Author Topic: DIY Solar Powered Power Bank for charging mobile phone  (Read 9719 times)

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Offline Shivram10

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DIY Solar Powered Power Bank for charging mobile phone
« on: November 15, 2014, 08:28:17 pm »
Hello EEVBloggers,

I want your help in designing a Solar powered Power bank out of Li-Ion 18650 batteries
I don't want to buy a cheap Solar Power bank, I want to build this project for the fun of building it.
I have a laptop battery which contain 6 Sanyo UR18650F R1112 2400mAh Lion-Ion which shows individual voltage of 3.59 to 3.7v.

The Phone Battery Specifications :-
Battery - 3000mAh Lithium Polymer
Charging - 5v 1amp

I am an hobbyist and I have a limited knowledge of electronics and I don't want to use Arduino, is it possible to build a power bank out of the 18650 batteries and use a small solar panel to charge the batteries. Is there any schematic available to build a charging circuit as there are no ready made PCBs available where I live, as used in this DIY guide
I have searched many websites and they all use readymade PCBs or use a 3V to 5V Boost Converter Charger Module like this to charge a single battery, I want to use minimum 3 batteries if possible all 6 batteries in the powerbank.

I can get DC-DC 3V to 5V Boost Converter Charger Module though it is available here, any help will be appreciated.

Thanks in advance

Offline Azhar

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Re: DIY Solar Powered Power Bank for charging mobile phone
« Reply #1 on: November 16, 2014, 12:22:11 am »
This is the most simple and affordable solar battery charger that the hobbyist can make. It has a few drawbacks over other similar controls, but offers numerous advantages. It is intended for charging lead-acid batteries, but may also be used for charging any battery at a constant voltage. Voltage output is adjustable.

More details on this links

Offline Azhar

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Re: DIY Solar Powered Power Bank for charging mobile phone
« Reply #2 on: November 16, 2014, 12:26:10 am »
And here is another battery charger with Auto Cut-Off

you can do some modifications and make it suitable for your use

Offline eas

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Re: DIY Solar Powered Power Bank for charging mobile phone
« Reply #3 on: November 29, 2014, 08:10:26 am »
Those circuits Azhar aren't suitable for lithium ion batteries, which require constant current charging up to the termination voltage (4.2v for those cells), and then constant voltage until the current drops to a termination threshold (typically 1/10th the initial charge rate). Voltage drops a bit after charging is terminated, and to avoid excess wear to the cells, the charge controller shouldn't restart charging again until the voltage drops to 4.1v or so.

You have a few problems to solve:
  • Implementing the charging profile described above
  • Preventing overcharging, overdischarge, excessive currents
  • Obtaining optimal power capture from the solar panel
You could simplify #1 by avoiding the constant current phase at the expense of giving up some capacity (~10%).
For #2, you could probably rely on the boost converter to limit discharge current, but you'd still need something to cut off discharge when the battery drops to 3v.
I think you may be able to ignore #3 if you match the panel size and charging current properly, and make sure the panel isn't shaded.

The schematic is going to depend on what components you can get. There are chips that do most of the heavy lifting for you. The ones I'm aware of are surface mount, which makes it a little harder to build your own circuit. For the charging, there are cheap TP4057 chips from China. With any luck, you might be able to get it on a cheap board like this one. There are also some that have built in protection for the output.

Some odds and ends you'll want to think about:
  • To deliver 1A at 5V from those laptop batteries, your battery pack will have to deliver at least (5v*1a)/3.7v = 1.35A of current because the boost converter trades current for voltage. However, with efficiency losses in the boost converter, it is probably safer to figure on 1.75A or so.
  • A single one of those 18650 batteries should be able to deliver that current if it isn't too worn, but you're better off using at least two in parallel, particularly since you'll want the added capacity, because...
  • To fully charge the 3000mAh phone, you'll need more than 3000mAh due to conversion and of inefficiency looses in the boost converter and the phone's battery charging circuitry.
  • I'm guessing your laptop pack was manufactured at least 5 years ago. Even if the cells haven't seen any use, actual charge capacity could be lower than the 2,400 mAh rated capacity due to aging. If the pack has seen much use, cell capacity could be lower still. I've seen 2,600mAh versions of those cells from packs with (only) ~100 cycles that only have ~75% of the rated capacity.
  • Assuming the cells have 1,800 capacity, and you use all 6, that will be 10,800 mAh. A reasonable charge rate for that many cells in parallel could be as high as 5.4A, but most commercial power banks of that capacity would only charge at 1-2A due to limitations of USB power supplies.
  • I'd suggest figuring out the typical output of your solar panel and then picking a charging current to match
  • Some people use two charger chips/modules wired to the battery-bank in parallel to obtain higher charging currents.
Good luck!  I'm interested to know how your project goes. I've started a blog to document my own experiments with recycling laptop battery packs. So far I've been focused on sourcing and grading the cells, but soon I'm going to design and build some of my own power banks.

Offline Paul Price

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Re: DIY Solar Powered Power Bank for charging mobile phone
« Reply #4 on: November 29, 2014, 09:36:57 am »
Maybe you can play with a circuit like this. I just designed this, looks like it might work.

It will limit charging current to 1.5 amp approx. LM317 must be on a heat sink.

Changing the value of the .5-ohm current sense resistor to .75 ohm will limit constant current charge to approx.  1-Amp and when charging current falls below approx. .65amp charging will terminate.

Upon near to full charge, when constant current charge current drops below approx. .8A, this circuit will terminate charging.

A N.C. momentary switch from the Solar Cell array to the LM317 input must be added to reset/restart charging.

Vadj sets the end of charge voltage of the battery pack.

Depending on the Li cell pack voltage, Vadj pot resistance is to be adjusted in value to set Vout to battery pack.
« Last Edit: November 29, 2014, 10:35:55 am by Paul Price »

Offline ErikaDeanda

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Re: DIY Solar Powered Power Bank for charging mobile phone
« Reply #5 on: May 23, 2019, 08:24:26 am »
Material: Solar panel 180mm*240mm*3mm 5.5v 5w .
           3.7V lithium battery 4500ma, 20 yuan, with protection board
           3.7v to 5v conversion interface 10 yuan.
          Schottky diode 0.1 yuan
          Ipad cover
          Several wires

My DIY  Solar Powered Power Bank has a theoretical maximum power of 5.5v 10w and can supply a maximum of 1.8A. In theory, a 1400ma battery full of phones can be filled in less than 50 minutes with a battery of 4500mA. Even with only half of the power generation efficiency, it can provide 900ma, which is the same as the current provided by a general charger and does not put any pressure on the iPhone and other devices.

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