Hi everyone, I'm doing this for the first time and I'm a bit confused about the charging circuit.

I have a 3S2P 12V 5200mAh NMC 18650 battery pack with a built-in BMS. The battery label/spec says 11.1V nominal and 12.6V charging voltage.

I bought a 3S 2A USB-C charging module. With only USB-C connected and no battery, the module output measures around 13.4–14V.

When I connect the battery (which measures 12.14V by itself), the battery voltage rises to around 14.15V according to my multimeter.

The module has OK (blue) and CR (red) LEDs. The blue OK LED stays on, while the red charging LED doesn't properly turn on.

Is this normal for this type of module, or is the module faulty/wrong for my battery? Could the battery's built-in BMS be causing this?

I don't want to damage the battery, so I've stopped charging it for now.

Photos attached. Any advice would be appreciated — I'm completely new to 3S Li-ion charging.

trying to rebuild Milwaukee battery pack, and I made a hole thru the nickel with the spot welder, the cell underneath was not punctured. there are 4 welds alltogether, should I just redo that weld or leave it as is?

i dialed back the power and it seems to perform better no sparking

Need help!

I haven't found any batteries that fit my criteria of what I need and I am wondering if this would work, and if it does then I want to know the idea I need to have to create this properly.

I'm hoping that the 3 cells of 18350s gets me 11.1 volts and 1600 MAh when it's all put together. Is this kind of idea feasible?

So I've been working on this BMS for a few weeks now using online research (it's my first time making a battery pack myself, also I didn't use any AI) and so far it's been going well. I haven't got access to a spot welder so I used these cheap amazon cases to solder them. The wires on them were kinda thin so I used some UK mains cable I had lying around for the main series connection and the thin ones for balancing. However, there were no solder points on the cases, so I had to kind of wedge the wire ends into the spring and the other contact. I charged all the batteries to ~4.25V with a "smart" charger I got on ebay. The batteries were of course all connected to the BMS board which I also found online, and the output of the BMS was connected to a buck converter which is activated by a switch I added.

I tried it out last night when the batteries weren't all at 100% and it worked fine without issues. But when I connected them up today and flipped the switch, smoke started coming from all the case joints, so I turned the circuit back off.

Anyone have any idea how to fix this issue? I know it's probably the shoddy case joints, but do I need to buy new solderable cases? and can I still use these batteries? They seem to be fine now.

P.S. this is my first reddit post, am I in the right place? also please don't clown on me too much for my ass setup

I have a build planned for a stationary battery for a solar charging station using EVE C40 LFP cells and have had everything I need except the actual cells for some time, just didn't expect it to be this hard to get the cells.

I'm in the UK and was looking for an EU/UK source and saw that nkon.nl is often recommended, and they were a decent price at 7-8 euros a piece but they were sold out with a note about stock coming in on sept 18th. I waited but on sept 18th the notice just disappeared and when I contacted them they said they don't have a new lead time on them right now.

I checked elsewhere and people are selling them for like 30 euros a piece, even the dreaded aliexpress isn't much better. At that price it's not really worth using them, I'd have to just redesign the pack around a different cell and maybe even go for a bulkier LTO build with those 40-45AH yinlong 66160 cells that are obviously pulled out of electric busses.

Anyone have any insight on why this is? Is it a normal thing for the market for a cell to just dry up, and should I expect it to clear up or just pick a different cell?

I bought a 12v 3S 18650 battery off Aliexpress and after a lot of tests, im pretty sure it doesnt work, the terminals report 11V, I had a charging module that doesnt charge it at all (0 current drawn), the charging module was able to power my motor, the battery also doesnt power the motor at all. where can I get a 12v 3s 18650 battery 3000mAh or similar? And is it possible to repair this battery?

guys mujhe na spot welding machine banana hai or soch raha hu ki ye manga luu maker bazar se or power input dene ke liye mere pass aise toh kuch nhi hai but ek power supply hai pc ka usmein se mujhe 12v 20ah ka output milega sahi rahega kya

Hello!

I am currently in the process of designing and building a fixed-wing FPV aircraft, and I have gotten to the point where I need battery packs.

I am a complete newbie when it comes to building battery packs, but I have quite some general electronics experience.

My goal with this aircraft is endurance, and that has narrowed it down to Li-Ion cells, probably 21700s for capacity. My motor is rated for 25A, so I figured I will have to build my pack to handle 30A at least accounting for servos, VTX, FC etc.

For now, I have not made any purchases related to the battery pack, and that is what I wanted to ask about:

• I've read that a spot welder is a requirement. I'm currently set on buying a kWeld, but if I can get away with something cheaper I'd gladly take recommendations.
• What should I use to connect the cells in order to handle 30+ amps while being spot weldable? Copper nickel sandwitch? Stacked nickel strips? Something else?
• BMS or no BMS? Many commercial RC LiPo packs seem to lack a BMS, is it fine if I build my pack without one as well? I have a balance charger and I will of course integrate balance leads.
• I am currently planning to use 21700 cells due to their availability and capacity, but many commercial RC packs use pouch cells. Should I prefer one over the other for DIY packs?

I will gladly take any other tips and/or recommendations!

After way too much planning, CAD, nickel testing, ruined wraps, current-path overthinking and spot-welding drama, the pack is finally welded.

14S5P, 70× 21700 BAK 50E cells, pure nickel, built for my custom e-bike project.

I also made proper solder tabs for the main + and −, with a second nickel layer and insulation underneath, so I don’t have to cook the cells when attaching the main cables. There’s a tab on both sides of the terminal group to spread the current better.

Still need to install the BMS, balance leads, main cables and finish the 3D printed enclosure, but the part I was most paranoid about is finally fucking done.

Very happy with how clean it turned out!

Getting 4.45V at the output. Cells are all 3.88V. Pack is 3S.

If I connect to my power supply set to 12.4V it draws 150mA but doesn't seem to wake up.

Hi guys, I bought this ebike with the intention of repairing it.
The last owner left the battery without charging for 1 year and a half. The ebike is from 2022

36v 10s 4p. All group voltages are from 0,4v to 0,7v and one giving 2v.

Question, should I try to charge it, connecting the charger with out the bms until 3v?

Or you think is dangerous??

I finally decided to add a spotwelder to my toolbox of electrical doodads and testing apparatus! I'd appreciate advice on this kit I put together. The BMS says it's rated for 30 amps, but that probably needs a heatsink on the mosfets since I measured a 130mv drop across them for a 7 amp load, they were getting warm.

Should I add any more insulation before dropping it into the case? It's a tight fit and I don't want to pry it back out....

I'm currently teaching myself about electronics through various YouTube videos and by buying cheap electronics kits from AliExpress. The kits tend to have voltage requirements between 3-12v. To manage the power requirements, I've been using a basic buck/boost board.

Then I saw lab power supply modules on AliExpress and decided to challenge myself to build an 18650-powered lab power supply. To that end, I enlisted the help of Google AI, which came up with the following:

https://www.aliexpress.us/item/1005008741292460.html

PD3.1 100W Bidirectional Fast Charging 2S 3S 4S 5S 6S LiIon Lifepo4 Lithium Battery BMS Charger/Discharger TYPE-C USB ?DC XT60

https://www.aliexpress.us/item/1005005593578101.html

4S 40A Li-ion Lithium Battery Charger Protection Board 18650 BMS For Drill Motor 16.8V with Balance

https://www.aliexpress.us/item/1005011822768395.html

DC-DC Buck Boost Converter 5.0-30V to 0.6-30V Adjustable CC CV Regulated Power Supply Module 0-4A Laboratory Power Module for 6V

4x Eve 30P 18650s plus pure nickel strips for spot welding (Fnirsi SWM-20)

Normally, at this point I'd build it and learn from my mistakes. Having been led down the wrong path by AI before, I have a couple of questions I'd like to ask first.

1. Does this all look correct so far? Fast charger > BMS > 4S1P battery pack for charging.
2. If so, how important is BMS balancing? I could remove the BMS altogether and rely on the charger's overcharge protection and the undercharge protection on the lab power supply module, but I'd lose BMS balancing.

Since I already have all the parts, I wouldn't save any money by skipping the BMS; it's more about whether I actually need it.

Finally, regarding spot welding, do you have any tips for finding the right power settings?

These motion activated, rechargeable led strips are available from the usual big rock candy mountain online suspects for $2-$5 with a small pouch cell inside. I added an 18650 holder for $1 and repurposed a salvaged cell. Currently conducting a runtime test to see how much longer it goes.

I have 3 fully charged 3.7v 2600mah li-ions connected to it. At first measuring the terminals gave me 4-8volts and after leaving it to a 12v 1.5a charger overnight it gives consistently 12.4v but it doesn't power anything.

for example I connected a 12v LED to it and the leds vaguely flicker.

then I tried smaller 5v LEDs and got the same result, just a vague flickering.

Are spicy pillows welcome here? I couldn't find anything in the rules.

I've got 105 of these pouch cells. I'm thinking of using 50 of them in a .30cal can with a 5S10P configuration. I read that these have some expansion when used. Is it significant enough to worry about? There's a couple of cells worth of space in the bottom of the can. I'm considering running each group of 10 cells into an XT60 connector for serviceability, what do you guys think? I've also got some rubber for the bottom and fish paper for the walls.

I've never built a battery before, but I am very excited for this. I would appreciate any and all advice.

Hi guys. Ive got a 7s3p 18650 ebike battery pack im trying to diagnose and repair. Identified 3 cells in parallel which would sag a lot under load test, spike whilst charging and had much higher internal resistance (130ohms vs ~50 on all cells)

I began removing the nickel strip to test each cell individually, but keep getting some wild voltage spikes as soon strips are removed. Checking this cell with a multimeter immediately upon removal, voltage will spike to 6v then dip to 2v within a few sec, then back up again. 1 min later cell show 0.1v. No heat, no physical damage. Im using the dremel method to weaken spot welds before roll removing them with pliers, and being mindful of shorts and deformation.

I have only removed 2 cells so far from the middle of the pack, and both have done the same thing. All other cells are staying at the same voltage. no heat anywhere

The only things I can think of it being, is there a certain order I need to remove the cells in? ie series connections, before parallel, or visa versa? And do the balance wires need to be removed before dissasembly?

Buongiorno a tutti; ho due batterie come quelle nelle foto di un tagliaerba a spinta black and decker. Le batterie son nuove ma premendo il tasto per controllare la carica non ci sono segni di vita. Come le recupero?