Copenhagen Wheel Battery Replacement

[bananu7]

It should be easy enough to find a 48V charger with variable current setting.

 

[jkrienert]

It should be easy enough to find a 48V charger with variable current setting.

As it turns out, I found a charger that also outputs the 16s nominal voltage, and then purchased and installed a new Rosenberger magnetic plug (same as original). Works well, just had to be sure and match the plugs wiremap that uses a pseudo interlock with the negative.

 

[jkrienert]

Started battery replacement in wheel #2. Got the bus bar design improved, aside from my bird shot style spot welds... At least they are well bonded and strong?

1. Note, I took the nice advice of @Zambam and soldered the ring terminals to the Cu ribbon first.
2. Then did minor surface prep on top of the ring terminals, including a rotary tool diamond wheel to plane the contact for the welds,
3. Then light acid wash (pH ~3 acetic acid) to clean burnt flux or any contamination from the weld site.
4. After that, I spot welded the Fe-Ni parallel tab on top.
5. The next step was trim excess of the Cu ribbon so it matches the footprint of the Fe-Ni parallel tab using scissors, then clean the edge with drum sander on rotary tool.
6. Lastly i precut all my bus cables and heat shrink, crimped and sealed.

The cell distributor only sent me 25 by mistake, and when I contacted after discovery on July 4th, they replied in less than 30 min on the national holiday and hustled a shipment to me with the missing cell at no charge. Awesome service by @DIY500ampbattery.

When that cell gets here in the next few weeks, I'll prep for final assembly and test ride.

 

[Zambam]

The next step was trim excess of the Cu ribbon so it matches the footprint of the Fe-Ni parallel tab using diamond wheel and drum sander on rotary tool.

Would scissors be faster to trim the copper to match the round ends of the Fe-Ni? I don't think slotting the copper was necessary. It would weld to the cells fine w/o it.

Did you get much solder splatter spot welding? Do you think you will get more splatter when welding to the cells?

 

[jkrienert]

Scissors would be, and were faster. I've updated the post with that aspect! I forgot to add that step.

When I tried soldering without the slot to dead cells the bond was not nearly as strong as when I did add the slot. It was a hassle but hopefully worth it for peace of mind in the welds holding up.

I strove to use as little solder as possible to avoid splatter and it worked mostly. I had a few drops weep out from the weld sites around the ring terminals, then used a flush cutter to clean off. If somehow the cells get hot enough to remelt the solder it would definitely be a problem, but if the cells are at that temperature and the BMS has not shut things off, there are other problems...

I also did my best to not get much solder towards the ends of the copper ribbon so that when I do spot weld to the cells, there should be very minimal to no solder local to the weld site.

 

[Zambam]

I test weldied old cells with and w/o the slot using Cu by itself and also 304 ss / Cu sandwich with my Awithz UF20B.

Cu by itself did not produce good welds w or w/o the slot.

304 ss/ Cu sandwich (0.1mm/ 0.2 mm) produced equally good welds w or w/o the slot. So I stopped using the slot.

You did your own tests with a different welder and materials. You made the right decision based on your own results. Looking good!