Larry, full wave retification would result in a voltage regulator that would be rather large, as you would have to apply a full wave bridge to each phase winding in the stator. And ground would float between the positive and negative outputs. The is no need for producing a negative voltage in automotive applications. So, instead of having 3 diodes, you would end up with 3X4 (4 diodes in a FWB config)or 12 diodes. Are we there yet???

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.