Copenhagen Wheel Battery Replacement

[99t4]

I actually asked the cell distributor some advice about welder setting based on my tests and one of their reps provided some outstanding emails to help me in less than 24hr. They (diy500amp) were not even the ones that sold the spot welder. Pretty cool.

You might like to give a positive shout out to the vendor in our Vendor Relations Corner

Might help future builders, we always get questions like "Recommend a battery source."

 

[jkrienert]

Pickled nickel. Figured this might be a simple way to test if the ribbon I bought is nickel plated or pure nickel. Coarse sanded half a piece of the ribbon and put in warm pickle brine for the next 24 hr...

 

[jkrienert]

Recommend a battery source

Heck ya, went ahead and added some support for the cell distributor.

Hopefully their service is consistent, since in this case my recommendation only comes from dealings of n=1. If i harken on another rebuild I'll probably look to them first.

When I tested the cells this morning they all were resting at 3.527v (+/- 0.001). That's pretty decent right?

 

[Zambam]

Pickled nickel. Figured this might be a simple way to test if the ribbon I bought is nickel plated or pure nickel. Coarse sanded half a piece of the ribbon and put in warm pickle brine for the next 24 hr...

Why nickel? Copper has 4x better conductivity than nickel. Your BH welder should handle 0.20mm copper and 0.1mm 304 stainless sandwich.

 

[jkrienert]

Why nickel? Copper has 4x better conductivity than nickel. Your BH welder should handle 0.20mm copper and 0.1mm 304 stainless sandwich.

Well, pure nickel (Ni) was favored over Ni plated steel based on my research. I also retrieved matching 0.1mm x 7mm copper (Cu) ribbon to make Ni-Cu sandwich. So I suppose I am sort of addressing your concern.

Bearing these resources in hand (0.1mm nickel and 0.1mm copper both 7mm width) what would be the recommended sandwich order?
Or maybe I should reevaluate, and pursue what you recommend...

 

[Zambam]

Well, pure nickel (Ni) was favored over Ni plated steel based on my research. I also retrieved matching 0.1mm x 7mm copper (Cu) ribbon to make Ni-Cu sandwich. So I suppose I am sort of addressing your concern.

Bearing these resources in hand (0.1mm nickel and 0.1mm copper both 7mm width) what would be the recommended sandwich order?
Or maybe I should reevaluate, and pursue what you recommend...

I have not used the BH spot welder you have, only hearsay from what other's who has the same welder. So take what I say with a grain of salt.

304 SS-Cu sandwich requires less power from a given welder compared to Ni-Cu sandwich of the same thickness, thus allowing use of thicker Cu.

I would suggest ordering some 0.2mm & 0.3mm x 7mm Cu ribbon and some 0.1mm x 7mm 304 SS ribbon. Do some test welds to see what's the thickest Cu your welder can handle.

 

[jkrienert]

Well... The Ni is just plated steel. 120 grit scuffed and soaked in 48hr pickle bath to check for corrosion.

Given this, is it acceptable to use this 0.1x7mm Ni-Fe over 0.1x7mm Cu, or maybe better to strive for 304-Fe?

That gage Cu is what's on hand, though I suppose I could order a thicker mill, or I have enough material of the 0.1mm thickness Cu to do a double layer? That might entail some experiments to see if it will weld strong enough...

Wow. I just arrived late to the party on this existing thread linked below. Much of my questions had and to be had about these bus connections are answered within...

"Copper/nickel sandwich" buses for series connections

There is a popular thread called: "Spot Welding Copper Strips to 18650 Battery Cells" Spot Welding Copper Strips to 18650 Battery Cells It is the place where the copper/nickel sandwich method was first reported, and enough interest has been shown that some members have asked that this method...

endless-sphere.com

Man, this community is an incredible wealth of knowledge. Thanks everyone for maintaining this library of wisdom.

I'm going to have a go at testing the infinite split busses for each 1S2P module, with the 0.1mm Ni-Fe top and 0.1mm Cu bottom to some spare 18650s sometime soon...

 

[jkrienert]

...carefully.

This is no joke @taneque . The internals we very complex. Maybe more importantly, the insides seem really strategic and well planned, ~clean. I took a lots of photos during disassembly to help with reassembly.

Your mention about the BMS maybe being toast has me, a bit worried now that I've made some investment in the repair already.

The pack was for sure gone though, each cells voltage was around 0.6v, or ~7.1v for the whole 13s pack. Since it had likely been at that voltage for more than the week of shipping, thats not a safe level for salvaging for me. The newly purchased 35E cells have a little different ratings than the original 29E cells, though nothing that would seem to prevent safe function that I know of ...

The wheel otherwise looked like it had never been used. In fact, it came in the original manufacturer box with all accessories and instructions, as well as the OG demagnetized freewheel having no detectable tooth wear.

So, I'm hoping that is all signs pointing towards the BMS, controller, and motor being okay.

 

[jkrienert]

Bit of prep and experimenting with connections of the parallel and series groups of cells...

• Image of upright cells shows the interface between each 2S2P module.
• Image of wire shows the pre-xisting harnesses series bus and BMS tap tabs that were clipped and saved from the removed dead cells.
• Images with Cu and Ni-Fe ribbon cuttings (both 0.1mm thickness, with narrower Cu folded ~0.2mm thickness) show orientation of sandwich layers and (best so far) test welds.

I do not yet know if this from-scratch bus will be what I use because even with the testing so far I cannot get a good bond between the Cu and Ni-Fe or the double layer Cu to single layer Cu. This, with the prev. mentioned super capacitor spot welder, when its outputting from 1-2.1kw power.

 

[Zambam]

the testing so far I cannot get a good bond between the Cu and Ni-Fe or the double layer Cu to single layer Cu.

Welding copper to copper is difficult w/o special flux. Just tried this on my AWithZ UF20B 10.5kW, 1750A supercapacitor spot welder set on 95 of 99 gears :

2 layers of 0.15mm Cu under 0.1mm 304 SS (w/o flux). I was able to easily peel off the weld spots with my fingers. Not acceptable!

 

[jkrienert]

I was able to easily peel off the weld spots with my fingers. Not acceptable!

Yep - that is a similar outcome I am having, and a sign to stop and reevaluate what method(s) I will be using...

@Zambam how well did the 304 to Cu single layer bond?

As silly as this analogy might be, my gut reaction... is make it like I make my sandwiches. That is, I like having lots of interlayers of flavor vs relatively thicker layers of each ingredient. Ya know, spread out the flavors .

The problem with adapting that analogy back to the metal sandwich is it probably necessitates a much thinner layer where the resistive heat forms to create the weld bond.

Maybe something like ~0.05mm thickness 304-Fe ribbon on top of and between two layers of 0.1-0.15mm Cu ribbon? That way, the resistive material is thin enough to not block penetration of the weld through the Cu, yet simultaneously able to maintain enough resistance for heat to securely bond the Cu. E.g. this might better distribute the heat throughout the entire thickness, rather than being 'top heavy'?

Another idea on this, instead of side by side placement of the weld probes on the same face using the infinity slot gap technique, I'm pondering experimenting (when I get off work this week) with orientating the material vertically on the workbench, and placing the welding tips on either side, e.g. the probe tips representing the metal sandwiches 'bread'. This would seem to me, to be more like a traditional alligator style tack/spot welder, that is, the ones I remember using in shop class 20+ years ago... Would this work I wonder?

 

[Zambam]

@Zambam how well did the 304 to Cu single layer bond?

Not much better


Give up the idea of layering 0.1mm Cu strips to increase thickness. 0.1mm Cu is too thin IMO. As I suggest earlier, buy 0.2 and 0.3mm Cu strips and 0.1mm 304 SS (they are not expensive) to experiment with.

Another good thread to look at on top of the one you already found.

 

[jkrienert]

Got a moment to do a bit more testing. I found some affordable .15mm Ni-Fe tabs for 2p and discovered that if I infinity slice the Cu below (here tested with 0.1mm Cu, waiting on order of 0.2mm) the bond is permanent and I can not pull apart without tearing.

Note though, I have the setting way to high for this test. However, figuring out that I also needed to split the Cu below the weld to drive the energy down in a full U through the stainless base, was essential to moving forward.

Photo shows my 'shotgun' test without the Cu slice that easily pulled off, I'm supposing because the current just traverses through the Cu rather than down through the stainless base (hypothetical cell cathode/anode). The other side with the infinity slice in both layers is a very secure bond.

Stoked.

 

[jkrienert]

0.2mm Cu ribbon arrived. Instead of making delicate infinity slots, I just ripped the 10mm width lengthwise.

With the 0.15mm Ni-Fe tab over onto the same SS-Fe sheet I get a strong bond, and the 0.2mm Cu tears before the spot welds do.

This test in the photo is with the welder settings maxed out, and it's leaving quite a bit of Cu electrode on the top and some oxidation halos of too much heat at the weld. I am going to gradually power back and see if I can overcome this while maintaining the secure bond...

 

[jkrienert]

All new cells returned to their modules and temp installed into traction battery housing. Verifying BMS tap harness colors and thermistors. Next up is prepping to spot weld buss connections between all modules.

Any recommendations on how to approach spot weld connections between cells? Previous design had 12awg wire that was crimped between each 2p buss for the series connections. I don't know if those series wires were done before or after the tabs were spot welded to the cells...

I'm supposing I should keep the workspace as wire and clutter free as possible, which suggests to me I need to first spot weld the tabs and Cu busses to each 2p cathode and anode. Then once all those are ready, gradually spot weld the series connections, in quarters of the entire pack voltage then connecting each quarter, all while making sure there is no connection or load on the + and - of each 2p and quarter section, and half, and so on to the entire 14S pack.

 

[Zambam]

0.2mm Cu ribbon arrived. Instead of making delicate infinity slots, I just ripped the 10mm width lengthwise.

With the 0.15mm Ni-Fe tab over onto the same SS-Fe sheet I get a strong bond, and the 0.2mm Cu tears before the spot welds do.

This test in the photo is with the welder settings maxed out, and it's leaving quite a bit of Cu electrode on the top and some oxidation halos of too much heat at the weld. I am going to gradually power back and see if I can overcome this while maintaining the secure bond...

If you used 0.1 mm 304 SS instead of the 0.15mm Ni-Fe, you probably wouldn't get much Cu electrode sticking.

With 304 SS, you probably would not need the infinity split on the 0.2mm Cu and you may even be able to use 0.3mm Cu (depending on the power of your welder).

You should be doing test welds on 18650 cells, not SS-Fe sheets.

 

[jkrienert]

Here is my hypothetical procedure for each 2p tab. Using the cells from the original pack, which are each at ~0.55v. Seemed like a safe way to go for experimenting and getting the hang of welding...

1. Tack the Cu ribbon to the tab.
2. Cut the Cu infinity slots with scissors using the tabs pre-made slots as a guide... I decided to go back to this way instead of cutting the Cu in half because it is easier to hold the parts in place when welding.
3. Trim edges of Cu round to prevent hot spots on shrink wrap.
4. Weld to cathode of one cell.
5. Weld to cathode of other cell.
6. Check secure.
7. Weld to anode of one cell.
8. Weld to anode of other cell.
9. Check secure.

I dropped the max power by 60%, and the welds are still very robust. Gripping the 0.2mm Cu and 0.15mm Ni-Fe with alligator vice grips and pulling they tear before the welds to the Ss-Fe cell cathode or anode.

Any tips or recommendations?
Proceed?

 

[jkrienert]

If you used 0.1 mm 304 SS...

I kinda have gone through the ceiling on my intended budget for this repair, so I am going to have to work with what I got which hopefully is acceptable. If this goes well, in the future I will most definitely take your advice on the SS being superior. Thanks for that guidance.

 

[jkrienert]

1. Weld to cathode of one cell.
2. Weld to cathode of other cell.

So, clearly by these photos I need to take a bit more care on position of the tabs before welding to the cell. The skew might lead to poor welds or uneven distribution of current to the anode/cathode and I want to prevent that.

Regarding 0.2mm vs 0.3mm Cu ribbon... it's a 500w peak hub motor, which at 48v is a maximum current across each bus of ~10A. The 9mm wide 0.2mm thick Cu ribbon should be more than enough cross section area (1.8mm^2) for that and remain cool, yes? That x-section can constant carry ~18A?

Side note, would typical hot glue be okay to use for securing the thermistors or is there another type recommended for this type of application? I even considered type2 silicone, yet that could be a mess due to cure time and there being 7 thermistors total.

 

[jkrienert]

doing test welds on 18650 cells,

I agree! I've moved to that level in the recent post. I was being especially cautious as this is my first approach at this method and this battery chemistry.

 

[jkrienert]

As far as the bus between each series, I am contemplating maybe soldering (pink) 12awg wire (green) onto the copper layer (yellow) before tack welding the two center spots that hold the NiFe tab on top before the final spots to the cells. Then using the tab (red) without copper below as my cell tap connection for the BMS.

Crude sketch hopefully shows what I'm saying. I'd rather have a crimped connection between Cu busses on each 2p end, yet that's sort of facilitated here by the spot welds that would sandwich the solder joint between?

Any advice on this aspect is welcomed and appreciated.

 

[jkrienert]

So I prep'd all the bus parts...
Then fanned the wire ends without existing tab and soldered those to the copper
Then spot welded the pre-slotted tabs to both ends of each bus (I probably over-did the number of spot welds per tab)
Then heat shrunk all the buses
Then started to assemble the 13s pack in sub-models for lower voltage during assembly.
Then the sun set...

Hope to finish connections and test in the next few days... Including charging the wheel from an extension cable outside and at a distance from home structure until max and min pack range is nominal for use.

 

[jkrienert]

Well ... the junction of wire to tabs I built had far to great of a stress on the joint and one of them became brittle and broke during test fitting. I inspected the others, and a similar susceptibility is present. This led me to abandon this method. I removed all the welded tabs carefully, fortunately I'd only done half at this point so half the cell ends are still pristine. The ones where I removed welds cleaned up well enough, show no breeches or damage. I used a diamond burr to smooth any remaining tab material rather than brute force tear and risk breeching the cells. I have no spares so I need to make what's here work.

My question now is... how the heck to I create a reliable junction that is semi flexible between each module around the ring without it being brittle. The originals had 14AWG wire crimped in metal that was spot welded to the tabs. I've lost those tabs and the BMS tap connections in this folly I am trying to navigate. I'll probably need to solder or spot weld the BMS tabs direct to the bus now, making them permanent to the battery rather than removable. That's okay, because if I get this repair done, I do not plan to embark on doing it again...

I though about just making the Cu ribbon continuous in the series, as big u shapes connecting each end, yet then I'd need a way to reliably insulate those 10mmx0.2mm Cu ribbons because their big relative to the volume where they are connecting, and two passing each other at each modules junction though with different # in the pack series raises the risk for short.

If I could distill a question from all my "blah blah blah" ... it would be:
Does anyone have advice on joining insulated wire between Cu and Ni-Fe ribbon sandwich tabs, to connect 2P 18650 cells in series, without that connection becoming (as) suspectable to work hardening, fatigue, and fracture?

 

[Zambam]

junction of wire to tabs I built had far to great of a stress on the joint and one of them became

Please post pic of broken joint.

 

[jkrienert]

I will get an explicit photo, but the break occurs here (yellow circle), and weakness the same in all the other tabs consisting of copper base, wire soldered to the copper, then Ni-Fe tab spot welded to the top. The solder also migrated up the wire naturally, though this is unfavored because it makes that leg of the wire also brittle, and less useful because it will not bend in the tight tolerance space between these modules.

The other side of the bus shown did not have near the amount of fatigue and brittleness due to it being mechanically crimped in the factory tab, that was then spot welded to the tab and copper below.

Yes, I know the spot welding is a bit shotgun and rough...

I am pondering making my own little copper wire ferrules (see added photo) that I could then solder or spot weld those to the tabs that will be welded to the battery. This is in homage to the observed superior connection that the mechanically crimped wire join to the tab by the factory.