Calculator
Enter the voltage, the number of batteries and Igas (or the maximum charger current) for at least one group. The calculation runs in your browser; nothing you enter is sent anywhere.
Required air flow: m³/h
| Group | Cells (n) | Igas | Batteries | One battery (m³/h) | Group (m³/h) |
|---|
With natural ventilation
- Inlet and outlet, each at least cm² (square opening ≈ cm per side)
- Free room volume at least m³
- Air speed in the openings at least 0.1 m/s; inlet low, outlet as high as possible
With forced ventilation
- Fan flow at least m³/h. Charge only while the fan is running.
Within 0.5 m of the cell openings there must be no open flames, sparks, arcs or glowing objects (maximum surface temperature 300 °C).
Formula
When lead-acid batteries are charged, almost the entire current goes into splitting water in the final phase, and hydrogen is released. Ventilation must keep the hydrogen concentration below the lower explosion limit of 4 % by volume. For traction batteries, DIN EN 62485-3 gives the required air flow as:
Q = 0.055 · n · Igas
- Q: required air flow (m³/h)
- 0.055 m³/Ah: a constant combining the gas evolution rate, the dilution of hydrogen and a safety factor
- n: number of cells; 2 V per cell for lead-acid (24 cells for 48 V, 40 cells for 80 V)
- Igas: the hydrogen-generating current (A), i.e. the current at the end of charging
The formula is given for 25 °C. Thanks to its safety factor it can be used unchanged over the whole permissible operating temperature range of the battery.
Where do I find Igas?
Igas is obtained from the charger manufacturer for the battery concerned. Pulse, multi-voltage or fast-charging functions must be taken into account. If Igas is not known and cannot be obtained, use at least 40 % of the maximum charging current on the charger's nameplate. When several batteries are charged in the same room, calculate each one and add up the results, assuming all of them gas at the maximum rate at the same time.
Natural ventilation
- The free room volume (room volume minus the volume of objects in it) must be at least 2.5 × Q m³.
- Each inlet and each outlet needs a cross-section of at least A = 28 × Q cm² (Q in m³/h).
- The air speed in the openings must be at least 0.1 m/s.
- Inlets near the floor, outlets as high as possible, with the air flowing over the batteries.
- If inlet and outlet are in the same wall, they must be at least 2 m apart.
- Doors and windows count only if they stay open throughout charging.
Forced ventilation
- If the conditions for natural ventilation are not met, install forced ventilation of at least Q.
- Charge batteries only while the forced ventilation is effective.
- Demonstrate the function and effectiveness at commissioning and at regular intervals.
- Discharge the exhaust air to the open air, away from air-conditioning intakes and not into chimneys in use.
- Ducts and components in the exhaust air stream must be acid-resistant.
Near the battery: 0.5 m safety distance
Even with sufficient ventilation, dilution of hydrogen cannot always be guaranteed close to the battery. Within 0.5 m of a cell opening (plug or valve), measured along the air path, there must be no open flames, sparks, arcs or glowing objects; the maximum surface temperature is 300 °C. Chargers and sockets therefore go beside the batteries, outside this distance, not above them.
Worked example
Two types of battery are charged in the same room (values from the ZVEI leaflet):
- Ten 80 V batteries (40 cells), Igas = 21 A from the charger manufacturer: Q = 0.055 × 40 × 21 = 46.2 m³/h per battery; 462.0 m³/h for ten.
- Six 48 V batteries (24 cells), Igas = 3.6 A: Q = 0.055 × 24 × 3.6 = 4.75 m³/h per battery; 28.5 m³/h for six.
- Total: 462.0 + 28.5 = 490.5 m³/h. The leaflet rounds the intermediate result to 4.8 m³/h and shows 490.8 m³/h.
- Natural ventilation opening: A = 28 × 490.5 ≈ 13,734 cm², about 117 cm × 117 cm each for inlet and outlet. The free room volume must be at least 2.5 × 490.5 ≈ 1,226 m³.
Press Fill in the example in the calculator to see it.
What this calculation does not cover
The calculation gives the ventilation needed during charging. Hazardous area classification of the charging area, equipment suitability and site rules belong in the explosion protection document. Lithium-ion batteries are outside its scope. If you need this for a site in Turkey, contact us.
Source
ZVEI (German Electrical and Electronic Manufacturers' Association), Batteries Division: Information leaflet No. 14, “Ventilation of battery charging rooms for lead traction batteries”, May 2020, a guide to the application of DIN EN 62485-3 “Safety requirements for secondary batteries and battery installations – Part 3: Traction batteries”.
This tool is for information. For design decisions, the current text of the standard and the battery and charger manufacturers' data apply.
Frequently asked questions
I don't know Igas. What should I enter?
Ask the charger manufacturer first; the value depends on the battery and the charging characteristic. If you cannot find out, use at least 40 % of the maximum charging current on the charger's nameplate. The calculator applies this for you.
Why is the battery capacity not an input?
Since 2014 the standard's formula takes the hydrogen-generating current (Igas) directly in amperes. Older formulas used capacity and a current per 100 Ah separately; keep this in mind when comparing with older sources.
Can I use it for lithium-ion batteries?
No. The calculation is for lead-acid batteries. Lithium-ion batteries do not release hydrogen in normal charging; their failure risks are assessed separately.