Converting classic motorcycle from 6v to 12v

Thread Starter

Bracken16

Joined Jun 24, 2019
5
The current setup is magneto coil earthed to bike frame and output to silicon half wave rectifier which charges battery and supplies lights etc. Simple I thought, take the coil output, connect input to bridge rectifier, conect other rectifier input to bike frame. Now I have full wave rectified output which gives me over 12v when smoothed! So now I connect the -ve output of the rectifier to earyh (bike frame) BUT I ger sparking and the voltage drops to around 5v. It appears the output is then +6v at +ve and -6v at -ve. Someone suggested isolate the AC alternator coil from ground then rectify and THEN connect the negative to earth. But its hard to modify the coil. Any suggestions please! See picture of circuit15613907511637534106092976742104.jpg
 

Alec_t

Joined Sep 17, 2013
12,248
Welcome to AAC!
You can't use a bridge rectifier like that if one end of the coil is grounded, because when the coil output goes negative it is shorted to ground by one of the bridge diodes.
Why do you want to convert the bike to 12V?
 

Thread Starter

Bracken16

Joined Jun 24, 2019
5
Welcome to AAC!
You can't use a bridge rectifier like that if one end of the coil is grounded, because when the coil output goes negative it is shorted to ground by one of the bridge diodes.
Why do you want to convert the bike to 12V?
I have managed now to isolate the coil ground from the frame so problem solved (I hope!).

Converting to 12v for better lighting and to fit 12v cdi. Current ignition is magneto. I shall utilise that coil to supplement power generation for battery, ignition and lights etc.

Many thanks everyone for replying
 
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