1930s. From over- + compound. Compare earlier overcompound.
overcompound2
/ˌəʊvəkəmˈpaʊnd/
Electrical Engin.
verb
[with object]To provide (a dynamo) with so many series turns (compared with the number of shunt turns) that the voltage which is generated increases as the load increases. Also (occasionally) without object.
Origin
Late 19th century; earliest use found in Silvanus Thompson (1851–1916), physicist and electrical engineer. From over- + compound.