Arcane Dynamo is a Wizard passive skill, unlocked at level 55.
The following skills are Signature spells:
Flash of Insight charges are gained and spent upon cast, not upon hit, even if the spell does not hit an enemy. However, non-damaging spells do not consume the Flash of Insight charges. It is therefore possible to charge up for the Archon Disintegration Wave, provided you cast it through the whole duration. One can also augment Arcane Orbit (charging all 4 orbs). All secondary damaging effects of the augmented spell are also empowered.
Spells only consume 5 charges; if having less, the spells will not spend them. The Wizard cannot store more than 5 charges at a time, though.
Flash of Insight charges have unlimited duration.