Noob batterypack questions

[PaleAle]

Hi,

I am new to creating battery packs and have a few questions (Li-Ion 3S)

Is it better (current draw) to create packs with more cells? 10Ah using 6 cells, (10.5 ah) 9 Cells or a 10Ah with 12 Cells.

Also I am searching for schematics how to setup 6 and 9 cells and where to solder the balence cable? (no BMS)

About bms, does it make a difference adding a bms using a regular charger compared to using a chager that has a balancer?

Many thanks in advance

 

[lnanek]

Yes, the more cells in parallel, the less each cell has to contribute towards the current you are drawing from the pack. Drawing 10A from a 3S2P battery means each cell is draining at 5A. Drawing 10A from a 3S4P pack means each cell only has to handle 2.5A.

A balancing charger requires more wires to connect to the battery compared to bulk charging a battery with a BMS. You also lose the ability to have a Bluetooth BMS that can report all your p-group voltages while you are using the battery.

 

[Chalo]

Hi,

I am new to creating battery packs and have a few questions (Li-Ion 3S)

Is it better (current draw) to create packs with more cells? 10Ah using 6 cells, (10.5 ah) 9 Cells or a 10Ah with 12 Cells.

It's best to use cells that have all the capacity you're looking for, so you don't have to make packs with hundreds of welds and lots of extra resistance from the interconnects.

If you only teach yourself to build with Lego, then you're stuck only building things out of Lego. Might as well teach yourself to build what you actually want instead.

 

[calab]

Once you start adding smaller packs to connect together, its a game called Lego, Lipo guys know that game well.

 

[amberwolf]

Not knowing anything about your specific usage scenario, it's tough to give specific answers.

The general ones given above may be enough, but if you give us details about the project / usage / capacity and current-delivery needs, cell types/sources you intend to use, construction methods, etc., we may be able to provide more specific useful help.

 

[PaleAle]

Ok,
Got it, so the max constant amp draw is multiplied by P, the cells I want to use are BAK N21700CG-50 5000Mah 15A as 3S3P would allow a max constant 45 Amp draw and I only need about 30 Amp so that would be fine.. I will probably end up wit 4P anyway

But about the bms, is it better to add one? I already have 2 chargers which have balancers...

 

[offGridDownUnder]

Consider:

Grin’s perspective of Ebike fires

endless-sphere.com

 

[PaleAle]

Ok I have the Samsung INR21700-50S cells including an 3s 40A balancing BMS.

It will be an 3S2P Pack (11.1v 10.000mah) and I want to charge at a rate of 2.5 to 3a.
The chargers is have are an 3a lipo charger and a SkyRC B6 v2.

The bms: has an overcharge protection voltage: 4.25 V Is that a safe value?

Is it better to not install the pack WITHOUT BMS but with balancing cable so I can let the balancing
be done by the charger?

Or, leave the BMS and charge it with the B6 until it reaches the set voltage?



Tnx

 

[docw009]

The BMS will protect you from running the battery below 3V/cell. If your applications have a smart low voltage alarm built in, then you're probably OK, but otherwise you may forget with a dumb load and let it run the battery down under 9V. When a cell gets much under 2.5V, it can be damaged.

For example, if running a 12V-110VAC inverter, the inverter will shut off around 10V. If running a 12V old style automotive headlamp, that will go down to zero.

 

[PaleAle]

The BMS will protect you from running the battery below 3V/cell. If your applications have a smart low voltage alarm built in, then you're probably OK, but otherwise you may forget with a dumb load and let it run the battery down under 9V. When a cell gets much under 2.5V, it can be damaged.

For example, if running a 12V-110VAC inverter, the inverter will shut off around 10V. If running a 12V old style automotive headlamp, that will go down to zero.

but what about the possible 0.5v orercharge, is that not a problem?

 

[docw009]

A BMS should work like the AC-B6 balance charger to prevent overcharge. I use a 3S drone pack yo run a spot welder and us an AC-B6 for it.

 

[PaleAle]

Ok, tnx