Help wiring first pack! - 3S4P 18650s

Hello from California!


I am new to making banks! Ihave some NCR18650B cells, I wantto wire them up in a 3S4P configuration for my bot. They are 3.4ah @ 3.7v nominal cells. I read that if youuse one ofthese battery protection boardsyou'll be able to safely balance charge the bank, so I picked one of them up. I also have a hobby charge for the turnigy cells I was using before.

From what I understand, you have balance leads from the pack, to the charger so the chargerreadsthevoltage of the individual cells and thenappliescurrent from the 2 main leads based on the reading, then whennear full,it will stop current flow to main leads, andput current to thebalance leads to top them alloff equally.I understand parallel and series connections, when it comes down to wiring with this board, I'm a bit confused.

On a side note, could one use a desktop PSU to charge multiple packs? I'm aiming to charge many packs at once, as cheaply as possible lol.



Is this accurate?Do I have the right approach so far?Can anyone show me how to wire this all upcorrectly? Thanks!
















I did my best with what I had. My solder point were very poor but I don't think it affected the battery, it feels like incorrect wiringor bad BMS.I'm sure its a trivial mistake but I failed, send help!xD


My cells were all at 3.50v, my pack at my main hot and ground read 3.5v as with all the rails on the pack... The when it was assembled the pack slowly became really hot, until it got to the point where I turned it off.

The BMS has the balance leads. The charger usually just has 2 leads. Unless you have a charger that specifically has balance leads on them (some hobby chargers do, iMax for example)

The BMS would connect to various cells to maintain balance. It can only bleed off a certain amount of current while under charge. With a 4p setup, that should be ok with that board you listed, but it would be pushing it hard if you tried to charge at the full 25A

Computer PSU is used by many here for charging. However, it is usually just the supply for the next portion that does the control of the charging. You need to have CC/CV ability to get the best out of the cells, especially for something like a bot as you want the longest capacity/power available.

For more details and quick answers, please visit the FAQ as there's lots of info in there for beginners in this area and basic general information.

It's accurate, more or less. There are two ways to balance charge a battery. The first one is slowly charging the entire battery after the first cell hits the end of charge voltage and burn off excess energy on the cells at end of charge voltage while the other cells catch up. The second one is stopping the main charge and and applying balancing currents through the balance connector to individual cells until they are all at the desired end of charge voltage. BMS with balancing usually do the first method and I believe smart chargers generally do the second method, but I'm not entirely sure. There will be exceptions for sure.

Whether a desktop PSU can be used or not depends on the PSU in question. If desktop PSU means an ATX PSU from a (desktop) PC, then yes, but not without additional equipment. If desktop PSU means a so called bench or lab PSU, then yes, as these usually bring all the necessary features to charge lithium batteries. Generally any source can be used to charge a battery but maybe you need additional devices. Same is true for charging multiple modules or batteries at once.

Do you have the right approach? Well, what is right and what is wrong? You certainly have ONE approach of several that are possible.

Good point bringing out the Lab PSU. As I don't have one myself, I didn't think about that one.

@DarkRaven: Would you consider a BMS/Charger that does the balancing method stopping the overall charge and balance currents to the individual cells that are lagging an Active Balancer?

I never thought about the definition of "Active Balancer" until this very moment. And I don't know if there is a widely accepted definition that I'm just not aware of.
I'd say there are generally three balance charging methods for lithium cells (if we skip bottom balancing and transferring energy from cell x to cell y, both of which don't really apply here):
1. No balancing at all, CCCV main charge across all cells, and you rely on the cells staying within their specs
2. Balancing by burning excess energy while maintaining the main charge at low currents
3. Balancing by stopping the main charge and applying balance currents to each individual cell

So what is active and what is passive? I'd say #1 is passive and #2 and #3 is active. But you could argue that #1 is nothing in this regard and #2 is passive and #3 is active. I don't know, I've seen people using both schemes. And there are people saying active balancing is only when transferring excess energy from cell a to cell b.

But I think it's not important if it's active or passive. It's important whether you do balance charge or not because that might make a real difference at some point. If you do balance charge then it's not important from my point of view if you do top balancing (and how) or bottom balancing (and how) or if it's active or passive. It's a balance charge instead of just relying on the cells to stay within their specs and that is the main thing.

Ok. Yes, I was referring to an ATX PSU. What more equipment is needed for that setup?

Also, I checked FAQ and didn't see anything that would help me with wiring. Lots of useful information though! I'm still unclear on how to wire these correctly using that charge board. I see 4 terminals for cell connection. None for balance, so I'm assuming I'd have to make some leads. I've been doing a fair amount of digging on the internet and haven't came across wiring solutions for that specific board yet.



It appears I can't attach local photos, check initial post for picture, I think this is how to wire it..?

Please forgive my lack of insight, trying my best here lol.. Thanks guys!

ATX PSUs have fixed voltages und no current limiting. You can use it to power a lithium charger with DC input but you can't charge lithium batteries directly.

Your wiring looks right, however without one of these boards here and without the installation instructions I can't say for sure.

The B# is the balancing pads. You need to solder on wires to those pads. So B1 would be between cells 1 and cells 2. B2 would be between cells 2 and cells 3, etc.

As far as paralleling more cells, your drawing is correct, as DarkRaven brought out.

https://www.electric-skateboard.bui.../67bc6269a8f75905156c7fdf3795ddb57cd032ad.jpg

Would work for balance leads? Looks pretty strait forward, I'm sure I could make it happen. I tried charging my turnigy battery without them and my charger would throw an error and not charge.

[ATTACH said:

20849[/ATTACH]




Username pid='33507' dateline='1531469714']
Hello from California!


I am new to making banks! Ihave some NCR18650B cells, I wantto wire them up in a 3S4P configuration for my bot. They are 3.4ah @ 3.7v nominal cells. I read that if youuse one ofthese battery protection boardsyou'll be able to safely balance charge the bank, so I picked one of them up. I also have a hobby charge for the turnigy cells I was using before.

From what I understand, you have balance leads from the pack, to the charger so the chargerreadsthevoltage of the individual cells and thenappliescurrent from the 2 main leads based on the reading, then whennear full,it will stop current flow to main leads, andput current to thebalance leads to top them alloff equally.I understand parallel and series connections, when it comes down to wiring with this board, I'm a bit confused.

On a side note, could one use a desktop PSU to charge multiple packs? I'm aiming to charge many packs at once, as cheaply as possible lol.



Is this accurate?Do I have the right approach so far?Can anyone show me how to wire this all upcorrectly? Thanks!

Click to expand...

This may help .

Username said:

https://www.electric-skateboard.bui.../67bc6269a8f75905156c7fdf3795ddb57cd032ad.jpg

Would work for balance leads? Looks pretty strait forward, I'm sure I could make it happen. I tried charging my turnigy battery without them and my charger would throw an error and not charge.

Click to expand...

Yes, that is the layout for having balance leads on a bms. I cannot recommend one as I have not myself used any. There are several who have posted results of testing these bms boards, daromer being one of them.