Lattice instanton action from 3D SU(2) Georgi-Glashow model

3D Georgi-Glashow model is studied on the lattice in the London limit in an infrared but an intermediate region before the screening appears. Abelian and instanton dominances are observed after abelian projections in a unitar y gauge and roughly in the maximally abelian gauge. Using an inverse Monte- Carlo method, we determine an effective instanton action in both gauges. Wh en we restrict ourselves to some regions of parameters beta and kappa, we o btain an almost perfect instanton action, performing a block-spin transform ation on the dual lattice. It takes a form of a Coulomb gas and reproduces fairly well the string tension obtained analytically by Polyakov. The almos t perfect actions in both gauges look the same in the infrared region, whic h suggests gauge independence.