono and poly panels, mono are slightly better but its less than 10% differance.

#### lemming

#6
##### Aug 20, 2019, 03:43 am
You will have limited to no success with this setup because the tp4056 relies on a constant voltage and reasonable current, neither of which those solar cells can provide.

Have a look at this unit: https://www.adafruit.com/product/390 and more importantly the explanation of how it works https://learn.adafruit.com/usb-dc-and-solar-lipoly-charger/design-notes and, unlike me, you will save yourself a lot of messing around trying to figure out why it oscillates and the battery isn't charging properly.

For balance I provide the link for a Sparkfun version; https://www.sparkfun.com/products/12885.

#### mauried

#7
##### Aug 20, 2019, 04:02 am
Heres a cheaper MPPT Solar charger for 1S lipo batteries.
Ive been using them for several years and they work well.
They dont however have a low voltage cutout, so its important to size the solar panel correctly based on what the battery has to supply.
https://www.aliexpress.com/item/32862470804.html?spm=a2g0o.productlist.0.0.29462a9bi20sXU&algo_pvid=aef3f0c1-41c7-4b14-8e49-aa9d44d2b228&algo_expid=aef3f0c1-41c7-4b14-8e49-aa9d44d2b228-0&btsid=f66acca7-caa0-4850-8654-a68bcfce80c1&ws_ab_test=searchweb0_0,searchweb201602_9,searchweb201603_60

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