You reset to your default total, one per PC, at the beginning of every scene.
There are two exceptions:
You accepted a compel that effectively ended the last scene or starts the next one. If that happens, take an extra fate point in the next scene.
You conceded a conflict to the PCs in the previous scene. If that happens, take the fate points you’d normally get for the concession into the next scene and add them to the default total.