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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 lately our conversations have centred on his quest to unravel diminished vary issues together with his 2018 Hyundai Ioniq EV. I stored saying to him: that might make an incredible article, write it up for me. Effectively, the difficulty has lastly been resolved, and right here is his story. Warning: this text comprises plenty 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 Advanced Management Methods 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 trade from 1954 till my retirement in 2020.” Wow, no marvel he was capable of resolve the vary conundrum!
By Brian O’Neill
On 24/9/2023, I travelled from Bribie Island to Cleveland Showgrounds and returned after leaving house “totally charged” with an indicated vary of 255km. This can be a journey I had made quite a few instances over the automobile’s lifetime & all the time returned with loads of spare vary. On this event, at about 30km (precise) from house, I seen that the indicated remaining vary was dropping very a lot sooner than the true distance, so I slowed to preserve vitality. About 5km from house, I obtained 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 gradual driving. The vitality used from “totally 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 virtually due for a 90,000 km service, I booked it in and requested for a battery State of Well being (SOH) verify on the similar time. After I picked up the automobile after the service, I used to be fairly stunned to listen to that the battery SOH was “nice”, so I bought an OBD2 (On Board Diagnostics System) reader to acquire additional info. 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 will not be being charged to 100% “displayed” SOC (95% “BMS” SOC) regardless of the automobile scanner and vitality meter readings. That is advised by the truth that a totally charged battery voltage studying on my automobile is simply 394 volts, while comparable vehicles of the identical mannequin cost to 398 volts on an AC charger. Vitality meter and Remaining Vary meter monitor fairly properly all the way 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 drawback. That is confirmed by screenshots of scans of different autos of the identical mannequin. (Voltages are persistently decrease on the similar SOC on this automobile.)
Hyundai don’t publish info 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 check readings from the later mannequin. After permitting for the truth that the 38kWh mannequin expenses to 97% while the 28kWh mannequin expenses to 95%, I discover that the present 100% SOC particular person cell voltage settings for my automobile and the 38kWh mannequin each are in keeping with the NMC622 datasheet. This means 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 various 28kWh autos had been recalled in 2021. (I’m unaware of the particular chemistry used for the alternative battery within the recalled Ioniqs.)
If the issue is, the truth is, attributable to 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 probably 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 alternative tyres had been responsible.
[Brian contacted the Hyundai dealership but …]
The Hyundai supplier service division was unable to assist, merely declaring 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 collection string of 96 parallel pairs of cells. (Be aware that the later model 38kWh Ioniq is configured in another way as two separate units of 88 cells in collection.) The BMS (Battery Administration System) is predicated on the Linear Expertise LTC6804/LTC6811 chip collection with proprietary Hyundai software program. Datasheets for the LTC6804 & LTC6811 had been additionally obtained from the producer and used within the analysis.
A few necessary takeaways from a research of the battery datasheet included:
- The battery degrades quickly when it’s saved at excessive State Of Cost (SOC), significantly at temperatures above 20°C. This means that ideally the SOC ought to usually keep below 70% and solely be totally charged instantly earlier than beginning on an extended journey.
- The State Of Well being (SOH) (which is seemingly derived from the battery inside resistance on this case) may be very poorly correlated with battery capability loss, significantly at temperatures under 35°C. Thus, the SOH is not any substitute for a full discharge take a look at and may solely be used as a rough indicator.
In accordance 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 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 stage BMS off for all balanced teams. Particular person cell voltage measurements have an error of +/- 0.5 millivolts over the temperature vary. Be aware that the cell stage balancing present is simply 0.2% of the ampere hour capability of the cell pairs in order that the utmost cell stage balancing fee on this case may be very gradual at round 0.2% per hour.
In depth evaluation of cost and discharge information confirmed that the Ioniq voltage and present sensors had been roughly right, however that the slope of the battery voltage vs kWh graph differed considerably from the datasheet information in that the inflection factors within the datasheet information had been smoothed out within the measured information. This advised the likelihood that the person pairs of cells comprising the battery is perhaps at completely 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).
As a way 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 diminished on the finish of cost was very quick — just a few minutes. The battery voltage on the finish of cost was measured at 394 volts, and this was in keeping 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 can 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 keeping with the voltage measured on different comparable 28kWh Ioniqs. The obvious rise in charger losses confirmed that extra vitality had been returned to the battery on the cost cycle than had been eliminated in the course of the corresponding discharge cycle. That is in keeping with the upper cost voltage obtained. Subsequent driving exams have proven that at the very least half of the obvious degradation has now been reversed.
Additional research of the Linear Expertise BMS datasheets suggests a attainable clarification. If the battery turns into sufficiently unbalanced, the pair of cells within the pack on the highest state of cost may pressure the charger to cease charging earlier than the battery voltage reaches a stage which might usually scale back the cost present and activate battery balancing. If this state is reached, battery balancing is successfully disabled. The one solution to re-enable it might be to set the traditional charging present at a low sufficient worth for battery balancing to happen at decrease states of cost for an extended sufficient time period to re-balance to under this tipping level.
To make sure that this drawback doesn’t recur, my intention is that the battery shall be re-calibrated at the very least month-to-month by charging at 8 or 10 amps from a SOC of 30% or under, significantly in an atmosphere like Queensland the place excessive ambient temperatures are widespread.
As this can be a drawback which has not been reported by different Ioniq house owners, it’s possible {that a} explicit mixture of charging/discharging circumstances has been a causal issue:
- Excessive ambient temperatures.
- Leaving the automobile totally charged prepared for a attainable emergency always.
- Charging on the most 7kW AC all the time — apart from DC charging 2-3 instances per 12 months.
I now retailer the automobile at 30%–70% SOC except a run of 100km or larger is anticipated, by which case I recharge simply earlier than leaving. I re-calibrate the battery month-to-month by charging from ~30% at 8A AC.
The only verify for attainable battery stability issues within the 28kWh Ioniq is battery voltage at 100% (displayed) SOC. A voltage measurement below 398V signifies that re-calibration is required. Sadly an OBD2 reader is required for this.
Brian tells me that there was a worldwide research of this challenge — you may see the video about this report right here. He cites one other Ioniq proprietor who has solved the issue as properly.
In a observe up e mail, he elaborated on his evaluation: “I imagine the issue is extra prone to happen within the Ioniq 28kWh due to a mix of very low energy passive BMS (0,67W per component) and the distinctive battery configuration of a collection of 96 parallel pairs of cells. Just one BMS component may be utilized to a parallel pair that are pressured to have precisely the identical voltage by onerous 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 components (2 parallel strings of 88 particular person cells every) within the 38kWh Ioniq. Actually battery balancing doesn’t happen al a 7kW cost fee (as confirmed by my measurements) on the Ioniq 28kWh, however does happen at 2kW and a couple of.4kW — i.e., on ‘granny chargers’.
“With the best way Hyundai sanitises the OBD2 information and makes use of very inaccurate (low decision) algorithms to derive their displayed information, it might be very troublesome for many Ioniq house owners to detect that this drawback was taking place. One needs to be a mathematical pedant (like me!!), or study the issue the onerous manner by working out of cost (like I did) – then doing the maths to find out that it was not simply distinctive driving situations on that individual day. I do have a good friend with the identical mannequin Ioniq on Bribie, and I’ve used my OBD2 reader to substantiate that his Ioniq doesn’t have the identical drawback (although his battery SOH is reported as 96% whereas mine is reported as 100%). I imagine that the small battery on this mannequin implies that most house owners who primarily use the ‘granny’ charger won’t ever see this drawback happen.”
Effectively executed, Brian. Hopefully your onerous work will assist different Ioniq house owners. Please add your ideas within the feedback when you have had comparable points.
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