The importance of long-period binaries on the formation and evolution of planetary nebulae is still rather poorly understood, in part due to the lack of central star systems known to comprise such long-period binaries. Here, we report on the latest results from the on-going Mercator-HERMES survey for variability in the central stars of planetary nebulae. We present a study of the central stars of NGC 1514, BD+30 623, the spectrum of which shows features associated with a hot nebular progenitor as well as a possible A-type companion. Cross-correlation of high-resolution HERMES spectra against synthetic spectra shows the system to be a highly eccentric (e~0.5), double-lined binary with a period of ~3300 days. Previous studies indicated that the cool component might be a Horizontal Branch star of mass ~0.55M_{sun}_ but the observed radial velocity amplitudes rule out such a low mass. Assuming the nebular symmetry axis and binary orbital plane are perpendicular, the data are more consistent with a post-main-sequence star ascending towards the Giant Branch. We also present the continued monitoring of the central star of LoTr 5, HD 112313, which has now completed one full cycle, allowing the orbital period (P~2700-days) and eccentricity (e~0.3) to be derived. To date, the orbital periods of BD+30 623 and HD 112313 are the longest to have been measured spectroscopically in the central stars of planetary nebulae. Furthermore, these systems, along with BD+33 2642, comprise the only spectroscopic wide-binary central stars currently known.