Charging to 100% -- voltages, SOC, and capacity

[Firn]

W = I x V. As you hit Vmax, the current will drop, thus the drop in W.

BTW, the effects of charging to 100% graphs MAY be dropping tomorrow

I think he was talking about the KWh (capacity) of the pack.



From the looks of it the truck is estimating capacity based upon the system voltage. When charging the system voltage was charger voltage and capacity was based upon that, which is higher than pack voltage. Once the charger kicked off the tested voltage dropped to paxk voltage, and capacity changed.

We can see an instantaneous drop in pack (and module) voltage the instan the charger shuts off. We then also see the voltage settle downward post charging as well.

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[MickeyAO]

I think he was talking about the KWh (capacity) of the pack.



From the looks of it the truck is estimating capacity based upon the system voltage. When charging the system voltage was charger voltage and capacity was based upon that, which is higher than pack voltage. Once the charger kicked off the tested voltage dropped to paxk voltage, and capacity changed.

We can see an instantaneous drop in pack (and module) voltage the instan the charger shuts off. We then also see the voltage settle downward post charging as well.

Once charging stops, the cell starts a polarization and the voltage will relax. Once again, W = I * V but the BMS will use I normalized instead of actual.

 

[Maquis]

W = I x V. As you hit Vmax, the current will drop, thus the drop in W.

BTW, the effects of charging to 100% graphs MAY be dropping tomorrow

All true, but what I was saying is that the stored energy (kWh) in the battery didn't drop.

 

[Firn]

Once charging stops, the cell starts a polarization and the voltage will relax. Once again, W = I * V but the BMS will use I normalized instead of actual.

And you can see the voltage of the cell, and pack start to drop and settle out.

That shouldn't be instantaneous however, right? There is an immediate drop in voltage, and immaediate drop in capacity, the instant the charger stops.


I'm also not seeing where W and I come into play here as the question is capacity.

 

[MickeyAO]

And you can see the voltage of the cell, and pack start to drop and settle out.

That shouldn't be instantaneous however, right? There is an immediate drop in voltage, and immaediate drop in capacity, the instant the charger stops.


I'm also not seeing where W and I come into play here as the question is capacity.

It is still W = I x V, but once the current stops, the BMS will use the nominal current for the calculation instead of the current before the the charging stops.

 

[Firn]

It is still W = I x V, but once the current stops, the BMS will use the nominal current for the calculation instead of the current before the the charging stops.

OK, but what Voltage and Current gets us Killowatt Hours? We are still missing a term in the equation.

By "nominal current" are you referring to the manufactures designated C rate for nominal capacity? C10, C20, or so?

I'm also not seeing how the chargerER current is used for the battery capacity calculation as you say. The current being applied BY the charger wouldn't change capacity.

 

[Wattsgas]

1 volt (either AC or DC) multiplied by 1 amp (either AC or DC) multiplied by 1 hour equals 1 watt hour.
1V x 1I x T = Watt hour
220 x 80 x 1 = 17,600 watts per hour divide it by 1,000 and you get 17.6 kilowatts per hour.
110 x 20 x 1 = 220 watts per hour divide it by 1,000 and you get 0,2 killowatts per hour.

 

[Firn]

1 volt (either AC or DC) multiplied by 1 amp (either AC or DC) multiplied by 1 hour equals 1 watt hour.
1V x 1I x T = Watt hour
220 x 80 x 1 = 17,600 watts per hour divide it by 1,000 and you get 17.6 kilowatts per hour.
110 x 20 x 1 = 220 watts per hour divide it by 1,000 and you get 0,2 killowatts per hour.

You bet.

The problem is W = I x V does not have any time component. The three components are literally Watts (W), Current(I), and Voltage(V). There is no "hour" in there to get to KWh and turn power into energy.

Nor does current make sense in this environment. You could calculate energy (KWh) by adding a time component to W = I x V x t but that is a very strange, and not very accurate, way to calculate available capacity. Integrating the power curve could possible give you total capacity, but it wouldn't drop when the charger cut off.

In the end it expect the system is simply estimating capacity based on voltage (and a few other things like temp, etc). When the charger stops and there is an immediate voltage drop we see a corresponding capacity drop.

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