Joined: Aug 2017 Posts: 1,740 Threads: 42
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Location: Malvern, Victoria, Australia
Is this an earlier Dynamo with the half charge wiring inside and no box on top ?
If so the wiring has failed (as often happens) and the charge rate is set at winter permanently by the wire between the two terminals.
Not a problem if the third brush is set to the correct charging rate - if the battery is overcharging do the modern thing and drive with the headlamps on.
Joined: Aug 2017 Posts: 908 Threads: 22
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Location: Near Cambridge, UK
Car type: 1928 tourer (mag type), short chassis Gould Ulster
Driving with the headlamps on will reduce the battery overcharging, but it will not reduce the dynamo output. It remains highly desirable to get the output down to the correct rating (8 amps) if the dynamo is to survive without burning out.
Joined: Jan 2019 Posts: 1,564 Threads: 20
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Location: Bala North Wales
Car type: 1933 RP Standard Saloon
The resistor should be about 1.7 to 2 ohms. I got a suitable power resistor from ebay.
Joined: Aug 2021 Posts: 185 Threads: 10
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Location: Petersfield, Hampshire
Car type: AG Tourer
Yesterday as a quick fix to keep on the road, I removed the wire across the dynamo terminals. Now the dynamo isn't charging, but the battery isn't spirting acid out. I'm only planning short trips and I'll use the battery conditioner when garaged. In the meantime I'll resource the correct resistor and sometime soon fit it and make the 3rd brush adjustment.
The suggestion of using headlights sounds feasible, except they don't work either ... another job on my to do list!
Thanks once again for the comprehensive replies.
Joined: Oct 2017 Posts: 1,499 Threads: 54
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Have you tried it with the switch in the winter/ full charge position ?