| Author | Message | ||
| CoryDane RTSII (66.155.188.34) Rating: |
I have been having a discussion and are at an impass. The Topic: Softening the squareWave of a MODIFIED SINE WAVE... My opposers say that the Modified sine wave cannot be changed, it is the result of electronic switching - PERIOD! I do not agree, entirely. I know the power company uses capacitors to increase voltage on lines that suffer "voltage droop" on distant customer locations with very good results. The SINE WAVE we are discussing is nothing more than the voltage peaks of the generating sources. True sine wave has a gradual voltage build up and down, indicated by a nice rounded sinewave following the raise and drop of the voltage the generator produces through magnatism and a rotating magnet in a stator coil. MODIFIED SINE WAVE is created with electronic circuits, there is no build up so the peaks and drops are imediate, creating the square wave, no gradual build up and drop of voltage as in the Sine Wave. MY SIDE of the argument is if the capacitors can help raise the voltage on AC lines, they could Modify the Sine wave of a Mod Sine Wave. At the very least, a capacitor would soften the voltage drop. I think there would be some affect on build up as the capacitor charges on voltage rise. I am not sure if it would only be an improvement of half the sine wave or if it would affect the entire voltage. Would it be possible to get by with a MOD Sine Wave inverter by adding some capacitors to the output thus making a more "SINE WAVE" result? Any Ideas out there? Thanks | ||
| Marc Bourget (209.142.38.81) Rating: N/A |
CD, I believe you are confusing the behavior of a capacitor under AC current with its behavior under DC current. Just because the inverter makes DC current "mimic" AC current does not make DC into AC. Quoting David Smead (but obviously lacking his knowledge and experience)"A capacitor does not pass DC current. When a voltage source is first attached to a capacitor, a high inrush of current results, without a corresponding increase in voltage. Eventually, (electronically, that is) the capacitor charges to the same level as the driving voltage, and current flow (into the capacitor) stops. If the voltage source is removed from the capacitor the charge on the capacitor remains until a load resistance across the capacitor discharges it. Since there is no DC current "through" a capacitor supplied with DC, I don't believe a capacitor will work in the manner you propose. I speculate that the "switched" reversal of voltage in a Mod SW Inverter doesn't act to "remove" voltage from the capacitor and without flow "through" it, the load on the "manufactured AC" circuit wont act to discharge the capacitor. Disclaimer, I ain't the expert here, I'm just trying to present a framework for discussion backed by my limited understanding and interpretation of what I've read. It remains for DD, Sean Welch and a whole host of others to weigh in at this time. I'm interested in the resolution of this one! Onward and Upward Marc Bourget. | ||
| DrivingMissLazy (66.168.175.51) Rating: N/A |
I have personally tried this to modify a square wave into a sine wave with fair results, however the cost is generally prohibitive. What works best is an LC filter, consisting of two properly sized capacitors and a properly sized inductor. There are formulaes to calculate this, but I really do not remember them. Due to the high harmonic content of the square wave, there is a large amount of ac current from these harmonics that must pass thru the capacitors and this creates a large amount of heating in the capacitors. Unfortunately, once you get the harmonics filtered out, the fundamental that you desire (60 cycles)is greatly reduced in amplitude and not really suitable for much of anything. I really do not want to try and get into this in any more detail, as it gets very complicated. Sufficient to say, that at least in my case, I decided it was not practicable. FYI, a 60 hertz square wave consists of the fundamental frequency (60) and an infinite number of odd harmonics including the 3rd, 5th, 9th, 13th and on up to infinity. Richard | ||
| Gary McFarland (Gearheadgary) (209.128.79.46)
Rating: N/A |
Ow! that is why I decided digital was the way for me, in my world, the damn thing is on or off. Analog Electronics just make my brain hurt. Gary | ||
| CoryDane RTSII (66.155.188.177) Rating: N/A |
LOL Gary Mc I like your logic.... Driving miss.. I agree also with you. I too can't recall the formula but I recall it is interesting to figure out, after you have all the numbers to crunch. I didn't think that the swing would actually alter the 60hertz though. Mark B It would serve no purpose to put the cap on the DC side, it would charge and just sit there until the DC was taken away then it would discharge, not very viable for our purpose. Now on the AC side, the capacitor charges and discharges with every swing of the 60hertz cycle. since the cap holds voltage, it would modify the step down the cycle swing. I can't recall but since the capacitor has such an inrush of voltage(and current) that it would also modify the up swing of the 60hertz sine wave. This is, of course, considering the size of the caps. You would really need an oscilloscope to see what you are really doing to the wave to be sure. I have always thought it might be a viable way to clean up the Modified sinewave but seems it might be just as cost effective to buy the Sine wave inverter. LOL, Well, I keep trying. cd | ||
| Marc Bourget (209.142.38.81) Rating: N/A |
CD, I did a bit more reading and discovered that there are uni-directional and bi-directional capacitators. I don't have it settled in my mind that the "switched" DC current is the same as AC. Are Capacitators subject to Back Electromotive Force like electric motors? Does switching the direction of the DC apply a "load" to the capacitator. Smead says without a load the Cap. stays "saturated" (my term, i.e.) The cap holds voltage until it either gets exposed to a higher voltage or a load is applied. In a true square wave, you never have a higher volatge. You, (more or less) have a single voltage since the plot of the voltage vs time is "square" Unlike GGH-Gary, my head is too empty to be filled to the hurting point with this stuff. Can you address these points a little further? Thanks, Marc | ||
| Gary McFarland (Gearheadgary) (209.128.79.46)
Rating: N/A |
We need to thoroughly explore the third state of boolean logic. Gary | ||
| Marc Bourget (209.142.38.81) Rating: N/A |
Like the guy who started working on his 2d $millon, cuz the first was too hard, I never made it past rudimentary boolean operations in my forays into basic programming Employing the same logic, might as well go for the 3d state, whatever that is! Onward and Upward Marc Bourget. | ||
| Gary McFarland (Gearheadgary) (209.128.79.46)
Rating: N/A |
First state: ON/Yes/1 Second State: Off/No/0 Third State: Don't Care. Gary | ||
| Jim Ashworth (Jimnh) (172.157.152.23)
Rating: N/A |
Ya know, for a few hundred more you could have someone else do all the engineering and buy a Sine Wave inverter. All sorts of extra features too. Some things just aren't worth the effort. There are more important things that you CAN do something about rather than trying to tweak a square wave. And people wonder why it takes years to do a conversion!!  Jim | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
The answer to your question is "yes". A "modified sine wave can be "softened". The deal is that as it comes out of the inverter, it is a messy looking square wave with all sorts of glitches hanging on to the waveform. Harmonically (which is what makes a sine wave a sine wave, a square wave a square wave, and a modified sine wave a piece of salesmanship) a modified sine inverter's output is not as complicated as a square wave, but the only way to "soften it" as you say, is to filter out all the harmonics that are there, leaving a sine wave as the result. The only practical filter in this application would be a big inductor in series with the load, followed by a big capacitor to neutral after the inductor (L/C filter). Capacitors are absolutely avaliable that will accomplish this job, as long as they are used in conjunction with a properly designed inductor. The hitch is that when you've finally created a filter that will remove all the crap from a modified sine wave in this manner, you will have substantially less voltage at the output- likely around 70-80 volts if that. It has to do with simple math- stuff like peak-to peak vs RMS, area under the curve, etc... And the indductor would probably weigh 40-50 pounds for a few KW worth of inverter. Believe me if this was a practical methodology, the manufacturers would use it. But it's not, and that's why you see modified sine inverters for cheap and true sine inverters for not cheap. There are a LOT of really smart engineers who have been dreaming for an easy solution (they would get rich quick), but to date not much has changed... Cheers Gary | ||
| Gary McFarland (Gearheadgary) (209.128.79.46)
Rating: N/A |
"...is to filter out all the harmonics that are there, leaving a sine wave as the result..." That's where I checked out. when the Instructor said "there's no such thing as a square wave", I was wondering why I didn't follow that lead on the matchbook cover for motorcycle mechanics Institute. Gary | ||
| Tim Hoskinson (Tdh37514151) (216.96.110.134)
Rating: N/A |
Hi Cory I don't want to imply that I know it all but I have worked in the electronics field for 27 years and have designed and built my own inverter circuts. Wile it is possible to wave shape a step inverter using ac oil filled caps it really is not feasible. In a muti step inverter it can help and they were use in early uninterruptale power supplies used for computer power. How ever most of the small inexpensive units you buy they do not have the fine step level required. The reason ac caps won't help you is simple. On the step inverter the voltage starts at its zero point steps to its first voltage in a six step inverter it would be approx 20 volts then steps another 20v then another. On the way up in voltage the cap draws larg amounts of current wile charging this is current you can no longer use to power any thing in your coach as the inverter has its limits. Even worse on the way back to the zero point each step the inverter takes down to reach zero volts is in opposite polarity of the now charged cap. Inrush of this added to any load can be more than the inverter can handel. The phase stabilizing caps you reffered to on the power lines charge and discharge from a sorce that changes polarity at the normal rate of speed . Sine wave speed. Even at this the chage time of the caps is carefully chosen by engineers at the power co. What is it that you need the inverter to do many times the unit you are trying to run can be modified to except the inverter power. Feel free to give me a call if you like I may be able to help. Good luck. Tim 740-404-0853 | ||
| CoryDane RTSII (66.155.188.14) Rating: N/A |
Marc I think your answer was given by the contributing others, otherwise, I would be happy to continue causing confusion and silence as we enter new vistas..lol, move over StarTrek. Tim, My discussion began with a stick/staple owner with a converter and they wanted to get the better charger in a mod sine wave inverter. The problem was they were "insecure" about the Modified wave, though, they have no room for a true sine wave unit, they are much bigger physically. We tossed around ways, Dreaming actually, of cleaning up the square wave, One of my suggestions was to buy only 12v dc electronics, lol, I was nixed. The Capacitor theory was mine as I recalled how a cap can clean up a power source on a oscillo. I also knew some of the Tech guys and they would deal with caps from time to time and were happy to show me things. I also had read a document many many moons a go that showed use on DC power as well as AC. And it was the AC side that was interesting. Following the voltage curve they showed the cap charging as the voltage sine wave increased and then the cap attempted to hold voltage as the sinewave voltage went to zero until the cap was at zero, then the process repeats over and over, I think they were talking about a filter at this point. I found caps interesting due to that article, funny I should remember all this after all those years, huh? Well, I was kinda right but they have to live with the ModSine or stay with the converter and lousy charger. LOLOL. I used to tease the tech guys about all these wild electrons that we claim to have harnessed to do our work but from time to time those little electrons revolt and things burn up or flash over or just plain go dead. The Tech guys just didn't see my humor in the subject. Anyway, besides enjoy opening a good topic of discussion, I had a real interest, but I don't think any of us have the need to tow a trailer full of capacitors to filter a Mod Sine wave inverters output. I think we all picked up on something here, now I'm gonna make a call and tell them to put the converter back in LOLOLOLOL. Thanks everyone cd | ||
| Sojourner (68.60.169.142)
Rating: N/A |
Capacitor to output source will clean. However to correct power source that require true sine wave begin at primary circuit before amplifies circuit. Square sine waves from simple electronic circuit such as Thyristors (SCR) device are “off & on” switching. They are not variable amplifier-able such as transistor & mosfet (high power) device. Which involve must more detail equip electronic primary circuit to produce a true sine wave. Another word, more parts, the more expensive to build. I have built many experiment projects at classes & home in the pass. The problem “square wave” (on-off-on-off) & “quasi or modified sine-wave” (off-off-on-off-off-on). Pure or home power sine waves are higher peak voltage then “square & modified wave”. Also all electronic or solid state appliances circuit relied on “peak-curve” instead of “long-flat high peak” 60 cycles pulse to function consistently and properly. Otherwise redesign appliance electronic system for modified sine wave would work at it best. http://www.majorpower.com/inverters/inverter_faq.pdf http://www.exeltech.com/ex_root/ex_literature/19_23_mx_manual_revd.pdf http://www.eere.energy.gov/consumerinfo/factsheets/bb8.html Smart choice is to have one or more duplex are connect to “true-sine” wave of lower power less expensive unit and all other duplex on “modified-sine” wave of more power unit. Would still have more or less humming with difference brand of “modified-sine” unit. For what it’s worth. Sojourn for Christ, Jerry |
