AGL Load with Failed Lamps Calculator
With the formula, a worked example and typical values.
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Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
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About this calculator
This page calculates circuit load, all lamps working, circuit load with failed lamps, change in load and 2 more results from fittings on the circuit, failed lamps, lamp power per fitting, isolating transformer efficiency and 4 more inputs. Change any value or its unit and the result updates. The steps below show the working for the default values, so you can check each line against your own method.
Limits of this calculator
A real open-secondary transformer is not a fixed power. Its voltage and loss depend on the core design, so treat the result as a first estimate and confirm it with the transformer manufacturer. Several failures in a row can still push the CCR toward its overvoltage or open-circuit protection.
Cross-check: 30 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review.
Verification status: Indicative
Indicative. Estimation only; further engineering checks are required. Basis: Open-secondary transformer treated as a fixed input power; the real value depends on the core design.
What this calculator checks
- The arithmetic of the simplified model for the values you entered.
What remains unverified
- Whether the simplifying assumptions listed on this page hold for your case.
- Any standard, manufacturer or site data. Treat the result as an estimate and confirm it by a further engineering check.
Verification register entry
| Calculation author | Rahul Sharma (author) |
|---|---|
| Technical review | No independent technical review has been carried out |
| Individual professional approval | Not recorded |
| Formula reference | not recorded |
| Standard and edition | IEC 61820-1-2; FAA AC 150/5345-47B, IEC 61820-1-2:2024; FAA AC 150/5345-47B (30 June 2005) |
| Standard review state | Public-scope screened; licensed clause review still pending |
| Scope-screening note | AGL series-circuit and isolation-transformer context is relevant. Open-secondary voltage/power behaviour is manufacturer-specific; the calculator requires user-entered failed-lamp/open-secondary assumptions and is indicative. |
| Cross-check test cases | 30 reference vectors (tests/reference_vectors.json) |
| Review date | not recorded |
| Next review date | not recorded |
| Status | Indicative |
Needed before this calculator can be marked Verified: reviewer name, qualification and review date; licensed clause-by-clause standard review; exact formula reference; formula source (textbook or standard); next review date.
Formula
Worked example
| Input | Value |
|---|---|
| Fittings on the circuit | 60 |
| Failed lamps (open circuit) | 3 |
| Lamp power per fitting | 45 W |
| Isolating transformer efficiency | 0.85 |
| Transformer input power with the secondary open | 10 W |
| Circuit current | 6.6 A |
| Series cable loop length | 4,000 m |
| Series cable resistance | 3.08 Ω/km |
- Fitting load = 45 W / 0.85 = 52.94 W, cable loss = 536.7 W
- All working: 60 × 52.94 + 536.7 = 3,713.1 W
- 3 failed: 57 × 52.94 + 3 × 10 + 536.7 = 3,584.3 W
- Vout = 3,584 / 6.6 = 543 V
Assumptions
- Each failed lamp leaves its transformer drawing a fixed open-secondary power
- Resistive series circuit, power factor near unity
- Current held at the circuit value by the CCR
A real open-secondary transformer is not a fixed power. Its voltage and loss depend on the core design, so treat the result as a first estimate and confirm it with the transformer manufacturer. Several failures in a row can still push the CCR toward its overvoltage or open-circuit protection.
Inputs and results
| Input | Unit | Allowed or shown | Note |
|---|---|---|---|
| Fittings on the circuit | (number) | 1 or more, up to 500 | |
| Failed lamps (open circuit) | (number) | 0 or more, up to 500 | |
| Lamp power per fitting | W | greater than 0 W | At the circuit current, from the fitting data sheet |
| Isolating transformer efficiency | (number) | greater than 0.5, up to 1 | |
| Transformer input power with the secondary open | W | 0 W or more | Example value only. Use the transformer data sheet or a measurement |
| Circuit current | A | greater than 0 A | |
| Series cable loop length | m | greater than 0 m | |
| Series cable resistance | Ω/km | greater than 0 Ω/km |
| Result | Unit | Allowed or shown | Note |
|---|---|---|---|
| Circuit load, all lamps working | kW | Shown to 3 decimal places | |
| Circuit load with failed lamps | kW | Shown to 3 decimal places | |
| Change in load | W | Shown to 0 decimal places | |
| Change as % of the working load | (number) | Shown to 1 decimal place | |
| CCR output voltage with failed lamps | V | Shown to 0 decimal places |
How it is calculated
Each input is converted to the base unit of its quantity, the formula above is applied in the order shown in the worked example, and each result is shown in the unit you choose. Results are held at full precision and rounded only for display, except where a step selects a standard size, as the worked example shows. A value outside its allowed range is refused with a message instead of giving a result.
How the result changes with lamp power per fitting
| Lamp power per fitting (W) | Circuit load, all lamps working (kW) | Circuit load with failed lamps (kW) | Change in load (W) |
|---|---|---|---|
| 4.5 | 0.854 | 0.868 | 14 |
| 11.3 | 1.334 | 1.324 | -10 |
| 22.5 | 2.125 | 2.075 | -49 |
| 45 | 3.713 | 3.584 | -129 |
| 90 | 6.89 | 6.602 | -288 |
| 180 | 13.243 | 12.637 | -605 |
| 450 | 32.301 | 30.743 | -1,558 |
Other inputs are the same as in the worked example above.
Standards and further reading
- ICAO Annex 14, Volume I (aerodrome design and operations)
- ICAO Doc 9157, Part 5 (aerodrome design manual, electrical systems)
Photometric and circuit requirements come from the edition of Annex 14 and the regulator's rules that apply at your aerodrome, and from the fitting and regulator manufacturers' data. These are named as background reading. Elecmetric does not embed clause text or rating tables, and the reviewer record for this calculator is separate from this list.
Frequently asked questions
What do I need to enter?
Enter fittings on the circuit, failed lamps (open circuit), lamp power per fitting, isolating transformer efficiency, transformer input power with the secondary open, circuit current, series cable loop length and series cable resistance. Change the unit of a value with its selector and the result stays the same.
What does this calculator assume?
Each failed lamp leaves its transformer drawing a fixed open-secondary power. Resistive series circuit, power factor near unity. Current held at the circuit value by the CCR.
Which calculators should I use next?
Common next steps are AGL Series Circuit Load and CCR Size, AGL Isolating Transformer Current and Loading and AGL Lamp Life at a Different Circuit Current. The related links at the bottom of this page open them.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. 30 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review. Check design values against the standard and the equipment data you work to.
Formula guides and reference
Longer explanations with worked examples and tables, written for the same topic.
- AGL Series Circuit Load and CCR Sizing Formulas: AGL series circuit formulas: the load of a 6.6 A constant current circuit, the cable loss
- AGL Isolating Transformer Formulas: AGL isolating transformer formulas: the secondary lamp current, the lamp voltage
- AGL Maximum Fittings on a CCR Formulas: AGL maximum fittings formulas: how many fittings a constant current regulator of a given kW rating can carry on a…
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