Charging,?.

[David.H]

ChittI is close to being used...when we are allowed,BUT
The dynamo is putting out lots of volts. New belt !
The ammeter used to show a charge with the engine running...and the new wIring in place..but the warning light is now lit all the time. (It is a12 v bulb as I didn't have a 6v one.) It did go out before ....And now it doesn't! 
I have the dash out and all the wires are in the right place,
The bulb holder has 6v at the base contact, but the earth  ( outside threaded part ) seems a bit dodgy and I think I can get it to show 6v! I had tried to put an earth wire to that outside, but it was a bit Heath Robinson, so I have discarded it.
Could this cause the regulator to play up? Or what am I missing 
D

[Bill Dixon]

avid suggest you go on to the Dorset site look on their technical site ELECTRICS & INGITION. This has a lot of good advice on the charging circuit,
The ignition warning lamp does not have a earth connection,if you look at the circuit diagram it can be seen how the lamp is connected.
Hope this helps.

[David.H]

Thanks
Job for tomorrow!

[Bob Culver]

The igniton lamp has to have characteristic similar the original combination or the cutout can get a bit confused.  Assuming the car is all Seven and later based, John Cornforths diag on the Dorset site will likely prove conveneient and save you having to piece together the same from the wiring diagrams. Not sure what lots of volts means but if very substantially more than 6 indicates connection to the battery is not being established.

[David.H]

When I put my meter across the terminals of the dynamo with the engine running it read 10-14v! It is a 6v dynamo. I did not run it for many seconds, nor was I tempted to touch the cut out!
Thanks for all advice....I am not an electician!! The rewire was done with the aid of a very competant auto electrician who, drawing on rally car wiring, succeeded in wiring up the headlights with relays ( they double dip using the original tiny dip switch on the column, but are not Lucas Graves any more!) The car did charge correctly when we started up after the rewire, so it is a gremlin in there somewhere...I did have a go at the switch panel to clean it up......so( too ) many variables!
D

[Bela]

The ignition bulb must be for 2,3 to 2,6V. It only measures the different voltage between battery and generator - no earth connection as mentioned. If the 6V dynamo really generates 10-14V the lifetime will end soon if you try further. There is a problem with the field coil.Call your competent auto electrician.

[Bob Culver]

Digital meters often read haywire near running engines and esp so near unsuppressed Sevens. A resistor  of a few hundred or much more ohms across the input may cure. Or buy a very cheap analogue meter and calibrate it from the digital one which are much more accurate.

[David.H]

Bela
Do you mean 2.3-2.6 volts or 2.3-2.6 amps...? The "Dorset" site suggests using a bulb of 3.5-4 volts, but then mentions a 6v 0.3 amp bicycle lamp, but this is all about repairing the later ignition light which is separate from the switch panel.
My car does have a mixture of parts ....hydraulics, 17" wheels, Nippy manifold & carb, 4speed sports box etc, but the electrics are  basically 1931(AG)
I have happily (innocently!) used 12v 2.3 bulbs in 6v cars....I happened to have them left over from when I had a TR3A!
Just a bit dim....!
I wish you success with the TuV, I have a friend in Osnabruck rebuilding an XK120 (he bought it from USA 40 years ago and is at last getting it together...!) and it is a real problem knowing what they will accept. I think your car is really interesting. All "specials" are different as I am finding out!
David

["Slack Alice" Simon]

Dynamo voltage not a problem, they supply 12 volts to lots of people who have converted their systems.

The dynamo is regulated when the battery is in the circuit - 6 volt battery means a 6 volt system, 12 volt battery is a 12 volt system.

The cut out senses the difference between dynamo and battery, when dynamo voltage reaches battery voltage, the cut out closes and the dynamo is supplying voltage to the required level.

Austin missed a cost saving trick when in production - you just fit a 12 volt bulb in place of the "ignition" light, you don't need an odd voltage bulb and dropper winding.

[Bela]

....

The dynamo is regulated when the battery is in the circuit - 6 volt battery means a 6 volt system, 12 volt battery is a 12 volt system.

The cut out senses the difference between dynamo and battery, when dynamo voltage reaches battery voltage, the cut out closes and the dynamo is supplying voltage to the required level.

Austin missed a cost saving trick when in production - you just fit a 12 volt bulb in place of the "ignition" light, you don't need an odd voltage bulb and dropper winding....

@"slack Alice" Simon

If the insulation of a device is designed for a voltage it is not sure to resist to the double voltage. That is not a problem at cars because a 6V starter can also be used with 12V. I guess it is no problem with a dynamo.

But a dynamo must be regulated. As far as I know the cut out prevents from discharging and some pre war dynamos have a build in regulation. Later boxes have a voltage regulation and a cut-out function.  Charging a battery must end at a specific voltage. That's what a regulator must do. What is the base of your statement.  I still want to learn what happens in pre war cars and how it works. Any hints in the www?