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AIS 156 Standard – additional safety requirements | Practitioner’s Perspective

FLASH update on Sep 28, 2022 – In response to clarification sought by OEMs and battery manufacturers, Amendment 3 notification from MoRTH came a few days back on 27-Sept-2022.  There have been few changes from Amendment 2 and the timeline for Implementation is also split into 2 phases, with Phase-1: effective from 01-Dec-2022 and Phase-2 effective from 31-Mar-2023.

The main changes are that the RFID tag requirement and the time-based charge cut-off requirement in the charger are removed.  The requirement of 5 charge/discharge cycles at the cell level is changed to 1 cycle. 

Many of the features like Earth leakage detection charger, EMC testing of BMS as per AIS 004, IS 16893 testing from NABL accredited lab for cells, Thermal propagation test, Audio-visual warning in case of a thermal event, four temperature sensors in BMS and Active Parallel Circuits are moved to Phase-2 which is effective from 31-Mar-2023

Other requirements such as traceability of packs, additional safety fuse, protection against regenerative braking, cell-to-cell spacing, and microprocessor-based BMS with all protections are effective in Phase-1 from 01-Dec-2022.

The Ministry of Road Transport and Highways (MoRTH) had constituted a committee in May 2022 to formulate the safety requirements for traction batteries.  The committee was constituted mainly in the wake of recent fire incidents in the electric vehicles, and this had experts from several renowned institutes, including ARCI, IISc, IIT etc. Based on the committee’s recommendation, MoRTH had proposed this amendment to the AIS 156 & AIS 138 Rev 2 standard.

This article by Venkat Rajaraman (CEO at Cygni Energy) gives an overview of the proposed changes in the amendment, mainly from a Battery Safety perspective.

Summary of additional safety requirements

The proposed changes can be broadly classified into three major categories – first at the pack level, second at the cell level and third at Battery Management System (BMS) level.  

First, at the pack level, it is now mandated that all the battery packs will be IPx7 compliant, where the manufacturers will have to make sure that the battery pack is protected against water ingress.  All the packs will also have to include a Pressure Relief Valve (PRV) or a pressure vent so that any gaseous leak and subsequent pressure built up inside the battery can be released, thus protecting the battery pack.  There is also a requirement for an RFID tag in the pack so that all the information about the battery is stored in the RFID tag (equivalent to a black box in an aircraft).  The BMS should be capable of reading and writing into the RFID tag with all the relevant information. There is also a traceability requirement for battery packs at the pack level, cell level, BMS level and at charger level.  The BMS need to do data logging, although the memory size for data logging is not specified in the amendment. 

Figure 1: Principles of pressure relief valve operation. Source: Charged EV Magazine

There is also a detailed requirement for the manufacturers to do the thermal propagation test. The requirement is that even if there were a thermal runaway condition in any one of the cells in a pack, it does not propagate to the rest of the cells, so the battery pack is still safe. There is also a requirement for an audio-visual warning in case of a thermal event.  There needs to be at least four temperature sensors inside the battery pack with additional safety at the string level and also a fuse at the battery pack level. In case there is any anomaly, the fuse should blow off to protect the battery and the rest of the system. There should be protection against regenerative braking as well.

Second, at the cell level, it is mandatory that the date of manufacturing of the cell is very clearly specified in simple DDMMYY format without any code. Cell to cell spacing should be provided on the battery pack. Cells have to be compliant per the AIS 16893 Part 2 & Part 3 specifications from an NABL-accredited lab. Cells should have undergone a minimum of 5 charge-discharge cycles, and the data to be maintained by the manufacturer.

Third, at the BMS level, the BMS should be microprocessor based (Smart BMS), and it should have all the protection against overcurrent, overcharge, over discharge, over voltage, short circuit, and over temperature. BMS is also expected to pass the Electro-Magnetic Compatibility testing as per the AIS-004 standard.

At the Charger level, the charger will have to have a communication port with the battery pack either through CAN bus or some other port. The charger will have cut-offs based on time as well as based on voltage.  The charger should have a soft-start function and earth leakage detection and protection.

Consequences for OEMs and battery pack makers

What are the consequences for the OEMs and the battery manufacturer on account of this? The official notification came on 3rd September 2022 with an effective date of 1st October 2022, and hence the manufacturers are given less than 4 weeks to implement all of the changes.

Based on various discussions with OEMs and battery manufacturers, the key concern is that the one-month duration to implement all of these changes is too short for the following reasons:

– RFID tags are typically not there in any of the battery packs today

– Battery Management System (BMS) to have a Read/Write functionality would involve changes to the BMS and subsequent testing and recertification. 

– The amendment talks about very specific ways to do the thermal propagation tests on the battery packs. This requires a specific test set-up, and many test labs in India are not equipped to handle such tests yet. 

To get the above accomplished in four weeks’ time would be impossible for any manufacturer.

Concluding thoughts

Though this is a timely amendment from the battery safety perspective, in order to be compliant on all the points, manufacturers have a lot of work to do and the expectation that this should be done in less than a month seems unrealistic.

For example, take a look at five cycles of data to be made available on each and every one of the cells. Typically depending on the cell form factor and the cell capacity, a battery pack has hundreds of cells. Now to have five cycles of charge-discharge data would need several days and would require a sizeable investment in charge-discharge equipment. Most of this equipment is imported, which would also mean that they would take about six to eight weeks to procure them and then have them commissioned. Unless the manufacturer has multiple of these battery cyclers with them, this cannot be done in a short duration. It is preferred that this is done on a sampling as otherwise, the infra required would be bigger than the battery assembly line itself.  

General consensus is that it would take at least 3 months to fully implement all the changes as suggested in the latest amendment, mainly because of equipment lead times and lack of sufficient NABL-accredited test centres for IS 16893 testing. While this is a step in the right direction, the manufacturers are to be given sufficient time so that they can be implemented fully and correctly to yield the desired result. So many things to do, yet so little time!

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