diy solar

diy solar

portable emergency battery pack recharged by multiple renewable energies

miky94

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Jun 6, 2021
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4
Hello,
I'm new to the forum and solar power, for a travel around the world on my Vespa for charity against climate change, I'd like to build an emergency battery pack recharged by renewable energies like sun and wind to recharge smartphone etc.
I'm thinking about:
- LiFePo4 (or LiIon) battery pack e.g. 4S2P 18650 12,8V 3600mAh (or bigger)
- balanced charging
- ~3.425V (75% of capacity? or 3.65) charging cut-off
- ~2.975V (25% of capacity? or 2.5) over-discharge protection
- button to display charging information
- multiple charging inputs (solar/wind)
- short protection
So I'd like to buy or to do myself a BMS able to do all these things.
I know that I can charge a lithium cell up to 90% of capacity with only the constant current charging step but I'm not sure what a solar cell outputs, e.g. a 5.5V 1.6W solar cell should output 5.5V@0.29A with the sun at 100%, but with the sun at 50% what's going down, voltage, current or both?
Then how do I handle multiple inputs (solar/wind) that can work one at a time or simultaneously?
Thanks in advance for your help
 
There are so many small 10,000/20,000 mAh battery packs on the market not much bigger than a cell phone, why build one?
Travelling on a Vespa? Size and weight will be the biggest obstacle.
Even a small foldable solar panel that will charge your pack in 5-6 hours of sun is about the size of a briefcase. Why do you need 12V to charge a cell phone?
 
thank you for replying any help is really appreciated
There are so many small 10,000/20,000 mAh battery packs on the market not much bigger than a cell phone, why build one?
for learning, customization, costs, and for demonstration purposes for the charity
Travelling on a Vespa? Size and weight will be the biggest obstacle.
it will be just a small backup battery, with LiFePo4 (or LiIon?) it shouldn't be a problem, I would like to use it to replace the lead acid battery recharged by the Vespa but I don't know how to handle multiple charging inputs
Even a small foldable solar panel that will charge your pack in 5-6 hours of sun is about the size of a briefcase. Why do you need 12V to charge a cell phone?
I would mount it on the Vespa to charge all day, 12V would be more versatile e.g. to also power a light but yes I could build a 2S pack if it is more efficient

what about the questions above?
 
Hello,
I'm new to the forum and solar power, for a travel around the world on my Vespa for charity against climate change, I'd like to build an emergency battery pack recharged by renewable energies like sun and wind to recharge smartphone etc.
There are plenty of existing off the shelf solutions for this in forms of "power banks" that have a solar charger built in.


no need to reinvent the wheel.
 
Something like this off the shelf would be a better idea. It has both 5v usb outputs to charge up something like an Anker powerbank, (or your phone directly, but I'd use a powerbank instead) and has the 19v output to which you attach an external solar charge controller (like a small Morningstar Sunsaver, or perhaps a Genasun) to charge up your vespa main battery:


Done. And easily reproducible by those you are demonstrating it to. Otherwise, they'll see some sort of DIY one-off contraption and walk away. Even though WE may like it. :)

Forgot - don't be a total fool and strap a panel to your backpack like they show in most marketing materials and think that traipsing around the countryside will net you much charge. That's a fashion-statement.
 
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I use a very small 10 to 12 amp portable battery meant for recharging cel phones or tablets to power my GPS on my eBike - It will run it all day and then some. What's nice about it is, you can recharge it from any 12 volt source (like your Vespa battery) with a USB adapter or from household power with a wall USB charger. No need to deal with a bulky solar panel. And best of all, it's really cheap!

Don
 
I could have written in the buysolarforum :)
As said I would like to learn and customize, even if in the end it will be less efficient and more expensive, I'm a DIY lover and I would like to try.
From the solar cell tests I see on the internet the real power delivered is about 25-50% of that rated, I guess better known brands solar cells (that I don't know) have higher percentages and as I'm size-limited I would buy these to not have the briefcase-solar-panel, but I would like to know how much bigger should I size it relative to what I need?
My smartphone's battery is about 15Wh so I would make a battery pack twice bigger but using half the capacity (25-75%) to maximize its life, e.g. 2S2P 18650 6.4V 4700mAh LiFePo4.
As the smartphone's battery lasts me two days I would be happy if I could produce this W/h.
 
To heck with recharging your cel phone - To fight climate change, we need to put a battery pack and an electric motor in the Vespa and then design a solar trailer to recharge everything so you can travel the world with a zero emissions vehicle! :cool:

Don
 
Ok, if you want a project, there are easy builds, kits, etc.
I ordered a pack of 4s kits, tie two together, slap on a BMS, attach some usb circuits, and voila! Instant bank...

most of the 10,000-30,000 MAH banks are all 3.7V... huge parallel banks of cells... you want to build a 12V pack. I would use 32650 LFP cells, with a 4S BMS, have a better safety margin, and more useful voltages.
You also need a solar charge controller, but tiny ones can be had cheap if you stay PMD.

image.jpgimage.jpgThis kit used to be a cordless hedge trimmer power pack, I tossed the old SLA cell, and slapped in some 3S packs to make a nice useful 11Ah 12V pack...

I rebuilt an old jump starter pack with an air compressor built in... very handy.
image.jpg
I found online 18650 holders already setup for 4S and am working on a project for those...
image.jpg
heck, even small plastic ammo cans make nice sized battery box projects...
image.jpg
a simple low cost BMS, and the batteries stay in line...
image.jpg
 
for learning, customization, costs, and for demonstration purposes for the charity
There are lots of vendors (I'm thinking of batteryhookup) that sell used 18650's and small lithium cells. USED being the key word. You would be recycling cells that are perfectly good, which lines up with charity stuff.
 
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