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New Type BTH Magneto
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<blockquote data-quote="Magnetoman" data-source="post: 52534" data-attributes="member: 2806"><p>The answer is yes, you do need to be careful. Under normal running conditions your plug fires at less than 5 kV so the HT coil never experiences a higher potential than that. However, if you don't earth the plug, in a "normal" magneto the voltage will rise to greater than 20 kV. That puts a lot of stress on the insulation of the coils, and if/when an arc develops between adjacent coils, or between the coil and the housing it creates a tiny conducting channel of carbon (from the burned insulation). That channel doesn't heal itself, and only will continue to grow in the future.</p><p></p><p>I don't know how high the potential gets one of the new BTH magnetos if the lead is left dangling, but it will be a lot more than 5 kV (unless there is some internal equivalent of a spark gap). Also, I don't know how robust the internal electronics are. Either way, you're asking for trouble if you don't earth the plug on any ignition system, including an older points/coil one, because you are putting a lot of additional stress on the system.</p></blockquote><p></p>
[QUOTE="Magnetoman, post: 52534, member: 2806"] The answer is yes, you do need to be careful. Under normal running conditions your plug fires at less than 5 kV so the HT coil never experiences a higher potential than that. However, if you don't earth the plug, in a "normal" magneto the voltage will rise to greater than 20 kV. That puts a lot of stress on the insulation of the coils, and if/when an arc develops between adjacent coils, or between the coil and the housing it creates a tiny conducting channel of carbon (from the burned insulation). That channel doesn't heal itself, and only will continue to grow in the future. I don't know how high the potential gets one of the new BTH magnetos if the lead is left dangling, but it will be a lot more than 5 kV (unless there is some internal equivalent of a spark gap). Also, I don't know how robust the internal electronics are. Either way, you're asking for trouble if you don't earth the plug on any ignition system, including an older points/coil one, because you are putting a lot of additional stress on the system. [/QUOTE]
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