Making sure the batteries are charged no longer applies just to the flashlight. Whether it is an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a growing number of vehicles are running on electricity rather than gasoline or diesel fuel. Keeping them running requires careful maintenance of the batteries and powertrains in these environmentally friendly vehicles.
Running out of gas was once a concern for a vehicle with an internal-combustion engine; now, with an EV, HEV, or PHEV, it is a matter of keeping the vehicle’s batteries and charging system in shape for the long haul. The battery chemistries in EVs, HEVs, and PHEVs differ, such as lithium-ion, nickel-metal hydride, and lead-acid batteries or ultracapacitor electrical energy storage configurations used to drive a vehicle’s traction motor. But batteries and their charging systems can be evaluated with a handful of straightforward measurements and suitable test equipment.
Commercial battery packs for EVs, HEVs, and PHEVs are designed to produce a certain amount of current for a given amount of time, with typical operating lifetimes of 8 years and 100,000 miles. Vehicle owners desire certain battery characteristics, such as the greatest number of charge/discharge cycles and low self-discharge rate, for the longest battery lifetime possible. The battery chemistries may differ, with nickel-metal hydride having longer life cycles than lithium-ion or lead-acid batteries but higher self-discharge rates, but the health of each battery type and its vehicle charging system can be monitored with several basic measurements and the right test equipment.
Two of the more useful measurements for evaluating the health of batteries used for systems in EVs, HEVs, and PHEVs are an internal resistance test and a battery capacity/discharge test. Test equipment should be capable of checking whether EV, HEV, or PHEV traction motor batteries can handle short circuits, over-voltage conditions, imbalanced charging, over-charging, and even how they are affected by thermal stresses due to changes in ambient temperature. For charge and discharge cycle testing specifically of lithium-ion battery cells, the Chroma 17216M-10-6 tester is a large but full-featured modular rack-mount measurement system designed to duplicate the wide range of operating conditions faced by those battery cells throughout many miles on the road.
The model 17216M-10-6 performs lithium-ion battery charge capacity testing, battery cycle life testing (how many charge/discharge cycles a battery can perform), AC internal resistance (ACIR) testing, DC internal resistance (DCIR) testing, electrical double-layer-capacitors (EDLC) capacitance testing, and even hybrid pulse power characterization (HPPC) per the U. S. Department of Energy. It is an AC/DC bidirectional regenerative test system with automatic thermal management and an energy-conserving architecture that feeds discharged energy back into the AC source. It has 16 channels, each rated for maximum of 10 V and 6 A, but which can be connected in parallel for a maximum current rating of 96 A.
The NH Research 9200-4904 is a full-featured battery test system that is also quite energy efficient during discharge cycles, returning as much as 87% of the energy discharged from tested cells/batteries to the AC power source. However, it is more versatile than the Chroma test system since it can test all battery chemistries, including lead-acid, nickel-cadmium, and lithium-ion rechargeable battery packs and modules. It is designed for modular flexibility and speed, handling battery testing with 40, 120, 240, or 600 V bidirectional DC loads and millisecond voltage and current switching speeds. The rack-mount system is a “set and forget” solution, weighing in at over 1400 lbs. and 6 ft. in height.
For precise power analysis, the Yokogawa WT3000 precision power analyzer offers impressive accuracy of within 0.02% of a power reading across wide voltage measurement ranges from 15 to 1000 V. It can measure AC and DC voltage, mean active power, spectral analysis with a fast Fourier transform (FFT) function, voltage fluctuations, and even battery-powered motor torque and speed with a special version. It can investigate relative changes in DC voltage and the times in which such changes take place and perform simultaneous input and output voltage measurements to determine inverter efficiency. The analyzer is an accurate tool for evaluating the inductive AC/DC power converters used in EVs. It can be equipped (as an option) with harmonic measurement capability to perform pulse-width-modulation (PWM) measurements of electric motor drive voltages.
The WT3000 power analyzer has a built-in printer for quick recordings of test data. Test results are easy to see on an 8.4-in. diagonal TFT color liquid crystal display (LCD) and results can be transferred to a computer over a variety of interfaces, including GPIB, RS-232 (as an option), Ethernet (as an option), and USB ports. Although the analyzer hosts a horde of complex measurements, it is easy to use and fits within a few standard slots in a 19-in. rack-mount cabinet.
When a reliable voltage source is needed as part of electric motor drive or EV/HEV/PHEV battery pack testing, the Keysight RP7935A regenerative power system is a bidirectional DC power supply designed with many functions supporting safe testing at the higher voltages and power levels needed for electric vehicle drive systems. It can generate low noise/ripple outputs with output voltages as high as 80 V and load regulation within 3 mV and output currents to 250 A with 25 mA load regulation. The voltage source offers DC output power as high as 10 kW although higher levels are possible through routine parallel connection of multiple voltage sources. When large amounts of test data are needed for analysis, the RP7935A can switch output levels at millisecond speeds to accommodate high-volume testing of battery packs and cells. For its extensive capabilities, the RP7935A fits within a 3U-high rack-mount enclosure.
Of course, these are just samples of the test instruments that can be used for checking the batteries and drive trains of EVs, HEVs, and PHEVs. For example, the Chroma 17216M-10-6 is one member of a series of four instruments with different current ratings and the same company offers its 62000D series of bidirectional DC power supplies with current ratings as high as 540 A which can be used in series and in parallel for EV, HEV, and PHEV electrical drive system testing. Another example of bidirectional DC power supplies would be the Elektro-Automatik PSB10000 series which ranges from 40 A-1000 A. More information on these and a variety of instruments from different manufacturers can be searched for sale or rental from the Axiom Test Equipment (www.axiomtest.com) website. Keep those batteries charged through regular charge/discharge cycles and that EV, HEV, or PHEV will make it well past 100,000 miles. For more EV's resources and equipment used in EV Testing visit our EV / HEV industry page.