Workshop Q&A Helpdesk
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Steve Rothwell answers more of your technical questions, from an Austin Gipsy with charging problems to a jerky Merc.
AUSTIN GIPSY CHARGING PROBLEMS Q
I have an Austin Gipsy ambulance, the first pre-production prototype and the last surviving model of the production run, which is a very interesting project. I have been restoring it for 11 years now even though it was originally a five year plan, but I’m enjoying it. (I have attached a photo of how she was when bought.) However, I have hit a problem. I was advised to convert it to negative earth, but to use a Dynator instead of the dynamo for better output. Not being totally confident with electrics I have followed the diagrams to my best ability, but on the dynamo there are three terminals with two white wires connected to one of the terminals, but nowhere for them on the Dynator. Please can you guide me? Alan Dunderdale
AThe two white wires connected to a third terminal on the dynamo means that the original dynamo fitted was a three brush unit. Three brush dynamos don’t use voltage regulators because they were designed prior to the development of the regulator.
It is the third brush that controls the output, by tapping off a voltage somewhere along the commutator and using this tap to supply the current to the field coil. By moving the third brush towards or away from one of the main brushes across the face of the commutator, the output of the dynamo can be controlled manually.
As this is a restoration project and the vehicle has not been used for over 20 years, some modification of the wiring will be needed, and existing wiring may need replacing if it is timeexpired. Because the Dynator regulates the voltage automatically, the two white wires from the third brush of the dynamo which would have carried out the voltage change will not be needed so they can be isolated, whilst the positive wire and warning light wires can be connected up to the Dynator. The positive wire must be checked to ensure it is capable of carrying the 50 amp output of the Dynator, and that it is connected directly to the battery and not via a switch which may overheat when loaded.