Arc Skills / Architecture and engineering budgets
Build a system power budget
Power adequacy depends on what is on at the same instant, while battery energy depends on how long each load runs. Arc Skills takes mode, rail and duty-cycle inputs and returns both comparisons separately.
Use this skill
Use Arc Skills to build my mode-specific electrical power and energy budget.
Inputs:
- Load list, rail voltages, current or power values, and input/output measurement boundaries
- Operating modes, simultaneous loads, duty periods, startup and inrush conditions
- Source ratings, conversion efficiencies, and governing reserve policy where known
Return load-by-mode peak demand, time-integrated energy, source comparisons, formulas, and unresolved loss or transient terms. Do not use average duty cycle to hide an instantaneous deficit.What you provide and what you get
| What you have | How it is used | What you get |
|---|---|---|
| Loads and rail definitions | Normalizes electrical input power by rail | Mode-by-load contribution rows |
| Modes, overlap and duty periods | Separates simultaneous peak from average energy | Peak W and one-hour Wh totals |
| Source rating and efficiency | Compares the same electrical boundary | Deficit and unresolved input-energy terms |
Cold start challenges a 25 W source
Illustrative engineering example.
In this fictional example, the computer draws 10 W whenever active and the heater draws 20 W while on. Both are on together during cold start. Across a one-hour operating profile, the heater is on for 0.2 hour, including cold start; the 25 W source is inadequate during that overlap.
Computer: 10 W for 1 h
Heater: 20 W for 0.2 h, including an overlapping cold-start interval
Source: 25 W rated at the load-power comparison boundary| Load / comparison | Cold-start power | One-hour energy | Result |
|---|---|---|---|
| Computer | 10 W | 10 W × 1 h = 10 Wh | Continuous in stated profile |
| Heater | 20 W | 20 W × 0.2 h = 4 Wh | Duty cycle affects energy, not on-state peak |
| Combined load demand | 10 + 20 = 30 W | 10 + 4 = 14 Wh | Conditional profile demand; source cannot serve the peak |
| 25 W source | 25 W available | Battery energy and efficiency TBD | 30 − 25 = 5 W peak deficit |
Simultaneous load demand is 30 W, which exceeds the source rating by 5 W. Applying the 20% heater duty cycle to the instantaneous demand would hide that deficit. The 14 Wh one-hour figure describes load demand if both loads actually receive their specified power throughout the stated periods; the undersized source cannot deliver that cold-start demand unaided. Energy demand upstream of the stated load boundary could be higher if conversion losses exist.
These figures assume the listed wattages and source rating are comparable at the same electrical boundary and under compatible conditions. Rail conversion efficiency, startup inrush and source derating are unspecified, so the table cannot size the battery or establish transient electrical suitability. If wattages already include conversion at the comparison boundary, do not add that same loss again. In this example the energy calculation is a conditional load profile, because the stated source cannot sustain its peak.
Keep power and energy separate
- List loads by mode and rail; confirm whether each figure is electrical input or delivered output.
- Sum loads that can be on at the same instant for source-capacity checks.
- Integrate each load over the stated duration for energy, then add supplied conversion losses.
- Compare each peak mode with the source rating and mark absent inrush or derating data.
Questions about this task
Can average power prove source adequacy?
No. A source must also serve the simultaneous peak and relevant transients in the modes where those occur.
Is 14 Wh the battery energy requirement?
It is energy at the listed load boundary. Battery energy needs conversion-efficiency and battery-operating assumptions.
Sources and further reading
- NASA Systems Engineering Handbook: appendix: Terminology for budgets, margin and technical resources.
- NASA Systems Engineering Handbook: system design processes: Stakeholder expectations, logical decomposition, functional allocation and design decisions.