Maximizing capacity Question!

Hey!

I'm trying to harvest information on the advantages/disadvantages of different volt systems in battery builds.
As I have 100x 18650 li-ion cells of 3000mah each to play with, I'm trying to determine what's the best set up.

I've been dwelling over a 12v 4s set up or a 24v 7s set up.

I understand that it depends on the application of the battery,
but I guess what I'm looking for is the best all round option, if there is any.

To start off with I'll be powering 12v devices. But for the future I have plans to get an inverter and hook up other devices too.

It's worth mentioning that I have a DC step up-step down converter at hand (from 4v to 35v, and 0.1a to 5a), if that makes any difference I am not sure.

My question in a nutshell would be , does a 24v battery miss out on a lot of capacity/ampH if only powering 12v devices?

Thanks!

I would look at what the successful battery makers who use small cells do, and learn from them (aka do what they do). Battleborn comes to mind. Here is a teardown video that has a lot of info packed in it.

Vega said:

does a 24v battery miss out on a lot of capacity/ampH if only powering 12v devices?

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Assuming you are using the same number of cells, it will have the same watt hours regardless of the voltage.
3.6v cells?

3.6v x 3000mah x 100 cells = 1,080000 mah no matter how they are arranged (4S or 7S).

Your only losses will be using a voltage converter from 24v to 12v or vice versa. You can minimized this by building a battery(s) that best match your greatest use.

MisterSandals said:

Your only losses will be using a voltage converter from 24v to 12v or vice versa. You can minimized this by building a battery(s) that best match your greatest use.

Click to expand...

Thanks for your reply!

How great is the loss of using a voltage converter?

I think I will go for 98cells in a 7s14p formation, so 24V 42AmpH.

The cells are rated at 2C, so if I have understood everything correct, my BMS should handle at least 84 continuous amperes (3Ah x 14 x 2C)
, correct?

Vega said:

How great is the loss of using a voltage converter?

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I'd bet its less than 10%, probably more like 5% DC to DC. It may depend more upon the
quality and size of the converter. An quality converter sized to your needs/usage would be best.

I mess a lot with 18650's but I've never made them into a big battery.

Have you seen the threads with the DIY spot welder? Looks super cool - i am VERY tempted to make
one just for the fun of it (well i have a 3 cell failed power brick i could fix but that's hardly worthwhile).

MisterSandals said:

Have you seen the threads with the DIY spot welder? Looks super cool - i am VERY tempted to make
one just for the fun of it (well i have a 3 cell failed power brick i could fix but that's hardly worthwhile).

Click to expand...

i've seen a few here and there online, but nothing that appealed to me too much. Any one design in particular you'd recommend?

I thought this was clever and simple: