[NH Research] Testing Without Batteries

IntroductionThere are many benefits to testing batteries by emulating, or simulating, battery characteristics rather than using a real battery. The emulated battery dramatically reduces testing time, provides highly repeatable test results, and creates a safer test environment. Also, preparation time, operator errors, and result variations due to battery temperature or aging, are eliminated.Battery Emulation Reduces Testing TimeTesting a real battery often requires operator preparation for each step. Batteries must first be charged, or discharged, then allowed to rest, and finally tested. The significant battery preparation time can be avoided by using an emulated battery.Figure 1 above shows actual customer data from nine (9) tests conducted with both a real battery and then an emulated battery. Upon comparison between the tests, in these cases, emulation reduces the total test time by more than 70%.Battery Emulation Provides Repeatable Test ResultsOver time, batteries provide inconsistent test results, wear out, and need to be replaced. Battery age, internal temperature, and cycling are all contributing factors to the limited battery life-span. Manual battery operation, including rest time facilitation, can also cause inaccurate test results.Battery emulation provides consistent and repeatable test results, unlike those from real battery testing, during which battery changes and operator errors cause variations in test results.Battery Emulation Improves SafetyAlthough batteries are generally safe when operated within normal operating ranges, they are high energy devices that may pose serious risks upon battery or unit under test (UUT) failure. Such risks include exposure to dangerous gases, fires, explosions, or corrosive chemicals. These concerns have led to safety policies stating that tests must be conducted and monitored during working hours.Furthermore, testing extreme cases of over-discharged or over-charged batteries can pose unpredictable risks and safety hazards.Battery emulation creates a safe testing environment without any of the concerns that arise when real batteries are used. Also, emulation safely verifies UUT behavior when a battery is outside a normal operating condition.Using an Emulated BatteryBatteries can be modeled as a bi-directional voltage source along with a series resistance, as seen in Figure 2. The NH Research Battery Test Systems (9200 & 9300) provide an electronically programmable “Battery Emulation” mode, allowing any battery to be simulated at any state of charge. When programmed, the system automatically adjusts the terminal voltage, Vbatt, based on the amount of current flowing to, or from, the battery test system. Vbatt = Vocv+Rs .Icharge Just like a real battery, the test system will accept or deliver current while maintaining voltage.Both the voltage and resistance are programmable and can instantly represent any desired state, eliminating battery charging or discharging before testing. Corner case testing of over-charged or over- discharged batteries can be safely and repeatedly simulated, testing how a UUT will react to batteries in these conditions.The programmed voltage can be adjusted, or slewed, at a very slow rate, emulating the increase in voltage when a battery charges. Figure 3 shows battery emulation with a charger, and this slow slew rate to emulate the voltage increase while being charged.In the example shown, the charger periodically checks that the battery is being safely charged by reducing the charge current, indicating a slight decrease in the terminal voltage. Voltage drop is proportional to the amount of current provided by the charger, along with the programmed series resistance term. This method allows both new (low resistance) and old (higher resistance) batteries to be simulated, verifying the charger algorithms.Chargers may operate in more than one regulation mode. This example shows the charger transitioning from constant current to constant voltage. The voltage transition is completely charger controlled and does not require reprogramming of the simulated battery.Using emulation produces test results faster, provides a consistent test, and can safely test power electronic devices that typically require a real battery. Contact NH Research to further discuss how removing real batteries from existing test fixtures will improve both safety and repeatability in testing.

[NH Research] Battery Cycler VS. Bidirectional Power Supply for Battery Test

[NH Research] Battery Test Safety Requirements

Battery Test Safety RequirementsSafety is Paramount in Battery Testing When testing batteries which are hazardous by nature, safety  should be a major part of your battery test set-up. The details of  safety requirements are often something customers think about after  purchasing the test equipment. As a result, engineers end up having  to integrate external fixtures and control mechanisms, adding to the  complexity and cost of their system as well as schedule delays.In this article, we’ll share three safety features that should be at the  top of your list at a minimum when looking for a battery test solution.1. Safety Contactors: Ensures Isolation and Safe “Off” Conditionsafety contactors are needed for isolation to create a safe “off” condition. A safety contactor provides isolation  between your power source and the UUT (battery). When your battery cycler is off, a safety contactor provides the  physical isolation to ensure there is no power flow from the cycler to the DUT. Without the contactor, even in an off  state, power flow could still occur with your DUT. In most cases, if the hardware is still physically connected to thebattery, there may be enough resistance created between those terminals that the power source will continue to draw current and drain  the battery, or cause other safety hazards.NHR uses a built-in hermetically sealed safety contactor that is designed into the test equipment. When our test systems are off, our  instruments do not draw power and the contactor physically breaks the connection between the cycler and the UUT.2. 2Polarity Checker: Protects Operator and Equipment from User ErrorA polarity checker is necessary to prevent damage to the battery and the equipment in the case of incorrect wiring  by the user, which happens quite frequently. A built-in reverse polarity checker prevents inadvertent damage by  disabling output power when a negative voltage is detected at the output terminals.For example, if the instrument were to detect a reverse polarity, the instrument will prevent the safety contactor from  closing. This prevents a customer from accidentally reversing a battery, and then trying to charge or discharge it,which is extremely hazardous. Accidents such as this could also damage the instrument and/or cause a fire or explosion. NHR includes a built-in reverse polarity checker, which provides the ability to ensure proper voltage at its output terminals.3. Pre-Charge Checker Circuit: Reduces Inrush Current and Prevents Early Degradation of HardwareLastly, the built-in pre-charge circuit is significant to prevent inrush current and stress onto the system, which is  dangerous to the battery cycler and the UUT components equally. This inrush is due to the output capacitance of  the test equipment which can be detrimental to the UUT when it is connected and not at the same voltage level. A  pre-charge circuit matches the internal voltage of the instrument to the battery, preventing arcs and large inrushes  of current onto the system.For example, if you are using a DC source, DC load or bi-directional instrument to test a 600 V battery, the instrument initially starts at0 V (zero potential). Since these source/load instruments do not contain a pre-charge circuit, the moment the wires from your instrument  are connected to the battery, you’re completing that path and in turn, applying 600 volts to the instrument. This instantaneous connection  results in an inrush current. This large difference in voltage levels is the cause of the inrush as the instrument’s output capacitors are  charged. This usually leads to early degradation of the relays and switches. A pre-charge works together with the safety contactors by  matching the instrument’s output voltage to the battery before the safety contactor closes.NHR’s battery test systems have a built-in pre-charge circuit which provides a “soft start” that automatically matches the voltage on the  DC output to the battery voltage.