AC line filters

I've heard of some electronic devices having problems running on the output of a modified sine wave output inverter or small generator that may not have
the best sine wave shape. Would there be any problem using a 1, 2, or 3 stage AC line filter to clean up the output waveform of either, and would it do any good? They aren't that expensive so adding one to a generator would seem to me to make a lot of sense. What am I missing?
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Carl Ijames
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Oops, meant to post to sci.electronics.design, sigh.
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Carl Ijames
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AC line filters reduce higher harmonics but have little effect at the fundamental frequency. The components simply aren't big enough to store much energy and return it later.
Ferroresonant transformers are 60 Hz sine wave filters with voltage regulation, but look at the weight: http://www.hammondmfg.com/CVR.htm
http://www.lamarchemfg.com/productdetails-A31 -(Ferro-Resonant-Inverter)/263.html
See pages 13 and 14: http://www.etmsolar.com/INFO2011/pvclass/how%20inverters%20work.pdf "Unfortunately, inductance causes the transformer to have a relatively low efficiency (typically about 50%) and the waveform is very load sensitive."
-jsw
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"Jim Wilkins" wrote in message

AC line filters reduce higher harmonics but have little effect at the fundamental frequency. The components simply aren't big enough to store much energy and return it later.
Ferroresonant transformers are 60 Hz sine wave filters with voltage regulation, but look at the weight: http://www.hammondmfg.com/CVR.htm
http://www.lamarchemfg.com/productdetails-A31 -(Ferro-Resonant-Inverter)/263.html
See pages 13 and 14: http://www.etmsolar.com/INFO2011/pvclass/how%20inverters%20work.pdf "Unfortunately, inductance causes the transformer to have a relatively low efficiency (typically about 50%) and the waveform is very load sensitive."
-jsw =============================================================Grr, I misread the frequency scale on the datasheet attenuation chart I was looking at, it was in kilohertz not hertz. I knew there had to be simple reason or everyone would already be doing it.
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Carl Ijames
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Here's an idea of what it takes: https://www.shapellc.com/linetamer-power-line-conditioners.html
Before stumbling onto the free APC1400 SmartUPS I was looking for a good, cheap sine wave inverter that would run my fridge, which needs 12A to start, <2A to run. What I found got terrible reviews. The TV and all my laptops run fine on cheap "modified sine" square pulse inverters.
The APC would be a good answer if it wasted less idle current and was more tolerant of AC from portable generators. It has a button on the back to reduce sensitivity to bad power but that isn't enough. -jsw
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On Sat, 17 Jun 2017 20:22:55 -0400
<snip>

I had one either like or very similar to this that was used in a system I serviced:
http://www.ebay.com/itm/BEST-MICRO-FERRUPS-ME-SERIES-120VAC-14A-UNINTERRUPTIBLE-POWER-SUPPLY-ME1-8KVA-/291181299549
A lot of the operating parameters could be changed/set by using the RS232 connection and a terminal program. As you have noted they are real energy pigs just idling. That whole system got scraped and I had this unit setting underneath my workbench for backup, playing around. I gave up on it when the batteries degraded to the point of it being useless. I'm not sure but it may be possible to set the operating parameters for input to work with a generator.
It probably should have disappeared with me when I left, nobody else really understood it... The batteries aren't cheap though and you sure don't want to leave it plugged in if you don't like high electric bills :)
It was awesome to see it working though. Just cut power and watch everything keep running without so much as a hiccup. It had internal memory and kept alarms and faults until they got written over. The RS232 port was hooked to a dial up modem. I could call the site up, interrogate it for faults, alarms, settings... and see where the sites backup generator (big propane Gererac) had been exercising. Or some other wacky thing must have happened at say 2:00 am causing the system to fail and generate user complaints. Very nice.
There was enough equipment cooking at that site that it didn't need heat. Always nice inside, even on the coldest of winter days. Summer time was a different story. It took a 3 ton a/c unit to keep it cool enough so over-temp alarms weren't generated.
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Leon Fisk
Grand Rapids MI/Zone 5b
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wrote:

The APC isn't ferroresonant, it synthesizes a sine wave. Talking to it requires making a non-standard serial cable. I found the commands it accepts in the manual for 'apcupsd' on SourceForge and wrote a program to adjust it and display parameters in a small window. The most tolerant line quality setting still rejects one engine-speed-regulated generator and frequently reverts to battery on the other.
We've had only short outages since I bought the HF generator so my upgraded backup system hasn't had serious use. I assume the fridge will run overnight on batteries which I will partly recharge in the morning and evening with the generator, and from whatever solar is available during the day.
I can't fully recharge the batteries inside the house in one day without generating hydrogen, but can outdoors after the grid returns. They don't bubble at 13.6V or below, and only fizz lightly at 13.8V. Supposedly 13.6V gets them to ~3/4 charge quickly and full charge in a few days. The APC charges at 6A to 13.6V, then hold that voltage as the current tapers off.
I could put the batteries and APC on a cart and fully recharge them in the driveway from a generator if necessary but I don't want to attract thieves. The practicality of that will depend on the weather and how loud the neighborhood is from other generators. The Predator's sound at idle doesn't carry very far. -jsw
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Jim Wilkins wrote:

Most items will run fine on the generator output. The only item in my place that has any issue is a ceiling fan. It generates a strange buzz on genny power. I'm guessing it is due to the multiple winding design of the motor.
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Steve W.

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And their output voltage is a function of frequency; so when the generator speed varies. It's also difficult to design F-R tanks to deliver sine wave output.
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writes:

They flatten the peaks as the core saturates, which isn't that bad. The rise and fall is still close to a sine. -jsw
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writes:

They work well enough to have survived on the market, but I don't see them as a practical DIY project to clean up a modified square wave (what they really are) inverter unless you find a suitable second-hand unit cheap and have the gear to test it. My old Sola constant voltage isolation transformer isn't nearly big enough to start my fridge's compressor, which draws 12A for 0.3 seconds.
https://public.magnet.fsu.edu/graf/Manuals/Sola/SOLA%20CVS%20Ferro-Resonant%20Tranformer.pdf "In general, the Sola constant voltage regulator must have a capacity nearly equal to the maximum demand made on it, even for an instant. "
-jsw
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A friend designed the 3-ph sine-wave-out F-R transformers for Lorain Products' large UPSi [100 KW & up]. He was the only person I know who really understood *and could explain* how they worked.
That's a good datasheet, and makes important points; no-load draws 30+% of full load, they are short-circuit proof, etc.
LPC tested their designs with a LARGE motor, as I recall it was ~4 ft in diameter. They'd hook up way-too-small inverter module to it, and power it up. The motor would sit there, while the power module put out its rated current (& hummed mightily.)
If you looked carefully, you'd see the motor twitch, and then rotate a tiny bit. If you waited, you'd see it move a little more, finally a full inch of travel. Over many minutes, it would keep going, gaining speed. After 15-20 minutes, the motor would get up to 1725 RPM. The module had passed.
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That is ok - some of us are qualified.
The filter would be just fine. Remember it must pass the current and handle the voltage and the power rating be all high enough to allow it to function as a 'passive' filter.
Often high voltage caps across the power line will take out the fast edges (shunting the RF and middle frequency 'noise'. Remember caps drop wattage. Some have series resistance and they all have reactance that drops wattage. Typically L's are present - the inductance of the wire used and reactance across the lines. If the lines are short - use inductance or resistance to form the L filter. T's are better.
Martin
On 6/17/2017 5:16 PM, Carl Ijames wrote:

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