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Two recent posts have told us how the owners connected the battery the wrong way.

Once upon a time, before alternators, there were generators that had a regulator thing that could be adjusted to control the amps / volts being sent to the battery. My Ford 9N tractor had a generator. It now has an alternator and electronic ignition. But that is not the story. Some vehicles had the battery connected positive to earth / ground. Henry Royce an electrical engineer did this. It had something to do with corrosion I think, but I do not know the whole story.

The problem with that is, you can not use halogen head lights, or a CD player. The battery needed to be changed to negative to ground, which was easy enough to do. But the generator has other plans. To rearrange its thinking, the sparky would flash the generator with a battery and cables, and most times that was enough to change the attitude of the generator to charge with a negative to ground system.

I write this, to suggest to folks to check the charging rate, after wyring the battery the wrong way around. It may not rearrange the alternator's identity, but it is best to check. It probably will just blow a fuse. I have not done it, so I do not know for sure.

I have had the generator flashed as above.

UK
 

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More likely, the rectifier/regulator will sacrifice itself to protect the fuse; this is based the schematics for my Valkyrie and the Suzuki I used to have. My old CB450 has no fuse between the r/r and battery, so the rectifier will just smoke. Some bikes may survive, but I don't think many will. I think one should try testing the r/r before connecting the battery the right way around, as you may just do more damage.
 

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Moderator - Loves All Motorcycles
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The one time I connected a battery the wrong way was with a Chinese scooter. It promptly blew the fuse to the battery and no harm was done. :)
 

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We had to "flash the generator" on my buddy's '68 XLCH chopper, but that is a DC generator on a bike that has no battery, and uses a magneto for ignition and the power from the generator for lights and horn only.

I'm fairly sure that "flashing" to create polarized residual magnetism in the field core windings is not needed for alternators on bikes with batteries. The regulator will power the field from the battery, and because the power generated is AC, the stator doesn't care what polarity the magnetic field is. Pretty sure flashing is not needed for bikes that use permanent magnetic rotors either. In this case there's no field coil and the magnet field is created with the permanent magnets, and I don't think that the stator needs to be magnetically active to generate power. This is my understanding, but I could be wrong, I'm a mechanical engineer, not electrical.

Still a bad idea to connect your battery backwards, though, something to be avoided.
 
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