Electrical Engineering - Filter Question! How to get rid of SPIKES!

Author

Filter Question! How to get rid of SPIKES!

Victor ippolito

2007-01-27, 1:25 pm

Hello,

I have a 60Hz AC voltage comming from a transformer 120/220V that=20
powers some cooling fans, but it's got some spikes at the output, and=20
Im having problems with that. The spikes are burning the fans.

Here is the link of the wave form: http://br.geocities.com/suellemtosi/
wave.jpg

What the main problem is at 2Khz, am I right?

I want to make a filter to attenuate those spikes, but I=B4ve never done=20
a filter for voltages above 12V. I know just how to use op-amps, but=20
for 220V Its got to be a passive filter.

Does anybody have an idea of what type of filter would be more=20
appropriate? Low pass, tuned filters....

I have JUST some 3,9mH inductors to make it, the other components can=20
be anything to match the configuration.

Anything will be helpful!!!
Thanks a lot!
Victor

TimPerry

2007-01-27, 1:25 pm

Victor ippolito wrote:
> Hello,
>
> I have a 60Hz AC voltage comming from a transformer 120/220V that
> powers some cooling fans, but it's got some spikes at the output, and
> Im having problems with that. The spikes are burning the fans.

really? what size fans? little computer chassis fans or big building
ventilators?

>
> Here is the link of the wave form:
> http://br.geocities.com/suellemtosi/ wave.jpg

the dog is named 'Spike" ?

>
> What the main problem is at 2Khz, am I right?
>
> I want to make a filter to attenuate those spikes, but I´ve never done
> a filter for voltages above 12V. I know just how to use op-amps, but
> for 220V Its got to be a passive filter.

A; use a constant voltage transformer from Sola or some other mfr.

B: use an appropriatly sized MOV.

>
> Does anybody have an idea of what type of filter would be more
> appropriate? Low pass, tuned filters....
>
> I have JUST some 3,9mH inductors to make it, the other components can
> be anything to match the configuration.
>
> Anything will be helpful!!!
> Thanks a lot!
> Victor

transformers mostly do not generate "spikes". it is likely that whatever you
are seeing is caused by the load.

No Spam

2007-01-28, 9:25 am

Do NOT use a constant voltage transformer.
A constant voltage transformer is a special type of transformer that
is tuned to give the correct voltage at 60Hz, which means that they
don't really filter out anything
CV xfmrs are also designed to run with a magnetically saturated iron
core. This means that they run HOT, which wastes electricity and
costs $$$.

An MOV will also NOT solve the problem, only make it a little bit
better.
An MOV will keep the voltage from getting too high, which means it
will clip off the top & bottom peaks, but the spikes in the middle of
the waveform will still get through.

You should add an MOV, but mostly you need LC filters. Put all
components at the primary side of the transformer. The MOV connects
to hot & neutral. Then put one inductor from hot to one side of the
primary, and another inductor from neutral to the other side of the
primary.
Put the capacitor directly across the primary.

Values can only be determined by experimentation. Use a voltage
rating for the C which is much higher than the RMS primary voltage.
E.g. 120VAC = 120 x 1.414 =169V peak = 340V p-p so you need 400V
minimum. The MOV will keep any input spikes from exceeding the
capacitor voltage rating.

Capacitor value can only be determined by trial and error. Start with
0.001 uF and increase.

Also put an MOV rated at the transformer output voltage across the
secondary, in case there are any turn-on spikes.

As another check, is it possible to montor the transformer secondary
voltage with nothing connected to it? Maybe something in your gear is
generating the spikes, so you need to put a filter between the fans
and that stuff.
------------

On Sat, 27 Jan 2007 13:24:22 -0500, "TimPerry"
<timperry@noaspamadelphia.net> wrote:

>Victor ippolito wrote:
>
>really? what size fans? little computer chassis fans or big building
>ventilators?
>
>
>the dog is named 'Spike" ?
>
>
>A; use a constant voltage transformer from Sola or some other mfr.
>
>B: use an appropriatly sized MOV.
>
>
>transformers mostly do not generate "spikes". it is likely that whatever you
>are seeing is caused by the load.
>

billb@abc.net

2007-01-28, 1:25 pm

The advise sounds OK, if you have the surges on the primary side of the
transformer, except I would also suggest an MOV on the primary side of the
transformer. The MOVs need rating at the line voltage plus 10% to allow for
variations in the supply voltage, plus another 10% to allow for the
tolerance on the MOV itself, otherwise you could end up very short MOV life.
As I have read your posting you have a primary voltage of 120VAC, therefore
plus 10% = 132, plus another 10% = 145VAC. The nearest standard MOV rating
is 150VAC. On the secondary side the voltage is 220V, therefore plus 10% =
242, plus 10% =262V rms. The nearest standard MOV voltage easily available
is 275V rms. To protect the MOVs form going off with a bang when it fails
you should fit a fuse in series rated at the full load current of the
fan(s). To size the MOV is no easy, but if you can post the fan's full load
current(s) I will try and advise you.

If the surges are actually been generated by the fan, this will need a
better suppression circuit on the secondary side of the transformer.
Do you have a on/off contactor or relay in the circuit where you switch the
fans on and off?
If the surges are due to the fans I would suggest MOVs line to line and line
to ground, (three MOVs).
This offers the best protection. again the sizing of the MOVs depend on the
full load current.

On similar systems I have measured surge voltages of 5000 volts, but with a
supply of 480V, these were reduced to less than 700 volts peak once the MOVs
were installed. you can also add a simple RC network to help reduce the peak
value.

MOV can be dangerous so please read the Littlefuse publications regarding
there installation for more detailed information,
http://www.littelfuse.com/metal_oxide_varistor.html
also have look at:
http://en.wikipedia.org/wiki/Varistor

Do not try installing MOVs in parallel as it does not increase the ratings
due to the tolerances on the MOV's voltage, fit a larger MOV.

Hope this helps

Michael Moroney

2007-01-28, 5:25 pm

"Victor ippolito" <victordippolito@gmail.com> writes:

>Hello,

>I have a 60Hz AC voltage comming from a transformer 120/220V that=20
>powers some cooling fans, but it's got some spikes at the output, and=20
>Im having problems with that. The spikes are burning the fans.

>Here is the link of the wave form: http://br.geocities.com/suellemtosi/
>wave.jpg

Since there are 6 spikes per waveform, with two of them at the peaks,
I'll _guess_ that a cause may be lots of computer equipment with switching
power supplies plus poor (high impedance) wiring. If it is, the equipment
(whatever it is) is on all three phases of a 3 phase supply.

Maybe a separate circuit is all you need.

I'm somewhat surprised that a motor (fan) would be bothered by those
spikes, even though they are large.

w_tom

2007-01-29, 1:25 pm

MOVs would not even appreciably affect those larger spikes. MOVs=20
for 120 VAC typically set with a let-through voltage of 330 volts. =20
Anything less is mostly ignored. The many recommendations for MOVs=20
simply do not understand how MOVs operate; would not solve your=20
problem.

Consider a line filter. Of course filtering must be sized to handle=20
the load (current). Some examples:
http://www.schurterinc.com/products/usa/pemfilter.asp
http://www.cor.com/PDF/Q.pdf
http://www.interpower.com/ic/p30-35list.asp
http://www.ethanwiner.com/dimmers.html

Meanwhile, a better solution identifies source of that noise. If it=20
is adversely affecting fans, then AC electric noise is doing same to=20
other building electrics. Furthermore that noise may be the symptom=20
of something else about to fail - a suspect list also includes utility=20
power transformer. IOW solve the problem - the source of that noise. =20
Filtering the fan would only cure a symptom.

On Jan 27, 11:27 am, "Victor ippolito" <victordippol...@gmail.com>=20
wrote:
> I have a 60Hz AC voltage comming from a transformer 120/220V that
> powers some cooling fans, but it's got some spikes at the output, and
> Im having problems with that. The spikes are burning the fans.
>
> Here is the link of the wave form:
> http://br.geocities.com/suellemtosi/wave.jpg
>
> What the main problem is at 2Khz, am I right?
>
> I want to make a filter to attenuate those spikes, but I=B4ve never done
> a filter for voltages above 12V. I know just how to use op-amps, but
> for 220V Its got to be a passive filter.
>
> Does anybody have an idea of what type of filter would be more
> appropriate? Low pass, tuned filters....
>
> I have JUST some 3,9mH inductors to make it, the other components can
> be anything to match the configuration.

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