The procurement
The laboratory had been contracted to run environmental testing for an automotive Tier 1 supplier entering the EV battery module market. The test programme included IEC 62660-2 performance testing and UN 38.3 thermal cycling — both of which required a walk-in climatic chamber capable of accommodating full battery modules.
The laboratory did not have a walk-in chamber. The contract justified the capital investment. The procurement was approved. The facilities manager was assigned to specify and purchase the chamber.
He had specified laboratory equipment before — benchtop instruments, calibration rigs, a reach-in climatic chamber the previous year. He had not specified a walk-in chamber. He approached the task the way he had approached the others: he identified the key parameter, found a chamber that met it, and submitted the purchase order.
The key parameter, as he understood it, was volume. The battery modules were large. He needed a large chamber. He specified a chamber with a nominal internal volume of 8 cubic metres — a standard walk-in size available from multiple manufacturers, with a lead time of sixteen weeks. The chamber was ordered.
The specification
The purchase order specified: nominal internal volume 8 m³, temperature range −40°C to +85°C, humidity control to 95% RH, ramp rate 3°C/min. Standard configuration. The manufacturer confirmed the order. Sixteen weeks.
The facilities manager filed the paperwork and moved on to the next item. He did not measure the battery modules. He did not calculate the clearances required between the DUT and the chamber walls. He did not consult the test programme to understand how many modules would need to be tested simultaneously. He did not ask the manufacturer for the usable volume figure — the volume available for the DUT after accounting for the evaporator coils, the air circulation system, the structural supports, and the floor reinforcement.
He had ordered an 8 m³ chamber. He assumed 8 m³ would be available for testing.
Delivery day
The chamber arrived on a Tuesday morning, sixteen weeks after the order was placed. Installation took two days. The chamber was positioned, connected, and commissioned. The temperature validation ran overnight. The chamber passed.
On Thursday morning, the first battery module arrived for testing. It was a prismatic module — 1,200 mm long, 800 mm wide, 400 mm tall. The test programme called for three modules to be tested simultaneously, with instrumentation cables routed through the side wall feedthroughs.
The laboratory technician opened the chamber door and began to plan the layout. He measured the chamber interior. The nominal internal volume was as specified — 8 m³, which the manufacturer defined as the total enclosed space. The usable space — after the evaporator coils on the ceiling and rear wall, the floor grating over the drain system, the air circulation plenum on one side, and the minimum clearances required to maintain airflow around the DUT — was considerably smaller.
He calculated the available floor area. He measured the module dimensions. He checked the clearance requirements in the test standard.
One module would fit. Possibly. With no clearance to spare on three sides.
Three modules would not fit. Not even close.
The chamber's nominal internal volume: 8.0 m³. The usable volume after the evaporator coils (ceiling and rear wall), the circulation plenum (left wall), and the floor grating: approximately 5.2 m³. Three battery modules at 1.2 × 0.8 × 0.4 m each: 1.15 m³ total DUT volume. Required clearance per IEC 60068 practice: minimum 100 mm on all sides between DUT and chamber walls, and between DUTs. Total volume required for three modules with clearances: approximately 6.8 m³. Available usable volume: 5.2 m³. Shortfall: 1.6 m³ — equivalent to one additional battery module.
The calculation that was never done
The facilities manager was called to the chamber room. He looked at the situation. He called the manufacturer.
The manufacturer confirmed the nominal volume figure and provided the usable volume figure — 5.2 m³, clearly stated in the technical documentation that had accompanied the installation manual. The facilities manager had not read the installation manual. He had read the sales specification sheet, which listed the nominal internal volume as the primary dimension.
The manufacturer was sympathetic. They offered to quote a larger chamber — 12 m³ nominal, approximately 8.5 m³ usable — with a lead time of twenty weeks. The price was 40% higher than the original order.
The laboratory manager called the Tier 1 supplier to explain the situation. The test programme start date had to be moved by five months — the sixteen weeks already elapsed, plus the twenty weeks for the replacement chamber. The supplier's vehicle programme had a fixed timeline. A five-month delay was not acceptable.
The laboratory subcontracted the first phase of testing to another laboratory that had a suitable chamber. The subcontract cost was substantial. The replacement chamber was ordered. The original chamber — now too small for its intended purpose — was repurposed for component-level testing.
Root cause
The chamber was specified by nominal volume rather than usable volume. Nominal volume is the total enclosed space — the number the manufacturer uses in sales specifications and that appears on the chamber's nameplate. Usable volume is the space actually available for the DUT after the chamber's internal components occupy their share of the nominal space. For walk-in chambers, the difference between nominal and usable volume is typically 30–40%. A chamber with a nominal volume of 8 m³ typically has a usable volume of 5–6 m³. This figure is always available from the manufacturer — it is in the technical documentation — but it is not always the figure quoted in sales materials.
The DUT dimensions were not measured before the chamber was specified. The facilities manager knew the chamber needed to accommodate battery modules. He did not measure the modules, confirm the quantity to be tested simultaneously, or calculate the volume required — DUT volume plus clearances — before selecting the chamber size. The calculation is simple. It was not done.
Clearance requirements were not included in the specification exercise. Environmental test standards require minimum clearances between the DUT and the chamber walls to ensure adequate airflow and temperature uniformity around the specimen. For IEC 62660-2 battery testing, the clearance requirements are significant given the thermal mass and heat dissipation of the modules. The clearances consume a material fraction of the usable volume. They were not accounted for.
Nominal vs usable volume
Every walk-in environmental test chamber has two volume figures. The first is the nominal internal volume — the total enclosed space, which appears in sales specifications. The second is the usable volume — the space available for the DUT, which appears in technical documentation and is the figure that matters for chamber sizing.
The difference between the two is consistent across chamber types. Evaporator coils on the ceiling and rear wall occupy space. The air circulation system — fan arrays, plenums, baffles — occupies space on one or more walls. Structural supports and door mechanisms occupy floor area. The floor grating or access panels for drainage and services reduce usable floor space. Together, these internal components typically reduce the usable volume to 60–70% of the nominal volume.
The correct sizing calculation for a walk-in chamber is:
Required usable volume = (DUT volume × number of simultaneous DUTs) + (clearance volume per DUT side × 6 sides × number of DUTs) + inter-DUT clearance volumes + instrumentation and fixturing volume
The required usable volume must then be divided by the usable-to-nominal ratio for the specific chamber model to arrive at the nominal volume to specify. A chamber sized by nominal volume alone — without this calculation — is sized for the manufacturer's specification sheet, not for the test programme.
What changed after
The laboratory updated its equipment specification procedure. The updated procedure required, for any chamber procurement, a completed sizing calculation — DUT dimensions, quantity, clearances, fixturing — before a chamber size was selected. The calculation was a one-page form. It took fifteen minutes to complete. It had not existed before this incident.
The procedure also required that the usable volume figure be obtained from the manufacturer and documented in the purchase specification, alongside the nominal volume. The two figures were required to appear together in any procurement document. If they did not appear together, the specification was returned for completion.
The replacement chamber was installed twenty weeks later. It accommodated three battery modules with adequate clearance on all sides. The test programme started. The subcontract arrangement was closed out. The subcontract costs were recorded as a direct consequence of the original specification error.
The original chamber — 8 m³ nominal — was retained for component-level testing. It was suitable for that application. It had always been suitable for that application. It had never been suitable for the application it was purchased for.
Before specifying a walk-in chamber: calculate DUT volume plus clearances first. Then ask the manufacturer for the usable volume figure.
Walk-in vs reach-in: the full guide →Frequently asked questions
Can a thermal shock chamber be used instead of a cycling chamber for JESD22-A104?
No. JESD22-A104 NOTE 2 explicitly states that air-to-air or liquid-to-liquid thermal shock chambers shall not be substituted for thermal cycling chambers. The ramp rate of the DUT matters for the failure mechanisms A104 targets — too-fast a rate produces unrealistic damage during interconnect testing that does not represent field conditions.
What is the difference between JESD22-A101 and JESD22-A110 (HAST), and are they interchangeable?
Both target moisture ingress failure mechanisms. A101 runs at 85°C/85% RH for 1,000 hours; A110 (HAST) accelerates this with temperature (typically 130°C) and pressure (~2.3 atm), reducing the duration to 96 hours. They are not directly interchangeable for all device types — some qualification frameworks accept HAST as a substitute for 85/85, but this requires documented justification and is not automatic.
Does JESD22-A104 require DUT temperature measurement or just chamber air temperature?
The standard requires that the specimen reach the nominal temperature during each soak period — not just the chamber air. For small packages the difference is negligible. For larger assemblies, boards, or power modules, a thermocouple on the DUT is the only way to demonstrate compliance with this requirement. JEP 140 and JEP 153 provide the measurement methodology.
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