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Simulating Degraded Secondary Batteries with DCPower Supplies

How to Achieve Variable Internal Resistance Functionality Easily Using PBZ Series High-speed Bipolar Power Supplies

The stabilized DC power supplies sold by Kikusui Electronics are often compared with batteries. In the sense that direct current can be drawn from both, in terms of purely voltage or current, they are the same, but in fact there is a decisive difference. This difference relates to internal resistance values.

When used in constant voltage (CV / voltage priority) mode, stabilized DC power supplies attempt to maintain a constant voltage using their control circuitry, even if the current value changes depending on the load applied. This is not the case with batteries. With batteries, as current increases, output voltage falls according to the battery’s internal resistance value. In particular, in the case of secondary batteries where the battery has deteriorated due to repeated charging and discharging, internal resistance values rise, and this effect of voltage decrease also becomes greater. The fact that secondary batteries that are nearing the end of their useful service life become unusable (i.e. the output voltage falls) almost immediately, even after recharging, owes reasons such as this.

In recent times, there are numerous electrical products on the market that make use of secondary batteries, and we sometimes hear of client needs to check (i.e. during product testing) how products will behave when their batteries are nearing the end of their useful life. In other words, we are asked if there isn’t some way of simulating this current-dependent voltage drop with test-use power supplies.

One conceivable way of achieving this is to monitor the power supply’s current value using a computer, and create a program that feeds back voltage settings to the power supply according to the current value observed. But there is no denying that this feels like quite a bothersome approach.

Here, I will present an easy method for achieving variable internal resistance functionality with Kikusui Electronics PBZ Series high-speed bipolar power supplies, using standard functionality alone. What is more, the only other piece of equipment required is a single BNC-BNC cable.

The only preparation step is to connect the EXT SIG IN and I MON terminals on the front of the PBZ Series power supply directly to one another.

PBZ Series high-speed bipolar power supplies are equipped with EXT SIG IN (controls the output voltage based on external voltage input) and I MON (current monitor) terminals. These terminals are located on the front panel of the power supply. As a preparatory step, we connect these two terminals together using a BNC cable, as shown in Photograph 1. The only other thing remaining to do is to set the EXT SIG IN signal gain settings using the control panel.

Photograph 1

EXT SIG IN signal gain settings.

Next, we determine the gain value for when inputting I MON current monitor values (i.e. output current values) into the EXT SIG IN terminal. By setting minus gain for the EXT SIG IN terminal with respect to output current values, we can achieve a setup in which output voltage will fall as output current values increase. We calculate the appropriate gain setting value from the required internal resistance value, and set that internal resistance using gain setting. When using the EXT SIG IN terminal, it is necessary to make offset adjustments. Make offset adjustments at the maximum output current value using the FINE setting.

  • Settings
    <Panel settings>
    Output voltage setting: DC setting
    Offset setting: FINE setting
    <CONFIG settings>
    SIGNAL SOURCE setting: as in Photograph 2
    SELECT: ADD → Add internal signal source and EXT SIG IN signal
    EXT, SELECT: BNC → Select EXT SIG IN terminal
    EXT, GAIN: - oo.o → Gain setting (internal resistance value setting)

  • Formula for calculating gain setting value from internal resistance value
    G = - (R×I)/2
    G: gain setting value, R: internal resistance, I: rated current, 2: I MON output voltage
Photograph 2

Function testing.

Below is an actual example in which variable internal resistance setting was carried out using a PBZ20-20 power supply (Figure 1 and Figure 2).

Figure 1. I-V characteristics
  • Offset adjustment has been made at a maximum output current of 10A. The adjustment was made such that at output current 10A an output voltage of 10V is produced (from the formula: output voltage = maximum voltage 20V - (internal resistance 1Ω × output current 10A)). The Adjustment voltage is 0.183V (made using the FINE setting).
Figure 2. Output voltage response characteristics
  • Waveform measurement conditions (equipment and settings, etc.)
    Use a PBZ20-20 front panel binding post (as with voltage waveform measurement).
    Current waveform measurement current probe: TCP202
    Electronic load device PLZ1004W settings: waveform setting 0-10A / 1kHz square wave D=50%, slew rate setting: 1.6A/us (M range)
    Wire/cable length: approximately 3m

In this way, simply by connecting the PBZ Series power supply’s I MON and EXT SIG IN terminals together with a BNC cable, we can set an internal resistance value using the EXT SIG IN signal gain settings, and achieve variable internal resistance functionality easily.

However, please do be aware that setting resolution for internal resistance values is dependent on the gain setting resolution (as shown in Figure 3).

Model

Setting resolution (Ω)

PBZ20-20

0.01

PBZ40-10

0.1

PBZ60-6.7

0.1

PBZ80-5

0.1

Figure 3. Internal resistance setting resolution

TEXT BY
Koichi Ito
Chief Engineer, SE Section, Solution Business Promotion Department

[Major achievements in product development]
The PAT-T Series DC stabilized power supplies

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