Copenhagen Wheel Battery Replacement

[Zambam]

Solder wicking up the wire strands, making it not flexible is problem. Crimping to a ferule then solder to the copper strips may be your answer. Very fine strand wire tend to wick solder a lot more than coarser strand wire. May be worth a try if ferules don't work out.

Your added ferule pic with bent copper sheet does not look like it will hold the wire well enough. How about copper tubing as crimp ferules?

 

[jkrienert]

copper tubing as crimp ferules?

That is a novel idea. I might have a go at that.
I also thought about trying to spot weld store-bought ring crimp terminals, then crimping in the bus wire after welds are completed.

Though thickness around the ring might prove challenging to spot weld. Id suppose i could nip the tip of the ring to still facilitate the infinity slot method, all be it in arc form.

 

[jkrienert]

Here goes something...
Tac on the top Ni-Fe to the tinned copper ring then tack Ni-Fe copper on sides of ring to cu base, then through tab wings thru cu base and into cell top?

Or solder the ring to cu base and don't try tac to it from above?

One negative I have found with using solder in these efforts is...
If you have too much ketchup (solder) in your sandwich (Ni-Fe + Cu layers) it's a mess,
And solder mess on the cathode of a 18650 cell, needs to be avoided.

 

[jkrienert]

Green is to cell
Blue is tab to spot weld mechanical fixing of the ring to the copper base
Tab and copper would be 1:1 overlap, this is just to show the ring between

 

[jkrienert]

Dude it works great!

 

[jkrienert]

A bit more consistent now
One center tack sets two on one side, and the other sets the other side to lock the ring into a pocket.

 

[Zambam]

Dude it works great!

Looking good! Being a mechanical contact between lug ring and copper, corrosion down the road may be an issue. Instead of welding the lug ring center hole, punch a hole in the Ni-Fe so you can drop some solder in there after spot welding around the ring. Pre tin the ring before welding, add a drop of liquid flux to make soldering quicker.

 

[jkrienert]

I... Am for the reasons mentioned, cautious about using solder and it wicking into the wires and leading to brittle-ness and breaking, as well as the risk solder poses close to the cell cathode. I might avoid this if at all possible...

Maybe I can add a few more welds instead to maintain structural integrity? I actually started doing that on each tab by making at least 1, and for many 2 where there was enough surface area, spot weld from the tab to the tinned copper ring near the crimp ferrule.

Here is another path I might follow. As @Zambam rightfully notes, there is a likelihood of water vapor corrosion occurring inside these tab assemblies...

I'm wondering if I packed the ring tab sandwiches with anti-oxidation paste (instead or as a substitute for solder) that would be enough of a mitigator to make this less a concern?

Adding a few more shots of the dragonflies for sake of the decent tolerances of the ring terminals and wires before crimping even, as well as the general assembly in case anyone needs some visual reference on a method that might help with repairing the batteries on these hubs.

• Wires: 14 -AWG Stranded Black GPT Primary Wire (Manuf. rated @ ~30A max constant)
• Ring Terminals: 22-16 AWG Ring Red 6 -Count (Manuf. rated @ ~30A max constant)
• Isolation (not shown yet): 4.7-mm diam. heat shrink tubes

Nice thing about this method, is that aside from the Ni-Fe tabs, the other parts were available locally at a basic hardware (rings, wire, shrink, anti-corrosion paste) and craft (copper ribbon) store.

 

[Zambam]

I think soldering the lug to the copper is a necessary step. It gives you a sealed corrosion resistant connection. Do the soldering before crimping, spot welding to 18650 cells.

edit: soldered ring lug to 0.2 Cu 10mm strip. 80W iron fat tip, flux, solder applied from inside the hole to flow out. Not the neatest, does the job. Weld over it with your Ni-Fe tab.

 

[jkrienert]

That is outstanding. And, if I ever rebuild this battery I will do that step.

However, I already spent my afternoon with additional spot welds without solder. That might have been a mistake...

It's assembled now and test charging in a surplus rocket container. Once I see it take a full charge, I'll disassemble, seal the battery perimeter with rtv and a desiccant pack inside.

I had to discover that in order to make it all fit, you have to loop each wire bus one time, as it was originally. Don't forget that step anyone out there that embarks on replacing the battery. I don't recommend it, personally. It was a lot of work and there is more I could have done to make it better... Like solder the rings as recommended.

If it fails eventually due to corrosion, well... Maybe that will be after the 400 or so charges it'll have. If it doesn't fail catastrophic, then I'll definitely make the ring solder step on the next battery replacement.

 

[Zambam]

Good job putting it back together! I see why the loops in the wires are needed, to position the tabs relative to cells for spot welding and maneuverability.

It’ll be interesting to see how well it performs and for how long.

This is what I imagine can happen:
During high current demands on the battery, if the contacts between ring lugs to cells are insufficient to deliver that current, it heats up. The cycles of heating and cooling degrades the contact and create high resistance. The BMS will detect low voltage and shut down.

 

[jkrienert]

@Zambam your message is both very helpful and supportive (thanks!) as well as sobering (...still thanks).

It was pretty stressful assembling, yet it honestly gave me a lot of good preparation for the other battery I'm building and sort of putting off...

Anyway, I stayed up till about 4am cst checking on it every 15 min as it charged in a 1945 steel rocket ammo can in the yard at the end of an extension cord last night. Not messing around with safety.

Your note about hot/cold cycling is... Well the scientist and engineer in me does cringe at that legitimate risk. I agree with you fully that having some additional fixture for the ring would be superior...

Some due diligence on my part though... I ended up soldering the BMS taps as a backup. I figured I did not want those to fail, and the original idea of using the disconnects on those was skipped because the tabs I cut were just a little bit too small and the NiFe too thin for a secure connection without solder.

Also, I just kept having a vision that, the size of these tabs and the minimal amount of copper to transfer heat anywhere but the solder joint, left me wanting to avoid the potential for liquid metal in this assembly.

When I was testing, the spot welder easily reheated the whole tab sandwich including the soldered ring. That led to a spray of molten metal across the top of the cells cathode. Remarkably that didn't cause a short, though I forsee if I'd done that with all 23 cathode ends the chance that one would have shorted is... uncomfortable.

I didn't want to risk that happening during full assemble, nor the possibility that after assembly, a thermal overload during could cause solder to liquify in the wheel, and lead to T2000 level problems...

Maybe for the next round of battery replacement if it makes it that far, I will improve my soldering skills such that there would be only a very small amount around the base of the ring.

 

[jkrienert]

to position the tabs relative to cells for spot welding and maneuverability.

Exactly!

 

[jkrienert]

One aspect I'm also concerned about, is you can see in the original posting that the BMS tap harness and thermistors run along the bottom of the cell series modules. When I was assembling, I couldn't get that aspect of the design to line up with enough slack on the taps.

So, I made a decision to proceed with top mounting the harness. It doesn't look as pretty, however, from a service perspective (which I hope I don't ever have to least replacing the batteries in ~400 cycles) it's nice that I can access all the taps and thermistors there. I will probably add additional tape over the harness leads to prevent any chafing. Though, this case and the original design is rather, beautifully snug and I don't suppose vibration related work hardening or abrasion is as great a risk, as the ring solder dilemma.

 

[jkrienert]

It works!!!

I was up through the night trying to figure out why it was not working when pedaling on track stand. Reopening the case, checking wiring... etc...

Come to figure out
.. It is entirely torque based and just spinning the cranks without road or rider load produces no assist. When I set it down right side up, and lept on the saddle to try in turbo mode I was surprised and delighted!

What fun!

This is a photo on my buddies test bike. I might just gift it to him for his bravery in letting me test the battery repair
(yes, front tire is flat, right before airing up to ride)

 

[jkrienert]

Little update,
The Sammy 35E cells that replaced the original 29E cells add some range beyond the manufacturer listed.

I did about 15km in turbo mode with several big long hills, and it dropped the charge from 75% to 30%. That includes about 4-7% charge return from regen.

That was on a humid and hot Midwestern day, 87% hum. And around 89°F. When I stopped after the ride, that ended with about a 1 mile long flat grade constant sprint, left the center silver aluminum plate with the charge port and power switch rather warm, and too hot to hold you hand on it very long.

I gave it time to cool, and recharged back to 100%. So far that's the third cycle and no anomalies yet. The warmth concerns me, and I wish there was a way to maybe facilitate wind to get inside the hub chamber and exhaust... Any thoughts on mods to that effect welcome. Because as is, there is basically a heat jacket inside the hub that surrounds the battery pack, and seems like a caveat to this design. I'm supposing it might be a culprit for short lived pack if ran hard... Though I have no clue what their BMS software is doing, so ... Shrug...

Based on my limited real world testing so far, Im supposing with the upgrade from 2800mah to 3400mah 35E cells, the range in turbo mode of a mix of hills and flats and assuming nearly constant pedal cadence and assist, is about 14-20 miles with some likelihood for v-sag at the end of that range. In standard or eco mode, I'd suppose that 20-35 miles wouldn't be a problem.

These estimates are on a gross weight aluminum upright style frame with the wheel, of about 50lb. Then there is me, a 6'3" wind resistance accumulating dude weighing in at 175lb ish.

So, 20 ish miles on one little hub motor moving 225lb is, kinda amazing and cool to me. This seems like it would have been one of those innovations that could have evolved into something much better with the right support and design changes. Bummer it didn't work out 'then' but maybe someday someone will resurrect and improve the ideas therein.

One thing that I qualitatively noticed. The really noticable weight of the rear end this wheel adds might be a challenge when pedaling unpowered, however when powered and at peak cadence and assist... You can feel a strong 'flywheel' effect. It lends this wheel to maybe being most efficient at sustained speeds rather than the urban stop an go. That's again, qualitative, so more real world testing would probably elucidate if that's the case or not.

 

[99t4]

The warmth concerns me, and I wish there was a way to maybe facilitate wind to get inside the hub chamber and exhaust... Any thoughts on mods to that effect welcome. Because as is, there is basically a heat jacket inside the hub that surrounds the battery pack, and seems like a caveat to this design.

You have discovered the main drawback to having the battery pack and controller inside the hubmotor-- multiplied trapped heat from the two extra heat-generating components.

IDK if Statorade would be a safe addition, but there are posts here about drilling ventilation holes in the side covers and even adding "scoops" to direct air in and out. Hubfins might help?

This seems like it would have been one of those innovations that could have evolved into something much better with the right support and design changes. Bummer it didn't work out 'then' but maybe someday someone will resurrect and improve the ideas therein.

Gotta solve the heat issue. Also the inconvenience/difficulty of changing or repairing the battery and controller.

 

[jkrienert]

Hubfins might help?

The circumference is round and would certainly be awkward to mount anything too. However, with the capabilities of scanning and 3d printing, someone (probably not me) could certainly achieve this.

I will have to search for the posts about air transfer inside the hub, as I had looked a bit but didn't find anything yet.

I don't know if statorade would work, only because I don't know much about how it functions, and any of its own inherent limitations. I will say that the red external casing that rotates is not liquid tight. There is a thin 2-3mm diam. Gasket that runs around the lid of the.red casing yet it's not a seal of anything beyond maybe ip4 ? If you put any fluid, even if viscous, I'm fairly sure it would leak.

Heat pipes would be an interesting method of cooling the static stator which the batter is mounted and the little piece pan plate with the charge port and power switch mounts to the rear dropouts. That warrants some research for sure, as you do have this high contrast gradient that, if I remember correctly, is how heat pipes work in principle.

 

[Zambam]

The warmth concerns me

You say the disc is too hot to touch. How hot is it? Have you measured it? Maybe it's OK? Max operating temp of NMC cells is 60C. The disc is where the motor is. Is that what's heating up and not the on/off switch, which should not be carrying full battery current. Were you using a lot of regen? That'd heat up the brushless motor excessfully from what I read.

 

[Zambam]

I don't know if statorade would work

Not in your red flying saucer.

 

[jkrienert]

How hot is it?

Well, I can touch it, it just isn't comfortable to hold your hand against it. I don't presently have a way to measure the surface temperature. Not hot enough to cause a burn, and I'm supposing below 60C, but as you mention the plate is indirectly connected to the batteries, and the batteries themselves are thermally isolated from heat conductance through their fixture, because its just plastic casing making the contact between battery pack and motor stator.

Its not the switch thats the source of warmth, but its on the same plate so its privy to it. Fairly certain it was the regen I was using, and using it well, trying to push it to see if I could use it to stop the bike on a steep grade.

The remade app for the wheel (RedWheel) is pretty clean. I wish there was an 'advanced' tab where it offered a bit more data, though there is a neat trip saved feature that gives you a pie chart of power and regen use.

 

[Zambam]

I don't presently have a way to measure the surface temperature.

What you really want is the internal temperature, to find the source of the heat. I can recommend a device if you are interested.

 

[jkrienert]

a device if you are interested.

You are more than welcome to. However, I probably wont invest much more $ into this repair. What would be awesome, and more explicitly useful than any secondary instrument... would be if the app writer for the RedWheel utility could offer a developer option, which accesses the wheels BMS data. Each of the 7 cell group modules has its own thermistor. If I could read those, that would be the most ideal way... Now that you ask, and I mention this... I might email the programmer that made this wonderful app, and see if there is any vision or possible way to access that metadata.

 

[Zambam]

You are more than welcome to. However, I probably wont invest much more $ into this repair.

It's only 5 bucks! I have 5 of these. One thermocouple bead has been epoxied to my TSDZ2 motor lamination for a few thousand miles now.

 

[jkrienert]

I will look into thermal monitoring... I also, found another wheel needing a battery repair for a really low price so I swooped it up. Full disassembly for new battery's in a lot less time than the first go. Interestingly, this one's internal construction was sloppyer than the previous. I wonder if they changed manufacturing source at some point in their companies short lived supply.

Anywho... This wheel didn't come with another charger. Which brings me to this post.

I cannot find any stock charger with the right combination of rosenberger and 48v (54.6v) 2a charge. There are the same settings with 4a, though I have concerns... I would have to modify those to include the third interlock pin which I presume based on the original charger is just a lower amp tap on DC charge negative (see photo).

Here is the really concerning part, if I am going to order or modify a rosenberger plug, I want to make sure I'm doing that with a charge current which is going to extend the lifespan of my cells as long as possible.

The 35E has a maximum charge of 2A, noting that is not for the full estimated cycle life. To achieve that full cycle life, it's recommended charge at 1A.

Since this pack is a 13s2p, a 4a charger would be 2a per cell. Seems like that might be avoided and I should go with finding a 2a charger to modify?