Yoy're right, of course, but the frequency of the rectified sine wave would
still be well below the radio frequency range to cause interference. It/s
interesting, John, that you've had a scope on the output. I was thinking of
doing this but no longer have ready access to a 'scope. Was thinking of
going back to my old employer and borrowing the portable. May do that yet.
It's my understanding also that the regulator controlled the voltage output
and hence the charging rate into the battery. I did notice in the Bosch
Automotive Handbook that they mentions the use of zener diodes for the
rectifiers. These would clip the wave form if the regulator couldn't contol
it. Also, good point about an open diode. Wondered what that would do.
Hadn't worked it out yet. I agree with Bill that the best course is to
control the noise at the source. In some cases, like the plasma cutting
machines I worked on, it is just not feasible and we had to make the
circuits immune to the noise. The best method when practiable was physical
separation of the "dirty" wires from the "clean" wires. On our cars that
would mean keeping the cable from the alternator away from all of the other
cables, especially the sensitive ones. It would be interesting to put a
scope on the regulator voltage. I suspect that is where most of the noise
is coming from. If so, then separation of this lead is paramount. As it
usually comes from the "ignition" switch on the dash, that may not be too
easy.
----- Original Message -----
From: "Randall Young" <ryoung@navcomtech.com>
To: <fot@autox.team.net>
Sent: Friday, August 18, 2006 6:19 PM
Subject: RE: [FOT] alternators
>> 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
>
>
> === Help keep Team.Net on the air
> === http://www.team.net/donate.html
|