Definition
A transformer coil arranged so that the output (secondary) voltage is higher than the input (primary) voltage. It achieves this by having more turns of wire in the secondary winding than in the primary winding, with the voltage ratio matching the turns ratio.
Plain English
A coil that takes a lower voltage in and gives a higher voltage out. It does this by winding more loops of wire on the output side than on the input side.
Context Anchor
Seen in aircraft ignition and magneto discussions, especially when explaining how spark plugs get high voltage.
Derivation
The name describes exactly what it does: the voltage is 'stepped up' from a lower level to a higher one, just as you step up to a higher stair.
Why Pilots Care
A functioning step-up coil is essential for reliable engine starting and operation; a faulty one can cause weak or absent sparks leading to engine failure.
Intuition Check
A step-up coil does not create free electrical power. It raises voltage while reducing the amount of electrical flow available.
Example Sentence 1
The magneto uses a step-up coil to convert the low primary voltage into the high voltage needed to fire the spark plugs.
Example Sentence 2
During preflight, any issue with the step-up coil could prevent the engine from starting properly.