Understanding 10s4p 18650 battery packs

Awesome thanks man. Now BMS leads go where?

The Bs on the diagram represent the balance leads. Credit to @whitepony for the diagram

@Racetored check out the Beautiful Diagrams thread there are diagrams of all the common battery layouts. BMS wiring is shown there as well. Note that there is variation in the way you wire BMSs, they aren’t all the same (some use the same ports for charging and discharge, others don’t, for example) Any BMS you buy should give you instructions.

Hi, I’m not sure if this is the right thread to be posting but you guys all seem battery savy, I’m a carpenter not an electrician so struggle with the workings.

I’m thinking of making a battery pack 5s4p with these batteries :

Panasonic NCR18650B 3.7V 3400mah Li-on Battery

  • Low discharge rate, no memory effect. SPECIFICATION Description Capacity (Ah): 3.4 Ah Charging Voltage (V): 4.2 V Energy (Wh): 12.2 Wh Energy Density (Wh/L): 730 Wh/L Nominal Voltage (V): 3.7V Weight (g): 45 g Diameter (mm): 18.3 mm Height (mm): 65 mm Model: NCR18650B Made in Japan Made by Panasonic

I can get 20 of these including postage for £75

So I’m asking are their any issues using these for a build and if not does the price seem fair?

Bad idea. The discharge current is probably only 10A at the most. 4 in parallel is only 40A. Not enough to minimize voltage sag.

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I don’t fully understand your comment as I’m a novice on all things that spark,
what would be your choice of battery for the job?

Also am I right in assuming mah is increased by reducing discharge rate?

As batteries hold more energy, they cannot discharge as much current. Yes that is correct.

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Samsung 25R, LG HE4, HG2s. These are all 2500mAh+ cells with 20A discharge rates.

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Super, thanks for the advice. I’m off shopping.

Hey. I know it’s been a while since you posted this but can you link the thread on ES which says you shouldnt put cells in series and then parallel? I do it all the time with no ill effects.

How do you balance them? That is the reason.

Same way you balance the same pack thats connected first in parallel and then in series. Not the reason

Oh okay. Could it have been that if a cell went bad in a series pack, it would bring the voltage of the whole pack down, but if a cell goes bad in a parallel pack, the capacity drops, not voltage.



"A cell that develops a high resistance or opens is less critical in a parallel circuit than in series configuration, but a failing cell will reduce the total load capability. It’s like an engine only firing on three cylinders instead of on all four. "

Nope. If a cell goes bad in a soldered/welded parallel batch, you wont realize it’s bad until all of them are bad and you have to dispose of the whole batch.

If a cell goes bad in a soldered/welded series batch, you will realize as soon as you charge as the one cell will have higher IR and its voltage will be different than the good cells. In this case you can cut out the bad cell and keep going with the others as they have not been affected.

E: I see what they are saying. If a cell is going bad in a parallel pack, the other ones will compensate as the weak cell will match the voltage of the good cells. If it goes bad in a batch of series cells, then your total voltage drops and it would underpower your system.

This is all true, but as stated above, you would quickly realize you have a bad cell in a series pack by checking voltages. You wouldn’t realize it as easily in a parallel pack unless you’re constantly measuring capacity.

I’m still curious how you plan on hooking up a BMS to it. All BMSes are wired for parallel first battery packs because it is easier to wire.

In a series format, you will overcharge the pack that contains a dead cell with the same charger voltage. You’ll end up damaging the rest of the cells in the series pack before realizing.

Where did U get that 100 for a 10s 8ah deal

Each series pack has a balance port. All you need is this guy to connect to bms. $8 on amazon I think.

I would post a pic of it all connected but it’s work related.

As for charging. No, I would not blow anything up before I realized I had a bad cell. I dont charge connected straight to a brick charger (that is idiotic). If you used a BMS, it would not let you overcharge any single cell, if you use a balance charger, it shows all of your voltages like below.

E: This is why I want to see the ES thread @lox897 mentioned. I want to see if there is any actual science behind it for me to learn. If it’s just because doing parallel and then series is easier then I dont really care lol

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Other than having the bad cell drops voltage vs drops capacity, I don’t think there is anything else.

This just makes the pack more complicated and harder to manufacture. When making a pack of these dangerously powerful batteries, simpler the better.

Yeah, there are pros and cons to each method. I make all kinds of crazy packs for work (up to 10S10P Li-ion setups). I’m just looking to further my knowledge :stuck_out_tongue:

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