The standard MGB charging system was designed for a modest electrical load. On a car fitted with additional accessories, used in heavy traffic, or where the original dynamo has reached the end of its service life, an upgraded charging unit makes a meaningful difference to electrical reliability. The 55-amp 16/17ACR alternator is the standard replacement for negative earth cars from 1967 onwards. The Dynamator is the most sophisticated upgrade available, a purpose-built unit that fits directly into the original dynamo mounting points, uses the existing pulley and fan, and is indistinguishable from the original dynamo from outside the engine bay.
Internally it contains a modern alternator delivering improved output and low-speed charging capability. The Dynamator is available in positive earth and negative earth versions, covering both the early pre-1967 positive earth MGB and later cars where an alternator-in-dynamo-body installation is preferred for originality.