Q60 Class 3 Self Made Magnetics

---
name: q60-class-3-self-made-magnetics
description: "Validate an in-house wound magnetic part built for Class 3 equipment under ECSS-Q-ST-60C clause 6.6.8: refuse a part standing on no wire specification, no core specification, no qualified winding procedure and no named recognised practice, resolve the peak flux density from the volt-second product and its utilisation of core saturation, take the window fill factor and the current density, carry the copper and core losses across the thermal path to a hot spot margin below the derated insulation index, catch a winding resistance taken below the hot spot its own losses reach, price the dielectric withstand voltage, then derive the screening sequence the construction and the flight lot call for. Use when a transformer or inductor is wound in house rather than procured. Trigger: ecss, q-st-60c, q60-class-3-self-made-magnetics, q60-c3-magnetics-volt-second-flux-density, q60-c3-magnetics-hot-spot-margin, q60-c3-magnetics-screening-sequence."
license: Apache-2.0
compliance: STANDARDS-REF
standards:
  - id: ecss
    reference-only: true
gated: false
domain: space-systems
pack: space-systems
compatibility: "agentskills.io SKILL.md; any SKILL.md host (Claude Code, Hermes, OpenClaw)"
metadata:
  domain: space-systems
  subdomain: ecss
  tags: [ecss, q-st-60c-eee-component-procurement, q-st-60c, q60-class-3-self-made-magnetics, q60-c3-magnetics-volt-second-flux-density, q60-c3-magnetics-window-fill-factor, q60-c3-magnetics-hot-spot-margin, q60-c3-magnetics-dielectric-withstand, q60-c3-magnetics-screening-sequence]
  version: 0.1.0
  author: Aero Agent Skills
---

# ECSS EEE Class 3 — Self-Made Wound Magnetic Parts (space-systems/ecss/q60-class-3-self-made-magnetics)

Use when the task is clause 6.6.8 of ECSS-Q-ST-60C: a magnetic part wound in
house for Class 3 equipment rather than bought against a component
specification. This leaf checks the design against recognised practice and
derives the screening the part owes before it may be fitted.

## Domain quick reference

- A self-made part has no procurement history to lean on, so the evidence is
  built rather than inherited. Without a stated wire specification, a stated
  core specification, a qualified winding procedure and a named recognised
  practice there is nothing to assess. Class 3 relaxes who may sign each one,
  never whether it exists.
- The flux the core sees is set by the volt-second product, not by the
  current. Applied voltage times the time it is applied, divided by the turns
  and the effective core section, is the peak flux; a design that looks
  conservative on current can still be sitting at the knee of the loop.
- Saturation is a datasheet maximum, not a working point. The recognised
  practice figure is a fraction of it, and a part exactly on that fraction is
  compliant because the limit belongs to the acceptable side.
- The window is a budget with three claimants. Turns, conductor section and
  insulation all draw on the same bobbin, and a fill factor computed on bare
  copper is already optimistic about what will physically go on.
- The hot spot is computed, not measured — and the computation has a loop in
  it. Copper loss follows the winding resistance at temperature, that
  temperature is what the losses produce, and a resistance stated at twenty
  degrees for a winding that will sit at ninety understates the loss that
  heated it. A declared winding temperature below the hot spot the losses
  reach is a finding in its own right.
- Core loss follows a power law steep in flux, so it is never a small
  correction: a modest rise in working flux can multiply it several times and
  turn a comfortable thermal design into a marginal one.
- The insulation system is graded twice. Once on temperature, where the index
  less the Class 3 derating is what the hot spot is compared with, and once on
  voltage, where the withstand the working voltage calls for has to be inside
  what the system is rated to stand.
- Screening is what a self-made part has instead of lot acceptance. The
  construction decides which extra step attaches — a potted assembly hides its
  winding, a toroid hides its start — and the flight lot decides whether a
  destructive sample can be drawn at all. A lot of two cannot spare one, so
  the whole lot is screened without destroying any of it.

## Workflow

1. Validate the case and name the foundations the part does not stand on. If
   any is missing the part is not admissible and the design numbers are not
   worth computing.
2. Resolve the peak flux density from the volt-second product, the turns and
   the core section, and take its utilisation of the core saturation figure.
3. Take the window fill factor from the turns and the conductor section, and
   the current density the winding runs at.
4. Resolve the winding resistance at its declared operating temperature, take
   the copper loss, take the core loss from the material power law at the
   working flux and frequency, and add them.
5. Carry the total loss across the thermal resistance to a rise, add the
   ambient, and take the margin against the insulation index less the Class 3
   derating. Check the declared winding temperature is not below that hot
   spot.
6. Price the dielectric withstand voltage the working voltage calls for and
   compare it with the insulation system rating.
7. Derive the screening sequence from the construction and the flight lot
   size, subtract what has been done, and return the disposition in precedence
   order: not admissible, then design nonconforming, then screening
   outstanding, then practice satisfied.

## Pitfalls

- Sizing the core from the current alone. The flux comes from the volt-second
  product, and a winding that is comfortable on current density can still
  drive the core into saturation on the first long pulse.
- Designing to the datasheet saturation figure. It is the boundary the
  material stops being a core at, not the point a design should sit at, and
  the fraction held back is what absorbs temperature, tolerance and an
  off-nominal duty.
- Computing the winding resistance cold. Copper gains roughly four parts in a
  thousand per degree, so a winding sized on a twenty-degree resistance
  dissipates materially more once it is hot, and the rise feeds the resistance
  that produced it.
- Taking the core loss as a small correction. The power law is steep in flux,
  so a modest increase in the working flux can multiply the core loss several
  times over.
- Reading a hot spot against the bare insulation index. The Class 3 derating
  sits below it, and the margin between them is the reason the part survives
  the mission rather than the acceptance test.
- Grading the insulation system on temperature only. It also has to stand the
  withstand voltage the working voltage calls for, and a system chosen purely
  for its thermal index can be short on volts.
- Planning a destructive lot sample the lot cannot spare. A flight lot below
  the sampling floor has no part to give up, and the sequence has to change
  rather than the lot.
- Comparing a computed utilisation, fill or margin with its limit by bare
  arithmetic. The core law runs through a fractional power that is not
  correctly rounded, so a case sitting exactly on a limit can land a few units
  in the last place the wrong side of it.

## Behavior contract (gate 3)

The policy merge, case validation, foundation gaps, volt-second peak flux and
its saturation utilisation, window fill factor, current density, winding
resistance at temperature, copper and core loss, temperature rise, hot spot,
its margin against the derated insulation index, the resistance-reference
check, the required dielectric withstand voltage, the screening sequence with
its lot sampling floor and the four-way disposition in precedence order are
exercised by the gate 3 contract test:
scripts/test_q60_class_3_self_made_magnetics.py against
scripts/q60_class_3_self_made_magnetics_logic.py (stdlib unittest, offline).
Run: python3 scripts/test_q60_class_3_self_made_magnetics.py

## Compliance

- ECSS standards are freely downloadable (ESA); cite the source and
  paraphrase per standards-map.yaml.
- compliance: STANDARDS-REF, gated: false.