AC VOLTAGE

[chiz]

Hi just quick question... It has been reported elsewhere that bike alternators produce about 20 to 30 vac between each alternator wire at idle and may go as high as 50 to 70 vac at 5000rpm.. Is this generally true?
Chiz

[fj1289]

I don't know your answer, but here's a couple rabbit holes you may find some relevant info.  I followed the second one years ago to make a rectifier for my XS650 cafe/rat/bobber

https://www.google.com/amp/s/www.instructables.com/How-to-make-a-reliable-motorcycle-voltage-regulato/%3famp_page=true

http://www.chopcult.com/forum/showthread.php?t=17378

[HydroDog]

Well I'm not sure on the FJ but on my KTM it put out over 30 volts.

[Waiex191]

Our alternators are permanent magnet generators (PMGs) and have a 3 phase AC output.  The voltage will vary with load and speed.  More load, less voltage.  More speed, more voltage.  My 1981 Suzuki GS650E had something like 80 volts RMS open circuit from leg to leg at some RPM above idle, I forget the RPM as that was a long time ago.  So that AC voltage goes through a rectifier and then a buck converter to make it ~14VDC.

Those stators used to fail and they would be down around 20VAC open circuit when the battery would not charge anymore.  I assume the insulation breaks down and you get stator coils shorted out.

At my company we build aircraft generators for transport category aircraft.  They all have PMGs to power the generator control unit.

[chiz]

OK   So I saw an instructor and students do testing on modern bike and he demonstrated the AC output from the alternator. It was a bit shocking to see the amount of AC being produced I know nothing about rectifiers but wonder how they handled all this juice ... quite well it turns out. It's surprising the number of riders that reject the high AC output as poppycock.
Chiz