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So, when the main battery konked, you basically unplugged it and plugged one of those in, when it croaked, swapped to the other?

Aaron

no, both work in parallel and dshare the current during discharge and recharge and It is hapenning with fully protected BMS and safety!

Maybe what you are calling "flatband" are the cells in pouch format?.. if so, that is a nearly impossible job. At least I know nobody that ever replaced a dead cell inside these fully potted battery. It would be VERy difficult to remove the dead cell without damaging the other cells. That potting is like a harder balistic gell that is both plastic/elastic and gummy and ultra difficult to work with. The closest job I have ever done was to solit one of the zero brick in two half back in 2014.

In my opinion it will be easier for you to simply disconnect that bad cell and connect an external cell to replace it but that external cell will need to be atthe same temperature to the battery so it will require to be stick close to it and well protected. here is a video I made where I converted a ZERo brick of 102V to a 51V

Doc

When pack are deffective ( at the cell module level) it can be:

1 - All cell internal resistance are  high = no more usable due to voltage sag too low under load
2 - Magic charge = one or more cell have connection problem in serie ( bad crimp between cells tab) = making voltage sag under load to one or more cells
3 - One or more cell having high internal resistance  = voltage sag anyway which also make the BMS to shut down the power prematurely

for 1, your pack is pretty DEAD
for 2: It is possible to  open the pack and re-crimp or spotweld  the bad cell connection with couple hours labor and patience and care.. but you will have to dig the potting manually without puncturing the cell below. I did it when i reconfigured a ZF2.5 brick into a 51V module for my nefew 's electric ATV. The battery was a situation 1 where all cells were too high internal resistance, but spliting the connection into two seperate groups of 14s in parallel made enough power to get about 2.2kWh out of it and make his mini electric ATV to go 90km

For 3, It is possible to solve the single cell internal resistance problem by paralleling another high C current  low capacity cells to it to rematch to the other cells the internal resistance  and have all internal resistance the same again.  I am making it for a Long brick ZF7.2 that I use as range extender on my 2017 SR. The problem is that the cell group no 17 always charge higher voltage than the rest and always sag lower voltage than the rest under load. My plan is to measure the actual internal resistance of the deffective cell group no 17 and to measure the internal resistance of all other cells and to match the calcualted internal resistance to put in parallel to the problematic  cell. I think that this job really worth if it can save a 7.2kwh battery that already fit in a ZERO if it can cost let say 100$ in material and 4-5 hours of work.. maybe more

So what it involve:
- Measure all the cells internal resistance ( 28 total) by applying a load to the pack direct terminal ( before the contactor), using a 500w or 300W light bulb and measure all the cells voltages with and without the load.
- Find the deffective one that have higher internal resistance than the rest
- Calculate the resistance of the cell to parallel to it to make it having the same internal resistance than the rest ( https://www.allaboutcircuits.com/tools/parallel-resistance-calculator/)
- Open the long brick aluminum sheet that is hardly stick to the putting material inside
- Find the location of the deffective cell  tabs under the semi transparent potting
- Dig with cutter, exacto and grip carefully until you reach the metal tabs
- Unfold the crimped tab
- Solder connections to it and take care to not transfer too much heat to the tabs... or drill a horizontal hole thru the crimped tab and install wires with terminal and screw
- extend these wires outside the pack,
- Connect a permanent high current ( high C rate) NMC chemistry cells
- Redo the load test with the bulb and make sure the voltage sag of all celsl are now the same. If not adjust the cell capacity or C-rate until getting uniform Internal Resistacne on all the channels 

IMPORTANT: YOU MUST HAVE A MINIMUM OF BATTERY DIY SKILL TO MAKE THAT.

I made a video to explain the concept in french but you can use the auto translate as well.
( Dont forget to subscribe to my channel if you like it! there are videos in english and video in Français)

https://youtu.be/5WSYysw-4cM?si=eqSow1lNeui6EjcR

Doc

I thought it would be interesting to have a thread related to the controller that are no more the Sevcon brand  since gen 3!
 
Controller brand: SME Group (SME group has been bought by DANA/TM4 in 2019) https://www.danatm4.com/sme-group/
Controller name: Tautronic or Smartmotion AC
Controller model number: HyPer-Drive X144 (similar to this one maybe the same but with proprietary ZERO features)
interesting fact: This controller is also offered in some DIty kit from Netgain motor.

24V / 36-48V / 72-80V / 80-100V / 120-144V ?
75A– 1100A ? ( Gen3 is rated 900A phase and 82kW)
Asynchronous and Synchronous motor control?
System or Slave Softwares
Up to 50% higher power density than direct competitors
High efficiency and long life power stage – DBC (Direct Bonded Copper) patented MOSFET multilayer power module technology
Field Oriented Control algorithm optimized for asynchronous and synchronous motors
Fully customizable I/O
Easy tuning with TAUTM Software

https://www.danatm4.com/products/inverters-2/tautronic-series/



There is a great review made by LogicalBlizzard from reddit here:

from r/electronics

Some technical details he observed:
1.   Each "power module" is a half-bridge with 6 MOSFETs in parallel "per switch" (6 on the high-side, and 6 on the low-side). Each phase is then composed by 2 power modules in parallel, resulting in 12 MOSFETs in parallel "per switch". Or 24 per phase, or 72 for the whole drive. You can see those thin wires from that "internal PCB" going to each MOSFET - they are the gate and source terminals. There is also one 1Ohm resistor in series with the gate terminals as a dynamic sharing resistor.
2.   I played around with it, to check their Rds,on, and yes, one pair of pins are the gate-source terminals for the low side, and the other for the high-side. Applying 15V in one of them connects the output to one of the rails (depending if low or high-side).
3.   Yup! It is from LEM. It is a hall-effect based closed-loop current transducer. I checked it again, but couldn't find any part number. Maybe it is on the side closer to the board. I know it is from LEM because the terminals are identified as "LEM1" and "LEM2" on the PCB.
4.   Each of those two "middle terminals" is a terminal for the DC link. At the bottom of the DC link board, they split into those two rails that extend to the power modules. They are overlapping each other, so instead of going side-by-side, they are top-and-bottom. The rail on the top (imagine the DC link board seen sideways, then we can define top and bottom rails better) is the negative. It connects to those 2 raised aluminum terminals on the power boards. The rail on the bottom is the positive one, and it connects to those 3 aluminium-copper contacts on the power modules. All power modules receive both rails, and the terminal on the other side of the modules (that post-like aluminium structure) is the "AC output". The AC output of two modules of the same phase are connected together through that weird aluminium structure that resembles a bridge in the DC-link board. It leaves the drive through those three raised terminals. Since both the positive, negative and AC terminals of two power modules of the same phase are connected together, they are in parallel.
5.   That's one thing that I would love to see. However, an experienced coworker told me that these are likely manufactured by SME (now Dana/TM4) themselves. There are no part numbers nor any identifier on the modules. All I can say is they are rated for 130Vdc max, and 162.5Arms continuous output current, or 350Arms output current for 2 minutes.

I also thought that 9kHz is not only a low switching frequency, but kind of a "weird number". Why not 10kHz? Well, it is their design hahaha
These drives can work with basically all machines that lie within that range. If you want to check the full details, just Google "TM4 Tautronic AC-X1", and the first result is the drive's datasheet. Or product sheet... Even though the original design is by SME, they were bought by Dana/TM4. So it is their stuff now. This one came from a Zero motorcycle, that has an air-cooled PM machine. I hope someday you get to disassemble one of these yourself! Maybe if one of these trucks get terminally damaged, you can try and ask to open them? Yeah, but big companies are usually really restrictive on having fun...
I must admit, it is quite fun to disassemble one of these things. At least to check their hardware. All the finer and funnier details, like control and modulation, as you mentioned, unfortunately stays as a huge question mark. I don't think we will be able to get those information, even if we ask them nicely.

By any chance do you know the total weight of your chargers, and have you drilled and tapped additional holes in the frame to mount the pan? I'm currently working on adding a second charger under my bike and the plan was to use the mounting holes for the stock charger. I took the bellypan off earlier to take a look at the bolts and see what size they are and they're only M4 compared with M5 for the pan. Not only would it be less secure but it's also a pain finding hardware in the lengths needed so it's got me considering just mounting the second charger using the pan/pan mounting points instead.

The cold plate is bolted to the pan from the inside. I have taped holed in the cold plate. Then i have installed the charger back on the same original holes.

The pan is bolted on the 2017 SR frame in the existing threaded instert. The pan and 3 chargers weight about 60 pounds.

Doc

After re reading thru your setup...
I am not sure how much power this thing will EVER need in either direction, but an SB50 Anderson connector is only good for 50 amps.  Is this sufficient for your gadget here? 

Also, and I am sure this is trivial but, Anderson connectors come in different voltage ratings.  The one you picked (the color coding I think is how you can tell but please verify that), can it handle the max voltage the battery pack can be under, even with a high potential kickback from the motor etc etc?  The teeniest, tinyest, arc over, arc / burn thru will turn into a Green flash and a glowing ball of plasma in milliseconds.  Those are not fun either!

Aaron

The battery is protected with a BMS that I installed It is also short circuit protected so I could make a dead short to the output and the mosfet will just open and no high current spoke can happen. the SB50 anderson connector are capable of 120A continuous on 6 gauge acording to the specs when used with silver plated contacts  https://www.andersonpower.com/content/dam/app/ecommerce/product-pdfs/SB50/ds-sb50.pdf. These SB50 were even used by ZERO on a battery with a 300A fuse back in 2009. I use them on 4 gauge and these remain cold. I use these Anderson connectors as well as the Powerpole 30 and 45A for 20 years now on multiple ebikes projects and I know them very well. I understand the engineering of a proper contact installation, cromp, derating on ambient temp ans ampacity for various wire size as well.  The housing color is just an indication. ex; Blue for 48V, grey for 12-24V etc.. but I use grey for all my projets as these are the easiest to find and i am not developpong a commercial product but only making DIY projects

Well it's not really a problem if the radiator is broken. It's not a gas engine that'll overheat. The TCChargers have temperature protection, they'll simply turn off. (At least mine did).
As doctorbass had one die from heat, it seems they don't like the heat but they definitely don't die from one time charging on a broken radiator.

Well I also believed that the built in temperature protection would protect them against overheating but apparently not!.. I found one of my unit not working after I came back from one hour shopping during a hot weather day and that I forgot to install the 55W 120mm suspended fan below the pan.

It happened couple times where I saw the temperature hitting 88Clsius over the 5 last years and everything worked well with the output power automaticly droped.

From about 75Celsius to 90 Celsius the power is derating but at 90 celsius it is prety toasty.. just enough to break the circuit inside apparently.