Minus three blades, no loss of range

I did a range test today without trying to be very efficient. I went 34 miles before several of the cells started getting low. There are still marked variances in the cells. Awaiting bench tests on the three blades recently removed.

Quest for an Electric Porsche Boxster.

K2 26650EV Battery Pack Testing

Quest for an Electric Porsche Boxster.

After 2 months of Chris' hard work reprogramming the BMS software to automatically shut down the charger, we finally have the car back for more range tests. We also have a very nice graphical interface that is much easier to look at than the raw data! As requested by K2, we overcharged the pack to 3.8v for about 3 days. The idea is to try and force more capacity into the cells since they are supposed to hold more. Well it hasn't worked. Today I ran a second range test with similar results. The same damaged cell in the front pack comes up first. Then after turning off the front pack, I am able to squeeze out a few more miles, but nothing close to the expected 55-60mile range predicted from K2 specs. The graph shows all 3 strings: 64 cells on the left is the front pack, 64 in the middle, the mid packs, and 64 on the right the rear pack. The first graph shows the maximum range before limitation from the previously damaged cell in the front pack.

I turned the front string off and eeked out another 4.6 miles.
Here is the second graph at the end of the range test at 38.7 miles:

This was mixed driving, trying to be at least somewhat efficient. I suspect if I did all highway I would have had a couple more miles, perhaps 45 miles if the damaged cell in the front pack was replaced. 45 miles is the best I have ever done with this pack.

So far, these cells are not improving with 3 days of overcharging at 3.8v. None of the blades in the mid and rear pack stand out as being bad compared to the rest, and there are a few that seem a bit higher capacity than the rest. But I doubt much more. We should pull the front bad blade, one of the lower and one of the highest blades from the mid and rear packs. Then test them all for capacity to show K2 and see what they will do.

Analyzing the graphs indicate 2-41 and 3-24 did come up as the next lowest cells again in the mid and rear packs... although 19 cells were within close proximity. It is also interesting that there is a disparity between the two mid packs. One has a lid on it and the other doesn't. The front and rear packs do not have lids. Still I think the difference is probably marginal in total capacity. I am removing the lids as the packs get hot when the car is driven a bit hard, especially if its hot outside. We want to keep the temps within spec, no greater than 60 degrees C. So, we will need to put some fans on the battery boxes at some point.

Local Coverage on the Porsche!

Quest for an Electric Porsche Boxster.

Austin Energy Installs Electric Car Chargers: MyFoxAUSTIN.com

Bottom Misbalancing Act III

Quest for an Electric Porsche Boxster.

I bottom balanced again, this time down to 2.5v +/- 0.05v with shunt balancers. About 68Ah went into pack before blade 42-1 became full which I carefully allowed up to 3.8v at 1A on charger. The closest next cell was at 3.3v. Following is at the end of test drive conservatively averaging about 65mph, mostly freeway:

01 2866 037 2869 037 2862 037 2862 037
02 2860 038 2882 038 2855 038 2852 038
03 2705 041 2584 041 2688 041 2505 041
04 2697 045 2732 045 2694 045 2519 045
05 2677 047 2653 047 2714 047 2694 047
06 2913 043 2931 043 2926 043 2865 043
07 2463 046 2628 046 2633 046 2623 046
08 2635 044 2613 044 2634 044 2685 044
09 2615 042 2635 042 2664 042 2567 042
10 2739 050 2734 050 2648 050 2669 050
11 2710 048 2737 048 2699 048 2691 048
12 2641 048 2684 048 2678 048 2699 048
13 2739 048 2730 048 2724 048 2616 048
14 2672 047 2699 047 2672 047 2687 047
15 2723 047 2707 047 2665 047 2672 047
16 2656 045 2657 045 2648 045 2630 045
17 2606 044 2623 044 2649 044 2639 044
18 2657 051 2650 051 2642 051 2623 051
19 2852 044 2863 044 2849 044 2847 044
20 2646 047 2649 047 2667 047 2695 047
21 2862 044 2884 044 2878 044 2824 044
22 2851 044 2866 044 2857 044 2860 044
23 2634 051 2669 051 2667 051 2646 051
24 2836 043 2864 043 2814 043 2802 043
25 2663 047 2662 047 2703 047 2686 047
26 2619 049 2643 049 2590 049 2646 049
27 2656 053 2635 053 2698 053 2628 053
28 2667 053 2634 053 2688 053 2695 053
29 2577 051 2540 051 2543 051 2600 051
30 2593 049 2647 049 2671 049 2664 049
31 2651 051 2554 051 2657 051 2667 051
32 2636 042 2598 042 2623 042 2588 042
33 2640 044 2675 044 2713 044 2700 044
34 2663 049 2702 049 2684 049 2686 049
35 2660 051 2502 051 2618 051 2676 051
36 2571 053 2583 053 2647 053 2628 053
37 2615 049 2657 049 2656 049 2669 049
38 2876 047 2882 047 2894 047 2893 047
39 2595 049 2578 049 2612 049 2588 049
40 2917 048 2927 048 2923 048 2899 048
41 2616 049 2663 049 2672 049 2695 049
42 2506 051 2706 051 2740 051 2745 051
43 2573 051 2566 051 2613 051 2597 051
44 2672 049 2661 049 2663 049 2681 049
45 2874 046 2881 046 2908 046 2882 046
46 2664 048 2653 048 2705 048 2700 048
47 2625 048 2617 048 2599 048 2640 048
48 2644 041 2639 041 2667 041 2667 041

Max Voltage: 2931 (62)
Min Voltage: 2463 {71)
Max Temp: 53
Min Temp: 37
under load coming into driveway
66.4Ah 41.3m, 1.6 Ah/mile

after 5min, increased to 2.8v drove around block again:

01 2912 038 2917 038 2914 038 2910 038
02 2897 041 2906 041 2910 041 2912 041
03 2778 042 2754 042 2778 042 2731 042
04 2801 047 2811 047 2796 047 2750 047
05 2759 050 2761 050 2787 050 2783 050
06 2921 044 2930 044 2932 044 2910 044
07 2745 047 2762 047 2774 047 2773 047
08 2761 045 2750 045 2767 045 2787 045
09 2743 044 2750 044 2766 044 2726 044
10 2802 052 2804 052 2770 052 2786 052
11 2790 049 2803 049 2787 049 2784 049
12 2764 050 2783 050 2779 050 2787 050
13 2800 050 2794 050 2795 050 2758 050
14 2773 049 2787 049 2770 049 2770 049
15 2791 049 2789 049 2758 049 2774 049
16 2757 047 2757 047 2764 047 2756 047
17 2744 044 2760 044 2768 044 2762 044
18 2782 052 2777 052 2773 052 2777 052
19 2906 046 2908 046 2906 046 2904 046
20 2749 048 2754 048 2748 048 2756 048
21 2906 046 2910 046 2912 046 2905 046
22 2903 045 2914 045 2909 045 2908 045
23 2753 052 2771 052 2767 052 2765 052
24 2908 044 2912 044 2907 044 2894 044
25 2765 049 2759 049 2760 049 2759 049
26 2750 050 2748 050 2714 050 2748 050
27 2767 054 2750 054 2769 054 2746 054
28 2770 055 2746 055 2763 055 2761 055
29 2737 053 2711 053 2708 053 2735 053
30 2746 051 2775 051 2763 051 2774 051
31 2760 051 2756 051 2752 051 2761 051
32 2755 045 2764 045 2742 045 2744 045
33 2760 045 2773 045 2784 045 2774 045
34 2790 050 2799 050 2783 050 2788 050
35 2796 052 2579 052 2783 052 2790 052
36 2736 055 2735 055 2751 055 2740 055
37 2761 050 2780 050 2767 050 2787 050
38 2924 049 2921 049 2925 049 2924 049
39 2755 050 2742 050 2753 050 2727 050
40 2920 049 2925 049 2918 049 2909 049
41 2762 051 2778 051 2764 051 2774 051
42 2671 053 2784 053 2790 053 2794 053
43 2738 053 2738 053 2739 053 2740 053
44 2753 050 2733 050 2736 050 2757 050
45 2924 048 2929 048 2926 048 2920 048
46 2774 049 2771 049 2785 049 2785 049
47 2757 049 2752 049 2734 049 2755 049
48 2780 040 2792 040 2787 040 2788 040
Max Voltage: 2932 (63)
Min Voltage: 2579 {352)
Max Temp: 55
Min Temp: 38
68.2Ah, 42m, 1.62Ah/mile

I squeezed out another 3Ah on the last test drive, but went a bit lower on average end of discharge voltages. The overdischarge two weeks ago cost me 6-7Ah total capacity and about 4 miles range compared to best range test before overdischarge. I believe the loss is mainly from 42-1 which was low to begin with. I don't think blades 5 or 27 are seriously damaged. But they are lower than the average blade in the pack which is about 15% less than it should be after accounting for perhaps 4% per year loss in storage with K2 cells. I am not sure other LiFePo4 cells have the same problem as most are not documenting it.

I don't think bottom balancing will work with this many cells and without similar capacity cells, so I am going back to top balancing for now. I will recheck conservative range after top balancing, and I think it is about the same since I was getting about 65Ah capacity after the overdischarge event.

Bottom Misbalancing Act II

Quest for an Electric Porsche Boxster.

I was trying to bottom balance again after 35-2 was early reaching 2.5v after driving this evening. The pack took a few hours before 42-1 shunted down to the level of 35-2. I turned off the BMS ssh data stream for a few minutes to take a break from the warning texts I receive when any cell goes below 2.5v. When I checked again 15 minutes later 35-2 had magically jumped up to >2.8v while 42-1 stayed down at <2.5v. I had not turned off the breakers to the strings. The charger is off and the car unplugged. I double checked 35-2 manually and it was at 2.8v and now shunting. An hour ago it was manually 2.5v and not shunting. Perplexing. Now 35-2 is the max voltage cell in the pack! The connections look fine and manual meter matches the BMS board.

01 2814 028 2844 028 2821 028 2823 028
02 2848 028 2869 028 2850 028 2853 028
03 2777 022 2812 022 2791 022 2807 022
04 2777 032 2812 032 2793 032 2794 032
05 2746 033 2764 033 2756 033 2770 033
06 2794 033 2839 033 2814 033 2810 033
07 2812 032 2828 032 2826 032 2827 032
08 2772 032 2801 032 2781 032 2772 032
09 2783 030 2812 030 2788 030 2790 030
10 2771 037 2797 037 2788 037 2790 037
11 2751 035 2773 035 2750 035 2736 035
12 2746 036 2779 036 2731 036 2776 036
13 2755 037 2775 037 2767 037 2760 037
14 2720 037 2761 037 2729 037 2748 037
15 2783 034 2802 034 2778 034 2795 034
16 2811 035 2849 035 2822 035 2835 035
17 2802 033 2823 033 2802 033 2811 033
18 2772 041 2787 041 2771 041 2785 041
19 2798 034 2824 034 2801 034 2809 034
20 2741 042 2771 042 2752 042 2751 042
21 2831 035 2864 035 2856 035 2844 035
22 2818 035 2860 035 2835 035 2834 035
23 2716 041 2772 041 2774 041 2787 041
24 2861 032 2887 032 2878 032 2878 032
25 2789 036 2813 036 2794 036 2795 036
26 2764 037 2786 037 2779 037 2780 037
27 2773 040 2796 040 2777 040 2780 040
28 2709 042 2730 042 2714 042 2732 042
29 2735 040 2759 040 2738 040 2754 040
30 2752 035 2768 035 2765 035 2772 035
31 2723 037 2749 037 2724 037 2741 037
32 2763 033 2792 033 2779 033 2787 033
33 2571 031 2641 031 2636 031 2655 031
34 2783 035 2812 035 2796 035 2800 035
35 2785 036 2914 036 2789 036 2807 036
36 2796 038 2802 038 2796 038 2805 038
37 2771 037 2797 037 2786 037 2801 037
38 2796 038 2861 038 2854 038 2850 038
39 2771 038 2800 038 2777 038 2794 038
40 2816 039 2848 039 2813 039 2819 039
41 2777 038 2796 038 2776 038 2791 038
42 2490 037 2798 037 2787 037 2797 037
43 2767 037 2800 037 2791 037 2789 037
44 2775 037 2791 037 2782 037 2795 037
45 2835 037 2882 037 2845 037 2857 037
46 2794 035 2815 035 2804 035 2802 035
47 2765 033 2792 033 2766 033 2770 033
48 2788 029 2801 029 2782 029 2787 029
Max Voltage: 2914 (352)
Min Voltage: 2490 {421)
Max Temp: 42
Min Temp: 22

Bottom Misbalancing Act

Quest for an Electric Porsche Boxster.

I am not sure what to say... I bottom balanced, and it seemed to work the first full charge and discharge. But the second full charge and discharge seems to indicate drift. And this time it is blade 35-2 which is much lower than the rest! I don't get it. It is in the SAME string as 42-1, and now 35 is the lowest cell in the string and pack by far. 35 hasn't even really come up before as a low capacity cell. I manually checked the voltage and it was true, 2.5v. I am going to try and bottom balance one more time, this time down to 2.6v to see if the drift occurs again. If it does, I don't think these cells discharge or charge consistently, perhaps due to wide variations of internal resistance and capacities. I like the power output, but the capacity and consistency of these cells has been a real pain.


01 3055 029 3066 029 3064 029 3069 029
02 3063 031 3071 031 3064 031 3072 031
03 2996 022 2986 022 3001 022 3000 022
04 3001 034 3011 034 3011 034 3015 034
05 2979 035 2979 035 2982 035 2995 035
06 3046 034 3068 034 3057 034 3059 034
07 2958 034 2991 034 3000 034 3007 034
08 2987 034 2992 034 2996 034 3005 034
09 2985 032 2990 032 2995 032 2985 032
10 2999 039 3006 039 2998 039 3007 039
11 2984 037 2993 037 2981 037 2985 037
12 2977 037 2985 037 2968 037 2996 037
13 2991 037 2990 037 2989 037 2986 037
14 2968 037 2976 037 2970 037 2983 037
15 2991 036 2994 036 2982 036 2999 036
16 2996 036 3009 036 3004 036 3005 036
17 2992 032 2998 032 3005 032 3007 032
18 2993 038 2991 038 2987 038 3000 038
19 3042 033 3047 033 3047 033 3055 033
20 2963 035 2968 035 2967 035 2981 035
21 3050 034 3062 034 3057 034 3060 034
22 3045 033 3058 033 3048 033 3054 033
23 2977 037 2992 037 2990 037 2997 037
24 3059 032 3075 032 3067 032 3068 032
25 2993 036 2992 036 2986 036 2996 036
26 2977 036 2970 036 2964 036 2982 036
27 2982 039 2975 039 2982 039 2980 039
28 2970 040 2957 040 2966 040 2984 040
29 2962 037 2952 037 2945 037 2967 037
30 2974 035 2982 035 2979 035 2996 035
31 2962 036 2963 036 2959 036 2983 036
32 2983 031 2991 031 2977 031 2990 031
33 2938 033 2946 033 2955 033 2960 033
34 2992 037 3018 037 3013 037 3023 037
35 3008 038 2504 038 3007 038 3014 038
36 2987 041 2988 041 2987 041 2994 041
37 2993 038 2998 038 2995 038 3014 038
38 3064 038 3070 038 3077 038 3079 038
39 2995 038 2995 038 2997 038 3010 038
40 3057 039 3070 039 3055 039 3058 039
41 2987 038 2992 038 2982 038 2995 038
42 2775 039 3016 039 3005 039 3015 039
43 2991 039 2990 039 2994 039 3003 039
44 2991 038 2987 038 2987 038 3001 038
45 3063 037 3077 037 3063 037 3064 037
46 3010 036 3003 036 3008 036 3013 036
47 2993 036 3000 036 2995 036 3003 036
48 3008 031 3010 031 3012 031 3019 031
Max Voltage: 3079 (384)
Min Voltage: 2504 {352)
Max Temp: 41
Min Temp: 22

Bottom Balancing Act I

Quest for an Electric Porsche Boxster.

As with most things in life, I often have to learn things the hard way. The last deep discharge probably did damage the weakest blade, 42. I don't seem to be getting as much capacity out of the top balanced pack, and I am at risk of running the weakest blades down to reversal every time I drive the car too far. So after some soul searching and a little help from my friends Jack and Tim, I decided to buck from my team at Revolt, and bottom balance. Thankfully, bottom balancing with a BMS was not so painful to accomplish. I drove the car to help discharge the batteries, then I reset the BMS shunts at 2.75v. It took another 36 hours for the top balanced cells to shunt down, and then I gradually charged up the lower cells to 2.75 +/- 0.02v. I then reset the shunts to 3.9v and charged up the pack, manually shutting off the charger when 42-1 got to 3.7v taking in about 71.3Ah.

I drove the car and it was much more predictable discharging and none of the cells went much below 2.5v at rest. I took out exactly what I put in, driving pretty hard, having a good time with the top down on a perfectly sunny day in Austin. The Zilla does a good job of cutting current at the end of a bottom balanced pack, so I think there was little if any risk of damaging a blade from overdischarging. I can also better trust the low battery indicator from the Zilla as another last ditch warning for when I need to stop and recharge. I like that. I set that indicator at 172v or avg 2.7v/cell, and the low voltage cutoff at 129v or avg 2.0v/cell.

I didn't bottom balance again. I just charged up and this time I trickle charged at the end and got 74Ah into the pack. That would be about 44 miles range if driven very conservatively. Blade 42 was again the capacity limiting blade, and I stopped the charger at 3.66v. I get the feeling with bottom balancing, that I will be able to put more Ah into the weakest cells. I doubt I will get 96Ah, but I may get 85Ah which would be nice. K2 did tell us to possibly expect some decline in capacity over time, maybe 3-4%/yr. So at 4%, that would be 88Ah. So 85Ah is pretty close and I should be happy with that I guess.

I will drive it to and from work this week, and next weekend I will recheck to see if there has been any drift and re-bottom balance. We should be able to prove whether there is any drift, and if so how often one must re-bottom balance to maintain a safe pack.

Overdischarged, but seems to be OK!

Quest for an Electric Porsche Boxster(click for evalbum).

Started with 374Ah on eVision, and drove aggressively today. Did not bring laptop assuming I had a safe 72Ah. I was wrong. When driving hard, more capacity may be lost as heat on high amp loads, but Evision does not account for this and I was not watching pack voltage. When I hit 307Ah (67Ah used) I started to see the low voltage battery indicator from the Zilla at moderate loads, followed by loss of power from the Zilla low voltage cut off, so I pulled off the freeway and into a parking garage as quickly as possible. I immediately turned off the breakers for all the strings to stop any 12V draw. I left the Porsche there for about 20-30 minutes and got a ride back to the house to get a long extension cord to use at a nearby outlet in the parking garage. Here is the BMS readout when I returned with the laptop:

rob@ubuntu:~$ ./summary.sh
spawn [open ...]
blade/millivolt/temp in C (4 columns of cells in a blade)
Rear Pack String:
01 3193 034 3213 034 3198 034 3198 034
02 3200 035 3208 035 3185 035 3192 035
03 2589 037 2712 037 2576 037 2720 037
04 2526 044 2645 044 2574 044 2619 044
05 2516 046 2460 046 2463 046 2505 046
06 3189 043 3197 043 3194 043 3190 043
07 2701 042 2740 042 2751 042 2753 042
08 2867 040 2770 040 2850 040 2844 040
09 2682 039 2718 039 2692 039 2691 039
10 2572 050 2554 050 2706 050 2736 050
11 2533 048 2551 048 2501 048 2513 048
12 2540 049 2559 049 2505 049 2615 049
13 2605 049 2535 049 2578 049 2587 049
14 2517 048 2512 048 2511 048 2597 048
15 2598 046 2570 046 2557 046 2562 046
16 2677 044 2724 044 2722 044 2678 044
Middle Pack String:
17 2773 037 2825 037 2799 037 2780 037
18 2498 046 2529 046 2507 046 2540 046
19 3188 042 3205 042 3185 042 3194 042
20 2463 044 2517 044 2502 044 2487 044
21 3191 042 3212 042 3195 042 3191 042
22 3189 041 3207 041 3194 041 3190 041
23 2633 045 2666 045 2706 045 2720 045
24 3191 036 3208 036 3189 036 3189 036
25 2486 042 2495 042 2575 042 2549 042
26 2587 047 2515 047 2722 047 2692 047
27 2437 053 2462 053 2448 053 2451 053
28 2515 054 2487 054 2475 054 2538 054
29 2728 050 2644 050 2636 050 2681 050
30 2561 047 2509 047 2593 047 2574 047
31 2535 047 2527 047 2460 047 2524 047
32 2495 038 2561 038 2613 038 2636 038
Front Pack String:
33 2573 039 2657 039 2726 039 2777 039
34 2578 046 2562 046 2559 046 2617 046
35 2588 048 2636 048 2541 048 2612 048
36 2780 051 2707 051 2745 051 2809 051
37 2584 048 2530 048 2558 048 2659 048
38 3192 048 3207 048 3198 048 3198 048
39 2708 048 2710 048 2598 048 2689 048
40 3192 049 3211 049 3187 049 3184 049
41 2512 049 2554 049 2518 049 2546 049
42 0723 054 2505 054 2536 054 2543 054
43 2652 051 2638 051 2660 051 2670 051
44 2612 049 2534 049 2570 049 2572 049
45 3186 046 3211 046 3186 046 3188 046
46 2582 045 2568 045 2551 045 2585 045
47 2814 044 2767 044 2784 044 2802 044
48 2612 038 2582 038 2585 038 2624 038
Max Voltage: 3213 (12)
Min Voltage: 723 {421)
Max Temp: 54
Min Temp: 34

After charging 45min at 120V 10A, I was able to drive home safely. I turned off the front pack breaker since 42-1 was at about 2.9V at rest. I charged up the pack and it took in about 85Ah. 42-1 did not charge up first, or lag behind its peers in the same blade, so I think this is a bad blade even before this run. I performed a partial range test on Sunday, and the pack seems fine so far. I will try and perform more range tests after the pack is balanced fully.

PERFORMANCE

Quest for an Electric Porsche Boxster.

The car is really fun now. Except for range and battery capacity, the car is meeting expectations as far as performance. After emailing Tim Catellier who has a lot of experience with his BMW Z3, and discussing the batteries with David Anderson at K2, I decided to reduce the low voltage limit on the Zilla to an average of 2.3V. This really loosened up the amp output, and now I am getting close to 840A on demand, and more rapid output overall. That means more acceleration! I roughly measured 0-60 times using my cell phone's stopwatch, and on relatively flat ground I am seeing less than 7 seconds, maybe 6, in optimal conditions. That means a full pack and relatively warm weather. The battery voltages sag on heavy load, with the lowest blades at 2.3-2.4V, and an average minimum of around 150V. So one must wonder what the car would be like with a higher nominal voltage pack, say 260V? This would help cold weather performance too.

Austin, Texas has been rather cold in recent days. Last Wed, the temp dropped below 25 degrees. I left home with a half full pack and kept the car garaged that night. So the pack was relatively warm. But at the end of the day, the car was in less than 23 degree weather parked outside, not plugged in. The car was sluggish, and getting on the freeway was barely possible. The car requires about 100-130A to maintain speed on the freeway on level road or with slight elevations. The pack would not produce more than about 160A on the way home limiting acceleration severely. Granted the pack was more than half empty, but compared to warm weather this was a dramatic loss of power. Despite average voltages sagging as low as 2.3v, I was able to get home and the voltages returned to over 3.1v at rest. I tested range in warm weather the next day, and capacity was back at 72Ah. So it was evident the batteries can tolerate battery sag, at least above 2V briefly, without serious problems. So yesterday I decided to drop the Zilla limit to an average minimum of 2.3V. Now in warm weather the car feels like a PORSCHE. Much better than stock! I imagine driving like that may limit range even more, but it's worth it!

Back on the ROAD!

Quest for an Electric Porsche Boxster.

Finally back on the road today after a lot of work. Netgain diagnosed a fan failure and sent us a new fan. We tried to follow instructions, but the fan is so tightly fixed to the shaft, we broke the replacement fan trying to install it incorrectly. We paid for another fan, about $240, and used a PVC pipe over the motor shaft, with a 2x4 on top of the pipe, and a hammer on the 2x4 to force the fan onto the shaft. It took an hour of hammering, checking, hammering, etc. Finally got the fan on, reassembled and presto... IT SPUN UP! So, almost 4 weeks later and about 8 hours of work tearing down, fixing motor and reassembly. Back on the road!

If this happens to you, strongly consider sending back to Netgain for repairs, as if you break the fan you will have to pay for another and it will delay the repair by at least a week. If you repair it yourself, DO NOT HAMMER ON THE OUTER RIM OF THE FAN. It will not work and the fan is very strong, but brittle like ceramic. IT WILL CRACK. Also be sure and remove as many fragments as possible using a powerful vacuum and forced air if available. We had a small fragment we missed and were worried it caused some damage. Had to take the fan grate off and remove it. The fragment fell out, and it was fine afterwards with no damage to the new fan.

Warp 11 Fan Destroyed, Netgain to Rescue!

Quest for an Electric Porsche Boxster.

Here are some photos of the fan failure... Netgain is sending a replacement and we will hopefully have it fixed in a week or so without having to ship it back.

Warp 11 Motor failure

Quest for an Electric Porsche Boxster.

Drove out to the lake and back. Something came loose in the motor when driving in 2nd gear up to about 4000rpm when leaving the marina parking lot . It clinked and scratched loudly at first, as if bouncing around, and eventually settled down, temporarily went away at lower rpms. I was able to drive home and heard the noises a few more times when going up hills or perhaps bumps as if something plastic was bouncing around in there. It wasn't as loud as at first. It would settle down on even road and had no perceptible noise for fairly long distances at 2500rpm going about 50-55mph. Once home, I tested the motor in neutral and you can hear scraping sounds. I think this motor is going to need TLC from Netgain.

On a lighter note, replacing the motor mount has made a noticable difference on take offs, and overall the handling going to the lake was very good. The efficiency on the trip was about 1.8Ah/mile which is pretty good, and power performance is pretty good too, particularly since lowering the minimum voltage limit on the Zilla. I don't think there is much more room for maximizing performance with this battery pack however, and I may swap out the Zilla Z2K for a Z1K as that should be more than enough for this pack.

Battery Capacity and Range part II

Quest for an Electric Porsche Boxster.

I did another capacity test yesterday. Started at 276Ah and went to 204Ah limping into the garage for a total of 72Ah. Blade 33 performed well, but this time 35-2 went south in hurry. I think the shoulder on this pack is about 2.75V with light amp draw of about 60-100A. At brief rest, 35-2 went back to 2.9V so I decided to go around the block again, which ended up being about 2.6 miles. Too much, and I briefly went to 1.4V on 35-2 when drawing 50-60A getting back to the house. I wish I could have taken 1 mile back. It went back up to 1.9V after brief rest. Most other cells including blade 33 went over 3V and a few were at 2.9V. The other cells in 35 were not as weak as 35-2. Anyway, I don't think blade 33 is a problem anymore than the general capacity of the pack. Various blades took turns as the minimum voltage with accelerations during the drive, and cells in blade 33 only came up once I think. Blade 35 came up a few times, but I wouldn't have singled it out earlier in the drive. So right now I think we have a fairly stable pack, of around 70Ah (safely at 1.8Ah/mile).

I left the charger on 2A overnight which eVision showed about 0.5A going to the pack. Before going to bed the pack was at 278Ah with 42-1 reaching shunt at around 3.56V, and the rest of the pack still around 3.3-3.4V. The pack balanced about 7.5 hours overnight to the following...
B#     mV   T
          cell 1           cell  2           cell 3           cell 4
01 3575 024 3583 024 3573 024 3584 024
02 3573 025 3577 025 3575 025 3576 025
03 3571 020 3576 020 3578 020 3578 020
04 3575 028 3577 028 3578 028 3577 028
05 3578 028 3578 028 3576 028 3575 028
06 3578 028 3576 028 3571 028 3571 028
07 3577 028 3577 028 3576 028 3572 028
08 3580 028 3577 028 3579 028 3574 028
09 3580 026 3579 026 3579 026 3579 026
10 3580 032 3579 032 3571 032 3570 032
11 3577 029 3576 029 3573 029 3575 029
12 3576 031 3579 031 3575 031 3573 031
13 3579 031 3579 031 3576 031 3577 031
14 3574 032 3576 032 3574 032 3575 032
15 3577 029 3577 029 3575 029 3574 029
16 3582 031 3583 031 3583 031 3582 031
17 3565 028 3570 028 3572 028 3572 028
18 3577 033 3577 033 3571 033 3572 033
19 3576 028 3577 028 3574 028 3574 028
20 3575 033 3575 033 3572 033 3576 033
21 3572 029 3572 029 3566 029 3566 029
22 3572 029 3573 029 3570 029 3571 029
23 3576 033 3577 033 3571 033 3571 033
24 3574 026 3575 026 3571 026 3569 026
25 3576 028 3576 028 3572 028 3571 028
26 3571 029 3573 029 3569 029 3566 029
27 3573 032 3572 032 3566 032 3564 032
28 3574 033 3575 033 3570 033 3572 033
29 3571 031 3571 031 3566 031 3565 031
30 3574 027 3576 027 3572 027 3572 027
31 3570 029 3573 029 3570 029 3568 029
32 3556 026 3561 026 3570 026 3567 026
33 3573 029 3571 029 3570 029 3571 029
34 3567 032 3567 032 3568 032 3565 032
35 3573 033 3575 033 3570 033 3570 033
36 3572 035 3574 035 3569 035 3572 035
37 3573 034 3573 034 3574 034 3574 034
38 3576 036 3575 036 3571 036 3571 036
39 3572 035 3572 035 3567 035 3566 035
40 3570 037 3567 037 3570 037 3568 037
41 3570 036 3571 036 3566 036 3564 036
42 3569 035 3571 035 3569 035 3567 035
43 3569 035 3572 035 3569 035 3566 035
44 3572 035 3572 035 3567 035 3566 035
45 3567 034 3566 034 3567 034 3566 034
46 3574 032 3573 032 3572 032 3572 032
47 3573 032 3574 032 3564 032 3565 032
48 3570 028 3571 028 3570 028 3568 028
Max Voltage: 3584 (14)
Min Voltage: 3556 {321
Max Temp: 37
Min Temp: 20

Most all the cells showed the orange lights shunting, so not all the Ahrs overnight shown on eVision went in the pack. Nonetheless the total on eVision was 285Ahrs from 204Ahrs before charging. So, even including shunt losses, the pack only took in about 81Ahrs. 35-2 was not the first to reach full, and so I don't think we have anymore blades that stand out as being bad. We just have a lower than expected usable capacity for this pack. If it is supposed to be 96Ahrs, then we are still missing at least 16-20% capacity. Unless something else is wrong, I think we have no more than 80Ahrs or about 47miles range at 1.7Ah/m at the very maximum.

I don't see this pack safely producing 10C continuous discharge rates. It barely produces 5-6C with a full pack. 5C discharge is what K2 lists as "nominal capacity" on their spec sheet. Without lowering the Zilla voltage limit further, 5-6C is probably the maximum useful draw on demand for acceleration in our arrangement. Therefore, the Z2K is probably not going to be better than the Z1K with this pack producing around 500-600A maximum. If I recalculate the cell capacity from the expected 3200mAh down to 2700mAh (about what we are seeing now), then discharge rates appear higher. So with 500A on acceleration, that results in a 6C discharge rate based on the lower capacity. 630A, which I saw once with a full pack, is about 7.7C, which is not too bad and overall performance is pretty good but not as exciting as we hoped.

Digesting all this, I guess we would like to know the maximum tolerable voltage limit we can set on the Zilla for brief accelerations without "abusing" the cells, since we are not seeing much beyond 5-6C discharge rates with Zilla set at average 2.4V sag. Will the cells tolerate going to 2.0V sag for less than 30sec? How about 1.5V, if brief rest brings them back to over 3V? And finally, why are we not getting closer to expected capacity from this configuration? These are all questions I will need to review with K2 to see if we are missing something or if they have any suggestions. These were much more expensive batteries than the Thundersky variety, and I am not seeing the energy density or power advantage at this point.