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High Amperage Ampera – By James Dillon of Technical Topics

By autotech-nath on May 24, 2018

The market is moving towards a point that borders ‘beyond doubt’ regarding the medium-term electrification of light vehicle transport. The impact of this for repair garages and workshops is that they will absolutely have to get hands-on with the service, diagnosis and repair of electric vehicles. Uniquely, alongside the business opportunities that electric vehicles present, there are significant safety risks, which shouldn’t be underestimated. These risks can be mitigated with appropriate education and training, using the correct equipment and implementing the correct procedures and processes.

The diagnostic case reported here has been carried out following the correct processes and procedures by a hybrid and EV trained technician. This article will indicate the types of processes, techniques and procedures that may be necessary. In all cases, the vehicle manufacturers’ procedures should be followed by a suitably qualified EV technician.

Here at the Technical Topics workshop, I have been involved in the diagnosis and repair of hybrid and electric vehicles for the past 10 years. Being an early adopter, I’ve had the chance to get hands on with some interesting diagnostic cases. Once such case, which is currently ongoing, is that of a Vauxhall Ampera, a type of extended range electric vehicle.

Initially, the Ampera uses energy from a 16.5 kWh battery pack to drive an 110kW electric propulsion motor. The batteries are charged from the main’s electrical infrastructure as well as from a 55kW on-board motor/generator. This motor/generator is driven by the kinetic energy of the vehicle during regenerative braking (KERS). The Ampera also has a 60 kW 1.4 l internal combustion engine, which is used primarily as a supplementary drive source for the motor/generator. This energy is delivered directly to the propulsion motor with any excess being stored in the battery pack. The three drive sources (main motor, generator motor and internal combustion engine) can blend two of the three sources depending on the operating mode.

Screen Shot 2018-05-24 at 19.52.37We recently had a poorly Ampera in the workshop that would not drive. It would power up on the ignition switch, but it was unable to move under its own power. This could be considered as the equivalent of a crank – no start condition of an internal combustion engine vehicle, (see left) Dash Panel warning. An additional issue was that the vehicle would not charge from its mains charging lead. The battery was in a low state of charge due to the fault. I hoped this would recover, but it was an unknown factor and this was communicated to the customer.

The problem occurred whilst the owner was driving the vehicle. The warning came on the dash and the vehicle soon lost power and it had to be recovered back to their house. Unfortunately, they had real trouble finding a repairer locally to investigate the source of the problem, including the franchised dealer. There appears to be real business opportunity here for early adopter garages to position themselves as local market leaders in the diagnosis and repair of this type of vehicle.

The suggested diagnostic process for hybrid and EV is to assess diagnostic trouble codes early on in the process to assess the type of failure and to see that the failure mode doesn’t represent a safety issue for the technician. A scan of the problem-child showed a DTC for drive motor high current (see below, DTC capture). At this point, the technician should be able to develop a test and measurement plan, and ascertain whether or not the vehicle should be made safe prior to testing.

Screen Shot 2018-05-24 at 19.52.55Screen Shot 2018-05-24 at 19.53.08

In this case, we assessed the GM technical info for the specific DTC. The guidance was to make the system safe and then commence testing. The test specified guided the technician (me) towards a system-off insulation/isolation test. The DTC information stated that the motor generator current exceeded the fail threshold during system initialisation; consequentially, as a safety feature, the vehicle enters a form of motive suspended animation. The external charging port is also isolated after the self-test failure is tripped. This has implications for the main battery state of charge.

Screen Shot 2018-05-24 at 19.53.53The isolation test is performed using a high voltage insulation tester (see right) under the correct conditions, whilst wearing the correct safety gear. I ran the test, which the system passed. The vehicle manufacturer’s trouble code diagnostic tree suggested as a next step to replace the inverter and if this didn’t cure the issue, to replace the motor generator. Wow! Better get a big parts canon, as this method required the firing of some very hefty and pricey ‘try-some’ parts. I chose to resort to some alternative testing methods to better establish a root cause.

Screen Shot 2018-05-24 at 19.54.12Using the PicoScope and a 3-phase induction current clamp set, I attempted to test the system’s function (see left). The clamps were placed in line between the inverter and the motor generator, half way along the potential problem.

The system was re-initialised and the appropriate safety gear was donned. The system was turned off and back on and the code reset whilst the current was monitored.

Screen Shot 2018-05-24 at 19.55.06The waveform (see right) shows that one of the motor phases was pulling a peak current of 350 amps during start-up. This looks like what was tripping the system and setting the code. This form of testing enabled me to observe the symptom directly. However, the next challenge is to try to diagnose the root cause: Is it the motor, the cables, the inverter or something else? I’m awaiting customer authorisation to proceed with the next level of testing and if I get the go-ahead, I’ll detail the next steps in a subsequent issue.

If you’d like to build your knowledge and experience, and gain a nationally recognised Hybrid and EV qualification, get in touch with Technical Topics. They are running a Hybrid and EV Diagnostic Bootcamp, which will equip technicians with the skills and knowledge to make money from diagnosing the next big thing in automotive transportation.

You can also catch James Dillon at Reading College on Saturday 30th June, see page 8 for details, call 01634 816 165 to book a place.



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