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'[EE] Alternator Whine Simulator'
2007\06\04@173821 by Carey Fisher

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I need to simulate alternator whine on a power supply so that I can
design a whine filter. (No, I'm not gonna use it on the kids...)
The specs are:  Power Supply is 12-14VDC and will supply about 1 A
to the Unit Under Test (UUT).  I want to be able to superimpose a 800-2000 Hz
sine wave (and/or triangle, square, whatever) on the supply line at .5Vp-p to maybe
6Vp-p.  I have an audio sig gen but I tried capacitive coupling to the
DC line and, of course, the input Z of the UUT is too low for good
results.
Anybody got any ideas on how to do this simply?
Thanks,
Carey


2007\06\04@175851 by Peter P.

picon face
Alternator 'whine' is the result of 3-phase rectitication in a full bridge
without suppression. Imho using a power amplifier to feed power to your circuit
using the signal generator as input and a simple bridge rectifier and cap should
come close. And also how to best get rid of the whine (by decoupling the bridge).

Peter P.


2007\06\04@181307 by microbrix

picon face
On 6/4/07, Carey Fisher <spam_OUTcareyfisherTakeThisOuTspamncsradio.com> wrote:
> I need to simulate alternator whine on a power supply so that I can
> design a whine filter. (No, I'm not gonna use it on the kids...)
> The specs are:  Power Supply is 12-14VDC and will supply about 1 A
> to the Unit Under Test (UUT).  I want to be able to superimpose a 800-2000
> Hz
> sine wave (and/or triangle, square, whatever) on the supply line at .5Vp-p
> to maybe
> 6Vp-p.  I have an audio sig gen but I tried capacitive coupling to the
> DC line and, of course, the input Z of the UUT is too low for good
> results.
> Anybody got any ideas on how to do this simply?
> Thanks,
> Carey
>
>
> -

2007\06\04@181419 by microbrix

picon face
big audio amplifier, and capacitive coupling, or use an lm-12 opamp,to
just do a 5A output mixer

On 6/4/07, Carey Fisher <.....careyfisherKILLspamspam@spam@ncsradio.com> wrote:
{Quote hidden}

> -

2007\06\04@185837 by Marcel Duchamp

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Carey Fisher wrote:
> I need to simulate alternator whine on a power supply so that I can
> design a whine filter. (No, I'm not gonna use it on the kids...)
> The specs are:  Power Supply is 12-14VDC and will supply about 1 A
> to the Unit Under Test (UUT).  I want to be able to superimpose a 800-2000 Hz
> sine wave (and/or triangle, square, whatever) on the supply line at .5Vp-p to maybe
> 6Vp-p.  I have an audio sig gen but I tried capacitive coupling to the
> DC line and, of course, the input Z of the UUT is too low for good
> results.
> Anybody got any ideas on how to do this simply?
> Thanks,
> Carey
>
>
I would look at opening the supply up and feeding the AC into the
reference point of the regulating circuit, assuming there is one. You
will need to check it's AC response over the range of interest but if
this works, it will be far easier than trying to push the output around.

If you absolutely have to push the output around, try isolating it with
as big a resistor as your setup can tolerate.

2007\06\04@192034 by Bob Blick

face picon face
Hi Carey,
I've done it before. Couple it to the circuit with the
output of a transfomer in series with the positive
output of your power supply. Drive the primary of the
transformer with an audio amplifier.

You can get fancy with your choice of signal, but it
doesn't really matter. A triangle wave isn't a bad
choice, but a sine wave is fine, too.

All this reminds me of a 1981 Chevy Luv pickup I once
owned, that developed a dead diode in the alternator.
It still charged enough, pretty much, but the ripple
was 4 or 5 times higher.

Cheerful regards,

Bob


2007\06\04@200545 by Carey Fisher

face picon face
Peter,
Thanks for your response.  I've got an old stereo amp around here I'll try.
Thanks!
Carey

Peter P. wrote:
> Alternator 'whine' is the result of 3-phase rectitication in a full bridge
> without suppression. Imho using a power amplifier to feed power to your circuit
> using the signal generator as input and a simple bridge rectifier and cap should
> come close. And also how to best get rid of the whine (by decoupling the bridge).
>
> Peter P.
>
>
>  

2007\06\04@200655 by Carey Fisher

face picon face
Thanks.  I'll try the amp with an old stereo amp I have.
Carey

microbrixspamKILLspamgmail.com wrote:
{Quote hidden}

>> --

2007\06\04@200923 by Carey Fisher

face picon face

Marcel Duchamp wrote:
{Quote hidden}

Marcel,
The thought occurred to me but I dismissed it as "too hard" and not sure
it'll work but it does
sound like a good approach.  Thanks!
Carey

2007\06\04@201433 by Carey Fisher

face picon face
Bob,
Thanks!  Using the transformer sounds like a real workable solution.
I'll dig out an old stereo amp, a transformer and see what happens.

We've got some customers that use "heavy duty" alternators and they
report whine that others with stock alternators don't have (or just don't
report).  And I don't have whine in my vehicle so I've got to develop a
solution to a problem I can't replicate easily.  All the replies here will
help.

Thanks,
Carey

Bob Blick wrote:
{Quote hidden}

2007\06\04@203828 by Russell McMahon

face
flavicon
face
> Thanks!  Using the transformer sounds like a real workable solution.

Should work well in many cases - but see below.

The FET solution below allows you to handle very high DC currents at a
modest cost. The transformer solution is arguably more elegant but
transformer saturation with DC may be an issue. As noise effects may
change with DC load, being able to simulate high load levels may be
useful. So -

Another possible approach is a MOSFET in series with the supply.
Modulating it's gate takes about zero power and a pot divider (or
variable sig gen output) would allow any degree of modulation desired.

If you put the FET in the ground return you can probably drive it
directly from the sig gen. If it's on the high side you need to float
the sig gen or AC couple the signal. Capacitive coupling would work
fine for this as the impedance is very high.

In either case you could provide a DC gate offset with a pot and a
battery and then add the AC signal to that so that the FET is never
fully cut off. A 1 meg pot across a 9 volt battery with the FET gate
on the wiper and one end of pot to FET Drain plus AC capacitively
coupled to the wiper should work well. Battery will last indefinitely.
Opto-coupler coupling also an option.



       Russell


2007\06\04@233140 by Carey Fisher

face picon face
Russell,
That's good. I like it and am gonna try it.  Seems simpler than having
to use an audio amp etc.
Thanks!
Carey


Russell McMahon wrote:
{Quote hidden}

2007\06\05@012027 by Steve Smith

flavicon
face
ARB and an Audio amplifier.

Set up the sweep frequency on an ARB and add the DC offset then use an audio
amp to make the signal the correct level (needs to be DC coupled)

Just an idea...

Steve

{Original Message removed}

2007\06\05@040552 by Peter P.

picon face
Hmm, 'hevy duty' alternators sound like they could have much lower output Z than
normal, and/or switching mode field coil drive. I think that a low pass filter
will have to be used to cure it. But if the noise is conducted then this may not
be enough. It is easily possible that the 'heavy duty' alternator installation
does something not quite ok with the grounding and that it is not your circuit
that needs changes. That may also make it impossible to duplicate.

Peter P.



2007\06\06@081802 by Michael Rigby-Jones

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{Quote hidden}

This is exactly the scheme we use for testing power supply rejection during developement.  Note that to acheive some headroom for modulating above and below the supply, the FET needs to be biased to drop some voltage under static conditions which means you need to provide more voltage from your PSU and probably provide some heatsinking for the FET.

Regards

Mike

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