Author Topic: checking miller alternator.  (Read 2848 times)

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Offline kncken

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checking miller alternator.
« on: 14 Feb 2014 at 19:06 »
     How does one check the Miller alternator 'on the bench'? My Dragonfly is still dismantled and I would like to check the stator and rotor before fitting to the bike. Perhaps I should forget it and fit a new modern item? Any suggestions would be much appreciated.


Offline eddie

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Re: checking miller alternator.
« Reply #1 on: 14 Feb 2014 at 20:27 »
About the only checks that can be done with the alternator out of the engine are, a) a continuity check to make sure the windings are sound, and b) an earth leakage check to make sure the individual coils are not leaking to earth. Even having done these checks, there may still be problems with the stator. On a unit I was intending to use on a bike that has been converted to 12 volt, the unit functioned correctly to start with, but then gradually faded until no charge was being generated. Having been washed out and blown out with compressed air, the same would happen again - I came to the conclusion that the unit had come from a badly worn engine and had become impregnated with metal laden sludge which, under the effect of the magnetic field, would gradually produce a track to earth. I considered using a modern replacement but the new units are slightly fatter than the original Miller unit, and there wasn't enough room in the timing chest - so the only solution was to rewind the Miller coils (which I eventually encapsulated in resin to prevent any re occurrence of the original problem). The new coils have the same gauge wire and the same number of turns as the originals, but the rewound unit gives a good 8 amps charge at 12 volts - 96 watts (not bad for a unit that was originally rated at 60 watts!)

  Eddie.

Offline kncken

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Re: checking miller alternator.
« Reply #2 on: 18 Feb 2014 at 18:20 »
Eddie, many thanks for your reply, all of which was food for thought. Yesterday I offered up an alternator from a 1960 Norton Model 50 I once owned, and it does look a bit hopeful ..... Thanks again,Ken Playfoot.  p.s. Is direction of rotation an issue with alternators,Iwonder ?

Offline eddie

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Re: checking miller alternator.
« Reply #3 on: 18 Feb 2014 at 19:48 »
Hi Ken,
            Lucas and Miller alternators are not direction sensitive. They just give off AC current in either direction - the polarity is governed by the rectifier.

      Eddie.

Offline kncken

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Re: checking miller alternator.
« Reply #4 on: 25 Feb 2014 at 17:02 »
   Thanks once again,Eddie,very helpful. Best wishes,Ken.

 

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