  We explore a class of compact charged spheres made of a charged perfect fluid
with a polytropic equation of state. The charge density is chosen to be
proportional to the energy density. The study is performed by solving the
Tolman-Oppenheimer-Volkoff (TOV) equation which describes the hydrostatic
equilibrium. We show the dependence of the structure of the spheres for several
characteristic values of the polytropic exponent and for different values of
the charge densities. We also study other physical properties of the charged
spheres, such as the total mass, total charge, radius and sound speed and their
dependence on the polytropic exponent. We find that for the polytropic exponent
\gamma=4/3 the Chandrasekhar mass limit coincides with the Oppenheimer-Volkoff
mass limit. We test the Oppenheimer-Volkoff limit for such compact objects. We
also analyze the Buchdahl limit for these charged polytropic spheres, which
happens in the limit of very high polytropic exponents, i.e., for a stiff
equation of state. It is found that this limit is extremal and it is a
quasiblack hole.
