Understanding DC Power Supplies (1)
Charging Batteries with Constant-Current and Constant-Voltage Using the PBZ Series High Speed Bipolar Power Supply
As a test equipment manufacturer, Kikusui is supposed to ask users to use our products as directed in the Operation Manuals. However, DC power supplies, as a prime example of general-purpose products, have many different uses, making it almost impossible for Operation Manuals to cover them all. This feature offers some tips and tricks on using DC power supplies within the scope of ensuring safe use, although they are not mentioned in the Operation Manuals.
Bipolar power supplies require one operation mode.
This edition looks at Kikusui’s PBZ Series bipolar power supplies. A bipolar power supply is a DC stabilized power supply in which the positive and negative polarities can be continuously interchanged through zero without changing the output terminal. Therefore, it performs so-called four quadrant operation as portrayed in Fig. 1. This means that it serves not only as a source that supplies electric power, but also as a sink that absorbs it similar to an electronic load.
Typical electronic components that require polarity changes of power supplies include motors and electromagnets (solenoids). This type of power supply may also be used to test secondary batteries with discharge and recharge operations.
Note that nickel-cadmium batteries and nickel-hydrogen batteries require constant current charging, whereas lithium-ion batteries require constant-current and constant-voltage charging. (See Fig. 2)
Most of Kikusui’s DC power supply products incorporate the constant current (CC)/constant voltage (CV) automatic crossover function. When the battery voltage reaches a specified level (preset voltage level for the DC power supply) during the process of constant current charging, the mode may be automatically changed to the CV mode.
However, the PBZ Series bipolar power supplies does not support this automatic control crossover function and requires prior setting of the control mode (CV/CC selection). This suggests that it cannot perform constant-current and constant-voltage charging for batteries during normal usage.
The following offers tricks of performing constant-current and concurrent-voltage charging of batteries using the V/I-LIMIT protection features incorporated into the PBZ Series.
Two approaches to charging.
There are two possible ways to conduct constant-current and constant-voltage charging of batteries using the voltage limit (V-LIMIT) and current limit (I-LIMIT) protection features of the PBZ Series power supply.
(1) Select the CC mode to control the charging current at a constant level and use the V-LIMIT function to control the changing voltage.
(2) Select the CV mode to control the changing voltage at a current level and use the I-LIMIT function to control the charging current.
The two methods may sound identical in theory. An experiment was conducted on these two approaches to measure and compare the waveforms of the output current.
Output current control test.
Fig. 3 portrays the equipment used for this test. The control was implemented through general purpose interface bus (GPIB) communication using the direct control and protection function settings of the Wavy for PBZ sequence creation and control software.
Waveform measurement results
- Charging method (1): CC mode with V-LIMIT control
CC mode selected (I-LIMIT at factory setting of 22 A), V-LIMIT set at 4.3 V, output in short circuit status, response settings at 3.5 μs for the CV mode and 35 μs for the CC mode
- Charging method (2): CV mode with I-LIMIT control
CV mode selected, output voltage set at 4.3 V (V-LIMIT at factory setting of 22 V), output in short circuit status, response settings at 3.5 μs for the CV mode and 35 μs for the CC mode
The CC mode combined with V-LIMIT is recommended.
The experiment compared the waveforms of the output current in the two possible charging methods with the current controlled.
In charging method (2), in which the current is controlled with the I-LIMIT in the CV mode, the rise and fall of the current is slower than the response setting and the waveform has a stepwise form due to the change in the I-LIMIT level.
I-LIMIT is a protective function and does not directly control the output current level. The control operation is slow at an appropriate recycle of 0.74 ms, which is why a sharp change in the I-LIMIT value induces a change of current in steps at an interval around 0.74 ms. As a result, the rise and fall of the output current waveform is slow and the waveform takes a step-like form.
Therefore, charging method (1) is recommended for applications where the charging current is controlled.
However, in a case where the charging current is constant and not closely controlled or where precision is not necessary, charging method (2) is recommended, in which the full charge voltage can be controlled with higher precision, because the V-LIMIT is a protective feature and has poorer setting accuracy than the CV control, as mentioned below.
- CV mode
Setting accuracy: ± (0.05% of setting + 0.05% of rtg)
Setting resolution: 0.001 V (Fine function setting resolution: 0.0001 V)
Setting accuracy: ± 1% of rtg
Setting resolution: 0.1 V
Note that V-LIMIT performs voltage detection at the output terminal and does not support sensing.
Chief Engineer, SE Section, Solution Business Promotion Department
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