Total resistance of the battery pack

[Jonndeka]

Hi,

If we want to calculate the total resistance of the battery module, what components' resistance should we consider?
Assume this module is 6S4P.
Except the internal resistance of the cells, do we need to consider busbar resistance and other things?
If yes, how can we calculate busbar resistance?

 

[DogDipstick]

Vd=xS/xP*Rc*I

You will get your Voltage drop by number of series cells divided by the number of parallel cells times average cell resistance in ohms time current draw in amps.

This equation considers the cells only themselves, the Vdrop and this will give the waste heat in dissipate power in the battery... based on Vdrop and intrinsic resistance.

This eq. DOES NOT take switch gear losses into account, or bus bar, wire, resistance, for these are typically negligible, in a well built pack, but can be measured with a meter ( good mOh meter). A good 200A contactor relay might be 0.6mOh, a very good 800A contactor might be 0.2mOh. Very little heat lost in this as current travels through. They are built to withstand current and not drop any voltage in the line ( heat created through that R to make the W dissipate) . The more current they are built for ( copper inline) the less they drop, typically, in a current transfer event at voltage.

Measure bus + measure cells and pack = total path of resistance current must travel upon applications of loading. How do we know this number? Milliohm meter or shunt data acquired from current travel at certain known voltage.


Two things every biker needs to know
1. There's old bikers and there's bold bikers, but there ain't any old bold bikers.
2. Never forget number 1.

 

[Jonndeka]

Vd=xS/xP*Rc*I

You will get your Voltage drop by number of series cells divided by the number of parallel cells times average cell resistance in ohms time current draw in amps.

This equation considers the cells only themselves, the Vdrop and this will give the waste heat in dissipate power in the battery... based on Vdrop and intrinsic resistance.

This eq. DOES NOT take switch gear losses into account, or bus bar, wire, resistance, for these are typically negligible, in a well built pack, but can be measured with a meter ( good mOh meter). A good 200A contactor relay might be 0.6mOh, a very good 800A contactor might be 0.2mOh. Very little heat lost in this as current travels through. They are built to withstand current and not drop any voltage in the line ( heat created through that R to make the W dissipate) . The more current they are built for ( copper inline) the less they drop, typically, in a current transfer event at voltage.

Measure bus + measure cells and pack = total path of resistance current must travel upon applications of loading. How do we know this number? Milliohm meter or shunt data acquired from current travel at certain known voltage.


Two things every biker needs to know
1. There's old bikers and there's bold bikers, but there ain't any old bold bikers.
2. Never forget number 1.

Many thanks for your explanation.
Do you think if we want to estimate SOH or investigate the aged battery in module level (6S4P), do we need to consider other resistance except the cells internal resistance? or busbar resistance and connectors are negligible?