You can cast spells by storing and releasing energy in Spell Dynamos.
Spell Dynamos
You power your spells through handheld arcane devices called Spell Dynamos, which each hold a single spell slot. The Dynamo Engineer Spellcasting table shows how many Spell Dynamos you have. The table also shows the level of spell slots held in your dynamos, all of which are the same level. To cast one of your Wizard spells of level 1+, you must expend a Spell Dynamo. You regain all expended Spell Dynamos when you finish a Long Rest.
Configuring Dynamos
Unlike other spellcasters, you must configure each of your Spell Dynamos in advance to cast a single Wizard spell you have prepared. You configure your dynamos whenever you finish a Long Rest, and can reconfigure each of your unexpended dynamos to hold different Wizard spells you have prepared when you finish a Short Rest.
Prepared Spells of Level 1+
You prepare the list of level 1+ spells that are available for you to cast with this feature. To start, choose three level 1 spells from the Wizard spell list. Feather Fall, Grease, and Magic Missile are recommended.
The number of spells on your list increases as you gain Alchemist levels, as shown in the Prepared Spells column of the Dynamo Engineer Spellcasting table. Whenever that number increases, choose additional spells from the Wizard spell list until the number of spells on your list matches the number on the table. The chosen spells must be of a level no higher than what's shown in the table's Slot Level column for your level.
Changing Your Prepared Spells
Whenever you gain an Alchemist level, you can replace one spell on your list with another Wizard spell for which you have spell slots.
Spellcasting Ability
Intelligence is your spellcasting ability for your Wizard spells.
Spellcasting Focus
You can use an Arcane Focus as a Spellcasting Focus for your Wizard spells.