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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Aftermarket magneto slip rings
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<blockquote data-quote="Magnetoman" data-source="post: 46384" data-attributes="member: 2806"><p>For convenience, I've simply cut/pasted information on this I wrote on BritBike Forum:</p><p></p><p><em><strong>Originally Posted By: Ken Tee</strong></em></p><p> <em><strong>The instrument I use has a spark generator that produces a 50 Hz spark across a 3-point test gap ... the component connected in parallel with spark gap. A good component has a negligible effect on the required driving current. The extra current required is a good indication of how leaky the component is. </strong></em></p><p></p><p> Both the Merc-o-tronic and Eisemann testers I discussed in my Bosch magneto restoration thread directly measure the primary current required for the secondary to jump an 8 kV 3-point test gap. Also, the normal way I use both instruments has the slip ring as part of the circuit. However, the point is, the aftermarket slip ring I diagnosed at: </p><p></p><p><a href="http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=507338#Post507338" target="_blank">http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=507338#Post507338</a></p><p></p><p>was fine when new but failed after ~2000 miles of operation. Because of the very high resistance of the resin that I measured (TOhms) this slip ring almost certainly had negligible leakage when new and would have easily passed such a spark gap test. However, it would have been quite incorrect to conclude it was a "good component" based on a spark gap test lasting only a few minutes because it would require running the tester for over 60 hours at 50 Hz for the slip ring to accumulate the internal degradation caused by 2000 miles of usage. </p><p></p><p><em><strong>Originally Posted By: Ken Tee</strong></em></p><p> <em><strong>...I'm not sure that the 1000 Tohm meter mentioned above, or the 20 Gohm meter or 5 Tohm meters mentioned in the other thread, would be up to the job of detecting a failed component when one doesn't know in advance that it has failed. </strong></em></p><p></p><p> This is precisely the point. For reasons I have discussed in detail neither a resistance meter nor a spark tester is appropriate for determining in advance the likelihood an aftermarket component like a slip ring will fail in only a few thousand miles. </p><p></p><p>Further, as I wrote about the slip ring, <em>"...the failure mode of this slip ring has resulted in me now investigating other ways for stress-testing slip rings that could be used by people who don't have the specialized instruments that I have available to me."</em> Rather than accepting assurances that they just bought a "good component," I am looking into ways to provide people with a test they can do themselves to know whether or not this is the case.</p></blockquote><p></p>
[QUOTE="Magnetoman, post: 46384, member: 2806"] For convenience, I've simply cut/pasted information on this I wrote on BritBike Forum: [I][B]Originally Posted By: Ken Tee The instrument I use has a spark generator that produces a 50 Hz spark across a 3-point test gap ... the component connected in parallel with spark gap. A good component has a negligible effect on the required driving current. The extra current required is a good indication of how leaky the component is. [/B][/I] Both the Merc-o-tronic and Eisemann testers I discussed in my Bosch magneto restoration thread directly measure the primary current required for the secondary to jump an 8 kV 3-point test gap. Also, the normal way I use both instruments has the slip ring as part of the circuit. However, the point is, the aftermarket slip ring I diagnosed at: [URL]http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=507338#Post507338[/URL] was fine when new but failed after ~2000 miles of operation. Because of the very high resistance of the resin that I measured (TOhms) this slip ring almost certainly had negligible leakage when new and would have easily passed such a spark gap test. However, it would have been quite incorrect to conclude it was a "good component" based on a spark gap test lasting only a few minutes because it would require running the tester for over 60 hours at 50 Hz for the slip ring to accumulate the internal degradation caused by 2000 miles of usage. [I][B]Originally Posted By: Ken Tee ...I'm not sure that the 1000 Tohm meter mentioned above, or the 20 Gohm meter or 5 Tohm meters mentioned in the other thread, would be up to the job of detecting a failed component when one doesn't know in advance that it has failed. [/B][/I] This is precisely the point. For reasons I have discussed in detail neither a resistance meter nor a spark tester is appropriate for determining in advance the likelihood an aftermarket component like a slip ring will fail in only a few thousand miles. Further, as I wrote about the slip ring, [I]"...the failure mode of this slip ring has resulted in me now investigating other ways for stress-testing slip rings that could be used by people who don't have the specialized instruments that I have available to me."[/I] Rather than accepting assurances that they just bought a "good component," I am looking into ways to provide people with a test they can do themselves to know whether or not this is the case. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Aftermarket magneto slip rings
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