Modified Sine Wave VS True Sine Wave Inverters

[Fred Mc]

What are the PRACTICAL differences between modified sine wave inverters and the true sine wave inverters (as in what can I run and what can't I run with each)?

Thanks

Fred Mc.

[luvrbus]

Fred 2 things I know you cannot use the modified wave for is the new flat screen TV's and the induction cook top and there are others things that don't like it (cell phone charger) on my new phone

[Nick Badame Refrig/ACC]

Hi Fred,

I'll second that... Most newer electronics will have a heart attack on modified sine wave inverters.

True sine wave is well worth the extra $$. There was a time when refrigerators and air conditioners were able to run

on a modified wave but, today most of them have some sort of printed curcuit board operateing them now.

Good Luck
Nick-

[NJT5047]

Not to belabour the issue, but my Aquos (sp?) flat LCD TV works perfectly when on my Trace MSW inverter.   Some TVs may not. 
I've read that computers (printers especially) and small battery chargers (cell phones) do not work well on modified sine inverters.   And some clocks may be confused by MSW inverters.  Our laptop will work without issues on the MSW inverter.
So I charge my phone in the 12V outlet.  That's the only issues that I've run into in 6 years of an MSW inverter use. 
The phones may charge on the MSW..I've never tried it.  I usually turn  the inverter off at bedtime.  Don't want it idling all night. 
I'll watch some TV at the end of the day, and everything I've plugged into our MSW inverter has worked...TV, microwave, all 110VAC lighting,    We do a right good bit of 3 day dry camping.   People's needs are different.   You may have some special requirements that just be powered by a true sine wave unit.   Most healthcare gizmos require pure sine power.   However, unless you have a huge battery bank, this requirement may require being plugged up. 
A better perspective might be to ask yourself what you're going to operate from the inverter, and for how long?   A battery bank must be up to the job.   
I run a genset for OTR AC...solves that problem.
IF you plan to operate an AC from the inverter while driving, follow Nick's advice.  He will not lead you astray.
But, if no AC, you may wish to weigh your options.    TSW inverters are expensive...
Because I have LP fridge, stove, hot water, and heat....I don't need an inverter running most of the time.   Something to add to your confusion! 
JR


   

[Fred Mc]

Thats ther kind of info I was looking for.

Thanks a lot.

Fred Mc.

[luvrbus]

Fred,  www.donrowe.com has a FAQ on his site that has great info on inverters my new Sony 31in will not work on modified sine but I have a Sharp 21 inch flat screen that will

[boogiethecat]

Uck here we go again. 
Modified sine wave inverters are salesman's hype for their true nature: square wave inverters with "some" harmonic filtering.  They are, in my humble opinion, crap.  Useful for running electric drills and other motors with brushes, resistance heaters, light bulbs, and even more useful for creating havoc with most electronic things, generating severe RF interference, computer glitches, overheating induction motors, and wasting your money.
Don't you like someone with an opinion !!!

I tried one in the earlier years, and tossed it as soon as I tried to use it- from then on I wouldn't have one anywhere near my bus, because I value the usefulness of my GPS, radio, computer, cell phone, and all the other electronics I have onboard, and I also like my AC and fridge motors.  The modified sine inverter  either trashed or severely interfered with most everything.
These days, pure sine inverters with some real capacity that are reliable and cheap are easily available thru ebay.

Yes there are folks who love them and will argue their usefuness, and yes they do have a place here and there, but so do 4 function calculators and horse drawn carriages.  These days there are so many better options at almost the same $, why bother the fight !!

A definitely opinionated Boogie on this one.... 

[JohnEd]

OHHHHHH,

Maybe some payback here.  ALL MSW inverters are not the same.  The M part is that the cycles are broken up into little steps....sort of "modified"....get it?  These steps are not always the same number per cycle of ac per manufacturer of the inverter.  The crudest form of "modified" sine wave is a "square wave" .  Lots of stuff that uses ac will hiccup on a square wave.   The square wave is a crude digital representation of a sine wave.  In a true sine wave the voltage goes through a cycle with the volts increasing and decreasing at a analog rate, if you will, and at any time the volts are different than the last time you looked and that includes the last micro second ago that you looked.  In the square wave the volts will be the same unless the wave has passed that point where the volt waveform switched and went the other way.  That id "digital' kind of stuff.  In the modern inverter there are lots of steps going from 0 to 120 and back in the "sine wave".  Really good MSW units have SOOOO many steps that they look like "pure" sine wave to most devices.  Some devices have such high tolerances that only the real McCoy only will do.  The old Harts that became Trace that are now Zantrex seem to do especially well cause they have lots of tinsy wensy steps.  Tom has a pocketfull of Hart Freedom inverters and he has had stunning performance.  There are lots of Zantrex models that are copies of the original Hart lineup.  MS series, freedom 458, freedom marine, RS3000, fleet power are some I think....did you get the "I think" part?  I just bought a Freedom Marine 3,000 watt for $360 but Zantrex has them for $1,600 out the door. (cough gasp)  MAGNUM is a good brand but I haven't spoken to anyone using one to get a feel for their compatibility with new electronics.  I know that Dick Wright is now handling Magnum and he isn't anyones fool but he isn't passing them off as true sine waves either.  Mag surely does make those also.  I guess the gist of this is that you can get a MSW that will power almost everything and when you buy you BIG screen do it with the understanding that it must prove to be compatible;e with your green power.

Maybe others can recommend other models of inverters that will work.  EBay is the answer as I couldn't afford the quality I needed at new prices. You need to know models and such to set you searches.  get a snipe bidder or you will loose on these items.  I did and then I did, happily.


HTH,

John

[JohnEd]

And Boggie is right...as far as it goes.  Harmonic filters for a square wave of any serious power have huge capacitors in them and the more current you draw the further away from a true sine wave the output goes as a distortion.  He is correct!

My Zantrex (Heart) Freedom is rated for 3KW and it has an enormous transformer but only two little caps that are the size of a "D" cell carbon battery.  It simply cannot be making a sine wave with "filters" alone but you can do that for sure.  Brace yourself for the size of the capacitors and coils on top of the transformer that are needed, however.  My 3K weight 60 pounds without "filters" and being an aluminum frame for boat applications that weight is mostly transformer copper.

But Boggie is right as far as it goes.   There are lots of MSW units out there that work.   If I had the money I would be going with the $4k Outback pure sine wave or the yet to be released power sharing model for 5 grand.   Truly I would.   Maybe the lottery will happen for me but probably not as you first have to buy a ticket.

I mean it about Boggie being right as he usually has been very correct in nearly everything he has said to date that I know of and this is more opinion on his part about inverters.  Make no mistake...i seek his advice. 

John the trouble maker and antagonist,



 

[boogiethecat]

Let's see if I can clarify.
Most modified sine inverters put out simple square waveforms, actually only two pulses, timed and width-modulated to be somewhat lined up in time as a sine wave would be. In other words, a modified sine wave inverter generates a blocky wave which has none of the smoothness of a sine wave, but fewer harmonics than a simple square wave. But that's about all.
There are some modified sine inverters that put out simple stepped waveforms that come closer to sine, but they are still "blocky".  Either of the two then attempt to filter out all of the unwanted harmonics with big capacitors and or inductors.  Neither ever attains the lack of harmonics that  a sine wave offers, and it's the harmonics that are the nasty part.

A "true" sine wave inverter does exactly the same thing- it approximates an analog sine wave with digital steps, with the big exception that it creates many, many digital steps instead of just two or four, and since the steps are correspondingly tiny, it's super easy to filter out any remaining harmonics with a simple filtering network- the result is an actual sine wave that approximates an analog sine wave well enough that no-one (and no equipment) has any issues with the result.

It's hard to communicate in words but diagrams are easy- here- In the illustration a squarewave is shown in green, a modified square wave is shown in blue, and a true sinewave is in red.



The basic reason that modified sine inverters suck is that any energy that is not exactly on the red line is "harmonic" energy, and it manifests itself as RF interference, excess heat in induction motors, etc.  In this diagram, all the energy your refrigerator motor won't get to use is in the yellow areas, which is energy that will get converted to excess heat and RFI.



In this diagram is shown what a "better" modified sine wave inverter might create:


But the big deal is that no matter what the theoretical waveform "should" look like using a modified sine inverter, depending on the load the actual waveform can easily get as messy as this:
(and this is what mine pretty much looked like under load)


...............

...and just for the sake of it, this is more or less what most true sine inverters create, just proir to the final filtering stages:
(although some do it slightly differently, the results are the same- a "true" sine wave! )



There's actually a lot more to all of this, both mathematically and electronically, and what I've presented here is definitely a simplification, but hopefully it gets the point across.
Clear as mud?

[jjrbus]

Out here in the real world, away froms labs and theorys and alogorithims. My Trace/Zantrex DR3624 runs everything I need to run.
Roof top AC   house type refrigerator, Aquios LCD TV, Poloriod LCD TV, 2 LCD computer monitors, Cell phone charger,  Ryobi battery charger, microwave/convection oven, lights both incadesent and flouresent. Dish network receiver, 2 different CD/DVD  players. I also have a Gateway desktop computer and lexmark printer. Many of these items have printed circut boards in them!!
The down side, the microwave clock goes biserk on inverter power, but functions well for cooking. The ceiling fan makes a humming sound, not anoying but I can tell when I am on inverter!
This MSW inverter has been working well for 7 years, if I was buring up lightbulbs, TV's and computers I would have replaced it long ago!

                                                                                          HTH Jim

[JackConrad]

   The only thing in our bus that does not work properly on our Heart Interface 2500 is a Sony digital clock radio. The clock will not keep accurate time. Both flat screen TVs, house type refrigerator, printer, and chargers wok OK.
   We do not run our microwave/convection oven or AC off the inverter.  YMMV, Jack

[luvrbus]

I have used 2 Trace 2012 stacked for years with no problems running anything till here lately the new Sony is 3 months old that I am making a overhead retractable cabinet for and when you try to use on the inverters like Nick said it has a heart attack and so does the induction cook top.JohnEd  do you know when  Mangum is going to release their new inverter they have been telling me for almost a year mine was going to ship

[junkman42]

A simple fix for MSW inverters is to run the output into a 1:1 transformer.  The output will clean up and become a true sine wave.  Normaly the items, particularly battery chargers that do not contain a transformer do not like the rapid rise of a square wave.  The magnetic propertys of a transformer will smooth out the rapid voltage rise of the MSW.  Yes you will have some loss in the transformer, but not as much as You might think.  Try it You will like it!  John

[jjrbus]

Jack got me on that one, I have never used the convecton part of the microwave on inverter power!!! So don't know if it would work. I did forget the electric shaver and vacum work well.
Sometimes  when people are talking about something not working on MSW they may be refering to the small inexpensive inverters, I have very little experience with them. 
Junkman, that is interesting. I am not an electronic person actually electrically challenged. So feel free to correct me on this. I have been led to belive that items like computers, LCD TV's etc do not run on 120 AC, but on DC they have built in transformers? to convert 120 AC to whatever voltage they need DC. I know my cell phone charger changes 120 AC to DC, is that in the true sense a transformer??
                                                            Jim