Which battery chemistry should I choose for a tiny beginner DIY solar system?

[Love.Sun]

So I have decided to finally dive in and try to make a tiny system.

I am planning on taking either a NiMH or a Li-ion cell. A single cell will probably be enough.
Then wire it with a tiny solar charger in order to charge it. Literally trying to make one of those solar power bank chargers that people use for cellphones. But instead of buying it I wanna make it and learn stuff in the process.

For now I am questioning which battery to take. I saw on Reddit /r/batteries the other day, someone posted this guide https://techmoment.net/best-18650-battery/ about the 18650 li-ion batteries.

I initially thought of getting exactly that battery for my project but that article states that those batteries can be dangerous and I am afraid that if I need to solder wires to their ends that it might not be something I am capable of doing properly + the article says that you should never solder them. I find that hard to believe because those cells must be soldered together when they are used in some devices.

Either way those batteries seem like a potential trouble on one hand but on another they seem to have much higher capacity and voltage than the NiMH.

And from what I learned from a few people here on the forum is that I can get more Watt energy if I have higher voltage.

So if I use a 3000mAh li-ion with 3.6v I will get 10.8Wh if I am correct in my calculations.

If I use 2000mAh NiMH with 1.2v I will get only 2.4Wh.

I am inclined to work with the stronger battery but I am not sure if its smart considering my lack of experience.

I would still love to do this.

What are your suggestions? Maybe I am completely off here. Should I try something else or a battery with completely different chemistry??

 

[snoobler]

Absolutely, positively do not use NiMH.

Absolutely, positively do not allow Lithium-ion (3.6-3.7) go outside it's stated voltage limits.

 

[DThames]

18650 lithium ion are great for small packs and can be easily scaled up. If you solder to any battery, you should have good solder skills, a large enough iron, and know how to make it happen fast and proper. In commercial packs, it is normal to weld them with a spot welder that pulses current for a fraction of a second. 18650 Lithium Iron Phosphate (LiFePo4) cells are less likely to (don't) catch fire. You can find new cells with solder tabs welded to them so with less skills you can just solder the tabs together. 32650 LiFePo4 cells can be purchased with screw terminals, so no solder.

Use some form of lithium (my suggestion).

 

[Love.Sun]

Absolutely, positively do not use NiMH.

Absolutely, positively do not allow Lithium-ion (3.6-3.7) go outside it's stated voltage limits.

Sounds like NiMH is a hard no xD hopefully I didn't propose something dangerous there or something like that xD
Thanks for your reply! I will keep the battery in its limits under the 4.2v

 

[Love.Sun]

18650 lithium ion are great for small packs and can be easily scaled up. If you solder to any battery, you should have good solder skills, a large enough iron, and know how to make it happen fast and proper. In commercial packs, it is normal to weld them with a spot welder that pulses current for a fraction of a second. 18650 Lithium Iron Phosphate (LiFePo4) cells are less likely to (don't) catch fire. You can find new cells with solder tabs welded to them so with less skills you can just solder the tabs together. 32650 LiFePo4 cells can be purchased with screw terminals, so no solder.

Use some form or lithium (my suggestion).

I know how to solder. Not much of a professional at it but I learned it from my grandpa and did it often with him. I can make it fast too. Now when it comes to the LiFePo4 cells they just seem too advanced or am I mistaking? Also do they come in cylindrical form? When i google the LiFePo4 all I see are prismatic shaped cells that look like something out of a 90s movie ? thats why they appear a bit intimidating. Like you really need to know your stuff.
Having a screw on top actually sounds really good as I would love to evade the whole soldering thing and keep my focus on making a solar system.

Edit: Yes they do come in cylindrical form. But those don't seem to be standard or?

 

[snoobler]

LFP is not advanced at all. Way more to go wrong with non-LFP Lithium chemistry.

All cylindrical cell sizes are standard. They may not be sizes where complementary products exist, but they conform to *a* standard.

Clamping and bolting together prismatic cells is faster and easier, and they are far more tolerant of mistakes with no risk of fire.

If you want to spend way less time on building a battery, LFP all the way.

 

[rin67630]

I will keep the battery in its limits under the 4.2v

...and above 3.3V
And buy batteries with solder tags.

 

[snoobler]

...and above 3.3V

Depends on the cells. 3.5V is typically optimal for 20% SoC, 3.3V for 10%, but many cell specs are down to 2.5V.

 

[Pappion]

How tiny? There are battery banks ready made that accept solar input. I have had 1 for years, along with a Car Jump Starter that can put out 12v. Both can charge my lap top.
Here is one: battery bank
My old one: unavailable
updated Jump Starter: Jump Starter

 

[DThames]

Get 3 or 6 of these cells. (3 in series for 12v, parallel 3 more for more power, longer run)
Get a couple of these charger boards. (one per battery pack)
18v solar panels (one per charger board, unless you want to charge faster)
Some BMS boards (one per battery pack)
That will get your battery pack and solar charger main parts
Wire it up to something like this.
Done
Maybe....Get a 3D printer and print a box for it

I have built small packs with a 12v outlet that I can just plug into the pack. Into that 12v outlet you can plug in one of those tiny inverters and have 110v for light loads. More battery cells, more run time. Lots of stuff will plug into those 12v outlets.

 

[Pappion]

I can understand wanting a DIY project. This one has fire hazard risk. Also risk of insurance coverage loss. I suggest using safer LiFePO4.

As a retired eng tech I no longer feel the need to play. Rewiring my TT 12v and adding solar is enough for now.

 

[Love.Sun]

Thank you everyone for your help!! You can't imagine how helpful your replies are! I will most likely be getting a LiFePo4 cell and doing what DThames suggested!

Thanks again! This place is a blessing!

 

[DThames]

If you want LiFePo4 you will need a 4s (4 in series) BMS specifically for LiFePo4. If you are okay with NOT tiny, these cells are very affordable and US shipped.
Get you some cell holders too. See photo below on how cell holders work. That is a pack for a mobility scooter (not tiny).
1x cell holder
3x cell holder

There are some good videos on Youtube about soldering cells. Basically tin them first and be reasonably quick. If you are interested I can describe my process.

 

[DThames]

4s LiFePo4 MPPT charger board, if you are going LiFePo4.

 

[Love.Sun]

DThames thanks so much for your trouble!

I will get those cells with the screw on them so that there is no need fo soldering. Everything else should stay as you described.
It may not be tiny but it will be safer and easier to make

 

[DThames]

Li-ion has been used for more than 10 years in laptops. How many have you seen catch fire? Just saying. Under the right conditions a car will catch fire, as well.

 

[Love.Sun]

Li-ion has been used for more than 10 years in laptops. How many have you seen catch fire? Just saying. Under the right conditions a car will catch fire, as well.

That does make sense. But I would also like to evade the soldering if I can.
I will think about it and decide which way to go. Either way I am covered now as I know what are the steps to do it ?

 

[Pappion]

Li-ion has been used for more than 10 years in laptops. How many have you seen catch fire? Just saying. Under the right conditions a car will catch fire, as well.

But you don't often find them in large formats. Tesla has excellent engineering for managing the danger.
BTW I saw many swelled laptop batteries when I worked for a charity refurbishing used laptops.

 

[DThames]

But you don't often find them in large formats. Tesla has excellent engineering for managing the danger.
BTW I saw many swelled laptop batteries when I worked for a charity refurbishing used laptops.

I use these when I start paralleling cells.

 

[wmills_92105]

Li-ion has been used for more than 10 years in laptops. How many have you seen catch fire? Just saying. Under the right conditions a car will catch fire, as well.

There's plenty of evidence that LFP will *not* catch fire like standard L-Ion cells will.

A simple search on the net for "laptop battery fire" is educational.