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RE: [FOT] alternators

To: <fot@autox.team.net>
Subject: RE: [FOT] alternators
From: "Randall Young" <ryoung@navcomtech.com>
Date: Fri, 18 Aug 2006 16:19:38 -0700
> Therefore, the waveform going into the battery and electrical
> system is made
> up of 6 half sine waves at double the frequency of the
> alternator, i.e. if
> the alternator is turning 6000 RPM, 100 revs per second or 100 HZ, the
> frequency of the half sine waves is 200 HZ.

Tim, you're assuming the alternator only has two poles.  Real units have
more than two poles, typically 10 or 14.

> I'm not
> aware of any automotive system that used capacitors in the alternator
> circuit for smoothing the sine waves or for noise suppression.

I have had to add capacitors to auto stereos, to eliminate "alternator
whine".  Recently helped someone else, whose "rearward looking radar"
wouldn't work right without some power line filtering.

It's also worth noting that an open (or shorted) output diode will cause a
big increase in the output noise.

> But on the cars they were used on there were little if any
> electronics to be affected.

Unless of course the owner tries to add some, like a CB radio ...

Randall



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