Rate my 13S2P battery build without any crossing wires

I'm currently building a DIY 13S battery pack for my TSDZ2 ebike motor. A few years ago, I did purchase an Enerdan 13s2p softpack. I do like that format. I don't like the BMS used in that pack. That BMS disconnects the power line when connecting a PZEM-031 voltage monitor (thus not showing a voltage reading).

To keep the price low I ordered LG INR21700-M58T cells at €2,44 per cell and 13S2P cell holders made of an unknown plastic type. The AC-IR of each cell was measured. Close AC resistance cells are matched as (2P) parallel pair cells.

The edges of the cell holders are square and sharp. To prevent routing sensing wires over these sharp corners, a lot of filing (24 times per bracket) and chamfering (12 times per bracket) was needed:


Unfortunately Nkon was out of 21700 nickel strips, thus opted for pure nickel 21700 2P connectors. To connect the sensing leads a drop of solder was initially placed on these connectors;


I forgot to order plain fish paper. Thus used green silicone backing mats as separator material. In general I don't like crossed wires, thus needed some thinking how to route the wires. I came up with this solution for my Daly Li-Ion 13S 48V BMS (1-1JE-62871-J15E1-1):

The double holes are to create 90 degree angled wire routing (bottom, is glossy, side view of the silicone baking mat):

The perforated silicon mat including sensing wires taped with thermally conductive tape on top of the cells looks like this:

First and last sensing wire are routed directly to the smallest sides. The most positive sensing wire needs fish paper. The negative black sensing wire doesn't need fish paper underneat:


The remaing 12 sensing wires are routed sideways. Even sensing wires are routed through the center hole and the uneven sensing wires are routed around the the edges:

I don't like to shorting sensing wires. Excess length of each sensing wire is stored between the cells in a (hidden) loop:


I am not totally sure if the is wise, thus for a second pack I placed the excess length loops outside the cells:

For a future version I'd like to:
(1) put a fiber glass braided sleeve around the sensing wire loop parts that are stored (hidden) between the cells. This to prevent short circuit at high temperatures or selectively use fish paper between the cells carrying a different voltage in comparison to the routed sense wire or use silicon sense wires,
(2) Use diameter 1.5mm perforations (f.e. made with Fiskars 1003816 hand puncher) instead of the current 3 mm holes.
(3) purchase an extra Li-Ion cell to practice some spot welding and tear testing up on
(4) also file the brackets on the short side, (main positive and negative conductor wires)

Why did you make holes in the fishing paper? You could have just used double sided tape.

Why not cut the sense wires to lenght? Now you get even more risk of wires shorting.
Same thing for the main black wire

I dont understand from the pictures did you do parallel nickel connection or only series?

Is that masking tape?

I am just interested how did you measure the ac-ir?

ak136 said:

Why did you make holes in the fishing paper? You could have just used double sided tape.

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Tape glue tends to become ineffective over time. Mechanical wire routing using these holes is more sustainable.

ak136 said:

Why not cut the sense wires to lenght? Now you get even more risk of wires shorting.
Same thing for the main black wire

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I am not so good at soldering/tinning. The sensing wire ends do come pre tinned.
As long as the wires are not routed over sharp edges (is my experience), I don't expect to see shorted wires. The only reason I can imagine is heat (a thermal runaway).

Also the sense wire resistance (about 38 mOhm for 45 cm of AWG24) is more equal without cutting sense wires to individual lengths.

ak136 said:

I dont understand from the pictures did you do parallel nickel connection or only series?

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Both, I start with series nickel connections, and later on spot weld the (wire soldered) parellel bridges.

ak136 said:

Is that masking tape?

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Yes it is. That masking tape is only there during the build phase to prevent accidental shorts.

ak136 said:

I am just interested how did you measure the ac-ir?

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Yaorea YR-1035+

Soldering is not hard, just look at basic tips on YouTube and practice making Like 30-40 connection and then you will be good

Tape glue still works in my battery after 3 years

The current thru the balance wires is small. I ignore any voltage drop effects there, It would drive me crazy to leave them unshortened, but well, you can reuse the BMS more easily later, I prefer to use a smaller BMS that I can locate on the end. I try to avoid making the battery 8 mm thicker in one section with a BMS on the side or on top.

I also do not worry about the difference between .0136 and an 0139 AC IR. although I believe it's unusual to see much variation on new cells. Something 10% different from the norm is a cell I would never use.

I usually only do two pairs of primary welds on a cell with my cheap welder. I often rely on only one parallel strip on this style of battery, although logically one should do two for redundancy,

It's not so critical for a 13S-2P on a TSDZ2 which is usually 15 amps peak, but I'll want to see the power lead connections before I rate your battery. Also how it's finally packaged.

Looking good so far,

docw009 said:

It's not so critical for a 13S-2P on a TSDZ2 which is usually 15 amps peak,

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That is why my Daly BMS is only 15A.

docw009 said:

but I'll want to see the power lead connections before I rate your battery. Also how it's finally packaged.

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A weak point is the Imaxx (HLP7335) miniOTO 58V fuse holder. The 2.5mm² pre-crimped leads can be pulled out of the housing:

Does this testing photo below serve your needs to see the power leads?

You seem to be very meticulous about your assembly, looks far better than a lot of batteries I've seen people make. You might be interested in getting some glass cloth electrical tape if you do another battery. It's one of my favorite tools for adding a bit of extra insulation and abrasion resistance where needed as well as securing things.

I employ several Daly Non smart BMS's.

I think it is best to view them as completely and utterly incapable of balancing, even on a small capacity 2P battery. If good cells are used this should not be an issue for several hundred cycles.

Thus the balance leads will never even be asked to carry thespec'd 30-50ma passive balancing current, and basically only serve to trigger the UVC or OVC, so arranging them to keep them all the same length is not worth the effort.

Also that beige masking tape, even if only temporary, will likely leave adhesive residue on the nickel strips. The blue masking tape is far better for temporary protection against shorts when building.

Invest in some Kapton tape, as well as the non stretchy fiberglass tape.

Some of the welds look really close to the edges of the nickel strips, and they look very inconsistent like you used different pressure on the electrodes and/or the welder itself was not delivering consistent pulses.

Did you do any tear off testing when dialing in your welder settings?

Some of those welds look like they would easily pop off.

Welding strips to cells also requires different welder power settings than welding nickel strips to nickel strips, especially if the welds are stacked.

I feel testing the weld strength is an absolute requirement to prevent future issues, as thermal cycing puts a lot of shear stress on the nickel strips. When the battery is also subject to vibration or shock loads like hitting a hard bump, less than solid welds will show up as weird intermittent issues and often incomplete charge or discharge as a parallel cell is taken out of the loop and the BMS removes the source or load to prevent under or overvoltage of the remaining good parallel groups.

sternwake said:

Did you do any tear off testing when dialing in your welder settings?

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My testing includes trying to tear off each and every nickel strip (using my finger nail).

A few times the nickel came lose. I did weld these spots again using a slightly higher power setting (f.e. 10 or 12 instead of 8), out of a maximum "Power" value of 30.

sternwake said:

Some of the welds look really close to the edges of the nickel strips, and they look very inconsistent like you used different pressure on the electrodes and/or the welder itself was not delivering consistent pulses.

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The spot welding pressure is actually quite consistent because I use a spring loaded Sunkko HB-70B spot welding pen.
The (mains connected = 100% battery) Frnisi DH30 ver. 1.3 (clone?) might deliver inconsistent pulses.

I would not trust the fingernail test, at all, on any battery I build.

I need to see the nickel or copper tear around the spot welds, leaving torn copper or nickel on the cell, and rarely is finger strength alone enough to accomplish this, when grabbing the strip and pulling, which is far more stress than getting a weak fingernail under a corner and prying..

I also need to see that both spot welds are the same size and strength, and leaving the same diameter of nickel or copper on the cell when teh strip is grabbed in some plyers and rolled off the cell.

If one of the pairs of welds is weaker than the other, I bump up the power in stages until both are equal.

My packs will be in a flexible electric skateboard, So the welds need to be stout in order to deal with intense stress and vibration and fatigue.

Is lesser weld strength acceptable for different applications?

My opinion says not, and I aim for such results on every spot weld.
The strip must tear and leave behind equally sized strips on the cell itself.
I accept this could be considered overkill, but even the worst assembled factory batteries that I have disassembled would easily pass the fingernail prying test, and would also tear the nickel, even if the bits left behind are far smaller than my own builds.




This pic is using 0.2mm copper under 0.1mm stainless steel using welding flux. I don't recall the exact settings used of my AwithZ p20b super capacitor based welder on this exact weld but anywhere from gear 320 to 380 yields similar results.
It really depends on the specific cell used, and the thickness of its nickel plating and surface texture whether 320 is enough or if I need to dial it upto 380.

Without the welding flux I need to use at least gear 550 to achieve the same results.

Stepping up to 0.25mm copper under 0.1mm stainless steel with flux requires gear 730
0.15mm pure nickel requires about gear 85(of 999)

I've no experience with Sunnko welders and my experiences with battery based spot welders were that inconsistent results were absolutely guaranteed, unless battery voltage and temperature and welder temperature were kept within strict ranges.
As the battery aged and degraded more and more power was required to achieve satisfactory welds and this required basically establishing new parameters on every subsequent build.

I'd really rethink that fingernail test. if you can get a narrow chisel, and put some fishpaper on it and get the sharp end under, and do a little lift and pry, I bet a lot of welds will pop right off.

Weak welds are likely point source heating which increases the rate at which weak welds will degrade as they thermally cycle.

Will they be strong enough in a low current low vibration application, very possibly. It is a risk, but an avoidable risk.

When someone says he cannot even solder balance wires well, then one might worry about safely soldering heavy power leads to the two ends of the batteries. That's where craftsmanship matters,

When I build a battery, I test out my welder on scrap cells, rolling off the nickel with a pliers. Like sternwake, i know what to look for. It's experience.

i've have bought a fake Daly BMS which didn't balance, but I have had good luck with real ones.

sternwake said:

My packs will be in a flexible electric skateboard, So the welds need to be stout in order to deal with intense stress and vibration and fatigue.

Is lesser weld strength acceptable for different applications?

My opinion says not, and I aim for such results on every spot weld.

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I agree, that lesser weld strength is not acceptable.

Especially with this small and long pack shape.
Twisting/torsion forces will all and up at the spot welds, most force on the most positive and most negative spot welds.

My velomobile is without suspension, thus loads of vibration there.

For a next pack I should invest in a better spot welder.

cj0 said:

For a next pack I should invest in a better spot welder.

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I own one of those kweld units, pimped with extra cooling and careful selection of batteries (with even more cooling) to run on. It seems general consensus here those kweld units are technically outdated. For a fresh start, I suggest looking for brand AwithZ

cj0 said:

I agree, that lesser weld strength is not acceptable.

Especially with this small and long pack shape.
Twisting/torsion forces will all and up at the spot welds, most force on the most positive and most negative spot welds.

My velomobile is without suspension, thus loads of vibration there.

For a next pack I should invest in a better spot welder.

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Since you stacked nickel strips, going back and welding again with higher power settings is not likely to increase the weld strength of that first layer.

So increasing the reliability of this battery in a high vibration high flex application, preventing as best as possible, the effects of torsional twisting and vibration needs to be considered.

If this weld or that weld breaks, what will be the effect? with the strip be able to short out on the subsequent parallel group?

Can you glue some G10 to the sides of the pack to increase its stiffness and nestle it in some foam padding so the enclosure can flex around the stiff battery?

Broken welds can be dangerous, and surviving the fingernail prying test means very little in a mobile application.

i would expect failure and take all additional steps possible so that a broken weld just opens the circuit, instead of shorting out.

If range suddenly seems to reduce considerably from one cycle to the next, and or the charger flashes its green light sooner than expected, it is likely a broken weld.

braunschweiger said:

I own one of those kweld units, ...It seems general consensus here those kweld units are technically outdated. For a fresh start, I suggest looking for brand AwithZ

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What or why is the Kweld spot welder technically outdated?
Which AwithZ model would you purchase/recommend and why?

cj0 said:

... weak point is the Imaxx (HLP7335) miniOTO 58V fuse holder. The 2.5mm² pre-crimped leads can be pulled out of the housing:

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The Imaxx (HLP7335) miniOTO 58V fuse holder is introducing another weak point.
It's not only the contact the can be pulled out of the fuse holder.
Also the wire contact to blade system can have high ohmic connections.

Normally the stripped wire to fuse holder blade measures around 12~20 mOhms.

In one pack that segment measured a whopping 500 mOhms (generating a lot of heat, thus burning 15A fuses at 8A).
The source of the resistance is not the wire: pack nickel strip to wire contact measures 6 mOhm.
Insert that CCS150FR contact into the housing and measure at the corresponding (fuse holder) blade increases the resistance value to 500 mOhm.

scianiac said:

You might be interested in getting some glass cloth electrical tape if you do another battery.

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Link please!

Zambam said:

Link please!

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https://www.aliexpress.us/item/2255...t_main.10.2c0b1802PJzqiI&gatewayAdapt=glo2usa
https://www.amazon.com/dp/B07TJ28QD7

I'm a bit of a tape connoisseur and this stuff is one of my favs. It combines the strength of something like a fiberglass strapping tape, the heat resistance of katpon, great abrasion resistance, adhesive is quite good (silcone based adhesive of course for the heat resistance), finish is good, of course basically no creep or stretch so you can wrap something and it will stay, sticks to itself reasonably well (unlike teflon fiberglass tape), and available in a wide range of widths. Only downside is it's not super cheap, but nor is it that expensive.

scianiac said:

Amazon.com

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That is:

APT Glass Cloth Electrical Tape, High Temperature Masking Tape, 260°C. UL Listed, White Heat Resistant Tape. Ideal for Class H Electrical, Powder Coating, Sand Blasting​

In Europe that APT glass cloth electrical tape (GTIN: 00628250733136) is crazy expensive at € 70,36 per roll.

The AE link looks similar to 3M Scotch type 69, a silicon based Glass Cloth Electrical Tape.

scianiac said:

https://www.aliexpress.us/item/2255...t_main.10.2c0b1802PJzqiI&gatewayAdapt=glo2usa
https://www.amazon.com/dp/B07TJ28QD7

I'm a bit of a tape connoisseur and this stuff is one of my favs. It combines the strength of something like a fiberglass strapping tape, the heat resistance of katpon, great abrasion resistance, adhesive is quite good (silcone based adhesive of course for the heat resistance), finish is good, of course basically no creep or stretch so you can wrap something and it will stay, sticks to itself reasonably well (unlike teflon fiberglass tape), and available in a wide range of widths. Only downside is it's not super cheap, but nor is it that expensive.

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Thanks! I have this unfinished 13S 21700 cells that works great when temporarily tested w/o BMS on my TSDZ2. I need to add the BMS and make a somewhat water tight enclosure so I can mount it on the down tube using heavy duty rubber bands, i.e. bicycle inner tube strip or equiv. if I can buy it. I will not be using the bottle cage riv nuts to mount the battery, just strapped to the down tube (I believe it will be strong enough)

Given the above, can you give me some guidance on what other materials to buy to finish the pack?

cj0 said:

That is:

APT Glass Cloth Electrical Tape, High Temperature Masking Tape, 260°C. UL Listed, White Heat Resistant Tape. Ideal for Class H Electrical, Powder Coating, Sand Blasting​

In Europe that APT glass cloth electrical tape (GTIN: 00628250733136) is crazy expensive at € 70,36 per roll.

The AE link looks similar to 3M Scotch type 69, a silicon based Glass Cloth Electrical Tape.

Click to expand...

You'll notice the aliexpress stuff is a fair bit cheaper, I have both of those, seem exactly the same to me. That's not always the case, sometimes you want the more premium quality version of the tape but this stuff is used a lot in electronics assembly and such and guess where that happens.

Zambam said:

Given the above, can you give me some guidance on what other materials to buy to finish the pack?

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That depends on tools and experience. I just 3D print my battery cases from ABS then seal the end cap and wires on with some PU sealant (seals well but I think I can pry them off later if I needed to). Then to mount to mount to the bike, contoured printed blocks for rotational stability if needed, little dense foam or rubber and some straps or cordage. Depending if you need to remove the battery determines what methods and materials to afix it.

This is the last battery I made, it's a split pack (goes on either side of the top tube right up under the bars due to weird weight distribution goals of this specific build, might not work but I can mount it somewhere else if I need to). I still have to do the mounting hardware but that shouldn't be too hard since I can just print the strap loops and mounts and glue them on, the magic of solvent weldable plastics. The bottom case has the bump-out for the BMS while the top case has that little panel with a fuse behind it. Panel is also glued in the PU sealant but I should be able to pry it off if I ever needed to replace the fuse.

If I didn't have a printer I think making a case from flat sheets of ABS/PVC/Acrylic that you make a box from and solvent weld it together would be a decent option if you wanted a waterproof hardcase. ABS would be the best option there, PVC can be itcky to work with, acrylic is brittle and a pain to work with unless you have a laser cutter. And then if you wanted to make some mounting blocks to contour to a tube or part of the frame to lock things in place I would get a piece of PVC foam exterior trim board. It's weird stuff, I used to use it a lot before printers, it can be gummy to work with but because it's a super dense foam it works easily and you can endlessly solvent weld it it itself and to ABS with the right cement.

My solution for mounting things to round or weird shaped frame tubes so far has been making a block that is contoured to the shape, then use some thick double sided tape (to fill gaps in your fitment) and then that along with what you are mounting gets strapped to the tube, I usually use dyneema line for this. So basically the tape is only stopping it from sliding around and rotating, like rubber but better. The actually strength comes from the strapping, which can be spread out along the object. So a battery maybe 4 loops of dyneema fishing line spread out along the battery, you've got around conservatively 1500lbs of strength holding the battery on. (500lbs line, in a loop so double that, 4 loops, lose 50% in the knots (use good knots), take away 500 to be conservative). Use versatackle knots with figure 8s as the loops and you can get it as tight as you please (at some point you just crush the battery case) and they stay tight pretty decent as even cheap dyneema doesn't have too much creep.

If you need to remove the batteries often replace the line with webbing straps but I'm still working on ways to use webbing in ways that can be tightened and are strong. So many things use webbing with those side snap buckles and like the webbing is real strong but those buckles sure aren't. D rings are strong but also hard to tighten. I'm experimenting with a toggle tensioner but it needs some refinement. If you use some foam between the battery and your mount, like some EVA foam, you can get the side snap buckles pretty damn tight as you compress the foam. I've had good luck with this but the battery was wedged pretty good inside the triangle so it had a lot of help in preventing motion.

Lets see what did I forget, ah to keep the battery brick secure inside the hard case I've either made the case so tight it's a press fit, sometimes unintentionally, or I use some dense foam or rubber to keep it in place. Either way adding a loop of stong tape around the back sticking out so you have something to pull the pack out of the case if you ever need to is a wise idea. I think just using like some fiberglass strapping tape is fine for stuff like this, don't need the fancy stuff.

Waterproofing I generally first conformal coat the BMS, which is a pain without taking it apart but the stuff wicks in pretty good, waterpoofing in layers so if your primary defense fails you have a fallback. For sealing the wires the PU sealant seems to work good, sticks a little better to stuff than silicone. I buy it in a calk tube and fill 50cc applicator tubes from that because they are just so nice to use. I've played around with foam gaskets and eh not worth it, I've used some butyl tape to seal some things, can be useful.

To address the "I just 3D print everything", at this point if you like makings things, you have the space and are willing to learn some CAD a 3D printer is worth every penny. They real issue with doing things that way has nothing to do with the printers, it's the CAD. CAD programs are overall not great and even with a lot of experience things take time to CAD. Free options have issues, paid options have different issues, I've been testing some options recently hoping some newer options are better than mine from 2017 but so far I've come up short. Freecad is capable but it has some fundamental flaws that in my opinion make it much slower to use for complex parts. If you don't care about the risk of your work being ransomed then use onshape I guess. Rhino might be an option by I've yet to try it. AI doesn't seem amazing yet for this type of stuff but I bet you could get some pretty impressive stuff by asking an LLM to write you openscad code for the part you want.

Edit: added some links

cj0 said:

What or why is the Kweld spot welder technically outdated?
Which AwithZ model would you purchase/recommend and why?

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why :
* kWeld - "Next level" DIY battery spot welder
* not powerful enough for 0.30mm copper (plus Ni or SS on top)
* requires extra lipo

which (hearsay - I am invested in my pimped kweld) :
* read up on diy500amp.com recommendations for your needs; seems pretty reasonable;
* search this forum