Testing batteries for an evolving world

Battery testing allows car producers, homeowners, and researchers to make knowledgeable selections, optimize car efficiency, and improve total person expertise.

Demand for electrical autos is amping up. Each certainly one of these autos wants massive batteries, and the business is responding by constructing crops. Vitality.gov forecasts that by 2030 electrical car battery manufacturing capability in North America will develop 20 occasions, ultimately supporting 10-13 million electrical autos per 12 months. 

Testing these batteries is a vital a part of battery manufacturing. The primary cause for testing is for security. As a consequence of a chemistry that helps runaway thermal occasions and sustains fireplace, Lithium-ion (Li-ion) batteries are harmful. After publicity to vibration and excessive ambient temperatures, even small manufacturing anomalies can result in catastrophic failure. Lately, Li-ion scooter batteries have been blamed for devastating constructing fires, and Jaguar Land Rover issued a recall of greater than 6000 autos after eight buyer fires have been brought on by battery thermal occasions. 

Moreover, patrons wish to know precisely how far they'll drive on a cost. Battery testing can simulate the load positioned on a battery throughout driving situations and predict a car’s driving vary.

Battery testing is getting more durable
Whereas battery quantity is rising, testing is turning into tougher. As car patrons demand extra storage for larger vary, the capability of batteries is rising. What’s extra, pulse testing requires exponentially extra present than the battery’s ampere-hour score. Given all this present, security turns into paramount. Fireplace is an actual danger brought on by voltage or present exceeding the bounds of the battery cells’ inner constructions throughout charging or discharging. 

For instance, if a technician forgets to set a voltage restrict throughout a relentless present discharge, then the temperature of a battery cell may rise from 23 to 400 levels Celsius in milliseconds. Catastrophic explosions are additionally doable. In reality, some producers have constructed explosion-proof rooms for his or her automotive battery testing. 

Add to excessive energy the necessity for throughput — testing a number of batteries on the identical time — and the battery automated take a look at gear (ATE) should be able to sinking and sourcing many kWs of energy. In some amenities, there isn’t sufficient house on the manufacturing flooring so as to add a number of racks of the ability provides used within the take a look at system. 

Greater voltages are one other problem for testing. To cut back the load of conductors within the car and to cut back warmth brought on by electrical resistance, car drivetrain voltages have climbed to 450 V and now are within the 800 V vary. Whereas take a look at engineers can add extra energy provides to extend the ability of their take a look at programs, they can't change the utmost voltage score of their take a look at programs. Present EV modules require testing at as much as 900 V. 

How a battery take a look at system works

The primary production-line exams for battery producers embrace:

• Battery cycle take a look at
• Drive cycle simulations
• Insulation resistance
• DCIR testing

To carry out these exams, take a look at programs use a number of bidirectional energy provides in parallel. A DC bidirectional energy provide operates in quadrants I and II, which means it's able to each sourcing and sinking DC energy. 

It's not uncommon for engineers to be confused when deciding on an influence provide system. Wanting on the batteries they count on to check, they suppose they want a 30-kW system. However they overlook the method P=IV, which says at 1500 V the very best present a 30-kW energy provide can output shall be 20 A. If the take a look at engineer wants the ability provide to output extra present, say 60 A, then they should decrease the voltage or purchase a take a look at system providing 90 kW.

In standard bidirectional energy provides, two working ranges are equipped, a excessive and a low. These are proven as rectangular bins in Determine 2. Because the take a look at voltage rises or falls, a technician could have to cease the take a look at and manually swap ranges on the ability provide. 

Some battery exams require a provide of fixed energy whereas various present or resistance. A programmable energy provide with a traditional rectangular output will provide most energy solely on the level of most present and most voltage. In distinction, some energy provides have a characteristic referred to as auto-ranging. The facility provide will mechanically output extra present when the load operates at a decrease voltage. This enables the ability provide to take care of a relentless energy load throughout that load’s full energy working vary. 

The crimson line in Determine 2 reveals the output of a real auto-ranging energy provide. With out switching ranges, the ability provide can output from 500 V to 166.6 V whereas sustaining 5 kW of fixed energy. With out this characteristic, the wattage of the ability provide should be outsized, or double the variety of energy provides shall be required, and due to this fact the take a look at system shall be extra expensive.

As the ability ranges in batteries rise, one of many challenges is testing throughout more and more vast ranges of energy and voltage. Within the plant’s analysis lab, technicians could take a look at particular person cells at 2.5 to 4.2 V, take a look at modules at 420 V, and take a look at full automotive battery packs at 840 V. True auto-ranging helps engineers take a look at from system stage all the way in which right down to cell stage utilizing one energy provide system.

Slew charge
Slew charge is a vital consideration for automotive battery drive-cycle or pulse-test testing, throughout which the output voltage or output present adjustments regularly. The slew charge is the pace at which an output adjustments from its present state to its programmed state.

The faster the slew charge, the squarer the pulses within the output, which permits for extra exact testing. The consequence of that is that energy provides with a gradual slew charge can't precisely measure the driving distance of a battery. If the take a look at system has a quick slew charge, the extra correct take a look at could lead to publishing an extended driving vary, which is supremely vital to shoppers.

Information acquisition pace
Throughout manufacturing testing, the battery administration system (BMS) experiences measurements to the take a look at system. Temperature, present, and voltage are recorded about as soon as a second. The aim of manufacturing testing is to validate key parameters, as soon as a second is enough. 

Battery analysis, then again, requires extra complicated testing. Engineers have to confirm that the BMS is reporting precisely, perceive the well being of particular person cells, and test the connections between elements. On a vibration desk, an intermittent occasion ensuing from a damaged connection could final solely a millisecond. If the info acquisition pace is simply too gradual, then testing could miss such occasions. 

Gradual information acquisition pace can also introduce imprecision. This may present up when testing an identical batteries with a drive profile take a look at. The outcome for the primary battery perhaps 400 miles, and the outcome for the second battery perhaps 405 miles. Truly, the driving ranges are basically an identical, however a gradual information acquisition charge limits the accuracy of the testing. This may occur when an organization buys a take a look at system made for manufacturing and makes use of it within the lab.

The above concerns will assist engineers put together for a future the place automotive batteries are a dominant facet of automotive manufacturing. In response to EYs Mobility Client Index, greater than 50% of individuals planning to purchase a automobile will select both a completely electrical, plug-in hybrid, or hybrid car. Quick, correct, and economical battery testing is important to anticipate shopper demand.

Editor’s observe
Learn after which watch the video interview by EEWorld Senior Technical Editor Martin Rowe with the writer who speaks about why RV batteries use such excessive voltages and take a look at them. Yow will discover that right here.