A this intersection, the towdster didn't weigh enough to trip the traffic light, I had to get out and press the pedestrian button. :lol:
I got the towdster out for its second shakedown cruise on Xmas, to baseline the pack's capacity. Last time, a cell dipped low after only 2kw of discharge, but had recovered by the time I got home. I hoped it was a cellLog issue but feared one (or more) low capacity cells were going to limit me to shallow discharges, adding to the punch list of things to fix.
The CellLog Array makes it so easy to baseline a pack, my installation was labor intensive but still saved me time in the long run. This time around, the fully-balanced 60ah pack gave up
57.19ah/7,532wh before the first cell dropped low, and the kill-a-watt says
9,430wh went back in on the charge. I was targeting a conservative
2.7v cutoff, and the cellLog pic shows most of the cells were in that region after the discharge. I'd be worried about the 2.16v low cell if it wasn't a123 and its voltage hadn't bounced back up after resting. Next time I have the body off, I might parallel an M1 cell so it has the same capacity as its peers.
Weak cell aside, these old a123 pouches delivered close to their rated 60ah at the top of the "knee" of the discharge curve, 2.7v. That is good news, more capacity than I hoped for. I wish all manufacturers rated their cells on usable capacity like a123, so we wouldn't have to lop 20% off the top to account for 80% DOD.
I travelled
24.9 real-world miles (hills, high winds, many stops and hard launches) during the discharge, which translates to
303wh/m. This meets MY needs, a 16 mile weekday commute leaves 9 extra miles for errands, or on weekends it can do a dozen trips to the beach. However, in the first post I set a target range of 35 miles (5 miles more than 60% of Americans travel daily) which would require 215wh/m.
Hopefully I can meet that target with tuning and technique. For example, I bet the wheel bearings need inspection/replacement/lube, given the work the rest of the car needed. The tires need air again, adding rolling resistance. The motor could have a voltage leak from carbon dust buildup. I did the test in third gear for simplicity, which isn't efficient for launches so I might do better rowing the gears. Depending on how bad I want to get there, I could add another 7s3p module for more range and volts, or tune the DC motor with timing and Helwig brushes, or even go brushless. What I will NOT do is mislead people by measuring on a banked oval at 25mph with no stops, then quoting it as real-world for the bragging rights. I have seen too many optomists over the years, and too little hard data.
Although it seemed unrealistic, part of me hoped that Rickard's "100wh/m per 1,000lb of EV" theory would apply to this build, so it would get
100wh/m and have a 75 mile range. He publishes a lot of data points to support this, but they are from long-range big-battery EVs that are a bit heavier, and I don't think it translates to lighter vehicles. My 70mph Vectrix weighed 500lbs, but instead of the 50 whm his theory would suggest, it used 130-160wh/m depending on how hard I was pushing it - that translates to 320wh/m per 1,000lbs. I typically get 35wh/m on 100lb ebikes, which translates to 350wh/m per 1,000lbs. Based on my own data points, I have a different wh/m theory.
Since I haven't added cooling yet, the other important data point was HEAT. The controller was good for about 10 miles of spirited hilly driving before it would start to cut back (more than enough for each leg of my commute). I am glad I had a chance to add a sense of heat dissipation to my design vocabulary, but summer is coming, so when it is convenient I'll downsize to the Z1K and use the freed-up real estate for a coolant reservoir. The motor got pretty warm in the same duty cycle - just enough for me to consider forced air cooling for longer runs. The battery pack was absolutely cool throughout the discharge.
Also, I finally posted details about 3D printing the CellLog holder and Cyclanalyst enclosure I made to my Kit-taz thread - CLICK HERE to see more.
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, and I feel released from the cloud of work that has been over my head. 8) The zilla is installed, the substandard POT throttle is no longer blocking the passenger seat, and I've sorted out the shifter, driveline, and suspension along the way. While I need to sort out the current startup problem, that is troubleshooting a known, previously working system, not engineering a new one.
