----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----
OK, Jack. Here goes: The alternator whine you hear is actually non-constant DC. The alternator itself has no inherent filtering. What it produces is a series of half-sine waves. If you visualize a never ending row of hills, that's what the signal on the alternator output looks like. The peaks are about 15-16 volts. The alternator is actually a three-phase device which means the valleys never to to zero but there is still significant ripple on the output. The electronics sees this ripple on the DC bus as an AC signal superimposed on the DC. Much of the ripple is filtered or "absorbed" by the battery. The battery behaves to the AC ripple like an extremely large capacitor. That's why the battery connections are one of the first things to check when trying to find an alternator whine problem. Even with a good battery, there is still a small amount of ripple on the alternator output. Another source of alternator whine is called a "ground loop". This is not the same thing as dragging a wingtip in the dirt! To complete the charging path of battery, manufacturers connect the negative side to the airframe. The circuit is completed through the engine mount, engine, and grounding braid from the engine to the airframe. When avionics are grounded to the airframe at random, part of the airframe path for the charging circuit is common to the avionics power circuit. Thus, the noise is induced into the ground side of the avionics power wiring. It is possible to get charging system noise from a generator, too but the frequency will be higher because of the higher commutation rate and more easily filtered by the battery. Another prime source of avionics noise is the power supply for navigation strobe lights. They draw a considerable amount of current for a short time and they are usually grounded to the airframe wherever the power supply is located. They are usually not powered directly from the battery, either. I hope this answers your question and I hope I haven't bored anyone to death. Dave Jack Lewis wrote: > ----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]---- > > > The high current AC is > > converted to DC by solid state diodes - no high current moving parts. > > Sorry to bore you with a doctoral dissertation on alternators but the > > article is well written and informative. > > Dave > > N93971 > > You seem to know what you are talking about. Now explain where the whin is > coming from. Is it the Alternator or the Voltage Reg. > > I think my alternator will, sometimes, put out AC voltage. > > Jack > > __________________________________________________ > To unsubscribe from this list please send mailto:[EMAIL PROTECTED] > > ____________________________________________________________ > T O P I C A -- Learn More. Surf Less. > Newsletters, Tips and Discussions on Topics You Choose. > http://www.topica.com/partner/tag01 __________________________________________________ To unsubscribe from this list please send mailto:[EMAIL PROTECTED] ____________________________________________________________ T O P I C A -- Learn More. Surf Less. Newsletters, Tips and Discussions on Topics You Choose. http://www.topica.com/partner/tag01
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