Reed Relays for Electric Vehicle and Charge Point Testing

The electrification of the drivetrains in pure electric vehicles (EVs), and partial electrification in hybrids and plug- in hybrids (HEVs and PHEVs), is only possible thanks to the presence of high voltage batteries, power inverters and powerful motors. Also, these high voltage components are ‘floating’, in that none of their power terminals are earthed to chassis. Accordingly, all components and high current-carrying cables are heavily insulated.

The design and manufacture of EVs and their derivatives require specialist equipment and procedures to ensure safety. As these vehicles enter service, their maintenance, repair and recovery will also require the same equipment and procedures.

As the Health & Safety Executive (HSE) notes: “People in the motor vehicle repair and recovery industry are now more likely to come across E&HVs and as a result need to be aware of the additional hazards they may be exposed to when working with these vehicles.”

The HSE also notes that, in addition to a wider range of skills and knowledge, those working on the vehicles will need access to specialist tools and equipment to be able to work safely. There is therefore a drive to develop instrumentation to safely test high voltages in the automotive sector. 

On an EV, high voltage DC is considered anything above 60V. Most EVs on the road currently use 400VDC battery packs, though some OEMs are switching to 800VDC, as twice the voltage means half the current (for the same power), and it’s current that determines wire/cable gauge and therefore weight. 

As mentioned, all power cables and HV components are heavily insulated, to protect against short circuiting against anything that is electrically connected to earth and for safety (as it is likely that anyone working on the vehicle will also be in contact with the chassis/earth). In addition to the need to measure high voltages (DC and AC) it is necessary to confirm the integrity of the insulation around HV components and cables. See figure 1. 

Vehicle-Test-Diagram

Figure 1 Voltage measurements (on the left) require connecting to a component (such as battery pack terminal) that could be at more than 400VDC. An insulation test (on the right) involves injecting a high voltage into a component and measuring the current that flows through a resistor of a known value (within the current sensing circuit) to the chassis. From that current, the insulation resistance (RINS) can be deduced. 

To read more download our new application guide about Reed Relays for Electric Vehicle and Charge Point Testing. The guide explains the high voltage and insulation resistance testing in electric vehicles. 

Contents of this application guide:

  • High Voltage & Insulation Resistance Testing
  • Switching Technologies
  • Reed Relay Terminology
  • Recommended Products
  • Why Pickering Electronics for Reed Relays?