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Author Topic: Modified Wave Inverter  (Read 1846 times)
Tikvah
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« on: November 30, 2013, 05:17:06 AM »

I have a 2000 Watt Modified Wave Inverter in my bus.  Someday, when I'm rich and famous, I'd like to upgrade to a better unit, but for now, it keeps my house-type refrigerator running when we're on the road and it provides the other necessities. 

However, there's some quirks while we're on the inverter that seem odd to me and I wonder if it is because of the Modified Wave, or if I have some other quirk in my electrical system. 

When on the inverter my convection oven needs to get unpluged.  The digital display goes all goofy and beeps. 
My charger plugs for my iPads get hotter than normal.
My coffee Pot won't function at all.

This isn't because of low voltage, these problems exist while driving as well as parked, so I know I have lots of charge going into the batteries.

I have two large golf cart batteries, and so far I've gone 14 hours running just the refrigerator and a few lights and still maintained... I don't know how long I could actually go.  I don't have a gauge. 

Thoughts?

Dave
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« Reply #1 on: November 30, 2013, 05:22:14 AM »

What is the model and name of the inverter the old modified Trace's were almost a true sine I have a one in a  Trek rv it runs everything without any problems 
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« Reply #2 on: November 30, 2013, 05:31:52 AM »

Sounds like typical modified sine symptoms and not that anything is wrong with your inverter. I changed out my Xantrex Freedom modified sine inverter for a Magnum pure sine inverter to avoid what you've pointed out. The microwave, tv, and wall warts (charging transformers) are all happier now and run cooler. The fridge works great on it too.

I did the upgrade when we put in a residential fridge and I've been very happy with it. I got lucky and grabbed a "used" Magnum inverter on eBay from a brand-new but wrecked motorhome and paid less than half of the cost of a new one. So if you're patient you may find a similar deal.
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Tikvah
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« Reply #3 on: November 30, 2013, 05:34:41 AM »

It's a Heart HF12-2000U

Not a good picture, it's pretty tight inside the bay right now.


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« Reply #4 on: November 30, 2013, 06:03:32 AM »

There are tons of those still in use in the all electric coaches stacked to make 4000 watts in Prevosts from the 80's they run everything, you are a little shy on the battery bank that could be the problem
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« Reply #5 on: November 30, 2013, 07:51:29 AM »

Dave -  I had a heart inverter that was modified sine and had the same issues.  I picked up a 2500w 12v true sine model for about 600$ new (search my posts...there is a link to it somewhere).  It doesn't have all the fancy stuff on it but it does its job. And its alot cheaper than most units out there.

 For a cheap way to monitor your bats...grab one of these and wire a cigaretter lighter outlet somewhere easily accessible.
http://www.adventurerv.net/digital-voltage-meter-p-4020.html?utm_campaign=partsfeed_ppc&utm_medium=cpc&utm_source=Froogle&gclid=CKPz2MTxjLsCFYVZ7AodGykADg   the lighter can double as a USB outlet, light outlet or anything else that plugs into a cigarette lighter.  The voltage may not be exact on the meter but consistent enough that once you start using it you'll know when you have to recharge (definitely way before it gets to 7volts Wink )

-Sean


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« Reply #6 on: December 01, 2013, 06:27:43 AM »

Dave also needs to be as close to the bats as possible as long as there is separation between them.
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« Reply #7 on: December 01, 2013, 08:41:08 AM »

I have an old Trace 2500 watt RV/Marine modified inverter with 130amp charger. It runs everything, but the microwave hums and takes longer to cook, the stove hood runs slower-all typical of a modified sine wave. But-it has been 100% reliable now for nearly 20 years.

I'll probably get a Magnum 2800 true sine for the truck. Or maybe an Outback-anyone have opinions on either? Good Luck, TomC
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« Reply #8 on: December 01, 2013, 09:04:30 AM »

Is there a practical difference between the "True" and the "Pure"?
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« Reply #9 on: December 01, 2013, 10:20:05 AM »

We had a pair of Heart 2500 inverters in our previous coach and they did everything, including powered a new Bosch refrigerator, ran the microwave, TVs, kept my computer charged etc.

Our current coach has a pair of Outback inverters hooked in series so we can run two AC units if we want (that will never happen) and from my layman's point of view the only difference I notice is the remote is significantly more sophisticated. I wouldn't know a sine wave, true sine wave or modified sine wave if I fell on them. I just know my stuff works.
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« Reply #10 on: December 01, 2013, 12:30:06 PM »

     Tom - I had "somebody who knows what he's doing" order my inverter.  I specifically said "load-sharing" meaning a unit that will "share" from the battery -- ie. if you're plugged into a small-capacity socket and you set it to pull only 10Amp but you need 12Amp, the inverter should pull 10Amp off the shore cord and 2Amp (or 240 watt) off the battery.  But until I was using the Outback that he sold me, I didn't know that the Outback was a "load switching" inverter.  If you have the max shore Amps set at 10 and momentarily you need 12A, it will switch off the shore cord and pull all 12Amp (2400 watts) from the batteries - then when your internal load is switched off, it will then pull the 10Amp off the shore cord to recharge the big battery drain that it just used. 
     I talked to the Outback customer service guy and he confirmed that that was the way they work and he generally but vaguely hinted that they were looking at models down the road that would actually load share. 
     But right now, I'd be careful to ask EXACTLY what I wanted.  (Just my experience, what I ran into.) 

BH  NC   USA
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« Reply #11 on: December 01, 2013, 01:59:32 PM »

Is there a practical difference between the "True" and the "Pure"?

Not really any True or Pure sine wave inverters (sine wave only comes from the generator), a smaller square wave is all it means
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« Reply #12 on: December 01, 2013, 03:50:38 PM »

We've got identical Heart 2500's on the boat and the bus.  They run everything just fine with the exception of digital heating blankets/mattress warmers.  The one in the bus makes the bed warmer controls go wonky but unplugging the blanket and plugging it in again puts everything back to normal.  On the boat I switched to inverter once with the blanket plugged in and it completely destroyed the blanket controller.  Different blankets but expensive lesson - we now leave the blanket unplugged unless we're on shore power.  The only other item that we've noticed any effect on is my electric hair clippers (I'm too cheap to hire a real barber so mama cuts my hair)  The clippers appear to run on the inverter but they pull my hair rather than cutting it.  Other than that we've never seen any ill effects from the Hearts which are advertised as modified wave.  I tend to agree with the earlier post which said that the only way to get a genuine sine wave is with a rotating field - anything coming off an inverter is going to be square if you examine it close enough. 
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« Reply #13 on: December 01, 2013, 05:15:18 PM »

We have a very old Trace modified sine wave inverter.  I had several complaints about how poorly it ran some things, but then found out that it was not the inverter's fault, but rather my anemic battery bank.
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« Reply #14 on: December 02, 2013, 02:52:13 PM »

Hi Dave,

I have 2 Xantrex modified sine wave inverters, RV3000s, and have similar problems.   Electronics do not like modified sine wave inverters.  My induction hot plate does not work.   Cell phone chargers get hotter.    Microwave makes odd sounds.   

I installed a new replacement, Whirlpool refrigerator, which was very similiar to the one I removed.   I burned-up 2 electronic defroster boards.   I replaced  the timer with an old style defroster control module and had no additional problems.

Electronics do not like modified sine wave inverters.

Ed Roelle
Flint, MI
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« Reply #15 on: December 03, 2013, 03:20:45 AM »

If anyone (like me, for example) is curious as to how a pure sine wave inverter works, here is a good explanation at a medium technical level:  

Edit:  couldn't make the link work, sorry...


In even simpler terms, a pure sine wave inverter uses an oscillator to create an absolutely pure sine wave reference waveform at the frequency desired (50hz or 60hz), then the sine wave is sampled at around 50Khz (fifty thousand times per second), that sampled output drives a pulse width modulator that creates an on/off switched signal that mimics the sampled sinewave and controls the output MOSFET's (which are power switches).  The 12V or 24V DC battery input voltage is sent to an oscillator, transformed up to 180 volts (the peak voltage of a 120 volt RMS AC waveform) and turned back into DC to power the output stage.  The MOSFET's create a 360 volt peak to peak square-wave output at 50Khz that is sent to a filter (simple capacitor and the output transformer) and the output is smoothed to a pure sine wave again, but at 60hz and with whatever power capacity you designed the MOSFET stage to.  Output distortion is going to be present, but at around 1% to 3% total harmonic distortion compared to a theoretically pure sine wave, not an issue.  The waveform has smooth zero crossing points, which is what induction motors and microprocessors like to see, and the distortion is usually limited to a little clipping at the peaks.  If you use the output to power an induction motor, the CEMF of the motor will further perfect the waveform to a pure sine wave.

This little exercise is why I love these bus forums - I learn a lot, not only from things I read here but from the places my curiosity takes me from questions I find here.  This morning I had no idea how pure sine inverters actually worked, aside from a vague idea of switching power supples and MOSFET output stages, and now I do.   Shocked

Brian
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« Reply #16 on: December 03, 2013, 03:49:23 AM »

DonRowe.com answers a lot of questions about both type inverters on his site I have noticed that over the last few years the Energy Star rated appliances struggle with the modified sine

 Keep your eyes open for a older SW Trace with load sharing it was the best inverter ever made
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« Reply #17 on: December 03, 2013, 04:00:04 AM »

looks like there is no free energy ride here!  sine wave/ pure...   If I get it correct?  if it has  brushes or a toaster= it does not matter which?  if it has  electronic-computer controls=pure sine wave.  Some of the old  units were not as sensitive to sine wave as the new latest and ...   I'm  out of my comfort zone hear..And would like to understand.   Bob
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« Reply #18 on: December 03, 2013, 04:20:04 AM »

Now days in the new high end conversions you are seeing more and more of the Denmark and Dutch made inverters my doctor has the WTC or WTG load sharing inverters in his bus where they are made I have no idea

 They are nice and look expensive lol but no matter the cost I probably paid for a set or 2 for him over the last couple of months
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« Reply #19 on: December 03, 2013, 05:39:52 AM »

Robert, the good news is that pure sine wave inverters are coming down in price quickly, in the smaller sizes and the consumer quality versions.  I bought a 1,000 watt model for $180 last year.  The high end commercial quality inverters are always going to cost more, simply because of quality and programmability.

It's hard to explain why some things work well on MSW inverters and other things don't work well, because it quickly gets into fairly sophisticated electronic and electrical theory.  Some things are easy - anything that is a plain resistive load, like an old-fashioned incandescent light bulb, a heater like a coffee maker, and so on, will work fine with MSW because the square wave output has the same basic amount of electrical energy as a pure sine wave would have.  Induction motors like on an air conditioner or a home style refrigerator work kinda OK, but have issues.  That type of motor is actually generating electricity as it turns, as well as using electricity - that is called the CEMF, or counter electro-motive force - and it pushes back against the input electricity as the motor turns.  The problem is that the incoming electricity is a square wave and the CEMF is a pure sine wave so they fight each other and the motor uses more power than normal.

Other kinds of devices change the electricity in order to use it, and somethings change the square wave easily while others can't change it well at all.  Something with a transformer on the input can take the square-wave and use it fairly well, but other things use filters, capacitors and other things, and they don't like the square wave at all - examples are small battery chargers and things that use some types of "wall lumps" for power. 

Another problem with the square wave is that it is actually made up of the sum of a sine wave plus all of it's odd harmonics, going up in frequency, so a 60 hz square wave has a big 180 hz component, a smaller 360 hz component, a smaller still 420 hz component and on up till they kind of fade away.  Many things can't deal well with the high frequency components of the signal, so even though it has the same amount of electrical power as the pure sine wave, it causes things (like induction motors and microwave magnetrons) to heat up or operate incorrectly.

The well known problem with clocks is down to the wave form that the square-wave inverter puts out.  Basically, as it goes through it's 60 hz pattern it sits at zero for a while, then it jumps up to around 180 volts, then it jumps down to zero again, then it jumps down to negative 180 volts, then it jumps back to zero and sits there till it starts over.  So there is a fair amount of time spent at plus or minus 180 volts, and a fair amount of time spent at zero volts.  Clocks, and timers of all sorts use the zero crossing point of a sine wave to trigger their clocks - it's easy to detect and very accurate.  The square wave doesn't have a zero crossing point to speak of - it just sits around at zero then jumps up or down - so the clock gets very confused.

There are all sorts of other things that work well, kinda OK, or very poorly with MSW inverters.  For example, some kinds of fluorescent lights have ballasts that can actually cause the inverter to overload, they act like a short circuit in a way.

I hope this helps, it's not particularly technically perfect as an explanation but I tried to make it relevant to a lay-person who probably wouldn't have a degree in electronics...

Brian
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« Reply #20 on: December 03, 2013, 06:42:55 AM »

Brian,


To reinforce your comment about capacitors - Earlier, I had said I burned-up 2 electronic defrost timers in my Whirlpool refrigerator.    The component was a capacitor that burned-up each time, as you commented in your last post.    I considered putting a larger capacitor in, but decided to eliminate the whole electronic board.

Ed Roelle
Flint, MI
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« Reply #21 on: December 03, 2013, 11:52:56 AM »

  ... There are all sorts of other things that work well, kinda OK, or very poorly with MSW inverters. ...

    I don't know why but I bought a (fairly nice and large but not expensive) Panasonic "inverter" microwave.  It works fine on the shore power and on the generator but through the Outback inverter, it acts like it's not happy* and seems to pull a lot of power but doesn't seem to get much of anywhere.  Have other people had similar problems?


(* That's the technical term that those of us who knows lots about them electrictrons use.)

BH  NC   USA
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« Reply #22 on: December 03, 2013, 12:09:23 PM »

Which model Outback do you have?

Brian
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« Reply #23 on: December 03, 2013, 02:00:29 PM »

    Which model Outback do you have?  Brian 

    I have an Outback FX 2012 MT. 
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Bruce H; Wallace (near Wilmington) NC
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« Reply #24 on: December 03, 2013, 02:23:12 PM »

That inverter should have no issues with any microwave oven, so all I can say is call the manufacturers help lines.  Sorry...

Brian
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« Reply #25 on: December 03, 2013, 03:28:52 PM »

  That inverter should have no issues with any microwave oven, so all I can say is call the manufacturers help lines.  Sorry...
Brian 

     Thanks.  I know I have a battery issue -- somebody who should have known better came very close to killing my house batteries (wet cell) so I'll get "real batteries" and try again.   BH
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Bruce H; Wallace (near Wilmington) NC
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« Reply #26 on: December 03, 2013, 07:31:13 PM »

FYI - the only current manufacturers of load sharing inverters that I know of are Victron, MasterVolt, and now at last Magnum.

We have a Victron and mostly love it, and I am about to start beta-testing the new Color Control GX control panel for it.

  - Chris
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« Reply #27 on: December 04, 2013, 02:09:31 AM »

 
FYI - the only current manufacturers of load sharing inverters that I know of are Victron, MasterVolt, and now at last Magnum.

We have a Victron and mostly love it, and I am about to start beta-testing the new Color Control GX control panel for it.

  - Chris 

      Thanks, Chris.  I am thinking of going over to the Victron.  They have some nice high-capacity inverters.  Is the quality good?
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