In this paper, we investigate the relay selection (RS) problem in power splitting (PS) based energy- harvesting (EH) half-duplex (HD) relay networks, where the relays are wirelessly powered by harvesting a portion of the received RF signal power. We expand the relay selection problem in PSEH-HD relay networks to allow multiple relays to cooperate simultaneously. Furthermore, the optimal PS factor is obtained in closed form to facilitate the RS. Simulations show that neither the single RS nor the all-participate RS is optimal across all SNR levels. To improve the capacity of the network by better exploiting the cooperative diversity, a heuristic RS strategy with quadratic complexity is then proposed. The performance of our proposed updated relay ordering based relay selection (URO-RS) strategy is evaluated by simulations, which achieves near-optimum performance in comparison with the exhaustive search based RS strategy but with significantly reduced complexity.