Tuesday, February 22, 2011

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

4 comments:

  1. Hi Rob, interesting blog and a worrisome finding.

    I'd be wary of disparate measuring devices.

    Did you disconnect the boards for charging and measured the cell voltages with the same meter?

    If not, have you considered swapping a couple of daughter boards to see if they read the same?

    Last but very definitely not least. Are your battery connections still good?

    All the best. A.

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  2. This weekend I will need to take a close look at all the battery connections between blades and BMS boards. Thanks for the input!

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  3. Yay, *if* you have a poor bus bar connection it will return a hot spot when in use. Too much heat causes harm :(

    Also, the lowest voltage cell is not necessarily the weakest when charged so did your BMS have a say when charging your pack?

    I'm sorry Rob. I've too many questions from flying blind so I'll shut up. :)
    A.

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  4. I have a infrared temp gun that I can use to test the bus bars next weekend. I'm driving the car and I feel like I am flying blind figuring out these batteries.

    ReplyDelete