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Forum • Résistance interne de la batterie 40 kWh

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Quelques essais et calcul de la résistance interne des batteries de la LEAF (US):

 

For those that have access to a 2018 Leaf, do QC charging, and use LeafSpy, your help obtaining battery data on that vehicle

would be very useful in determining what battery parameter could be contributing to having the charging time progressively

lengthened during a long distance trip. It appears that the 2018 Leaf’s BMS controller is reducing the charging current as the

battery gets progressively warmer during a lengthy trip. This has not been the case for earlier Leafs even though the BMS does reduce the charging current over time for the earlier Leafs, but it appears not based on temperature nor based on the number of previous QCs during a trip.

 

The process should only take a couple of minutes during the starting phase of the QC to obtain the data:

 

1. Once the vehicle is parked adjacent to the QC with the Leaf’s power still on with no accessories turned-on, e.g. the fan/AC,

measure the battery voltage (V1). It should be greater than 325 volts. Then measure the battery temperature (T - degrees C).

Write these values down.

2. Next the charging voltage (V2) and charging current (I) need to be written down immediately once the QC device begins

the charging process using LeafSpy. If the QC device provides these values, just use those values displayed on the QC

device like in this post; viewtopic.php?f=27&t=25519&start=70#p523610

3. Once all the data are taken and time permits, please post them in this thread using the following form;

V1 - XXX, V2 - XXX, T - XX, I - XX

4. The data will then determine the battery resistance by this calculation; battery resistance = (V2 - V1) / I

As an example, V1 = 355 volts, V2 = 365 volts, I = 80 amps, then battery resistance = .125 ohms or 125 mohms.

Battery resistance varies with temperature, so it's critical to determine the temperature at the being of the charging process.

 

Based on your values and other’s values, a comparative analysis between the early Leafs and the 2108 Leaf should provide

insight into how the chemistry might be different and what one might expect about long term battery degradation the result of lengthy and multiple QCs combined with high speed driving during a long trip.

 

Thanks for your help.

 

 

Doing multiple QCs yesterday using both ChargePoint & EVgo QCs, it took about 10-15 seconds to perform the above test.

The calculations from the data correlated with battery resistance data doing the LeafDD battery load test versus the above,

i.e. determining battery resistance during a QC mode.

 

Pack Volts Pack Amps Pack T1 F Pack T2 F Pack T4 F

344.5 0 83.1 80.1 75

344.83 0 83.1 80.1 75

344.83 0.061 82.9 80.1 75

349.25 -85.082 82.9 79.9 75

351.36 -119.445 82.9 79.9 74.8

 

338.11 0 104 100 91.2

338 0 104 100 91.2

338.4 -0.03 104 100 91.2

338.3 0.061 104 100 91.2

338.4 0.122 104 100 91.2

341.57 -74.065 104 100 91.2

342.34 -77.453 104 100 91

 

348.48 0 111.2 106.7 97

348 0 111.2 106.7 97

348.67 0.061 110.7 106.2 96.4

349.73 -16.509 110.7 106.2 96.4

351.36 -68.023 110.7 106.2 96.4

351.84 -68.542 110.7 106.2 96.4

 

(351 - 344) / 119 = 59 mohms

 

(342 - 338) / 77 = 52 mohms

 

(351 - 348) / 69 = 43 mohms

 

Using your charging data (I assume), the 2018 40 kWh Leaf battery has about the same battery resistance (55 mohms) as the 24 kWh battery.

Given that adding more cells in parallel (effectively) for more energy when using the same chemistry should have resulted in about .60 (24/40)

the battery resistance (on average) of the 24 kWh battery resistance, so one can possibly conclude a change in battery chemistry (worse).

Additionally, since the 2018 battery is running hotter with the approximate same battery resistance, i.e. same internal heat generation, one would assume that its thermal resistance to ambient has increased. Reg/LeftieBiker have noted/implied this up-thread.

 

A thanks to Dave. At least further insight now exists about the 40 kWh battery and that more data will be obtained over time.

This obviously is not to be considered a rigorous analysis, but just a simple approximation test. Hopefully I didn't misinterpret what he did.

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On verra si plus de mesures confirment ce mauvais niveau de résistance....

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