not charging
not charging
My 12/4 is not charging. To decide if the problem lies with the dynamo or the cut out if I disconnect the two wires from the dynamo and attach a 12 volt bulb to the terminals ,am I right in assuming the bulb should light up? I know this question will probably sound laughable to the experts but I just need conformation please. Regards Colin
Re: not charging
Hello Colin
The short answer is "No".
A longer answer is "Maybe, it depends on the wattage of the bulb".
Here goes with an even longer answer!
I am assuming you have the 3-brush 12volt dynamo system as fitted by Austin although this applies equally well to the 6volt cars.
The terminals are normally marked D or D+ and F. D is dynamo output and F is Field.
The switch on the dashboard connects D to F so the dynamo output is now fed to the field windings. Current flows in the field windings producing a magnetic field which induces a current in the rotating armature. This current now flows via the cut-out to charge the battery.
If you connect a bulb between D and F you will (should) get a small current to flow in the field windings but not as much as normal operation and unlikely to be enough to make the bulb light. You may get a bit of a glimmer from a low wattage bulb
If you don't have a meter handy, a better way to test the dynamo is disconnect the two wires to the dynamo and tie back so they don't touch anything. Connect terminals D and F together and then connect a bulb between D+F and ground, i.e. body of dynamo. Run the engine at low speed and the bulb should light.
A word of caution here as the 3-brush system relies on the battery for voltage stabilisation. With no battery connected the dynamo output voltage can (will) rise to 30, 40 or even 50 volts if run at high enough speed which of course will blow the bulb!
There are a couple of points I would add here. If this proves to be a dynamo fault the most likely cause would be brushes either worn down or stuck. I did mention if you have a meter handy. If you are tempted to obtain one avoid the digital types. They will not give a stable reading on fast changing voltages. You need a moving coil type which will have sufficient dampening to give a stable reading
Hope this helps and sorry for the verbosity!
Martin (KO870)
The short answer is "No".
A longer answer is "Maybe, it depends on the wattage of the bulb".
Here goes with an even longer answer!
I am assuming you have the 3-brush 12volt dynamo system as fitted by Austin although this applies equally well to the 6volt cars.
The terminals are normally marked D or D+ and F. D is dynamo output and F is Field.
The switch on the dashboard connects D to F so the dynamo output is now fed to the field windings. Current flows in the field windings producing a magnetic field which induces a current in the rotating armature. This current now flows via the cut-out to charge the battery.
If you connect a bulb between D and F you will (should) get a small current to flow in the field windings but not as much as normal operation and unlikely to be enough to make the bulb light. You may get a bit of a glimmer from a low wattage bulb
If you don't have a meter handy, a better way to test the dynamo is disconnect the two wires to the dynamo and tie back so they don't touch anything. Connect terminals D and F together and then connect a bulb between D+F and ground, i.e. body of dynamo. Run the engine at low speed and the bulb should light.
A word of caution here as the 3-brush system relies on the battery for voltage stabilisation. With no battery connected the dynamo output voltage can (will) rise to 30, 40 or even 50 volts if run at high enough speed which of course will blow the bulb!
There are a couple of points I would add here. If this proves to be a dynamo fault the most likely cause would be brushes either worn down or stuck. I did mention if you have a meter handy. If you are tempted to obtain one avoid the digital types. They will not give a stable reading on fast changing voltages. You need a moving coil type which will have sufficient dampening to give a stable reading
Hope this helps and sorry for the verbosity!
Martin (KO870)
Re: not charging
Hi Martin
Wow I am so impressed with your reply, your expertise has helped me immensely. Too hot to get involved today but will have a play in the next couple of days, I will let you know how I get on. Many thanks to you Colin
Wow I am so impressed with your reply, your expertise has helped me immensely. Too hot to get involved today but will have a play in the next couple of days, I will let you know how I get on. Many thanks to you Colin
Re: not charging
Hello everyone.
Regarding my faulty dynamo I have sourced a working CAV replacement, very lucky. I need to remove the drive coupling from my faulty dynamo and fit to the replacement. I have decided to send faulty one away to specialist.
Could anyone one please advise me on the removal of the coupling, I see it has a keyway and before I apply a puller is there a retaining screw I cannot see.
Hope one of you experts can advise
Best regards Colin
Regarding my faulty dynamo I have sourced a working CAV replacement, very lucky. I need to remove the drive coupling from my faulty dynamo and fit to the replacement. I have decided to send faulty one away to specialist.
Could anyone one please advise me on the removal of the coupling, I see it has a keyway and before I apply a puller is there a retaining screw I cannot see.
Hope one of you experts can advise
Best regards Colin