E3N Armature Winding Resistance To Earth

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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E3N Armature Winding Resistance To Earth

Postby 59G3LS » Sun Aug 13, 2017 5:12 am

Hi All,

I was so happy to have finally found an E3N dynamo, even with an incorrect sprocket fitted. I tried the drill test but had no output at all, then found one of the brushes was solid in it's guide due to corrosion. With that remedied, I was only able to achieve around 5 volts of output. After stripping and cleaning, field coil looks good at 3 ohms with no path to earth, commutator segments are all 0.5 ohms to the diametrically opposite segment and each segment is 0.2 ohms to the adjacent segment. Finally, there is a reading to earth from all segments. There seems to be some capacative effect as the reading starts at around 500K ohms, finally settling at 4.5M ohms. Obviously infinite resistance is ideal but is 4.5M abnormal?

Thanks in advance

Mark - Perth Australia

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Re: E3N Armature Winding Resistance To Earth

Postby Groily » Sun Aug 13, 2017 7:08 am

Given that dynamo removal and refitting is such a poisonous job on these, I think you are right to be picky here!

Field resistance is about right (3.2ohms officially I think) and the measurements across the segments of the comm sound right too.
The armature may very well be functional with a resistance that high from windings to earth but the proof of the pudding will be in the tests under load you do next. It's to be hoped you'll have improved on the weak performance of the previous attempt.

With D and F bridged, if the thing motors smoothly (for starters) and then produces enough juice (say 5 amps if you're measuring) to:
* light fully a 30W or 35W 6v headlamp bulb . . .
* while maintaining 7v output . . .
* by about 2200 dynamo rpm

then it's almost certainly fine.

Without load on it should produce its 7v by 1500 rpm of the armature, ideally a few fewer rpm.

Given that replacement parts are actually quite easy for these (but I appreciate there are postage costs from where you are), and given the unpleasant nature of having to open the primary side in the event of woe, in case of doubt I'd err on the side of caution and replace the crucial bits. I'd also get a decent modern regulator to protect the thing against being overfed by a maladjusted mechanical regulator, but that's another matter.

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Re: E3N Armature Winding Resistance To Earth

Postby 59G3LS » Mon Aug 14, 2017 9:09 am

Thanks Groily,

I'll get some new brushes and give it the load test you have described.

I'll let you know how it goes..

Regards - Mark

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Posts: 15
Joined: Wed Oct 12, 2005 9:45 pm
Location: WA AUSTRALIA

Re: E3N Armature Winding Resistance To Earth

Postby 59G3LS » Mon Aug 21, 2017 12:25 am

As this previously unknown dynamo had signs of corrosion internally, I thought I'd give the armature an afternoon relaxing on the windowsill in the winter sunshine.
It obviously enjoyed it as commutator resistance to earth rose from around 5M ohms to 10M ohms, so I gave it an entire weekend sunning itself and hey presto we
now have an infinite reading to earth. I can only assume that water got in at some time and maybe it was subsequently stored in a damp environment. However it
now looks we're all good to go.

Thanks Groily

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Re: E3N Armature Winding Resistance To Earth

Postby Groily » Mon Aug 21, 2017 6:45 am

Nothing like a dry spell on a sorcerer's window ledge then!
I'll bet it works OK.

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