Electronics testing using low voltage EMC testing standards
There are many standards defined by OEMs around the world calling for vehicle electronics to be rigorously tested to look for power supply related issues.
It is clear that as the design of automotive vehicles includes more complex functionality – particularly where these functions are provided by microcontroller-based designs – there is significant risk of system failure with low and transient voltage conditions, when applied to the supplies of a particular controller.
As more components develop possible failure conditions, bigger, more important system issues start to develop, due to the intermittent resetting of controllers, or non-communicating controllers on system-wide communications buses.
Consequently, these standards generally set out ways to test both components and systems under controlled conditions in a repeatable manner, to verify that there is a good likelihood that the system (or sub-system) will perform correctly in the real production environment. The LVTGO-VBS system assists with this process and the LVT-PSU can extend the scope of this testing.
Real-world test scenarios
Many existing standards specify conformance tests focusing on aspects of electrical supply testing at d.c. or relatively low frequencies, aiming to address particular use cases such as engine cranking, intermittent connection or relay chatter.
How ‘standard’ are these standards?
Each OEM’s EMC testing standards have similar aims, but each sets out to build on previously written standard, some of which are based on test methods dating back decades. As a result, each standard varies to a reasonable degree. However, it is possible to group tests into relatively few categories aimed at similar use cases.
These use cases are as follows:
- Engine cranking or starting issues
- Relay chatter issues
- Intermittent connection issues
- Alternator ‘whine’ or supply modulation issues
- Over-voltage issues
- Under-voltage issues
- Slow battery discharge or recovery issues
Engine cranking standards testing
Most OEMs require electronics to be tested for reliable operation during engine cranking or starting scenarios, attempting to identify power supply issues commonly caused by poor battery or connector performance, or poor controller design.
The standards tests that aim to check for correct behaviour during these situations are usually called ‘power cycling’ or ‘crank pulse’ tests.
Because engines start more slowly at lower temperatures this test may also be called the ‘cold start’ test.
‘Meet The standards’ reference document
We have compiled a list of many of the automotive low voltage testing standards into a downloadable form, detailing which hardware is required to test to these standards.
This document provides a very useful reference of many of the published standards and what is required to meet these.
Relay chatter issues
Relay chatter is caused due to either a low supply, poor drive voltage or external interference which causes a relay to rapidly switch on and off when connected to a load.
This relay chatter can cause electronics to fail due to further inference caused by the high rates of change of currents and voltages on the connected wires.
The standard tests that aim to cover these scenarios are usually called ‘dropout tests’ or ‘voltage dip’, and specify one or more pulses switched onto the power supply line.
Intermittent connection issues
Intermittent connection noise is created when cables, plugs or bare wires causing short circuits disrupt the power supply.
This noise can cause a wide variety of failures due to the potentially wide voltage changes and the fast rate at which voltages may change.
The standards tests that aim to look for this are often referred to as ‘fast transient noise’ or ‘immunity to voltage dropout’ tests. Sometimes these tests are also included in ‘reset Behaviour tests’.
Alternator ‘whine’ or supply modulation issues
These issues tend to come about as a result of high-energy systems on the battery supply, such as alternators or actuators, causing regular and significant electrical voltage ripple on the supply due to the a.c. nature of the generator or motor that is connected. This usually signifies a failed regulator, or that some other error condition has occurred.
The standards tests that aim to isolate this condition are usually called ‘continuous power line disturbance’ or ‘superimposed a.c. ripple’ tests.
There are a number of reasons for over-voltage issues but these can be usually broken down into two standard tests:
‘Dock start’ or ‘jump start’ tests, where two batteries or a large PSU is used to rapidly power a vehicle to move in an emergency situation. This is normally tested at a constant voltage for a period of time.
‘Alternator failure’, where the alternator regulation circuitry has failed, putting all the energy into the battery and causing a dangerous high battery voltage situation. This is usually tested using a predetermined voltage profile called a ‘load dump’ profile.
There are a number of reasons for under-voltage issues but these are usually due to a power source being unable to maintain a continuous good supply to the unit in question.
The standard tests for this are normally called ‘under voltage’ tests, and look for where a system might fail at certain low constant voltages.
Slow battery discharge or recovery issues
As vehicles can be left unattended for long periods, it is possible that low voltages or slow ramps will occur on the power supplies to the electronics within a vehicle.
The standards test that looks for this condition is called ‘supply ramp up’ and/or ‘supply ramp down’, but may also be called ‘battery recovery’.