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BQ40Z80: "System resistance" vs "Pack Resistance" vs "Interconnection Resistance"

Jurijs Varnels
Prodigy 30 points
Part Number: BQ40Z80

Hi,

I am trying to understand now the difference between "System resistance" vs "Pack Resistance" vs "Interconnection Resistance" registers and their practical meaning for BMS.

According to datasheet:
1) System Resistance:
1.1) It is mentioned in:

1.2) it is mentioned in chapter 6.8 TURBO Mode 3.0, that it is important parameter.
1.3) and here:

2) Pack Resistance:
2.1) it is mentioned here:

2.2) it is mentioned in chapter 6.8 TURBO Mode 3.0, that it is important parameter.

3) Interconnect Resistance:




My questions are:

a) Am I right, that Pack Resistance = Interconnecti Resistance + System Resistance + all Cell internal resistance? (Where Cell Internal Resistance parameter is stored in BMS Studio?)
b) Is only System Resistance taken into account for charging Loss compensation?
c) Are both System Resistance and Pack resistance taken into account by TurboMode mechanisms?
d) Where is used Interconnect Resistance.?

Best Regards,
Jurijs

  • +1
    TI__Genius 10370 points

    Jurijs,

    Here is the best way i can describe these three resistance values imaging you have a battery pack stand alone. This pack has a connector with Pack+/- that you click into your system.

    1) System resistance is the resistance from the battery connector to the endpoint where you need the voltage to stay above min_sys

    2) Pack resistance is from the same connection point as 1 (note to only count the connector resistance once) and the battery stack terminals. this includes the positive side and the negative side (sum'ed up)

    3) Interconnect. This is the resistance between the individual cells. So 1P to 2N for example. 

    Turbo mode on a high level added all these resistance up to compute a "total" resistance which allows us to know how much current you can apply to keep the voltage at the end of the system resistance parameter above min sys voltage. 

    Hope this helps.

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 30 points

    Thank you for explanation, Eric! now everything is much more clear.
    Just some extra questions:
    1) Should we measure for System resistance positive and negative side too?
    2) Do I understand correctly term "battery" above -it is cell pack soldered to BMS PCBA, that have connector?

  • 0 in reply to Jurijs Varnels
    TI__Genius 10370 points

    Jurijs,

    1) Yes both are in the current path

    2) Yes 

    Thanks,

    Eric Vos