What's the name for a device that is reducing THD in AC ? - Page 1
Forum section: electronics / beginners

author: poof
author_rank: Newbie
timestamp: October 26, 2017, 07:19:20 pm
content: Hi,I'm a newbie and I would like to know if there is a name, a commercial name for a product that I can find in the shop, for a device that will reduce total harmonic distortion when I have a "dirty" or just a bad modified sine wave .For example I would like to know how to filter and produce a good sine wave, even under load, even when running from a cheap AC generator that barely outputs a modified sine wave .The transition is AC to AC, so I know that I don't need a converter, I think that I need a subset of that which means that I probably just need a filter, but I don't know any "technical name" for a thing that will do what I'm looking for .

author: Shock
author_rank: Super Contributor
timestamp: October 26, 2017, 07:31:27 pm
content: Power conditioner?You might want to let us know what you have (details on brand and model etc) and what the problem is, it often leads to better advice.

author: free_electron
author_rank: Super Contributor
timestamp: October 26, 2017, 07:36:29 pm
content: filter ?

author: IanB
author_rank: Super Contributor
timestamp: October 26, 2017, 07:46:41 pm
content: Are you talking about mains power? Do you want a clean AC voltage?When you say generator, do you mean a motor-driven generator set? Or do you mean an electronic inverter?I think generators already should produce a fairly clean voltage. Maybe only a little bit of conditioning or filtering might be needed to remove unwanted noise.Inverters are a different story. If the inverter produces a bad sine wave, then possibly the best answer is to get a better inverter.

author: Awesome14
author_rank: Regular Contributor
timestamp: October 26, 2017, 07:53:46 pm
content: A full inversion device would do it. It converts the dirty AC to DC and then back to AC. Many UPS units operate that way. A UPS will also protect against spikes, brownouts and blackouts.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 26, 2017, 07:55:37 pm
content: Back in the days, there were magnetic voltage stabilizers. Due to their resonant mode of operation they also "cleaned" the sine wave to some extend. Don't know if these are still sold today, since our power grid is quite stable today.

author: poof
author_rank: Newbie
timestamp: October 26, 2017, 08:14:00 pm
content: sorry for the confusion .What I meant with "generator" is "gasoline generator", getting AC from gasoline, lubricant and a running motor engine .I had the idea about using a PC-class UPS too, basically I was going to use something from a computer store but I looked at the "efficiency" figures and they basically range from 80-something to about 95-7% efficiency for the really expensive ones from APC or similar brands .It basically means that, on average, if I get 1000W of dirty AC, and I want to filter it with an UPS, I have to waste 100W, which means that I have 900W nominal left, which is a big hit in absolute terms when you are running from a motor engine .I don't know if there is something more efficient than an UPS but a really good UPS is not cheap, it's way more expensive that a gasoline generator and this will make my idea an uneconomic one .I was hoping to find a device that does just that AC to AC transition as efficiently as possible an it's as simple ( cheap ) as possible . After all I don't really need all the functionalities of an UPS .

author: poof
author_rank: Newbie
timestamp: October 26, 2017, 09:27:12 pm
content: after some researches I found out that the word I was looking for is indeed "power conditioner" , they are the devices used when you want to keep a stable voltage and filter spikes and "bad waves" .I'm not sure if they really output a "pure sine wave" or they just try to average the noise, I haven't found a brochure for a real product that clearly states something like "pure sine wave under load" or "filtering a modified sine wave into a pure sine wave" .I have also noticed that power conditioner are also relatively cheap, not cheapy cheap but accessible and with a good nominal efficiency even for the basic ones ( >95% ) .

author: dmills
author_rank: Super Contributor
timestamp: October 26, 2017, 10:46:01 pm
content: Ferroresonant CVT transformer is the term you are looking for, but note that they are frequency sensitive (And heavy), so if your generator cannot maintain a stable frequency you will get output voltage variation, they are the business for harmonic reduction however.Names to conjure with "SOLA" and possibly the "AEL" group.For slightly bigger machines, and if third harmonic from the load is a problem you can use a delta-star transformer, all the triplen then ends up as heat due to circulating current in the delta winding, common for stage power where large third harmonic loads from stage lighting are in play.Personally for ~1kW class generation, if I had to use petrol (Yuck) I would just buy one of the Honda inverter sets (There are cheaper copies but you get what you pay for), and call it good, they really are exceptionally nice small machines, the EU1000i or EU2000iRegards, Dan..

author: hermit
author_rank: Frequent Contributor
timestamp: October 26, 2017, 10:54:32 pm
content: Do you have a scope output of the sine wave to share?

author: cvanc
author_rank: Frequent Contributor
timestamp: October 27, 2017, 01:55:07 pm
content: Hmmm, I'm not entirely sure what the OP really is looking for here, but I don't think it's a Sola-style constant voltage transformer ('CVS' ferroresonant type), as these are actually known to ADD some distortion to the AC line. A Sola CVS, or equivalent, will REGULATE the voltage to smooth out fluctuations as your generator and load wander about, but they do not clean up distortion - they actually add a little more.It sounds like maybe he's thinking of 'power factor correction' circuits, but again I'm not sure. These reduce THD but do not regulate.In any case I have used a great big Sola CVS on a 5KW gasoline generator for decades, it certainly works and delivers a more stable voltage than the generator alone. Never bothered to measure the distortion of my setup, however. The water pumps I was powering did not care.Good luck finding what you're looking for.

author: poof
author_rank: Newbie
timestamp: October 27, 2017, 04:27:02 pm
content: Quote from: hermit on October 26, 2017, 10:54:32 pmnope, just figuring out my best options on what is good for my applications .

author: poof
author_rank: Newbie
timestamp: October 27, 2017, 04:37:23 pm
content: In the end I think that the worst point is the lack of instruments from my part .I would need an oscilloscope ( and then some ) to test each option properly .But I think that even a medocre UPS will do a better job at reducing THD than a mediocre power conditioner or similar products; point being that UPS are ubiquitous and with a proven track record and more documentation . To buy a power conditioner you need to know what you are buying and be sure that it's doing what it says on the box .I have also noticed that the markets are different, UPSs are usually specific for sensitive computer stuff, power conditioner are even sold on the agricultural market which means that there are probably a lot more of low quality, poorly designed products .Do you know where I can find reviews of good quality power conditioners or Ferroresonant CVT transformer ?

author: IanB
author_rank: Super Contributor
timestamp: October 27, 2017, 05:05:07 pm
content: How do you know or why do you think that you have bad power quality coming from the generator?Do you have things that are not working properly, or are suffering from the distortion?I am puzzled by the question because a generator, by its nature, is supposed to produce a pure sine wave. I am wondering what is the source of the distortion you are worried about?

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2017, 05:06:18 pm
content: wait. gasoline generator that gives off a modified sinewave ? just use a real alternator instead of a DC generator followed by an inverter. you will get perfect sinewaves. after all that is what powerplants do ..sounds like : lets use the cheapest generator we can find , ten add the most expensive filter / conditioning system.

author: dmills
author_rank: Super Contributor
timestamp: October 27, 2017, 07:20:47 pm
content: Actually those small cheaply built machines often have severe flat topping under load (due to saturation of the magnetics), and will quite often exhibit large frequency variations as the throttle response and inertia are insufficient to maintain frequency on load changes, worse they often have sufficient flux leakage to generate fairly large transient over voltages if a load is suddenly removed....These are not I suspect what any engineer would call a proper alternator, and at this end of the market a DC bus feeding an good quality inverter is often a much better choice then undersized magnetics, compound wound to avoid the need for an AVR.I would however second the advice to do it right in the first place rather then trying to band aid junk.regards, Dan.