Charging,?.

[Tony Press]

Bela,
"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?"


The Austin Seven dynamo is 'third brush regulated' with only a cutout in the circuit - no other regulator.  

http://www.da7c.co.uk/technical_torque_a...dynamo.htm

http://www.vias.org/kimberlyee/ee_31_02.html

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David , way back in the 1920s/1930s Lucas used a 2.5volt 0.2amp MES bulb . This was a torch bulb and easy to obtain.The current ie 0.2 amp is the important part not the voltage of the bulb,as it is in series with the dynamo windings.I have replaced the resistance wire with a 27ohm .6 watt resistor
Are you seeing a charge on the ampmeter,?if so then it is only the wiring to the ing lamp that needs connecting.
Once some one puts extra wring in it can cause problems as you have found out.
Best of luck you will get there in the end.

There are a number of variations to the Austin 7 Lucas switch panel - or as my 'Lucas Spare Parts list for Austin 7 HP 1927-28-29-30' describes it- 'Switchbox'. 

This lists-

SM1 Magneto Ignition 1927

SM3/ER Magneto Ignition  1928 

SM3/BN7 Coil Ignition 1929-30

the Ignition light or as they describe the 'Warning Bulb' for SM3/BN7 is shown as MES 8/9V (no wattage mentioned).

I don't have the later Lucas catalogue but from checking I would think the switchboard SM3/BN7 was later renamed SM5.

I have seen a picture of an SM5 panel with a BN7 tag affixed at the back

My three 1929 'SM5' panels all have the plain MES (miniature Edison screw) bulb holes in the panel, fitted with 6 volt 3 watt bulbs which seem to work correctly.

The later version of the SM5 apparently has a different bulb fitting with a resistor wound around- I do not know the bulb details.

[Bela]

@Tony Press

Thank you for that documents which help to understand. But a question remains.

If the dynamo shall generate 12V - does it works with only a 12V battery or does it need an additional 12V cut out?

[David.H]

Bela,
It worked before!
I will put the meter across the battery terminals with the motor running & see what is getting to the battery.
If more than at rest, then the dynamo is working and if ~ 6-8volts then it would appear to be regulating I think.

["Slack Alice" Simon]

Yes, it needs a 12 volts cut out, and the light bulbs also need changing.

The starter is ok on 12 volts, the horn and windscreen wiper may be, or can be changed, or a resistor put in series with them to drop the voltage.

The fuel gauge and sender in the tank will need resistors or changing, too.

[Bob Culver]

Hi Bela and co

The basic dynamo test is to remove external connection, link D and F, run briefly and observe volts to earth. Should be 20,30 or so. Almost certainly proves dyn OK. Must reconnect the lead and once generating must establish connection to the battery via cutout. The dynamo is not regulated. The battery simply soaks up any charge, reduces the field volts to 6 or fraction of and drags the output down to 6. Reasonable overcharging did not greatly shorten life of older style batteries. All older cars were in the same situation. Any serious overcharging has to be managed by the Summer/Winter switch and  by use.
Do not prod the cutout or it will lock and heat the dynamo. Disconnect battery to release or pull open.

[Tony Press]

@Tony Press

Thank you for that documents which help to understand. But a question remains.

If the dynamo shall generate 12V - does it works with only a 12V battery or does it need an additional 12V cut out?

Not sure what you mean here- The Austin 7 always had a 6 volt system and I have always kept with this- messing about with a 12 volt conversion has never appealed - keeping it original is most of the enjoyment of a vintage car.

Of course the Austin 7 has a manual system of regulation. With a magneto engine and Lucas SM3 panel,  this is achieved by turning the dynamo on or off . 

The later SM5 panel with the Lucas/CAV dynamo had a field resistor built into the four pole winding with the switch having a full  (winter) charge and half (summer) charge switch.

From the pictures of your special the dynamo appears to be this Lucas/CAV dynamo.

The later Austin 7 Dynamos had external resistors providing the same service.

[Bela]

......- messing about with a 12 volt conversion has never appealed - keeping it original is most of the enjoyment of a vintage car....

I agree - but to fullfill the German rules it is necessary to expand the equipement with flashers, hazzard flashers, 2 stop and rear lights, side-, head and dip light with control lights. That needs more power than the dynamo is able tp deliver. On the other hand LED is not allowed. To leave that dilemma and get the most possible amount of safety in case of shorts in the circuit and in case of an emergency stop I deicided to convert to 12V with some more fuses.

[David.H]

Back to my original problem!
With the engine running I have 7-8 volts at the battery....up from 6.3 at rest. So the dynamo is clearly doing its stuff. Perhaps my problem is with the ammeter!

[Bela]

David

If the ammeter is showing one direction it would be sure that it indicates he other direction too.

Which wiring diagram did you use?

[David.H]

I will copy it & put it out tomorrow if I can
Thanks 
D