It’s a Dunn deal…
THE BIG FIX
Didn’t have room for this in the 3T project update this month, but when I ordered the new armature from dynamo specialist Paul Dunn, we had a chat in which I picked up a few interesting tips.
Paul recommends solid state regulators over original mechanical; they consume less current - but quality varies. He’s found some cheap ones marked wrongly for earth polarity – they blow as soon as connected, so not much of a saving there! Paul generally rates the Podtronics unit.
He says it’s seldom worth trying to repair an armature – especially if there are signs of ‘spark erosion’ between the segments. That’s a sure sign of failure, usually caused by the dynamo being overloaded – either by the regulator being set too high or a short circuit.
Current is produced by rotating a wire coil inside a magnetic field. A dynamo’s field is produced by an electromagnet powered by the dynamo itself, so in unregulated form a dynamo is self-fuelling and will keep increasing current cyclically... not infinitely, because the magnet eventually becomes ‘saturated’ and can’t get any stronger, but it’s enough to get it very hot and bothered and a short circuit can easily burn it out. As for setting the regulator too high, I had a mate once who did a ‘12v conversion’ on his 650 Ariel simply by winding out the regulator screw. Certainly it lit a 12v Halogen headlight – but from what Paul says, I doubt the dynamo would have put up with that indefinitely. That said, I’ve generally found that these units are pretty tough in normal use and tolerate a surprising amount of abuse – but if yours has given up and needs sorting, you can reach Paul on 01782 856839.