Accuspark Dynamator No longer available

[Stuart Giles]

A few days ago, I was looking at a charging issue on a friend's car where it became apparent that the despite the car's electrics being OK, the Dynamator wasn't charging. As said Friend needs the car for a an organised 'run' event in less than two weeks, it was decided to buy a new Dynamator and send the original back to Accuspark for repair. 

My friend was informed by Accuspark that they are no longer producing the A7 Dynamator, they currently have no plans to get any of these A7 specific items produced and that they had no spare parts in stock. So, having overhauled generators in my 'hands on' days at work, and mended a fair few modern car alternators over the years, I decided to have a go at the faulty Dynamator.



Having taken off the distributor drive end, it revealed the internal wiring, slip ring brushes and regulator. Initial joy at finding a dodgy connection on the internal D+ wiring was short lived as the D+ circuit to the chassis earth was still dead. Testing across the slip rings should result in a very low resistance, somewhere around 5 ohms; this was showing a very high resistance which I suspected was coming from the regulator which is in parallel with the brushes.



testing the rotor winding resistance with the rotor removed from the Dynamator showed an open circuit. There's no visible break in the copper windings. 



Until now, every single Alty I've rebuilt has either had knackered brushes, a faulty regulator or faulty diodes. As these items are fairly generic, they can usually be substituted with other bits. 
e.g. that regulator in the second picture which Google can't find an exact replacement for, could be replaced with this from ebay once the redundant brush gear is chopped off. https://www.ebay.co.uk/itm/123618455701?mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338722076&toolid=10001

Using a tiny permanent magnet Alty, I am engineering a replacement setup for this 12v A7 now, but if someone has a dead Dynamator that possibly has a good rotor inside, I'd be happy to hear from you.

Good work! From your description, the Chinese-made rotor is dead, unable to be revived and fit only for the scrap bin?

Yes, the rotor is done for. It's difficult to see from my picture, but the appearance of the actual coil winding wouldn't have made it past the QA people where I used to work; still surprising that it's failed though.

Hi Stuart
How can the brush gear be redundant please?   ( My experience limited to replacing brushes. incidentally any trace of grease on seems to hugely accelerate wear). Do you proposes some sort of regulation of the actual output as acheived  for PM motorcycle alternators by means unknown to me?
A wiring open without cooking would presumably be unususal. I cannot recall the setup but would rewinding be difficult

Bob, the regulator I hyperlinked in my original post, like most modern alternator regulators, has the brush carriers and brushes as an integral part of the unit. To use it in the Dynamator these bits need to be removed as the Dynamator has a discrete brush carrier setup. Which the 'new' regulator would be connected to with a pair of wires soldered onto its 'D' and 'F' connections.