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Tech. Advice: Series 'A' 500cc/1000cc Bikes
B.T.H Magneto-Generator Series 'A' Comet
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<blockquote data-quote="Chris. S" data-source="post: 154404" data-attributes="member: 4018"><p>Hi all. By chance I restored a BTH, permanent magnet dynamo, during lockdown. On test, after a thorough overhaul, including commutator skim on the lathe, it would produce barely 9 volts, with no load; and could just light a 6 watt bulb reasonably brightly, at approx 2000 rpm, on the magneto shaft. The windings tested o.k, so I recharged the magnets on an old magnetiser.</p><p>It now produces 15 volts, no load; and can light an 18 watt bulb. </p><p>Whilst experimenting with cut outs and diodes, I found that the BTH cut out required over one tenth of an amp to energise it. A not insignificant part of the dynamos tiny output. Experimenting with diodes, proved that they mostly dropped the dynamo output by around half a volt. This would be the difference between charging and not charging at lower rpm. I eventually found a special diode, developed for use with solar panels, to be the best; with just a few millivolts drop. Texas Instruments SM74611, for anyone who wants to experiment. </p><p>Regarding automatic battery charge control. Because of the vey low maximum output current, a simple transistor, series regulator, should do the job; or go with Vic's solution. The modern boost/buck convertor will accept a wide range of input voltages; and provide a, user preset, maximum output voltage. Their efficiency is often over 90 per cent.</p><p>Cheers, Chris.</p></blockquote><p></p>
[QUOTE="Chris. S, post: 154404, member: 4018"] Hi all. By chance I restored a BTH, permanent magnet dynamo, during lockdown. On test, after a thorough overhaul, including commutator skim on the lathe, it would produce barely 9 volts, with no load; and could just light a 6 watt bulb reasonably brightly, at approx 2000 rpm, on the magneto shaft. The windings tested o.k, so I recharged the magnets on an old magnetiser. It now produces 15 volts, no load; and can light an 18 watt bulb. Whilst experimenting with cut outs and diodes, I found that the BTH cut out required over one tenth of an amp to energise it. A not insignificant part of the dynamos tiny output. Experimenting with diodes, proved that they mostly dropped the dynamo output by around half a volt. This would be the difference between charging and not charging at lower rpm. I eventually found a special diode, developed for use with solar panels, to be the best; with just a few millivolts drop. Texas Instruments SM74611, for anyone who wants to experiment. Regarding automatic battery charge control. Because of the vey low maximum output current, a simple transistor, series regulator, should do the job; or go with Vic's solution. The modern boost/buck convertor will accept a wide range of input voltages; and provide a, user preset, maximum output voltage. Their efficiency is often over 90 per cent. Cheers, Chris. [/QUOTE]
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Tech. Advice: Series 'A' 500cc/1000cc Bikes
B.T.H Magneto-Generator Series 'A' Comet
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