Can we design a battery bank that takes unlimited 18650s?

Many of us have dozens upon dozens of 18650s, could someone with electronics expertise create a bank that you plug 18650s into and use them for powering things?
Say for example you buy a controller that has an inverter for 12V DC, 120V AC or 240VAC depending on your needs and a holder that is expandable, each one takes up to say 10 18650s, and controls each one individually, charging, discharging and so forth.
The idea is you buy the controller for getting the AC/DC you need and you buy holders for powering it, and you can use as many 18650s as you have or want to buy, so its infinitely expandable. And we can add some extra features, max voltage allowed (so you can charge to 80% max if you want longer life), discharge to 40% storage voltage, capacity test and so on.
The idea is we can put our batteries to use and we an create a battery bank of any custom size for use in emergencies, camping, solar power storage, anything we want, and it will be able to use batteries of differing capacity and age/usage, the idea being they don’t have to be uniform batteries because each one being individually controlled allows for this.

I don’t have the electronics background to design this, but if someone on BLF wants to take on the project i personally think it would be a good idea, and i bet many BLFers might be interested in it. If it exists already i would like to know about it

Your thoughts?

I don’t have the know how but it might be possible with a BMS board. You could hook up cells of different mAh in series. Once the the cell with the lowest capacity is depleted it will kick into protection. So if you have say 4 parallel holders you could hook em up in series connected to the BMS board. Each holder would need at least one cell. Then you could ad more cells in the holders.
I believe the cells in parallel should have about the same capacity. Downside of this set-up is that the pack will only have the capacity of the cell with the least amount of mAh.
This is just a brainfart and in no way am I sure this would work or be safe.

Just a friendly bump, really interested in the opinions of other people

I’d sure like to be able to run some of my older cordless power tools on 18650’s
I’ve got an older bosch 24 volt hammer drill that is useless because batts are over 100$, but have a drawer full of 18650’s

This guy has some pretty interesting stuff for making battery banks, charging etc. :
Batteryblocs

He is into ebikes and stuff and has some cool vids on youtube regarding charging balancing etc that may lead you in right direction.

*Edit: Here’s his youtube: Shawn McCarty on youtube

Very interesting indeed, thanks for the link and welcome to the forum

I love the idea!
The percentage in max charge sounds cool, haven’t seen a plug and play charger that does that.
Would be cool if it had a voltage feature from, dunno 1 to 24 volts by turning a simple knob.
120 or 240 sounds crazy to me like a powerwall or aggregate on li-ion’s :smiley:
Maybe even dangerous when having different 18650’s means different max amps drawn.
Though I might even know less of the tech and knowhow that goes into this project.

Put as many as possible parallel and try to match paralleled groups of batteries when you want to put those groups in series.
High amp regulation boards are quite cheap on AliExpress or ebay or banggood etc…
Some of them even balance charge them.
In 3S config you can power most 12 Volts devices.

The idea is i think this should be modular with each cell controlled independently, hence you can use mismatched cells because no cell will be over charged or over discharged, and you can add to it as you buy more cells and use cells of different capacities

It can be done a bit more simply, a device that puts put 12V DC, and the 120/240V can be handled with off the shelf inverters or designed later

When you put them in parallel you only need 1 regulation, they will all have the same voltage because they’re hardwired in parallel.

So in a 5 Volts output powerbank you can basically hook up any amount of different sizes of LiIon batteries in parallel.

That will work with matched cells, but differing capacities, differing ages, differing internal resistance from random cells it just won’t work.

Wouldn’t a couple car batteries be more efficient? We had a power outage two winters ago. Our wood stove has an electric fan which I powered with my marine battery hooked up to a cheap walmart power inverter. A single charge on the marine battery powered the wood stove fan for a little over 23 hours keeping the house warm. I have two marine batteries for our boat that I keep on a Deltran battery tender over the winter, indoors in the basement of the house.

Batteris in parallel are generally not a big deal as they have the same state of charge.
But if you have em fully charged and add a empty cell you got a very bad situation as this empty cell is charged with the max. current the other cells can provide, which can lead to an explosion.

If you got multiple banks in series they need to have the same capacity, so you cant simply add or remoce a cell.

What king of amperage does your battery have, I think mine is not a marine battery but it has 900-1000 peak Amps

Different capacities doesn’t matter.
Big differences in internal resistance (Ri) might cause some warmer high Ri cells, but the more cells you have, the less Amperes are drawn from each of them.
So, sure, 1 brand new VTC6 parallel with 1 tired old laptop pull wouldn’t be wise to do 3 or more Amperes with.
The new VTC6 will discharge faster because its lower Ri and then the tired old laptop pull will try to recharge the VTC6 without current limiting except its own Ri.
But when you have a large number of not so new cells that still work too good to recycle, it’s okay to use them in parallel.
Just stay under (let’s say) 1.5 Amperes per cell (that’s 15 Amperes for 10 cells) and it’ll be fine.

indeed, i was thinking about the discharge rate as well, it should be kept at a safe level, 1A may be universally acceptable?

i do not understand, i don’t think one battery recharging another is a good idea at all in this bank.

That would be totally safe.

Neither do i ! :smiley:
But it’s what could happen between a low Ri and a high Ri cell when the difference between the Ri is big.

I would not link them in series

I got 2 of these, 6 batteries, seems to do ok, I can charge my wifes iPhone, my ELeaf vaping rig, my phone from 0 to full charge and still have 1 led left on power meter

http://www.ebay.com/itm/311677727131

Very interesting idea!

To be able to use efficiently mismatched cells you would need some kind of ‘smart’ controller for each cell to control how the cell is put to use. It should be able to determine how much current it can draw… depending on a cell state of charge and capabilities… but how? It seems tricky but i know nothing about balancing cells.