The Shopping List

You may or may not find this interesting, but here's my shopping list for the car as of now.

Already got for the initial build (some of these may get upgraded later):

• Thrige-Titan TTL-200C motor
• AXE7245 90V 450A controller
• KP-L 2000W 87.6V charger
• 0-5k throttle
• 25pcs CALB SE40AHA 40 Ah cells
• Cycle Analyst instrumentation

On order at this time:

• Nothing

High priority items needed (car won't run without):

• Another 25pcs of cells (CALB 40, 60 or 70 Ah, preferably CA-series)
• Motor cooling (EVTV BlowMe or something else)
• Main contactor

Low priority items needed (car won't pass MOT without):

• JLD404 or similar voltage meter for main contactor activation
• DC to DC converter
• Auxiliary 12 V battery
• Vacuum pump (very important)
• PTC or liquid cabin heating (liquid is actually easier, but more expensive)
• High voltage warning stickers everywhere

Vanity items:

• ELECTRIC emblem of some sort
• Braided straps for cell interconnects for improved durability

The list may be incomplete and/or outdated. Just like me.

How To Bottom Balance

Warning! This article is about LiFePO4 cells. Some of it may or may not apply to other chemistries.

My earlier post on bottom balancing was long and mainly about why to do it. So I figured I might do a little step by step for those who just want to get it done without delving into the philosophy behind.

1. Drain all of your cells down to 2.75 volts. Note that the cells will bounce back after you disconnect the load. Repeat the discharge until each cell standing alone stays at 2.75 V.
2. Connect your cells to each other. Do not connect anything else between the cells but the bars, straps or fuses connecting cells to each other. Do not install BMS. Do not connect any other wires. Strictly cell interconnects only.
3. Charge the battery pack to a voltage of 3.5 to 3.55 volts times cell count. Examples: 25 cells = 87.6 volts = 3.50 per cell, 33 cells = 116.8 volts = 3.54 per cell. Use CC/CV profile which is the default in many LiFePO4 chargers. End charge when total voltage is reached.
4. Always discharge the pack as a whole. Always charge the pack as a whole, the same way as described above. Never put any load on only a part of the pack, no matter how small. Never install cell level monitoring or BMS which put any load on individual cells.

If you do this right you shouldn't need to repeat it. If you want, you can periodically drain your pack and measure the voltages. They should all be about the same. If you notice irregularities they are most likely caused by bad cells. Replace bad cells and repeat the bottom balancing for the whole pack.

Bottom balancing is not negligence. Bottom balancing is utmost cell care. You drain them one by one, manually or with a device like Revolectrix PowerLab. While you do that you will spot bad cells quite surely. When you charge them you end the charge well before overcharge and the charge is controlled by the one device which does it best, the charger. As an extra precaution you may also consider adding a meter which disengages the main contactor if pack voltage is not within limits.

On discharge you set your controller to a low voltage limit of over 2 volts per cell (for example, 60 V for 25 cells, 80 V for 33 cells, perhaps even lower). This will prevent any cell going too low, since they all empty at the same time. Since they're all empty they can't harm each other.

Fires happen when cells get overcharged. Bottom balancing doesn't cause overcharging.

Disclaimer: All of my battery ramblings are based on my own experience and Jack Rickard's original work on the subject. They are applicable to CALB SE- and CA-series cells. Other cells and chemistries may at least require different voltages. I take no responsibility for any problems or damage caused by anyone.

All Quiet on the Western Front

I've been keeping busy with other parts of life, hence no blog posts on EVs in a while. Also I have the car mostly outside, albeit under covers, but still in either bloody cold or nasty damp weather. No warm, dry garage for me at the moment. I have the motorbikes in the garage, but it's still cold.

It doesn't mean my brain has stopped working though and I've been thinking about the projects a lot. I even got around to making some inquiries on the possibility of obtaining some aluminium for the motor adapter plate. Turns out nobody has anything in storage, ordering costs more than actual material and aluminium isn't cheap either. There goes my plan of buying some and playing around with it.

That means it's back to the CAD program and having everything made somewhere based on my drawings. For some reason that also has near zero attractiveness at the moment. Someone on a Citroën forum did point me in the direction of a PSA XU engine brochure which included a priceless picture of the motor with proper measurements and angles of the transmission facing bits. Will make my life a lot easier with the CAD, as soon as I can get around to it.

Reprinted without any permission whatsoever.

I also find myself thinking about battery placement in the kWsaki and dreaming of doubling the amount of SE40AHA cells to get to the 80km+ range I originally had in mind. I think it will happen during spring/summer as well. The kWsara also needs more batteries to move anywhere, so the additional cells will double as both cells for the kWsaki and testing the kWsara.