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Continuing from the previous white paper, here are three more effective applications and examples of electronic loads.
6-1. Applying the Load to a Motor
Figure 6-1 shows a block diagram illustrating an example of the DC motor test system.
In this system, the test motor (DUT) is driven by the DC power supply. The coupling is connected to the DUT and another motor in order to apply torque to the DUT. The torque sensor is placed between the DUT and coupling in order to measure the torque and rotation speed. The electronic load is connected to the motor to draw the current.
If the motor’s current in increased by the load while operating the DUT, the DUT’s motor torque will also increase. So, the electronic load adjusts the torque applied to the motor in order to obtain the T-N characteristics: the relationship between the rotation speed and torque.

6-2. Absorbing the Motor Regenerative Current
Reverse voltage is generated and returned to a power source by reversing the direction of the motor. Batteries can absorb this regenerative energy, but typical DC power supplies*1 cannot. So, the overvoltage may flow to the output terminal of a DC power supply. This activates an overvoltage protection in the DC power supply, but this overvoltage may reach other devices on the same test system.
*1: A bipolar DC power supply can absorb regenerative power like a battery.

To prevent this, set the electronic load to the constant voltage (CV) mode as described in Part 3, Sec.3-1 or, set it to the constant current (CC) mode as described in figure 6-3 blow. In figure 6-3, the DC power supply and electronic load are connected in parallel. The electronic load operates in CC mode and this CC current should be set to exceed the DUT’s regenerative current. When the current (Io) flows from the DC power supply, the electronic load draws ‘Io’ and converts in into ‘Icc’. And when the test motor (DUT) is driven, the motor current (Im) is fed into the DUT. Therefore, Io = Icc + Im.

Figure 6-4 shows how the DUT regenerates the current to the DC power supply. During power regeneration the motor regenerative current’s (Irev) direction reverses and flows into the electronic load. However, the electronic load works to keep its current (Icc) constant. Therefore, Icc = Io + Irev. When ‘Irev’ increases, the DC power supply current (Io) decreases, and vice versa (‘Irev’ decreases = ‘Io’ increases).

This system is more effective for preventing overvoltage than clipping the voltage with the CV setting, but it consumes more power.

6-3. Building a Mid-Speed CV Power Supply System
The voltage rising and falling time of typical DC power supplies exceeds 10 milliseconds (ms), but high-speed DC power supplies limit it to 3 micro seconds (µs).
Instead of buying a high-speed power supply model, you can build a mid-speed CV power supply system (Tr/Tf: 100 μs to a few ms) by combining your own DC power supply with an electronic load. Let’s look at the two examples below.
1. Mid-Speed CV Power Supply System (1)
In figure 6-4, the DC power supply and electronic load are connected in parallel. For the DC power supply, set the CC value to more than the maximum current that the load uses. The electronic load maintains a CV set voltage, and you can adjust it using your PC.
Under the no-load condition, the output current from the DC power supply (Icc) all flows into the electronic load.
With the load-on condition activated, the load current (Io) is fed into the load by reducing the flow of the E-load current (Iel). Therefore, Icc = Io + Iel.
If you use a series regulator power supply, the response time could take a few milliseconds. For typical switching power supplies, the response time takes more than 10 milliseconds. However, this depends on how quickly the electronic load activates the CV mode, so you need to verify the actual time.
Note: this system can maintain speed even with capacitive loads because the electronic load can sink (absorb) current from the load. The regenerative current of the motor mentioned above can be absorbed.

2. Mid-Speed CV Power Supply System (2)
The system, as shown in figure 6-5, is faster than the system shown in figure 6-4, achieving about 100 microseconds.
In figure 6-5, the DC power supply and electronic load are connected in series to allow the DC power supply to operate in CC mode. The operation of this DC power supply is the same as the one shown in figure 6-4. For electronic load 1, set the CC value above the maximum current that the load uses. Since electronic load 2 operates in CV mode, it maintains a CV set voltage and you can adjust it with your PC.
Under the no-load condition, the output current from load 1 (Icc) all flows into load 2.
With the load-on condition, the load current (Io) is fed into the load by reducing the flow of the electronic load current (Iel). Therefore, Icc = Io + Iel.
The reason this system is faster is because the CC mode operation of load 1 is exceptionally fast (approx. 50 microseconds faster).
DC Power Supply Operates in CC Mode

A single-phase three-wire output can be achieved usually by connecting two AC power supplies. However, if you need to output from one AC power supply and the required current through DUT is small, you can output it by configuring the following circuit.
1. Single-phase Three-wire System
In the figure below, R1=R2. Appropriate resistance for power supply should be applied on R1 and R2. With smaller resistance, the output can be nearly equivalent to the actual single-phase three-wire. The L1 to N voltage and L2 to N voltage are half the L1 to L2 voltage.

Note:
With the above circuit configuration, the L1 to N and L2 to N at AC100V are not available to consume the power.
2. Other Method
Transformer can be used to provide the single-phase three-wire output.

Products Mentioned In This Article:

• Kikusui AC Power Supplies please see HERE

A regulated DC power supply (referred as DC power supply) is an electrical device to convert AC into a constant DC. Its function is to maintain a constant output voltage, however, unfortunately even if you use an intelligent DC power supply, improper wiring can mess up a whole system operation or performance.
In this white paper, we explain the best practices for connecting a power cable and load cable to the DC power supply (assuming that the DC power supply operates in constant voltage mode). It can help you learn more about typical wiring problems in an electrical system and how to avoid them.
1. If you use long power cable
A power cable is a fundamental component that transmits electric power to devices in any electrical system. Basically, as the more power is produced by a DC power supply, the more current flows through a power cable.
Also, a power cable resistance is proportional to its length. That is, an AC-line input voltage can drop over a long power cable. As the more power is produced by a DC power supply, the more AC-line input voltage drops.
If an AC-line input voltage falls to a minimum rated input voltage of a DC power supply, an output voltage can decrease or fluctuate. Even worse, an input voltage drop protection may activate to turn the output off.
Before you have such issues, check whether an AC-line input voltage meets a rated input voltage first and then take the following preventive actions, if needed:
1) Use a power cable as short as possible. If a cable length becomes half, an input voltage drop becomes half, or
2) Use a power cable as thick as possible. If a cross section area of a power cable is doubled, an input voltage drop becomes half, or
3) Check for a loose power cable connection and tighten it when necessary.

2. If you use long load cable
With a long load cable, a load current can increase and then a load voltage drops. To compensate for the voltage drops, some DC power supplies feature a remote sensing function. This section explains the different effects between using and not using the remote sensing function.
2-1 Using remote sensing function
The wire inductance is proportional to the length of the load cable. When the load current (‘IL’) is pulsating and rapidly fluctuates, the load voltage (‘VL’) also oscillates in response to IL (See Figure 3).

With the long load cable, the entire system may not work as expected because;
The transient load voltages may cause the malfunction to the load.
The transient cable current may become an EM noise source.
To avoid them;
1. Twist the positive and negative load cables together as shown in Figure 4 or 2. Place them as close as possible.

The twisted pair cable can reduce the effect of the EM noise and then reduce the transient voltage change (See Figure 5).

With or without above actions taken, if the transient voltages still persist, place an electrolytic capacitor (‘C’) as shown in Figure 6 below. The capacitor can prevent the transient current from superimposed on IL. For faster transient currents, place a ceramic capacitor in parallel with C. As shown in Figure 7 below, IL has no rapid change, and consequently VL is regulated.

*Note: All figures given in this section illustrate the equivalent circuits of the system. The wiring diagrams are simplified that the resistance and inductance components are illustrated on the positive terminals only.
2-2 Not using remote sensing function
See Figure 8 for the equivalent circuit of the remote sensing connection. All cables consist of resistance and inductance components and the voltage will drop across these components. The remote sensing function can compensate for this voltage drop and keep the load voltage (‘VL’) stable within a set voltage. However, sometimes it does not work that the cable inductance may induce the oscillation.

To avoid the oscillation;
1) Twist the positive and negative load cables together (or place them as close as possible) to reduce the cable inductance.
2) Twist the positive and negative sensing cables together or use a shielded twisted pair cable to reduce the cable noise and inductance.
For further improvement;
3) Place a capacitor ‘C1’ and ‘C2’ across each positive terminals and negative terminals as shown in Figure 9. It allows the DC power supply to make a slow response to the load voltage fluctuations at a high-frequency, but the load voltage may become unstable. To fix it, place an electrolytic capacitor (‘C3’) on the load line (Read Section 2-1).

Figure 10 and 11 show the multiple load connection examples. As you can see, the sensing connection should be made to only one unit of load.
In Figure 10, assuming that the wire resistance and cable length are the same in Load 1 and Load 2, then the similar load voltage can be achieved for both loads. Also note that, if Load 2 is in a light-load state, the voltage drop can be offset by the sensing function for Load 1, but this compensation voltage may be directly added to Load 2.

In Figure 11, the load cable connected between Load 1 and Load 2 are thicker and shorter to minimize the wire resistance. This is especially helpful in obtaining a stable voltage when Load 2 is in a light-load state.

Figure 12 below shows the incorrect example that the sensing connection is made to each load. In such connection, the following may happen;
First, the load current through the load cable depends on each load state, and the voltage across each load depends on the load current. If using loads with different capacity, the load voltage balance cannot be maintained and the potential difference may be applied between the loads. With the potential difference, the current may flow from the high to low voltage via the sensing wiring. For example, see the red arrows in Figure 12 (positive side example only). If this current is high enough, the sensing cable may burn out.
Caution: Always perform a single sensing connection on multiple loads for safety.

Part 1 has so far focused on the wiring effects on the DC power supply.
Next, Part 2 will continue how the DC power supply depends on load conditions. Please also read Part 2 to gain further understanding or insights.

Products Mentioned In This Article:

Kikusui DC Power Supplies please see HERE

The TOS9300 series of electrical safety testers is a robust all-in-one solution. When performing AC Hipot, DC Hipot and Insulation Resistance tests there are setting options which allow the user to optimise testing as necessary for all applications. In certain situations where EUT’s are being tested for very high insulation resistances the LPF can be used to significantly improve the accuracy of the tester.

WHEN TO USE THE LPF SETTING
The LPF of the TOS9300 series is a second order Bessel filter with a 3dB cutoff at 1 kHz. This filter was designed to remove the transmission line noise that causes stray capacitance to affect the measurement. Any application that expects an insulation resistance measurement higher than 50 M ohm should consider using the LPF.
When measuring high insulation resistances at high voltages we expect to see very low currents measured at the ammeter because of Ohm’s Law. Readings where the expected current is only nA are greatly affected by high frequency noise. This type of noise is hard to avoid so it is useful to have a LPF which removes the high frequency current components just before measurement. It should be noted that a longer test time should be used to compensate for the lower frequency signal being measured in the test. See the operation manual for more information.

Products Mentioned In This Article:

• TOS9300 Series please see HERE

In this white paper, we are going to share the techniques to make the system that our bipolar power supply PBZ Series acts as a constant resistance load.
1. System Details
First, we are describing the system. See Figure 1 below; two units of PBZ20-20 are required for the system to operate as an AC electronic load ‘PBZ20-20’ and an AC power supply ‘PS (PBZ20-20)’:
1. CC mode is set on PBZ20-20.
2. The resistances are placed at the output terminal of PBZ20-20 to divide the voltage.
3. The divided voltage is applied via EXT SIG IN (BNC) to control the output current from PBZ20-20.
4. When the AC voltage is applied from PS, PBZ20-20 operates as a constant resistance load.
5. To adjust the current, connect a variable resistance (VR1) to EXT SIG IN.

2. Test Results
Next, let’s look at the test results on this system.
Given below are the phase relationships between the voltage and current under this system. Figure 2 – 6 show the input AC voltage waveforms and current waveforms:
Test Conditions: PS PBZ20-20: 40 VP-P, PBZ20-20: 40 AP-P specified by VR1 Waveform in blue: Voltage, Waveform in light blue: Current

3. Conclusion
As the frequency is getting higher, the current leads the voltage. This implies that PBZ20-20 operates like a capacitive load at the higher frequency in this system. When the sinewave frequency is 8 kHz (Fig. 6), the phase difference between the voltage and the current is approx. 28°. From this phase difference, the power factor will be 0.88.

Products Mentioned In This Article:

• PBZ Series please see HERE

For PBZ Series, a magnetic relay is used to turn the output on/off. The relay is off to turn the output off; when the output is off, the output is in the high impedance state.
In addition, if the output-on/off is controlled by an external signal input, the embedded firmware in PBZ may cause a jitter on the output voltage.
Now we are going to focus on the following two topics of the output on/off behaviour of PBZ and explain how:
1. the output voltage and output impedance change during the output on/off operation
2. PBZ responses to the output-on/off external signal input.

1. Change in Output Voltage and Output Impedance during Output-On/Off Operation
Figure 1 shows: change in the output voltage (Vout) and output impedance when the output is turned on. Figure 2 shows: change in Vout and output impedance when the output is turned off.
* The rise and fall time of Vout is dependent on the response setting by PBZ.

1-1. Output On

1-2. Output Off

Output Impedance:
High:
・ PBZ20-20: 120 kΩ ・ PBZ40-10: 220 kΩ ・ PBZ60-6.7: 320 kΩ ・ PBZ80-5: 420 kΩ Low:
・ a few hundred Ω Very Low:
・ Output is turned on.

1-3. Recommended Method to Frequently Turn Output On/Off
If you want to repeatedly switch the output on/off over a long period of time, we recommend the following procedures to prolong the lifetime of the relay:
1. Keep the output on.
2. To turn the output off, set the output voltage (Vset) to 0 V.
For DC output only: If you want to set the high impedance when the output is off, place a diode in series with the output terminal of PBZ and set Vset to 0 V.
* For the battery charging application, also place a diode in series with the output terminal of PBZ.
2. Output-On/Off Response to External Signal
In Figure 3 and 4, you can find the jitters when the output is turned on/off via the external signal input: ● Signal lag for output-on: approx. 90 ms max.
● Signal lag for output-off: approx. 50 ms max. ● Jitter during output-on/off: approx. 45 ms
In Figure 4, the lag between the output-off signal input and when the output impedance becomes high is approx. 90 ms max. and the jitter is approx. 45 ms; this lag is 50 ms min. and 90 ms max.
2-1. Output On

2-2. Output Off

Products Mentioned In This Article:

PBZ Series please see HERE

PCR-LE/LE2 Series can produce a DC output that enables you to test DC-powered devices such as DC-input converters. This article introduces the important precautions and useful functions to effectively operate PCR-LE/LE2 Series in DC mode.
1. Circuit Model
See Figure 1 for the test circuit model with PCR-LE. It illustrates the DC-input converter/inverter that has a capacitor-input circuit but without an inrush current prevention circuit.

2. Rated DC Current and Maximum Instantaneous Current

2-1 Rated DC Current for PCR6000LE
From Table 1;
DC input 200V: The rated DC current (maximum current) is 21A. The maximum instantaneous current, 3.6 times the rated DC current, is 75.6A.
DC input 100V: the rated DC current is 42A. The maximum instantaneous current is 151.2A. The rated DC current is 70% of the rated AC current.

From Figure 2;
Example 1) If DC input is 100V and the output voltage is DC50V; the output voltage ratio is 50% → The output current ratio is 100% → The output current equals the rated DC current.
Example 2) If DC input is 200V and the output voltage is DC400V; the output voltage ratio is 200% → The output current is limited by 50% → The rated DC current is 10.5A and the maximum instantaneous current is 37.8A.

2-2 Maximum Instantaneous DC Current
As stated above, the maximum instantaneous current is 3.6 times the rated DC current. The overcurrent protection (OCP) in PCR-LE activates when the output DC current exceeds the maximum instantaneous current. See Figure 3 for the DC current limit characteristics. DC current can remain within this limit. If the RMS DC current exceeds the limit for 1 second or more, the overload alarm is triggered to shut off the current.

3. Inrush Current
The rise time of PCR-LE is less than approx. 80μs in any response setting. While large inrush current would flow to the model circuit shown in Figure 1, PCR-LE equipped the current limit circuit can hold the DC current level to the maximum instantaneous current. If the RMS DC current exceeds the limit for 1 second or more, the overload alarm is triggered to shut off the current. The alarm can be cancelled by pressing the ALARM CLR key.
To prevent such inrush current, the power supply capacity should be increased. In PCR-LE, you just turn Soft Start on to raise the output voltage gradually and limit the current through the capacitor. To set Soft Start, press OTHERS (SHIFT + MEMORY) > RISETIME (F1).

4. Impedance when output is off
When an output is turned off, PCR-LE has a high impedance as shown in Table 2 (approx. several kΩ to several tens kΩ). As shown in Figure 4, the voltage reaches 0V for approx. 200μs when the output is turned off, and then PCR-LE is in a high impedance state. During this 200μs, the capacitor in Figure 1 discharges its electric charge and the OCP activates to shut off the current.
Table 2: Impedance when output is off

If you have any trouble during this 200μs, it is recommended that you insert a diode in series for the PCR-LE output or set COFIG > Surge Suppression > OFF to leave the high impedance (Voltage does not reach 0V). To set surge suppression, press CONFIG (SHIFT + OPR MODE) > 1/2 (F6) > SURGE S (F2) > OFF (F/W Ver.4.50 or later).
5. Others
PCR-LE uses a high-speed amplifier. The output may become unstable due to capacitive loads or wiring conditions. With such loads, we recommend that you change the response setting to SLOW to keep stable operations.
To set the response, press OTHERS (SHIFT + MEMORY) > 1/3 > RESP.

Products Mentioned In This Article:

PCR-LE Series please see HERE

Parallel operation is very useful to expand an output capacity; especially master-slave parallel operation allows you to control an entire system by one master unit.
When making the master-slave connection such as signal wiring and load connection, you may find some issues with load connection. Improper connection may cause oscillation so that our user’s manual describes how to connect the load.
In this article, you will learn not only the basic connection methods also the advanced techniques to stabilize an unstable output, which can apply to almost all our DC power supplies (except for high-speed power supply PBZ Series).
1. Basic Connection Methods
1) Make the cable connection between the master/slave units and DUT as short as possible and each connection should be the same length; In Figure 1, the cable connection L1, L2 and L3 should be the same length and then connect them to the DUT as short as possible.
2) If the above cable length is too long, connect the master/slave units to a relay terminal block as short as possible. Then, tightly twist the relay terminal block cables and connect them to the DUT at an appropriate length (See L4 in Figure 1).
See Figure 1 for the example:

*1: The L4 cables should withstand the total current from the master and slave 1 & 2.

2. Advanced Connection Methods
If the output becomes unstable under the basic connection, the following methods are available. Use all or any of three methods as required.
1) Ground either the positive or negative terminal of output (See the green lines in Figure 2). If either of the DUT input is grounded, check if short circuit may occur due to the output grounding.
For the parallel operation, you also need to check that all paralleled DC power supplies have the same control common terminal. Keep in mind that the control common terminal differs by our DC power supply series as follows:

2) Add a large capacitor to the relay terminal block (See the red lines in Figure 2). If high speed power supply such as PBZ Series has been used, avoid this method.

Products Mentioned In This Article:

To view Kikusui’s DC Power Supply range please see HERE

1. Overview
In PCR-LE Series, simulated CC operation can be achieved by setting the current limit in AC mode. This method is based on its internal system as the ammeter monitors the output current and the arithmetic circuit controls the output voltage. The functions and characteristics of this method are described as below;
1) Response becomes slow with this method.
Figure 1 shows its response when the load is rapidly changed.

2) The output current is stable if the output voltage is around the rated voltage, while the output current is fluctuated if the output voltage is low.
E.g.) The output current is stable if the load is operated by 100V voltage. On the other hand, the output voltage is fluctuated if the load is operated by 10V voltage.
3) Applied power can be limited if the load voltage fluctuation is large.
E.g.) If the load voltage starts from 100V but decreases to 50V with time due to the load resistance fluctuation, the internal loss of PCR-LE becomes larger so that its protection circuit may shut off the output.
This method has some disadvantages as stated above, however it may be useful operation for an application that the load changes slowly such as a heater.

2. Operating Procedures
Please follow the steps below to perform this method:
1) Return to the factory default setting to be safe;
– Press PRESET (SHIFT+6) key. Then, ‘RESET’ is displayed and SHIFT+ENT are flashing. – Press ENT key while holding down SHIFT key.
2) Set the output voltage and frequency to be applied.
Note) If you do not want to rapidly apply the voltage due to using the load with resistance characteristics, the following step is recommended to minimize the voltage overshoot; – Set the output voltage to low.
– After step 7, gradually increase the voltage to switch from CV to CC operation.
3) Set ‘TRIP DISABLE (Circuit breaker trip is disabled.)’ (Refer to page 34 of user’s manual: ‘Action to perform when the current limit is exceeded’);
– Press I key.
– Press TRIP key (software key). – Choose DISABLE.
4) Press ESC key to go back to the home screen.
5) Set the current limit value. This value is equivalent to the simulated CC value.
6) Press ESC key to go back to the home screen.
7) Connect your load. Turn OUTPUT on to apply simulated CC.

Products Mentioned In This Article:

• PCR-LE Series please see HERE

PLZ Series Easy Way to Expand Electronic Load Capacity in CV Mode

Our electronic load PLZ Series has a well-known feature that a master/slave parallel operation expands an output capacity in the same model, controlled slave units by a master unit (except for PLZ-4WL).
In this article, we are going to further explain how to increase the capacity by parallel connection with different models such as PLZ-5W Series (CV mode) and PLZ-4W Series.
How to Build Parallel System:
1. How to Operate PLZ-4W Series
Connect PLZ-4W to PLZ-5W in parallel and set PLZ-4W to CR or CC mode.
2. How to Connect
See Figure 1 for the example:

3. System Principle
Figure 2 shows the equivalent circuit of the above system. The red dotted line describes that the DUT and PLZ1205W are connected in parallel; PLZ1205W is in CV mode so that
PLZ1004W and the DUT should be in CC or CR operation to keep a stable operation. Note: In the example below, operating PLZ1004W in CP mode may cause an unstable operation.

4. Note
In the example above, it is necessary that PLZ1205W will not become a full load while controlling PLZ1004W; it depends on the DUT’s characteristics how to sink the current by PLZ1004W.

Products Mentioned In This Article:

Kikusui Electronic Loads please see HERE

Using Electronic Load to Battery Charger Testing
A battery charger is a device that can recharge a secondary cell or rechargeable battery. Every battery charger being used requires the testing and such testing system must include something to simulate a battery.
An electronic load can provide the best solution for the battery charger testing to simulate the actual behaviour of a battery. It is very useful to test the charger operation over the entire battery voltage range.
Test Method
Figure 1 shows the schematic diagram of the testing setup to sink the current from the battery charger to the electronic load;
● Connect an electronic load and a DC power supply in parallel.
● Operate the electronic load in constant voltage (CV) mode to keep the CV at the electronic load terminals.
● Operate the DC power supply in constant current (CC) mode to flow the CC*1 into the
electronic load.
*1: The CC is set to 100 mA.
Figure 2 shows the equivalent circuit of this testing system.
Some battery chargers determine the state of the battery first, but there is no problem in this testing system that the charger can detect the voltage at the electronic load terminals.

Products Mentioned In This Article:

For the full Kikusui Electronic Load range please see HERE