Size a supply for a real build and compare against what is fitted

short · 40 min · Objective 3.4

Task

Do the wattage arithmetic for a specific machine and compare the result against the supply actually fitted, so that both undersizing and oversizing are quantities rather than opinions.

Steps

  1. Record the fitted supply in lab/psu/fitted.csv with header field,value,source covering total wattage, the 12 V rail capacity, efficiency rating and connector types present.
  2. Record the machine's components in lab/psu/draw.csv with header component,watts,source -- processor thermal design power, graphics board power, each drive, each fan, and an allowance for the board.
  3. Compute the total and add headroom, recording the arithmetic in lab/psu/sizing.md with the headroom percentage stated.
  4. Write lab/psu/verdict.md stating whether the fitted supply is adequate, generous or marginal, using both the total and the 12 V figure.
  5. Write lab/psu/symptoms.md listing four symptoms an undersized supply produces, and explaining why several components appear to fail at once.

Verify

awk -F, 'NR>1 && NF>=3 {n++} END {print n" supply field(s)"}' lab/psu/fitted.csv
awk -F, 'NR>1 && NF>=3 {n++} END {print n" component(s) costed"}' lab/psu/draw.csv
awk -F, 'NR>1 {s+=$2} END {print s" W total component draw"}' lab/psu/draw.csv
grep -Eic 'headroom|per cent|%' lab/psu/sizing.md
grep -Eic 'adequate|generous|marginal' lab/psu/verdict.md
grep -c . lab/psu/symptoms.md

Four supply fields, four or more components costed with a computed total, headroom stated, a verdict, and four symptoms. If the 12 V capacity is not in the fitted table, the label has not been read properly -- it is the figure that decides.

Notes

Do not open the supply to read anything. The label is on the outside, and the manufacturer publishes the same figures. Nothing in this course requires the cover to come off.

This is an independent study companion for CompTIA A+ Core 1 220-1201 and is not produced by or endorsed by CompTIA.