Engines > Restoration of Model Engines

Reconditioning a Stuart Dynamo

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redhouseluv:
Having finished the Stuart compressor, I'm now onto a Stuart Dynamo. I did one of these before and had to change the armature which proved quite pricey!

I have a couple of questions before I start:

Has anyone managed to get 4v out of one of these; even after changing the armature (I didn't change the permanent magnet) and spinning up using a drill the best I managed was 1.5v? The current output is 0.143v, that's not even going to power a small torch bulb!)

This leads to my second question, what exactly is the black gunk which holds the permanent magnet in place, it feels like some sort of semi hardened rubber? It'll come off using a blade, but I need to replace it

How do I know which way round and which way up the permanent magnet goes; this is the innocuous piece of metal in the picture?

Does anyone know of a company that can rewind these armatures; all the companies I have found are for big stuff?

Thanks.................

Jasonb:
Your drill may not be fast enough, you want at least 3000rpm so will have to use a larger drive pully to gear up the speed of the drill.

redhouseluv:
Ah yes, of course I didn't think about that!

I have learnt permanent magnets are not permanent; the one I removed from the old dynamo can barely pick up a nail compared to the new one.......let's see if that makes a difference.....I'm sure iit will, my schoolboy knowledge of electromagnetism says it will!

Roger B:
It is also important that there is no gap between the magnet and the pole pieces.

redhouseluv:
Thank you and yes, I can see how that would be an issue

I need to get the polarity of the magnet right. Having watched some videos, I'm going to borrow the compass from my daughter's science kit; this should tell me the poles of the original magnet and therefore how they were placed into the casing. Using this method, I should be able to identify the poles of the new magnet and position in the correct orientation  :thinking:

I cannot explain how weak the old magnet is, but am hoping it will still deflect a compass needle ...... please......

I'm so glad I marked the magnet before removing it and didn't wash the writing off  :)

Looks like my daughter and I will be having some science fun after school tomorrow, best way to get them interested is to get them involved and away from staring into a screen!

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