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Engineering Calculators
Reviewed engineering calculators for selected electrical, instrumentation and automation planning tasks.
Explore the relevant engineering page or send a technical requirement. Recommended RFQ inputs: project/asset, existing OEM/model, scope, drawings or specification, required date, site location, and any shutdown/mobilization constraint.
UPS / DC battery autonomy
How long will the battery hold the load?
Indicative autonomy6.75 hours
- Formula
- autonomy (h) = (capacity × voltage × usable%) ÷ (load ÷ efficiency%)
- Assumes
- Constant load for the whole discharge.
- Usable capacity accounts for the end-of-discharge voltage and ageing margin.
- Battery at its rated temperature, at the start of life.
- No allowance for the charger supplying load during the discharge.
- Does not cover
- Lead-acid capacity falls at high discharge rates (Peukert); a short, heavy discharge will be shorter than this figure suggests.
- Capacity derates with temperature and with age — commonly 80% at end of life.
- This is a sizing sanity check, not a battery sizing calculation. IEEE 485 or the battery manufacturer’s method governs the final design.
Generator and transformer loading
What apparent power does this load draw, and how loaded is the set?
Apparent power562.5 kVA75% of the stated rating
- Formula
- kVA = kW ÷ power factor · loading % = kVA ÷ rating × 100
- Assumes
- Balanced three-phase load at the stated power factor.
- Steady-state running load — no starting or transient contribution.
- Source rating is at site conditions, already derated for temperature and altitude.
- Does not cover
- Motor starting can demand several times running current; a set sized on running load alone may not start the largest motor.
- Non-linear loads (drives, UPS) draw harmonic current that this does not represent.
- Generator sets have a minimum recommended loading; running lightly loaded for long periods causes its own problems.
Indicative only. These figures support an early conversation about scope — they are not a design, and they do not replace calculation against the applicable standard, the equipment datasheet and the project specification. Every value that reaches a design is checked by a responsible engineer.