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Old 27-12-2014, 09:50   #1
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Inverters; Pure versus Modified Sine Wave

I need to upgrade my charger (currently 20 amp Xantrex) and I figured why not look into an inverter/charger combo. There is a decent price premium for pure vs modified sine wave (I am looking at a basic Magnum models with 2000W/100A). My TV on board is wired directly to 12V. My laptops have all worked on the cheap portable inverters so I assume they will work with modified sine wave. I don't plan on printing or scanning on board. My main use on the inverter function will be a small microwave and perhaps power tools (hopefully not).

What devices won't work with modified sine wave? Is there a general "quality of the unit" difference between a Magnum modified vs pure sine wave unit? Thanks for any and all advice.
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Old 27-12-2014, 11:44   #2
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Re: Inverters; Pure versus Modified Sine Wave

I have an eight year old 3,000 watt Xantrex modified sine wave inverter. I've been running power tools and a vacuum on it as well as my laptop inverter, toothbrush and electric razor charger, tv and stereo amplifier. Haven't used a microwave on it yet so can't help you there.

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Old 27-12-2014, 12:06   #3
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Re: Inverters; Pure versus Modified Sine Wave

Having just built an inverter/charger, I can say that indeed making a true sine wave is does require a lot of extra work.
Now I'm working on converting the microwave to be lower power and run on 12v. Was going to start on a thread on this, I would think such a unit would be marketable, they don't seem to be available, only one company makes a small one.
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Old 27-12-2014, 13:55   #4
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Re: Inverters; Pure versus Modified Sine Wave

Blew 2 phone chargers running on modified. So far no problems with pure SW. The pure SW cost $40 extra but I should have bought it in the first place.
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Old 27-12-2014, 16:05   #5
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Re: Inverters; Pure versus Modified Sine Wave

I've run modified sine wave inverters for years. The only things that I've tried that didn't like modified sine wave was an air conditioner (probably also because it drew too much current, but that poor little inverter wouldn't give up till the battery voltage sagged) but that was an accident.

The other thing is a microwave, it won't cook worth a darn, just makes a loud humming noise and barely warms anything up. I have not tried it yet, but I'm going to guess that some, if not all induction cooktops don't like modified sine wave either due to the way they work.

I've seen some cheap pure sine wave inverters but I'd be skeptical of the ones that are significantly cheaper than the norm, they might not be that pure or that powerful.
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Old 27-12-2014, 21:19   #6
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Re: Inverters; Pure versus Modified Sine Wave

I've had one of these for several years and like it a lot.
No frills, but works great.

OSP Tiger Claw 1500W 3000W Pure Sine Wave Inverter | eBay
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Old 27-12-2014, 22:22   #7
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Re: Inverters; Pure versus Modified Sine Wave

Anything with a transformer, is not going to like a modified sine-wave.

Some won't run at all some will run at a large efficiency deficit..ie; barely work.

Anything transformer and lower power factor will be crippled if it runs at all.

Anything diode rectified, will complain and fail, especially if it has a transformer prior to rectification..think double hit

Last but not least...inverters are rated at watts, but truly should be at KVA's

Watts = Voltage (root-mean-squared) x Amps (root-mean-squared) x Power Factor (PF)

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Quote:
Originally Posted by socaldmax View Post
I've run modified sine wave inverters for years. The only things that I've tried that didn't like modified sine wave was an air conditioner (probably also because it drew too much current, but that poor little inverter wouldn't give up till the battery voltage sagged) but that was an accident.

The other thing is a microwave, it won't cook worth a darn, just makes a loud humming noise and barely warms anything up. I have not tried it yet, but I'm going to guess that some, if not all induction cooktops don't like modified sine wave either due to the way they work.

I've seen some cheap pure sine wave inverters but I'd be skeptical of the ones that are significantly cheaper than the norm, they might not be that pure or that powerful.
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Old 27-12-2014, 23:03   #8
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Re: Inverters; Pure versus Modified Sine Wave

Why would a transformer 'fail' with a square wave??

Quote:
Originally Posted by FlyingCloud1937 View Post
Anything with a transformer, is not going to like a modified sine-wave.

Some won't run at all some will run at a large efficiency deficit..ie; barely work.

Anything transformer and lower power factor will be crippled if it runs at all.

Anything diode rectified, will complain and fail, especially if it has a transformer prior to rectification..think double hit

Last but not least...inverters are rated at watts, but truly should be at KVA's

Watts = Voltage (root-mean-squared) x Amps (root-mean-squared) x Power Factor (PF)

Lloyd
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Old 27-12-2014, 23:34   #9
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Re: Inverters; Pure versus Modified Sine Wave

Hint:

anything with a winding.

2nd hint:

anything restive.

Now you answer the Q.

don't forget rectification.

Lloyd

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Originally Posted by nimblemotors View Post
Why would a transformer 'fail' with a square wave??
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Old 28-12-2014, 00:22   #10
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Re: Inverters; Pure versus Modified Sine Wave

Flying C, you often seem pretty authoritative, but your recent post here flies in the face of a lot of years experience on board our boats. We've had an ancient Heart Interface 600 watt mod sine wave inverter on board since 1988. We have run all manner of devices off of it: computers, power tools, chargers of many sorts, everything we have on board. We even have used it as input power to a 2:1 stepup transformer to power small 240 volt power tools. It has always worked. The only issue noted is that some SCR controlled variable speed power tools don't have smooth transition through the speed range, and make funny noises at times... but they work.

I have never put a scope on the output to check the wave shape on the inverter, but it is clear that it is not a pure sine wave.

So, mate, I just can't agree with your damnation of the MSW boxes. They are not the spawn of the devil, and they have indeed worked for us for a bloody long time... on many of the things that you say it will not work on.

Jim
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Old 28-12-2014, 00:22   #11
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Re: Inverters; Pure versus Modified Sine Wave

A dc-dc converter uses a square wave into a winding,
A flyback dc-dc uses a transformer with square waves.

A difference with square waves is the peak voltage is less to get the same average voltage, and I think a microwave with a 17x step up, needs the peak voltage to generate microwaves. A shorter square with taller peak should be just fine, which might explain why some inverters work and some don't.


Quote:
Originally Posted by FlyingCloud1937 View Post
Hint:

anything with a winding.

2nd hint:

anything restive.

Now you answer the Q.

don't forget rectification.

Lloyd
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Old 28-12-2014, 01:00   #12
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Re: Inverters; Pure versus Modified Sine Wave

Quote:
Originally Posted by FlyingCloud1937 View Post
Hint:

anything with a winding.

2nd hint:

anything restive.

Now you answer the Q.

don't forget rectification.

Lloyd
Way too simplistic (and wrong)

First, a resistive load is ideal for modified sinewave inverters - the fact that it is resistive means there are no impedance effects at all.
Second, just because something has a winding doesn't make it a 'bad' load either.
A modified sinewave is basically a stairstep voltage form approximating the form of a sinewave. The 'step' part has a lot of harmonic high frequency content in it which can be harmful to components if they are selected without regard to that kind of an input. Most consumer products are built as cheap as possible and frequently the components used are stressed past their recommended ratings to keep costs down. In normal life this just shortens the life of the device but the manufacturer couldn't care less as long as the projected life is longer than the warranty. If you add further stresses from highly distorted power input you can easily cause components to fail in a much shorter time span.
One common failure in transformer based power input circuits is saturation of the transformer core which causes distorted output but also much increased heat. If the transformer runs hot to begin with, this can easily drive it over the edge. The distorted output can kill diode rectifier circuits if they are running on the edge as well.

From the speculation department: One can call something a 'modified sinewave' with two voltage steps per half wave output or one can call 10 voltage steps a modified sinewave. The former is cheap to produce but very hard on the loads, the second is much closer to a sinewave and will run a lot of things that a cheap unit would kill in short order. The average consumer will never know the difference but there is a world of difference between them.
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Old 28-12-2014, 01:29   #13
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Re: Inverters; Pure versus Modified Sine Wave

Quote:
Originally Posted by Jim Cate View Post
Flying C, you often seem pretty authoritative, but your recent post here flies in the face of a lot of years experience on board our boats. We've had an ancient Heart Interface 600 watt mod sine wave inverter on board since 1988. We have run all manner of devices off of it: computers, power tools, chargers of many sorts, everything we have on board. We even have used it as input power to a 2:1 stepup transformer to power small 240 volt power tools. It has always worked. The only issue noted is that some SCR controlled variable speed power tools don't have smooth transition through the speed range, and make funny noises at times... but they work.

I have never put a scope on the output to check the wave shape on the inverter, but it is clear that it is not a pure sine wave.

So, mate, I just can't agree with your damnation of the MSW boxes. They are not the spawn of the devil, and they have indeed worked for us for a bloody long time... on many of the things that you say it will not work on.

Jim
Jim,

I'm going to go out on a limb and say that not all modified sine waves are the same. Your unit, being older, may very well have a waveform that is closer to a pure sine wave than a lot of these newer, cheaper MSW inverters. At some point, a waveform that is very close is going to perform a lot like a pure sine wave, while others that look more like a square wave will give a lot more trouble to a wider range of devices.

It seems like a lot of things, electronics included, were built to last longer and work better back in the old days which explains why some people still have an inverter still working great while others have gone through 2 or 3 newer models in the same time span. Not only does it fit the old adage that they just don't make them like they used to, it would also explain why some people's experiences might be different than others. They are all correct, but the difference boils down to which brand inverter they were using.
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Old 28-12-2014, 03:36   #14
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Re: Inverters; Pure versus Modified Sine Wave

Quote:
Originally Posted by Jim Cate View Post
Flying C, you often seem pretty authoritative, but your recent post here flies in the face of a lot of years experience on board our boats. We've had an ancient Heart Interface 600 watt mod sine wave inverter on board since 1988. We have run all manner of devices off of it: computers, power tools, chargers of many sorts, everything we have on board. We even have used it as input power to a 2:1 stepup transformer to power small 240 volt power tools. It has always worked. The only issue noted is that some SCR controlled variable speed power tools don't have smooth transition through the speed range, and make funny noises at times... but they work.

I have never put a scope on the output to check the wave shape on the inverter, but it is clear that it is not a pure sine wave.

So, mate, I just can't agree with your damnation of the MSW boxes. They are not the spawn of the devil, and they have indeed worked for us for a bloody long time... on many of the things that you say it will not work on.

Jim
I could talk all day, but it is you, that has to listen... Someone talking, stops others from thinking.

Go and forage.

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touche touche

Quote:
Originally Posted by socaldmax View Post
Jim,

I'm going to go out on a limb and say that not all modified sine waves are the same. Your unit, being older, may very well have a waveform that is closer to a pure sine wave than a lot of these newer, cheaper MSW inverters. At some point, a waveform that is very close is going to perform a lot like a pure sine wave, while others that look more like a square wave will give a lot more trouble to a wider range of devices.

It seems like a lot of things, electronics included, were built to last longer and work better back in the old days which explains why some people still have an inverter still working great while others have gone through 2 or 3 newer models in the same time span. Not only does it fit the old adage that they just don't make them like they used to, it would also explain why some people's experiences might be different than others. They are all correct, but the difference boils down to which brand inverter they were using.

touche touche

Quote:
Originally Posted by Jd1 View Post
Way too simplistic (and wrong)

First, a resistive load is ideal for modified sinewave inverters - the fact that it is resistive means there are no impedance effects at all.
Second, just because something has a winding doesn't make it a 'bad' load either.
A modified sinewave is basically a stairstep voltage form approximating the form of a sinewave. The 'step' part has a lot of harmonic high frequency content in it which can be harmful to components if they are selected without regard to that kind of an input. Most consumer products are built as cheap as possible and frequently the components used are stressed past their recommended ratings to keep costs down. In normal life this just shortens the life of the device but the manufacturer couldn't care less as long as the projected life is longer than the warranty. If you add further stresses from highly distorted power input you can easily cause components to fail in a much shorter time span.
One common failure in transformer based power input circuits is saturation of the transformer core which causes distorted output but also much increased heat. If the transformer runs hot to begin with, this can easily drive it over the edge. The distorted output can kill diode rectifier circuits if they are running on the edge as well.

From the speculation department: One can call something a 'modified sinewave' with two voltage steps per half wave output or one can call 10 voltage steps a modified sinewave. The former is cheap to produce but very hard on the loads, the second is much closer to a sinewave and will run a lot of things that a cheap unit would kill in short order. The average consumer will never know the difference but there is a world of difference between them.
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Old 28-12-2014, 03:46   #15
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Re: Inverters; Pure versus Modified Sine Wave

Yep

It's by design.

Yet, if the design is not right, then it doesn't work, as well.

Now take 2 separate designs, and why don't they work together?

Lloyd

Quote:
Originally Posted by nimblemotors View Post
A dc-dc converter uses a square wave into a winding,
A flyback dc-dc uses a transformer with square waves.

A difference with square waves is the peak voltage is less to get the same average voltage, and I think a microwave with a 17x step up, needs the peak voltage to generate microwaves. A shorter square with taller peak should be just fine, which might explain why some inverters work and some don't.
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