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Battery simulator, sometime is called battery emulator, is a very important equipment for testing battery chargers and battery-operated systems. Many portable electronic devices use rechargeable batteries such as lithium ion (Li+), lithium polymer, nickel metal hydride (NiMH), nickel cadmium (NiCd), or lead-acid battery. Many of these rechargeable devices have charger circuits built inside. For testing these electronic devices, a battery simulator or emulator is often needed. For example a lithium ion battery emulator can easily vary the voltage to simulate a battery is being charged or discharged. This eliminates hours of test time. A battery simulator power supply is great for bench testing as well as production testing.


To simulate a battery, a power supply emulates many of the battery’s characteristics. The most important characteristic is the ability to sink current when the battery simulator is charged. The battery charger drives charging current into a simulated battery. Therefore, the current is flowing into the simulator power supply. At the same time the simulator must able to source current seamlessly. In fact it must be able to transition between sink and source current without any glitches, even at high speed.

TS250/TS200 Battery Simulator/Emulator

The TS250 and the TS200 modulated power supply can mimic sink and source current the same way a real battery does. They feature a DC OFFSET knob that can adjust the voltage to emulate battery voltage changes. It’s especially useful for simulating a battery for charger circuit testing.

Conventional power supply cannot simulate a battery. It cannot sink current like a battery can. It is equivalent to a battery simulator with a blocking diode.

Figure 1. A) Simplified conventional power supply circuit. B) Equivalent circuit.

Battery simulator circuit is using two transistors. It can emulate a battery being charged. Battery simulator equivalent circuit model. It can sink and source current like a real battery.

Figure 2. A) Simplified battery simulator circuit. B) Equivalent circuit.

A B A B

Battery Emulator Applications

TimeBattery Voltage (Blue)Battery Current (Red)Battery Voltage (Blue)Battery Current (Red)End of chargeTrickle chargeCC ChargingCV charging4.2V

Figure 6. Lithium ion battery CC/CV charging profile.

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Related Technical Information

    Charger Design

    Four Quadrant Power Supply

    TS200 Simulator Quick Start Guide

    TS250 Simulator Quick Start Guide

Selecting a Simulator

Both the TS250 and the TS200 can simulate batteries. The TS250 has an additional feature for output current LCD display. Thus, it eliminates the need for external current monitor. Use the below table for selecting a simulator power supply.

Model

Voltage Range

Lithium Ion

NiMH/NiCd

Alkaline

Lead-Acid

TS250-4

-6V to +15V

1-3 cells

1-10 cells

1-9 cells

6V or 12V

TS250-5

-6V to +30V

1-7 cells

1-20 cells

1-18 cells

6V/12V/24V

TS250-6

-6V to +45V

1-10 cells

1-28 cells

1-25 cells

6V/12V/24V

TS200-4A

0 to +15V

1-3 cells

1-10 cells

1-9 cells

6V or 12V

TS200-2B

-20V to +45V

1-10 cells

1-28 cells

1-25 cells

6V/12V/24V

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TS250 vs. TS200

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Conventional power supply can only source current, but cannot sink current. Thus a conventional power supply cannot effectively simulate a battery. Figure 1 and 2 show simplified diagrams for the difference between a conventional power supply circuit and a battery simulator power supply. Conventional power supply circuit is depicted with a single NPN transistor allowing current to flow only in one direction – sourcing current. On the other hand, the simulator power supply can sink and source current as shown in Figure 2A. The top NPN transistor is for sourcing current and the bottom PNP transistor is for sinking current.


A simulator can easily change the “battery” voltage by adjusting a knob, compared to a real battery whose voltage is slowly changed by charging or discharging. Thus a battery simulator test equipment is very useful for testing battery-operated systems. Instead of waiting hours for the battery to charge or discharge, a simulator can emulate the battery voltage behavior in seconds. In summary, a simulator is ideal for bench testing, debugging chargers and production testing.

Battery Simulator Power Supply

Battery simulator connection diagram for testing a charger.

Figure 3 shows a typical battery simulator test equipment connection for testing chargers.

Infinite Capacity

A real battery has a finite capacity. When a battery is charged or discharged, its voltage is changing slowly. On the other hand, the battery emulator keeps its voltage constant. This is equivalent to a battery with infinite capacity or a very large battery. Battery simulator power supply with non-drifting voltage is ideal for bench testing. Especially, when you want the voltage to be constant for the duration (minutes to hours) of the test.


Simulate Source Impedance and ESR

A real battery has its own internal impedances called ESR (electric static resistance). When current is draw from the battery, its voltage drops slightly. ESR is calculated by the voltage drop (delta voltage) divided by the current. Figure 4 shows a simplified model of a battery ESR. Figure 5 shows how the battery simulator can add ESR to emulate a real battery. Typical ESR is the range of 0.1 ohm to 1 ohm and depends on the battery chemistry, capacity, temperature, age, and state of charge. The TS200/TS250 battery emulators have a very low output ESR, in the range of 0.05 ohm to 0.1 ohm. Add an external series resistor will simulate the ESR. Don't forget to account for connection wire resistance and contact resistance.

Battery ESR model using a resistor. Battery ESR is simulated using an external resistor.

Figure 4. Real battery with internal ESR resistance.

Figure 5. Add an external series resistor to emulate battery ESR.

Battery Charger Testing

Most portable electronic devices have built-in charger that recharges the battery. During product development and final production testing, the charger circuit must be thoroughly tested to ensure its reliability and safely charges batteries. Figure 3 shows typical battery emulator/simulator connection for charger and system testing. It is basically replace the battery with an emulator. Use the Battery Simulator Quick Start Guide for setting up charger testing. A battery emulator is the most valuable instrument for battery charger testing.


Lithium Ion Battery Simulator and Testing

Battery emulator/simulator is often used to test the charger’s operation over the entire battery voltage range (e.g. 0V to 4.2V). For example, a lithium-ion battery’s normal operating voltage is 3.0V to 4.2V, but the voltage also can be 0V to 3.0V, if it is deeply discharged. Likewise a lithium ion battery can also be over charged to 4.3V – 4.5V. The charger circuit must be tested to ensure that it can charge a battery at any voltage within the limit. Using a simulator, you can easily simulate the battery at any voltage by adjusting the knob. You can measure the charging current at low battery voltage, less than 3V for Li+ battery, normal voltage 3V to ~4.2V, and high voltage greater than 4.2V, to verify against its specifications. While charging, adjust the lithium ion simulator knob to simulate the entire voltage range. Look for any unusual charging behaviors such as oscillation as you are charging.


Battery Emulator Advantages

Normally, it takes several hours to fully charge a real battery. For testing purpose, instead of waiting for the charger to charge a real battery, you can use a battery emulator to quickly vary the voltage to emulate the battery being charged. At the same time, you can observe and test the charger behavior to ensure it meets all of the specifications and safely charges the battery. Battery emulator power supply is important for charger circuit testing.


For example, lithium ion battery typically employed a CC/CV (constant-current, constant-voltage) charging method. At a low voltage, less than 3.0V, the battery is being trickle charged at a low current (one-tenth of the normal charging current). For voltage between 3.0V and ~4.2V, it is being charged at a rapid charging current. When the battery voltage reached 4.2V, it enters constant voltage mode where the voltage is held constant, but the charging current is slowly reduced. Figure 6 shows the detailed CC/CV lithium ion battery charging profile. An emulator is ideal for testing each phase of the charging cycle as well as testing transitions between phases. By adjusting the voltage knob, the battery emulator allows easy back-and-forth phase transition testing.

Multiple-Cell Battery Emulation

In some testing applications two or more cells are connected in series. Due to slight capacity variations, each cell voltage may be different from one other. In some rear cases one of the cells is damaged, its voltage is lower than the others. It is desirable to test these corners or fault cases.


To simulate multiple-cell batteries, two or more simulators can be connected in series as shown in Figure 7. Each simulator can set its voltage independently. This configuration simulates each battery voltage behavior, in order to test how the charger and the system respond in these cases.

Using three or more battery simulators connected in series to emulate multiple batteries. This configuration can simulate battery variations.

Figure 7. Three simulators connected in series to simulate a multi-cell battery pack.

Battery Simulator

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Simulating a battery for easy charger testing using the TS200 modulated power supply.

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This battery simulator test equipment is for testing chargers by varying the TS250 DC Offset voltage.

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