Get High-voltage system -> High-voltage battery AX2 Guide for Audi RS E Tron Gt 4 Door First Generation (2021-2026)

High-voltage battery AX2

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High-voltage battery 1 AX2 is bolted on centrally under the vehicle as a component supporting the body. The battery has 33 battery

modules which are fitted on two levels.

The battery housing is connected to the body via a live potential equalisation line. Potential equalisation refers to a suitably conduc-

tive connection that minimises differences in electric potential.

Switching unit for high-voltage battery SX6 is fitted on the high-voltage battery. The battery module control units are fitted on the

modules inside the high-voltage battery. Battery regulation control unit J840 is located in switching unit for high-voltage bat-

tery SX6.

Technical data

Designation

High-voltage battery

Cell modules

33

Cells

198s2p

Weight in kg

Approx. 650

Nominal voltage

Number of battery cells

Energy content in kWh

Maximum charging capacity in kW

Approx. size in mm

726

396 in 33 modules

93

270

2430 x 1670 x 325

If the vehicle is parked for a long period, the charge level of the high-voltage battery is reduced because the 12 Volt battery is auto-

matically recharged. If the charge level of the high-voltage battery goes below 10%, the 12 Volt battery is no longer recharged.

Reference

Additional information can be found in this SSP (refer to article “12 Volt power supply”).

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Operating temperatures

The battery has an operating range between -30 °C and 50 °C.

It is not possible to activate the vehicle’s drive system under -30 °C. Above 60 °C, the power contactors are opened/kept open when

the ignition is on. At temperatures between 55 °C and 60 °C, the current draw of the high-voltage battery is reduced.

High-voltage batteries that are not currently installed in a vehicle may be stored at temperatures between -40 °C and 60 °C.

Cooling

The coolant circuit for the high-voltage battery provides cooling for the battery. The battery modules release heat to the battery

housing via a layer of thermal grease.

The coolant in the coolant circuit for the high-voltage battery flows through heat sinks that are bonded to the battery housing with

thermal conductive adhesive.

Coolant temperature sender 1 for high-voltage battery G898 and coolant temperature sender 2 for high-voltage battery G899

measure the temperature of the coolant upstream and downstream of the high-voltage battery.

The coolant in the high-voltage battery is circulated by the coolant pump for high-voltage battery V590.

If the low-temperature cooling circuit for the high-voltage battery does not provide sufficient cooling, it is possible to cool the cool-

ant additionally using the refrigerant circuit (this takes place via the heat exchanger for high-voltage battery).

At low temperatures, the high-voltage battery can be heated up while charging via the high-voltage heaters.

Reference

Additional information can be found in this SSP (refer to article “Coolant circuit for high-voltage battery”).

Battery modules

A battery module is made up of 12 pouch cells and the battery module control unit. Each of these cells has a nominal voltage of

3.65 V and a capacity of 66 Ah.

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Note:

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For cells connected in series, the voltages are added together; for cells connected in parallel, the capacities are added together. In

the 6s2p circuit of the module, the nominal voltage of the module is 22 V, and the module capacity is 132 Ah.

Control units for battery modules

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A battery module control unit is fitted on every cell module. The battery modules control unit has the following functions:

›

Measuring the voltage of six cells

Reading signals from two module temperature sensors and one onboard temperature sensor

Passive balancing (max. 100 mA)

The battery modules control unit communicates with high-voltage battery control unit J840 via a twisted-pair cable bus.

The battery modules control unit cannot be renewed individually; it must be renewed together with the battery module.

Module circuits and numbering for the lower battery level

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The modules are numbered from 1 to 33, beginning with the negative battery terminal; the positive terminal is number 33. In oth-

er words, the numbers go from negative to positive potential.

Module circuits and numbering for the upper battery level

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The second level contains modules 18, 19 and 20, and the high-voltage battery fuse.

Switching unit for high-voltage battery SX6

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The switching unit is the divider between the high-voltage battery and the vehicle’s high-voltage system. It incorporates the follow-

ing components:

›

Controller for measuring current and voltage

Fuses for the high-voltage cables (front and rear)

Current sensor (Hall sensor)

Protective relays for high-voltage positive and high-voltage negative sides

Pre-charge protective relay with 30 ohms pre-charge resistance

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Switching order of the protective relays when the high-voltage system is switched on:

›

High-voltage positive - vehicle front end,

High-voltage positive - vehicle rear end,

High-voltage negative - pre-charge,

High-voltage negative.

The protective relays are opened in reverse sequence of the switching order; only if triggered by a crash are they all opened at the

same time.

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Battery regulation control unit J840

Battery regulation control unit J840 is fitted in switching unit for high-voltage battery SX6 and performs the following functions:

›

Monitoring the high-voltage battery

Controlling the temperature conditioning of the high-voltage battery

Controlling the coolant pump of the high-voltage battery

Event memory (storing and displaying entries)

Monitoring the charge level of the high-voltage battery

Monitoring the charge level of the cells

Calculating the capacity of the cells/battery

Calculating battery ageing

Insulation resistance monitoring

Monitoring the current

Switching off the high-voltage system in the event of a fault

Controlling the balancing function

Diagnosing the high-voltage battery

Cell balancing

In this example, a cell is 100% charged and the charging procedure is complete. However, the high-voltage battery charge level is

only 92.5 %. Balancing means that this cell is now discharged via a resistor and can thereby continue to be charged until all cells

have reached the same charge level. This allows the high-voltage battery to achieve its maximum capacitance.

To do this, the battery regulation control unit J840 compares the voltages of the cell groups. If cell groups have a high cell voltage,

the battery modules control unit responsible receives the balancing information. After the ignition is switched off, the battery reg-

ulation control unit J840 checks whether balancing is necessary and initiates the process as appropriate. Only the control units on

the sub-CAN are active when this is done. Balancing is performed at charge levels greater than 30%.

Cell balancing takes place passively, meaning that the energy is dissipated as heat via resistors. The high-voltage battery control

unit controls and monitors cell balancing. Cell balancing takes place only by discharging individual cells. Cell balancing starts every

60 minutes after the vehicle is switched off, once the difference in capacity between the cells reaches approximately 2% (120 mAh)

and the charge level of the high-voltage battery is more than 30%.

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High-voltage system -> High-voltage battery AX2 for Your Audi RS E Tron Gt 4 Door First Generation (2021-2026)

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