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I am trying to replicate the charging method of fast-charging stations for electric vehicles using one or two Li-po cells. The purpose of the experiment is to measure the impact of high C-rates on Li-po cells when charging.

Part of designing the experiment is finding out about the actual C-rates used in the market to charge EVs fast, as well as to identify the currents and voltages at which this is done.

I was wondering if the BQ2054 IC would be a good fit for this experiment, or if there are other valid options. Also, based on the info in datasheet, I couldn't find the actual C-rates at which this IC works. Is there an explanation for this?

ocrdu
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Carmen Selva
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  • But the C rate is up to the cell. So the C-rate is not about the charger. Whatever current the charging chip can do, it can be converted to a C value of the cell. – Justme Mar 26 '23 at 17:47

2 Answers2

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The BQ2054, like all charge control ICs that I have seen, regulates the charge current, but has no idea what C rate is.

Some ICs have what they call a "current programming" resistor connection. The BQ2054 (and many other such ICs) monitors the maximum current by measuring the voltage across a low value resistor.

From the datasheet:

enter image description here

You can rewrite the equation to find the resistor value needed for a specific maximum charge current:

\$R_{SNS} = \frac {0.250V}{I_{MAX}}\$

You (as the circuit designer) have to determine \$I_{MAX}\$.

Say you have a one ampere hour battery. A C-rate of one would charge the battery in one hour - you need a charge current of 1A, so you would do the calculation for the BQ2054 and find that you need a 0.25 ohm resistor. If you wanted to charge your battery at a C-rate of two, that would be twice the current as for the C-rate of one - that's 2A of current. You would need a sense resistor of 0.125 ohms.

Whether or not the BQ2054 is sufficient for your experiments will depend on the capacity of the cells you want to test and the C-rates. You are limited by the maximum 2A charge current of the BQ2054.

You could charge a 100 milliampere hour cell at any C-rate up to 20C using the BQ2054. You could charge a 1 ampere hour cell at a maximum of 2C with the BQ2054.

I couldn't begin to even guess how applicable such experiments with small capacity cells would relate to the larger, higher capacity cells used in electric vehicles.

JRE
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Maximum charging current for the BQ2054 is 2 A (from TI's information page you linked to; I didn't see that value in the datasheet at first glance). What C-rate that is depends on the capacity of the battery you are charging.

An IC manufacturer can't specify a C-rate because they don't know what batteries you want to charge. They specify a current, and the capacity of the battery used determines what C-rate that translates to.

With small-enough batteries you can use this IC to study how high C-rates affect Li-ion batteries (at your own risk if you go beyond the specs of the battery). The IC can charge at 2 A max., so it can charge:

  • a 2 Ah battery at 1 C;
  • a 1 Ah battery at 2 C;
  • a 0.5 Ah battery at 4 C,

and so on. The actual charging current can be set with the formula in the datasheet.

There are many other charger ICs that let you do the same. A closely monitored "manual" charging experiment with a current source could also work.

If you want information about "the actual C-rates used in the market to charge EVs fast, as well as to identify the currents and voltages at which this is done" I suggest consulting literature/googling around, or analysing actual cars.

If the experiment is in any way useful for predicting behaviour of large, real-world EV battery systems, or "replicate[s] the charging method of fast-charging stations for electric vehicles" in a useful way: your guess is as good as mine.

ocrdu
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