Ebikes – dual battery managment system more riding.

Two more days of testing, a week apart, building on the numbers from day one.

Total kilometres over the three days 66.4  and total time on road 3h22m, giving an average of speed of 20kph or thereabouts. The bike was definitely starting to get sluggish towards the end, and the gauge on the bike was showing either one bar or three bars depending on the battery.

Total Watt Hours used was 488.6, much less than the 1008 Wh calculated from 36 volts times 28Ah (13Ah plus 15Ah). Total amp hours used was 13.6.

Start voltage on the Lekkie on day one was 40.72, and it dropped 4.52V over the three days to 36.27 (at rest), and the Headway started at 40.2, and dropped 3.76 to 37.14.

If the total weight of me and the bike wasn’t close to 150KG, and if the climb each day was not 160metres, there might be some distance left in these batteries. On a long flat run without the hills I can see these figures getting closer to a 90 kilometre range. That should be another test in the near future.

Glitches with power drop, or Dead Spots are to do with the BMS or the state of one battery. Sudden heavy draw on the headway battery (twisting the throttle quickly, or switching batteries under full load) seems to make the Battery Management System switch the battery off briefly. This sort of implies a weak cell or a bad, intermittent connection somewhere internally, which is not showing itself in any other way at the moment. It takes a few seconds to recover, and it only really happens when the battery is really fresh, when the power is down a bit, its all good.

Swapping from one battery to the other becomes more obvious as the batteries lose power. The Lekkie battery is definitely much weaker than the Headway battery. There are still a few interesting features with using the two batteries together which I have to get my head around yet, but the DBMS and the Digital Power meter are both working well. Three full days travelling to Porirua and back is about as good as I could expect out of two batteries, 1.5 trips was about as good as I got out of each battery separately, and this bike is much heavier with a high rolling resistance!

The power meter is quite interesting in that at the end of the second day, the recorded Watt Hours used was 335.5, but when switched on at the start of the third day was 328.1. The only difference I can see is that a different battery was switched on with a lower voltage – implying the display is voltage dependent or it just doesn’t remember things very well. However, the bikes main display showed 66.4km total distance at the end of the third day, but when I connected the lower voltage battery read 65.8Km. Again, it looks like the display is voltage dependent. More analyses needed on these features.

I have uploaded a spreadsheet of all figures for the test here. DBMS Testing

Posted in Arduino, Dual Battery Management System, Electric Bikes, Programming, Yuba Mundo eV4

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