Australian Engineer Solves 2018 Hyundai Ioniq’s Diminished Vary Drawback

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I’ve been assembly Brian O’Neill at our “Espresso, Cake and EV” mornings for the previous couple of years, and just lately our conversations have centred on his quest to resolve lowered vary issues along with his 2018 Hyundai Ioniq EV. I saved saying to him: that might make an important article, write it up for me. Nicely, the difficulty has lastly been resolved, and right here is his story. Warning: this text accommodates a lot of “eye glazing” technical particulars. One for the techno buffs on the market.

First a little bit of background on Brian. He tells me: “I’m a Licensed Skilled Engineer (retired). I’ve a Grasp of Engineering diploma in Complicated Management Techniques and am a Fellow of the Establishment of Engineers (Australia). I’ve labored within the design and troubleshooting of digital instrumentation, sensors and energy methods in area analysis, geophysics, radar, meteorology, and electromagnetic subject {hardware} with CSIRO, academia and manufacturing business from 1954 till my retirement in 2020.” Wow, no marvel he was capable of remedy the vary conundrum!

By Brian O’Neill

On 24/9/2023, I travelled from Bribie Island to Cleveland Showgrounds and returned after leaving dwelling “absolutely charged” with an indicated vary of 255km. This can be a journey I had made quite a few instances over the automobile’s lifetime & at all times returned with loads of spare vary. On this event, at about 30km (precise) from dwelling, I observed that the indicated remaining vary was dropping very a lot sooner than the true distance, so I slowed to preserve power. About 5km from dwelling, I acquired the primary warning at a nominal 13.5% State Of Cost. Quickly after, the automobile switched to restricted energy mode (10% SOC), then “turtle” mode (3% SOC). The indicated vary ticked over to “—-” as I rolled into my storage. Thus, the automobile went from 13.5% SOC to zero in a distance of ~5km, very sluggish driving. The power used from “absolutely charged” to zero was 21.66kWh, as calculated from 190km x (11.4kWh / 100km) as indicated on the screenshot on the finish of this report. The desired usable battery capability is 28kWh.

Because the automobile was nearly due for a 90,000 km service, I booked it in and requested for a battery State of Well being (SOH) test on the similar time. Once I picked up the automobile after the service, I used to be fairly shocked to listen to that the battery SOH was “wonderful”, so I bought an OBD2 (On Board Diagnostics System) reader to acquire additional data. The automobile scanner confirmed a battery SOH of 100%, and, at 100% SOC (Displayed), no measurable voltage distinction between most and minimal particular person cell voltages. As at December 2023, the battery SOH has fallen barely to 99.2% — nonetheless a superb worth. Even at 20% SOC (displayed), there’s negligible voltage distinction between most and minimal particular person cell voltages and no drop in battery SOH, suggesting that the battery continues to be in good situation.

It seems that the battery just isn’t being charged to 100% “displayed” SOC (95% “BMS” SOC) regardless of the automobile scanner and power meter readings. That is urged by the truth that a completely charged battery voltage studying on my automobile is simply 394 volts, while comparable automobiles of the identical mannequin cost to 398 volts on an AC charger. Vitality meter and Remaining Vary meter monitor fairly effectively right down to about 50% (displayed) SOC, however under this worth each drop very a lot sooner than the precise km travelled. It seems that the discharge voltage curve doesn’t match that of the particular battery fitted to the automobile, suggesting a software program downside. That is confirmed by screenshots of scans of different automobiles of the identical mannequin. (Voltages are persistently decrease on the similar SOC on this automobile.)

Hyundai don’t publish data on the precise battery chemistry used on this mannequin, however the subsequent 38kWh mannequin apparently makes use of NMC622 batteries and I’ve used an NMC622 datasheet to match readings from the later mannequin. After permitting for the truth that the 38kWh mannequin fees to 97% while the 28kWh mannequin fees to 95%, I discover that the present 100% SOC particular person cell voltage settings for my automobile and the 38kWh mannequin each are in line with the NMC622 datasheet. This implies that my BMS might have been programmed for NMC622 batteries. Different (full vary) 28kWh Ioniqs are programmed for a better voltage. It appears unlikely that an NMC622 battery is definitely fitted, as this chemistry was not in manufacturing when my mannequin went into manufacturing, and my automobile was not recalled for a battery change when quite a few 28kWh automobiles have been recalled in 2021. (I’m unaware of the particular chemistry used for the substitute battery within the recalled Ioniqs.)

If the issue is, the truth is, resulting from an inappropriate software program replace, then we would want to find out simply when this replace occurred. It must have been after September 2022, because the spherical journey to Cleveland showgrounds confirmed no issues at the moment. The more than likely date was November 2022 when the automobile had its 75,000 km service. I did discover a 40 km drop in estimated 100% SOC vary at the moment, however, as I had changed the tyres on the similar time, I assumed incorrectly that the substitute tyres have been accountable.

[Brian contacted the Hyundai dealership but …]

The Hyundai supplier service division was unable to assist, merely stating that the SOH (State Of Well being) readout for the battery was 100%, so I used to be by myself for locating an answer to the issue. Background analysis confirmed that the battery was composed of 196 particular person LQ1729-A2 LG Chem NMC cells and a datasheet for these cells was obtained from LG Chem. Within the 28kWh Ioniq, 192 cells are configured as a single sequence string of 96 parallel pairs of cells. (Notice that the later model 38kWh Ioniq is configured otherwise as two separate units of 88 cells in sequence.) The BMS (Battery Administration System) relies on the Linear Expertise LTC6804/LTC6811 chip sequence with proprietary Hyundai software program. Datasheets for the LTC6804 & LTC6811 have been additionally obtained from the producer and used within the analysis.

A few essential takeaways from a research of the battery datasheet included:

• The battery degrades quickly when it’s saved at excessive State Of Cost (SOC), notably at temperatures above 20°C. This implies that ideally the SOC ought to usually keep underneath 70% and solely be absolutely charged instantly earlier than beginning on an extended journey.
• The State Of Well being (SOH) (which is seemingly derived from the battery inner resistance on this case) may be very poorly correlated with battery capability loss, notably at temperatures under 35°C. Thus, the SOH isn’t any substitute for a full discharge take a look at and will solely be used as a rough indicator.

In line with the Linear Expertise datasheets, passive battery balancing of teams of 6 cells (or on this occasion 6 pairs of cells) happens by discharging 0.167 amps from the very best voltage cell(s) within the group till all cell voltages are equal, whereas the BMS is turned on. Balancing between the 16 teams of 6 pairs of cells is thus managed by the administration software program turning the cell degree BMS off for all balanced teams. Particular person cell voltage measurements have an error of +/- 0.5 millivolts over the temperature vary. Notice that the cell degree balancing present is simply 0.2% of the ampere hour capability of the cell pairs in order that the utmost cell degree balancing price on this case may be very sluggish at round 0.2% per hour.

Intensive evaluation of cost and discharge knowledge confirmed that the Ioniq voltage and present sensors have been roughly right, however that the slope of the battery voltage vs kWh graph differed considerably from the datasheet knowledge in that the inflection factors within the datasheet knowledge had been smoothed out within the measured knowledge. This urged the likelihood that the person pairs of cells comprising the battery is likely to be at totally different states of cost; i.e., the battery was not balanced. This might not be confirmed from the OBD2 readouts, because the 96 particular person cell pair readings are truncated to a decision of +/-2 millivolts (regardless of the BMS chips speaking a a lot larger decision to the administration software program).

So as to take a look at this speculation, the 7kW charger was calibrated and the charger losses calculated to be 12%. An assumption made for this take a look at was that the BMS was switched off by the administration software program while the charging present was set to 32 amps. Monitoring the charger confirmed that the time interval for which the present was lowered on the finish of cost was very quick — only some minutes. The battery voltage on the finish of cost was measured at 394 volts, and this was in line with the values that had been measured over a 12-month interval. After discharging the battery to 10% SOC, it was recharged once more at a present of 8 amps. The belief was that battery balancing could be enabled at this decrease present worth. On the finish of this take a look at, the obvious charger losses had risen to twenty% and the “finish of cost” battery voltage had risen to 398 volts. This voltage is in line with the voltage measured on different related 28kWh Ioniqs. The obvious rise in charger losses confirmed that extra power had been returned to the battery on the cost cycle than had been eliminated through the corresponding discharge cycle. That is in line with the upper cost voltage obtained. Subsequent driving assessments have proven that not less than half of the obvious degradation has now been reversed.

Additional research of the Linear Expertise BMS datasheets suggests a potential rationalization. If the battery turns into sufficiently unbalanced, the pair of cells within the pack on the highest state of cost may drive the charger to cease charging earlier than the battery voltage reaches a degree which might usually cut back the cost present and activate battery balancing. If this state is reached, battery balancing is successfully disabled. The one option to re-enable it will be to set the conventional charging present at a low sufficient worth for battery balancing to happen at decrease states of cost for an extended sufficient time frame to re-balance to under this tipping level.

To make sure that this downside doesn’t recur, my intention is that the battery shall be re-calibrated not less than month-to-month by charging at 8 or 10 amps from a SOC of 30% or under, notably in an surroundings like Queensland the place excessive ambient temperatures are widespread.

As this can be a downside which has not been reported by different Ioniq homeowners, it’s probably {that a} explicit mixture of charging/discharging circumstances has been a causal issue:

• Excessive ambient temperatures.
• Leaving the automobile absolutely charged prepared for a potential emergency always.
• Charging on the most 7kW AC at all times — aside from DC charging 2-3 instances per yr.

I now retailer the automobile at 30%–70% SOC except a run of 100km or higher is anticipated, wherein case I recharge simply earlier than leaving. I re-calibrate the battery month-to-month by charging from ~30% at 8A AC.

The best test for potential battery stability issues within the 28kWh Ioniq is battery voltage at 100% (displayed) SOC. A voltage measurement underneath 398V signifies that re-calibration is required. Sadly an OBD2 reader is required for this.

Brian tells me that there was a world extensive research of this concern – you may see the video this report right here. He cites one other Ioniq proprietor who has solved the issue. 

In a observe up e-mail, he elaborated on his evaluation: “I imagine the issue is extra more likely to happen within the Ioniq 28kWh due to a mixture of very low energy passive BMS (0,67W per factor) and the distinctive battery configuration of a sequence of 96 parallel pairs of cells. Just one BMS factor may be utilized to a parallel pair that are pressured to have precisely the identical voltage by exhausting paralleling. Thus the BMS can solely stability 96 particular person voltages out of a complete 192 particular person cells. This compares with 176 particular person BMS parts (2 parallel strings of 88 particular person cells every) within the 38kWh Ioniq. Actually battery balancing doesn’t happen al a 7kW cost price (as confirmed by my measurements) on the Ioniq 28kWh, however does happen at 2kW and a pair of.4kW — i.e., on ‘granny chargers’.

“With the way in which Hyundai sanitises the OBD2 knowledge and makes use of very inaccurate (low decision) algorithms to derive their displayed knowledge, it will be very troublesome for many Ioniq homeowners to detect that this downside was taking place. One needs to be a mathematical pedant (like me!!), or find out about the issue the exhausting method by operating out of cost (like I did) – then doing the mathematics to find out that it was not simply distinctive driving circumstances on that exact day. I do have a pal with the identical mannequin Ioniq on Bribie, and I’ve used my OBD2 reader to substantiate that his Ioniq doesn’t have the identical downside (even if his battery SOH is reported as 96% whereas mine is reported as 100%). I imagine that the small battery on this mannequin signifies that most homeowners who primarily use the ‘granny’ charger won’t ever see this downside happen.”

Nicely performed, Brian. Hopefully your exhausting work will assist different Ioniq homeowners. Please add your ideas within the feedback in case you have had related points.