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Tech. Advice: Series 'A' 500cc/1000cc Bikes
B.T.H Mag-Dyno
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<blockquote data-quote="Simon Dinsdale" data-source="post: 144249" data-attributes="member: 58"><p>A zener diode will not work and may even damage the Dynamo. Please do not use a zener.</p><p>The BTH mag dyno had no automatic regulator but a very crude form of regulation was done via the rider and the headlight switch position. The switch was wired up to this:</p><p>Off = no charge at all as the Dynamo is isolated from the rest of the bike.</p><p>CH = Dynamo charges the battery through a resistor at half charge rate. No lights on.</p><p>H = Dynamo charges the battery flat out and no regulation at all as the headlight is on And the 1/2 charge resistor is bypassed.</p><p></p><p>The BTH did have a cutout and this was a electro magnet bobbin type which was mounted on top of the toolbox. It looks like it may be a regulator as well but it isn’t. The cutout is purely to stop the battery discharging back through the Dynamo at low RPM and this cutout can be replaced with a basic one direction diode of 10A rating (not a zener). One end of the diode go to the Dynamo output and the other to the harness of the bike but you need to get the polarity of the diode leads the correct way round. Basically cut the wire to the Dynamo and bridge the cut with the diode. I hid the diode behind the toolbox.</p><p>if you are not sure then get somebody local to help who knows electronics otherwise you could end up with a burnt out Dynamo and these BTH units are now rare and it’s difficult to find somebody who can repair / rewind them.</p></blockquote><p></p>
[QUOTE="Simon Dinsdale, post: 144249, member: 58"] A zener diode will not work and may even damage the Dynamo. Please do not use a zener. The BTH mag dyno had no automatic regulator but a very crude form of regulation was done via the rider and the headlight switch position. The switch was wired up to this: Off = no charge at all as the Dynamo is isolated from the rest of the bike. CH = Dynamo charges the battery through a resistor at half charge rate. No lights on. H = Dynamo charges the battery flat out and no regulation at all as the headlight is on And the 1/2 charge resistor is bypassed. The BTH did have a cutout and this was a electro magnet bobbin type which was mounted on top of the toolbox. It looks like it may be a regulator as well but it isn’t. The cutout is purely to stop the battery discharging back through the Dynamo at low RPM and this cutout can be replaced with a basic one direction diode of 10A rating (not a zener). One end of the diode go to the Dynamo output and the other to the harness of the bike but you need to get the polarity of the diode leads the correct way round. Basically cut the wire to the Dynamo and bridge the cut with the diode. I hid the diode behind the toolbox. if you are not sure then get somebody local to help who knows electronics otherwise you could end up with a burnt out Dynamo and these BTH units are now rare and it’s difficult to find somebody who can repair / rewind them. [/QUOTE]
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Tech. Advice: Series 'A' 500cc/1000cc Bikes
B.T.H Mag-Dyno
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