  We construct models with U(1) gauge group and matter with charges up to 6, in
the context of type IIB compactifications. We show explicitly that models with
charges up to 4 can be derived from corresponding models in F-theory by
applying the Sen weak coupling limit. We derive which type IIB models should be
the limit of charge 5 and 6 F-theory models. Explicit six dimensional type IIB
models with maximal charge 5 and 6 are constructed on an algebraic K3 surface
that is the double cover of $\mathbb{CP}^2$. By using type IIB results we are
also able to rediscover the F-theory charge 4 model in a straightforward way.
