Battery overcharging.

[Tony Press]

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.

[Robert Leigh]

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.

[Reckless Rat]

+1 what he said.

[Dave Mann]

And I. The dynamo is a C35 which have the field resistor in the base of a of a CFR2 cut out
  Photo 4 CFR2 cover removed.jpg (Size: 16.74 KB / Downloads: 186)
  Photo 5 CFR2 cutout underside view.JPG (Size: 17.14 KB / Downloads: 186) while earlier C35 dynamos had the field resistor in the box on the dynamo connected to a CF3 cut out. This car has the later C35 dynamo connected to what appears to be a CAV type E cutout which doesn't have a field resistor. So the options are find and fit a CFR2 cutout or a simpler solution is to fit a resistor between the dynamo terminals.

[David Stepney]

The resistor should be about 1.7 to 2 ohms. I got a suitable power resistor from ebay.

[Tony Press]

And I. The dynamo is a C35 which have the field resistor in the base of a of a CFR2 cut out  while earlier C35 dynamos had the field resistor in the box on the dynamo connected to a CF3 cut out. This car has the later C35 dynamo connected to what appears to be a CAV type E cutout which doesn't have a field resistor. So the options are find and fit a CFR2 cutout or a simpler solution is to fit a resistor between the dynamo terminals.

So that is why the two terminals are connected giving full charge ate all times which is OK with the present set up.

As noted the third brush must be reset to reduce to reduce the Dynamo charge but as I said if the battery is overcharging at this setting then turn on the headlights- simple.

There - exhausted my electrical knowledge 

Cheers, Tony

[Tony Griffiths]

Hello David,
Might you have a link to the resistor you bought?

The resistor should be about 1.7 to 2 ohms. I got a suitable power resistor from ebay.

[Ian Wegg]

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.

[Dave Mann]

Have you tried it with the switch in the winter/ full charge position ?

[David Stepney]

Hello David,
Might you have a link to the resistor you bought?

The resistor should be about 1.7 to 2 ohms. I got a suitable power resistor from ebay.

I now can't remember, but a similar resistor can be found on ebay. The seller is 'Bright Components' and  Part is described as '50 watt Aluminium Clad Power Resistor' The item number is 291418948986. They supply them in a range of resistances.