I hope that someone can help. I have dismantled my Ruby's dynamo to overhaul it and fit new brushes. It has not been in use for a long time and the terminal block on the outside is missing, meaning that the wires have been free to flap about. One of them was very wobbly when I got it and it has now fallen off.
I am left with one wire which runs comes outside of the body and has red insulation and another with black insulation which remains inside the body. The wire which fell off is quite thick, has black insulation and which ran out of the body, along with the red wire. There is 1 ohm resistance between the two remaining wires and no connection to earth from either. I have tried to remove the large screws which retain the coils, but to no avail.
Is there anything which I can realistically do to repair this or is time to look for a replacement? I plan on converting to 12 volts, if that makes ny difference.
If you plan on doing a proper and reliable conversion to 12 volts you'll need to replace the field coils with a pair wound for 12 volts. I'd worry more about removing the screws that hold the coils into the casing than the condition of the 6 volt coils.
I am not sure whether this will assist you, Jamie, but I attach a copy of two pages from the 1939 edition of The Motor Electrical Manual showing the internal wiring for a three brush dynamo.
Sorry that they are on their side. If I try to orientate them correctly, they become too small to read the print!
(01-06-2020, 04:12 PM)Jamie Wrote: I hope that someone can help. I have dismantled my Ruby's dynamo to overhaul it and fit new brushes. It has not been in use for a long time and the terminal block on the outside is missing, meaning that the wires have been free to flap about. One of them was very wobbly when I got it and it has now fallen off.
I am left with one wire which runs comes outside of the body and has red insulation and another with black insulation which remains inside the body. The wire which fell off is quite thick, has black insulation and which ran out of the body, along with the red wire. There is 1 ohm resistance between the two remaining wires and no connection to earth from either. I have tried to remove the large screws which retain the coils, but to no avail.
Is there anything which I can realistically do to repair this or is time to look for a replacement? I plan on converting to 12 volts, if that makes ny difference.
Regards,
Jamie.
I fitted 12 volt, higher resistance, field coils into my 1934 dynamo.
If you look for a replacement it might be no better than what you have already. What is the present armature like?
As for the two screws holding the field coils in... With the dynamo casing in a vice, hit the screws direct with a hammer. Point a blowlamp at the screw for a while. Then use a blunt centre punch and a medium sizes hammer to tap the screw around. They will come loose!
01-06-2020, 09:25 PM (This post was last modified: 01-06-2020, 09:28 PM by Bob Culver.)
On the Seven one main brush is earthed so only two wires emerge.
I assume you do not have an early 4 pole (4 field coils) dynamo where the brush locations differ and there can be further complications. Otherwise the only normal resistance vaguely about 1 ohm is the field coils.
The merits and not (esp in age of LEDs) been extensively covered before. Also the many 12v conversions from the very simple retaining 3 brush to the complex with electronic regulators and rewound fields. Many have retained the original field but with the voltage applied at least twice the original some particular provision is necessary to moderate the field current. As with the car on 6v great care is necessary not to exceed max armature current. Note the original lamp bulbs were only 18w each.
All should be available via Search.
Some opt for a token charge in the car and maintain with a smart bench charger.
Thank you for all of the replies and the scanned pages from the The Motor Electrical Manual. Having had a couple of cups of tea, looked at the scans which David posted and cast my mind back to when I dismantled the dynamo last summer, I realised that the only reason that the wire fell out was because I had unscrewed it from the brush holder........ How to feel like a twit.
Finally, I have managed to reassemble the dynamo. It seems to be a hybrid of sorts. The case says C35M, the nose cone is the style on the CAV dynamo and the third brush (middle) is fixed, not movable.
Testing it: I have bridged the field and dynamo leads in the terminal block on the outside and spun it slowly using a drill. The generates a couple of volts. I then put it on a 12v car battery, as described on the Cornwall Austin Seven website. It spins nice and quickly.
The same website then says to put a voltmeter between the wires on the terminals and the case to test the output voltage. Surely, though, this will pick up the input voltage from the car battery and give a false reading?
The voltmeter test refers to when it is spinning either on the car or by whatever means you contrive to drive it on the bench. If you are considering a proper 12v conversion with new field coils I suggest contacting EICS at Lincoln, https://www.eics-products.co.uk
