Forums

Filtering generator output?

Started by Unknown April 23, 2014
I have a 4500 watt generator that is for emergency use. When it was
new I checked the output with an oscilloscope just to see how pure the
sine wave was and how close to 60 Hz it was. Well, the main sine wave
looked good and the frequency was very close to 60 Hz. It floated
around a little as the load changed but then would stabilize very
close to 60Hz. However, there were lots of other smaller sine waves
present. I was told these were harmonics and were typical from the
generators made for home use. I see lots of generators that use well
filtered inverter power supplies to get a pretty close approximation
of a pure sine wave. But then at the same time hydro power plants
spinning huge generators have been putting out very clean power long
before there were solid state inverters that could be used to modify
the power output from a generator. So I'm wondering,  could I use
capacitors and/or inductors to clean up the power from my generator?
I have built a few rotary phase converters and used caps to balance
the voltage. And I have a box of oil-filled caps that were used for
power factor correction in street lamps just waiting to be pressed
into service cleaning up my generator. Any advice?
Thanks,
Eric
On Wednesday, April 23, 2014 2:16:16 PM UTC-4, et...@whidbey.com wrote:
> I have a 4500 watt generator that is for emergency use. When it was > new I checked the output with an oscilloscope just to see how pure the > sine wave was and how close to 60 Hz it was. Well, the main sine wave > looked good and the frequency was very close to 60 Hz. It floated > around a little as the load changed but then would stabilize very > close to 60Hz. However, there were lots of other smaller sine waves > present. I was told these were harmonics and were typical from the > generators made for home use. I see lots of generators that use well > filtered inverter power supplies to get a pretty close approximation > of a pure sine wave. But then at the same time hydro power plants > spinning huge generators have been putting out very clean power long > before there were solid state inverters that could be used to modify > the power output from a generator. So I'm wondering, could I use > capacitors and/or inductors to clean up the power from my generator > I have built a few rotary phase converters and used caps to balance > the voltage. And I have a box of oil-filled caps that were used for > power factor correction in street lamps just waiting to be pressed > into service cleaning up my generator. Any advice? > > Thanks, > > Eric
Hi Eric, First a disclaimer, I know "jack" about AC power. I'm comfortable with a volt and an amp. 100's of volts and 100's of amps are scary. In principle why not... you could make an L/C low pass to filter out the higher harmonics. (I'm not sure what you'd use for an inductor?.. it needs to handle ~40 amps.) But why bother? You'll lose some power in the LC filter, and I don't think any of your appliances care that much. (But I could be worng.. maybe someone will correct me.) George h.
In article <bevfl99akmnfavhjtlf6i3kpakmc6hs95g@4ax.com>, 
etpm@whidbey.com says...
> > I have a 4500 watt generator that is for emergency use. When it was > new I checked the output with an oscilloscope just to see how pure the > sine wave was and how close to 60 Hz it was. Well, the main sine wave > looked good and the frequency was very close to 60 Hz. It floated > around a little as the load changed but then would stabilize very > close to 60Hz. However, there were lots of other smaller sine waves > present. I was told these were harmonics and were typical from the > generators made for home use. I see lots of generators that use well > filtered inverter power supplies to get a pretty close approximation > of a pure sine wave. But then at the same time hydro power plants > spinning huge generators have been putting out very clean power long > before there were solid state inverters that could be used to modify > the power output from a generator. So I'm wondering, could I use > capacitors and/or inductors to clean up the power from my generator? > I have built a few rotary phase converters and used caps to balance > the voltage. And I have a box of oil-filled caps that were used for > power factor correction in street lamps just waiting to be pressed > into service cleaning up my generator. Any advice? > Thanks, > Eric
What you're seeing is not a harmonic, at least not one generated through the normal means. You're generator most likely has an alternator and those are current generating devices. The voltage regulator circuit is switching at a few multiples of the 60 hz to build a sinus wave that will stay with in spec with the load you are using. There is a little hysteresis in the field (rotor) so it makes it a little slow turning off the generator output. This explains why you see the sinus looking effects on top of the 60Hz. I have a Honda generator that is considered a very well built unit and that too generates a pulsed sinus wave however, if I load it down, it'll clean up. There are some harmonics but not at the level you're seeing it. Putting the scope on it isn't really enough load to make it stable. If you were to have a regulator that averaged over a couple of cycles it would make for a smoother output however, this is dangerous because if a heavy loaded appliance becomes detached or turned off during this cycle, the alternator is left at a state where it was cranking up the field and since it is a CURRENT device, the output voltage will ski rocket for a short moment. In auto's, it's not as much of a problem because the battery that is attached can briefly absorb that. Maybe you have heard of the term LOAD DUMP>. Jamie
On Wed, 23 Apr 2014 11:16:16 -0700, etpm@whidbey.com wrote:

>I have a 4500 watt generator that is for emergency use. When it was >new I checked the output with an oscilloscope just to see how pure the >sine wave was and how close to 60 Hz it was. Well, the main sine wave >looked good and the frequency was very close to 60 Hz. It floated >around a little as the load changed but then would stabilize very >close to 60Hz. However, there were lots of other smaller sine waves >present. I was told these were harmonics and were typical from the >generators made for home use. I see lots of generators that use well >filtered inverter power supplies to get a pretty close approximation >of a pure sine wave. But then at the same time hydro power plants >spinning huge generators have been putting out very clean power long >before there were solid state inverters that could be used to modify >the power output from a generator. So I'm wondering, could I use >capacitors and/or inductors to clean up the power from my generator? >I have built a few rotary phase converters and used caps to balance >the voltage. And I have a box of oil-filled caps that were used for >power factor correction in street lamps just waiting to be pressed >into service cleaning up my generator. Any advice? >Thanks, >Eric
Why does the waveform matter? -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
etpm@whidbey.com wrote:
> I have a 4500 watt generator that is for emergency use. When it was > new I checked the output with an oscilloscope just to see how pure the > sine wave was and how close to 60 Hz it was. Well, the main sine wave > looked good and the frequency was very close to 60 Hz. It floated > around a little as the load changed but then would stabilize very > close to 60Hz. However, there were lots of other smaller sine waves > present. I was told these were harmonics and were typical from the > generators made for home use. I see lots of generators that use well > filtered inverter power supplies to get a pretty close approximation > of a pure sine wave. But then at the same time hydro power plants > spinning huge generators have been putting out very clean power long > before there were solid state inverters that could be used to modify > the power output from a generator. So I'm wondering, could I use > capacitors and/or inductors to clean up the power from my generator? > I have built a few rotary phase converters and used caps to balance > the voltage. And I have a box of oil-filled caps that were used for > power factor correction in street lamps just waiting to be pressed > into service cleaning up my generator. Any advice? > Thanks, > Eric
it's probably not worth the effort to remove a little noise from the output. As long as you don't have square wave or really poor grade "modified sine wave" output, anything should run just fine with it. In fact, throwing a load on the generator may be the easiest way to "filter" the output. If you want to convert that 4500 watt generator into a 2000 or less watt generator with a "perfect" output that will probably struggle or fail to run any motor with a starting coil consider a ferroresonant power conditioner. It will give you the finest of sinewave outputs, complete with voltage and frequency regulation.
On Wed, 23 Apr 2014 17:36:18 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

>On Wed, 23 Apr 2014 11:16:16 -0700, etpm@whidbey.com wrote: > >>I have a 4500 watt generator that is for emergency use. When it was >>new I checked the output with an oscilloscope just to see how pure the >>sine wave was and how close to 60 Hz it was. Well, the main sine wave >>looked good and the frequency was very close to 60 Hz. It floated >>around a little as the load changed but then would stabilize very >>close to 60Hz. However, there were lots of other smaller sine waves >>present. I was told these were harmonics and were typical from the >>generators made for home use. I see lots of generators that use well >>filtered inverter power supplies to get a pretty close approximation >>of a pure sine wave. But then at the same time hydro power plants >>spinning huge generators have been putting out very clean power long >>before there were solid state inverters that could be used to modify >>the power output from a generator. So I'm wondering, could I use >>capacitors and/or inductors to clean up the power from my generator? >>I have built a few rotary phase converters and used caps to balance >>the voltage. And I have a box of oil-filled caps that were used for >>power factor correction in street lamps just waiting to be pressed >>into service cleaning up my generator. Any advice? >>Thanks, >>Eric > >Why does the waveform matter?
Maybe it doesn't. If I was just running motors then I wouldn't care. But my fridge has all these fancy electronic parts that control the temp and the manual warns against using a generator that doesn't put clean enough power. Actually, I think the manual warned against "power sources" that didn't put out AC in the proper frequency range and waveform. Something like that. Anyway, the main reason for the generator is running the fridge and chest freezer and I don't want to ruin the fridge. The chest freezer has no electronics, just electrics. But maybe the "power source" the manual was talking about is an inverter putting out stepped shaped approximation of sine waves. I suppose I could try an old computer out first and if it doesn't complain then maybe the fridge electronics won't either. Eric
I would never buy a refrigerator with electronics. It is not called for. Wh=
at's more, that electronics in there is probabyl cheaper than the old mecha=
nical thermostat and defrost timer.=20

They say it's a feature, but I think it is a bunch of junk. Like the old TV=
s weith mechanical tuners, suppoeedly a feature but after a few years of ex=
perienc building them, they were cheaper than a mechanical tuner. In fact u=
sing a chip to control the volume and other things is cheaper than potentio=
meters.=20

Audio ? Hell, making a real volume control even became almost a lost art, u=
ntil the audiophiles bitched about it. Then they made pots again and put a =
motor on it for remote control. That cost them.=20

Everything they do is to make more money. Same here.=20

Next I need to find an old microwave with a mechanical timer. A long time a=
go I saw a two power level jobv that didn't cycle it on and off, it actuall=
y had a second tap on the transformer for the lower wattage.=20

You probably couldn't buy one now using the US offense budget.
Of course I meant digital tuner...