Rate my first battery build with the Kweld

[murdomeek]

I’m starting to do more ebike battery repairs in my local community so I got my own Kweld and welding materials.

This is my first battery build with my Kweld!
Any feedback would be appreciated.

This 10s4p pack with cheap BAK cells was a ‘practice’ battery for my wifes low powered 250w ebike. The battery will sit inside a frame bag with foam cushioning.

• I used 0.2mm nickel plated steel. The wires were overkill for 25a max amps, but oh well.
• I used a 40a daly BMS with on/off switch
• Kweld settings: 25J. Did a test weld, and the nickel ripped leaving dots.

Step 1: Hot glued all the P groups

Step 2: Added fishpaper dots to separate the S groups.

Step 3: Hot glue all the S groups

Step 4: Spot weld!

Step 5: Add BMS leads

Step 6: Add the positive and negative leads

Step 7: Kapton tape, fish paper, heat shrink

It took me 4hrs from start to finish. And I think it turned out really well for a first time low powered battery

[BillGordon]

Personally, I don’t love the layered nickel (tends to come apart), the welds would ideally be more precise, and the soldering needs to flow better.

[marketthrowaway]

@murdomeek

Both of these joints look pretty cold just skimming thru. Didn’t look at the rest, but if they’re all like that probably crank the heat a bit, get a larger iron tip, & use more flux.

The wire could be poor too… what brand you using?

[poastoast]

the joints don’t actually look cold, maybe teheat the small red wire in the second pic (tho the joints can be cleaner, but that’s an experience thing)

the welds hlwever look way too hot in some areas

[murdomeek]

The bms balance wires solder is good for sure
I might need to get a fatter soldering tip for the output wires

@poastoast

the welds hlwever look way too hot in some areas

Thanks, I’ll try to lower the power next time and see how they look

[poastoast]

@murdomeek

fatter soldering tip for the output wires

not all the time, though it can help

you just need to make sure you apply good heat to get the solder flowing

flux is a big help if you burn up the rosin in the solder already (not all solder has rosin core but it’s easy to check)

if you got lead free solder, switch to6040 to 6337 solder instead

i would also recommend more isolation between cells/more structural elements, hot glue won’t always hold even if it’s heatshrunk (ie strapping(?) tape)

[383roadrunner]

0.2mm nickel plated steel? Is this correct? Pure nickel is the standard for batteries, not plated steel

[murdomeek]

Yes, 0.2 nickel plated steel.
Standard ebike batteries draw 15a - 35a. Nothing like the 60a-150a we see in esk8. These strips are fine for low current applications such as ebikes.

[383roadrunner]

I’m not familiar with plated current ratings, just wanted to point it out to make sure there was no issue

[Dinnye]

I am not a fan of the sharp nickel corners over the positive terminals. The balance cables should be run over fishpaper, not on the bare cells. Also if the balance cables cross, there should be fishpaper in between them. Most if not all spot welds are too hot, and I can see that you blew through the nickel a few times. I am a little worried about nickel on nickel connections usually, as they are hard to actually weld on robustly. The solder joints look like they will hold, but they don’t look clean. Probably low quality solder. But for an ebike, these issues are probably all passable, even though not ideal. I’ve seen worse in Chinese production ones from the factory… If you were to build a pack for an esk8 or escooter, then you would have to keep all these extra things in mind. I personally build all my ebike packs to meet the esk8 standards.

However:

@murdomeek

You absolutely need fishpaper under the folded nickel here! That’s really important

If you want some inspiration you can check out my thread. There are a couple ebike battery packs in there.

[magharees]

Fish paper under here

[murdomeek]

Thanks for the feedback guys

[Shadowfax]

@marketthrowaway

@murdomeek

Both of these joints look pretty cold just skimming thru. Didn’t look at the rest, but if they’re all like that probably crank the heat a bit, get a larger iron tip, & use more flux.

I agree with marketthrowaway. This doesn’t look like a good solder joint to me. Looks kinda cold and blobby.

Before you solder stuff together, put a healthy amount of flux on both things. heat and tin both things. Then heat them together and you’ll have a happy solder joint.

Otherwise, it looks like a pretty good pack to me. No other notes besides what people have pointed out.

[marketthrowaway]

@murdomeek can you post a pic of the label of the solder you’re using?

[murdomeek]

[marketthrowaway]

Oh yeah lol. You don’t wanna be using that in esk8 at all. That’s why those joints look the way they do.

Too many recommendations I could make, I’ll let somebody else. But any genuine 63/37 or 60/40 will be way better for you.

[monsterbuilder]

Try this solder instead: link here

[magharees]

Austerity solder? But we huff lead fumes for shinye results

[BillGordon]

Yup, or MG Chemicals.

[murdomeek]

Oh snap! Thanks for the heads up

Is there anything special I need to consider with leaded solder?
(Other than washing my hands after)