ISO 16750-2: The Code Letter Is the Specification, Not the Voltage
EV & automotive · 4 min read · 55 cited facts
Ask which standard governs an EV's electrical testing and ISO 16750-2 comes back first — often for the wrong bus. The document governs the 12 V and 24 V control supply: the ECUs, the board net, the low-voltage side of the electronics. The high-voltage traction bus sits in LV 123, a different document entirely, and ISO 16750-2's own scope excludes it. A customer who hands you a traction-bus requirement citing ISO 16750-2 holds the wrong document, and settling that before quoting a bench saves everyone a redesign.
The current revision, the fifth edition of 2023, replaces ISO 16750-2:2012. Its electrical clauses hang off a code system: Table 3 defines codes A to D for 12 V nominal systems, Table 4 defines codes E to H for the commercial-vehicle net, and each code fixes the minimum and maximum supply voltages that the rest of Clause 4 references, with code Z left for values agreed between customer and supplier.
The code letter is the specification
| Parameter | Value | Clause |
|---|---|---|
| Supply-voltage codes, 12 V systems | Code A 6–16 V; B 8–16 V; C 9–16 V; D 10.5–16 V; Z as agreed | Table 3 |
| Supply-voltage codes, 24 V systems | Code E 10–32 V; F 16–32 V; G 22–32 V; H 18–32 V; Z as agreed | Table 4 |
Code A reaches down to 6 V because that class of equipment must keep working through cranking; code C bottoms at 9 V and may degrade while the starter turns. Two devices on the same nominal system can carry different codes — different minimum voltages, different severities at every downstream clause, different benches. The code letter, not the nominal voltage, carries the specification. A requirement that says only "12 V system" has told you almost nothing; ask for the letter.
What the code feeds into
| Parameter | Value | Clause |
|---|---|---|
| Jump start (12 V systems only) | 26 V for 60 ± 6 s, rise/fall ≤ 10 ms, from USmin 10.8 V | Table 5 / Figure 2 |
| Transient overvoltage | 18 V (12 V) / 36 V (24 V) for 400 ms, rise/fall 1 ms (12 V) or 2 ms (24 V), 5 pulses at 1 s rest | Table 6 / Figure 3 |
| Reset behaviour at voltage drop | staircase in 5 % steps of USmin down to 0 V, ≥ 5 s per drop, functional check at each return to USmin | §4.6.2.2 / Figure 12 |
| Starting profile (24 V, severest level) | drop to US1 6 V for 50 ms, then cranking plateau US 10 V with 2 Hz ripple; profile applied 10 times, ≥ 2 s recovery | Table 12 / Figure 13 |
What the bench has to do
A source for this document covers 0–36 V steady state with millisecond sequencing — cranking profiles with 2 Hz ripple, transient edges of 1 ms — plus superimposed ripple swept from 10 Hz to 200 kHz at up to 15 A peak-to-peak under Table 7 and Table 8, slow ramps per §4.5.2, and polarity reversal to −26 V per Table 15 and Table 16. Micro interruptions under Table 9 need a series switch opening within 10 µs to at least 10 MΩ — §4.6.1.2 specifies the switch, not merely the waveform. Load dump wants a pulse from a defined source resistance, 0.5–4 Ω for 12 V systems under Table 13, at up to 101 V. A supply that merely reaches the voltages runs none of this.
Qualifying to a code letter?
Send the supply-voltage code from your customer's specification — the letter, the system voltage and which clauses of Clause 4 apply. The code decides the bench.
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