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Old 28-12-2014, 03:52   #16
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Re: Inverters; Pure versus Modified Sine Wave

Jens,

I didn't say resistive didn't work...now did I?

I said:

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)

Now we have to regard capacitance. As well as ?

Lloyd



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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, 03:58   #17
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Re: Inverters; Pure versus Modified Sine Wave

Certain generators have a perfect sine-wave...no load.

As soon as the load is applied, it goes to something less than sine-wave.

A restive load affects differently, then an inductive load, and differently than an SCR.

Why?

Lloyd

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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.
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Old 28-12-2014, 06:33   #18
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Re: Inverters; Pure versus Modified Sine Wave

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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 certainly won't equate MSW with devil spawn, and don't discount your experiences. However, our experiences were different, and more in line with FC's.

We used to have an older, quality MSW inverter/charger (Trace U2512). While most things ran with it just fine, it often caused transformer-based power supplies (wall-wart chargers) to buzz. It always caused them to get pretty hot. We actually burned up two of them - one smoking and almost catching fire before I caught it, while the other was found dead with brown discoloring and swelling. These were supposedly quality transformer-chargers, as they were standard on our quality equipment (one was an Apple laptop, and the other was a handheld VHF charger).

I never could get my cordless drill chargers to work with it, and while the microwave "worked", it took forever to cook anything in it. Stereos and TV's would have a constant audio buzz in the background. In addition, I could not install GFCI outlets with it because they would just pop and be worthless.

All of these problems went away when we changed to a quality sine-wave inverter/charger.

Mark
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Old 28-12-2014, 06:44   #19
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Re: Inverters; Pure versus Modified Sine Wave

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Originally Posted by colemj View Post
Jim, I certainly won't equate MSW with devil spawn, and don't discount your experiences. However, our experiences were different, and more in line with FC's.

We used to have an older, quality MSW inverter/charger (Trace U2512). While most things ran with it just fine, it often caused transformer-based power supplies (wall-wart chargers) to buzz. It always caused them to get pretty hot. We actually burned up two of them - one smoking and almost catching fire before I caught it, while the other was found dead with brown discoloring and swelling. These were supposedly quality transformer-chargers, as they were standard on our quality equipment (one was an Apple laptop, and the other was a handheld VHF charger).

I never could get my cordless drill chargers to work with it, and while the microwave "worked", it took forever to cook anything in it. Stereos and TV's would have a constant audio buzz in the background. In addition, I could not install GFCI outlets with it because they would just pop and be worthless.

All of these problems went away when we changed to a quality sine-wave inverter/charger.

Mark
It is funny you guys bring this up as I just had a customer who's second microwave bit the dust in October. He installed his third a few weeks ago and noted that it was "louder" when run off the inverter than it was when run off shore power.... Yep...

While I was there I threw my Kilowatt meter on it and and ran it off shore and his inverter. It drew 1510W +/- on shore power and 990W +/- on his old Freedom inverter. He then understood why they were dying and why they were loud... After some Q & A it appears he's also destroyed a lot of camera and other batteries off the inverter as well, but never attributed them or the microwave failures to the inverter.

We weighed the cost of a new inverter, vs. a new microwave every few years, and he will now charge computers etc. off 12V. He decided to stick with the old Freedom until it dies, and then he will likely go pure sine......

As has already been said not all inverters put out the same wave. Some MSW's are much better than others. Most Freedom's I do not find too bad. His particular Freedom was horrible..
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Old 28-12-2014, 09:49   #20
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Re: Inverters; Pure versus Modified Sine Wave

Isn't it about time for someone to say how things not designed for a marine environment will not last in a marine environment..

Sounds like someone would be a customer for a lower power, more efficient 12v microwave. The ones I have taken apart use solid wires from the transformer to the capacitor. These are fine in a house, but can work harden and break in a marine environment.
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Old 28-12-2014, 10:02   #21
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Re: Inverters; Pure versus Modified Sine Wave

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Originally Posted by nimblemotors View Post
Sounds like someone would be a customer for a lower power, more efficient 12v microwave. The ones I have taken apart use solid wires from the transformer to the capacitor. These are fine in a house, but can work harden and break in a marine environment.
With regards to the type of inverter, how the microwave is wired/built isn't the issue. The issue is the peak power of the source. Our microwave is 16yrs old and runs just fine in the marine environment. I don't see how its environment on our boat is any different than that in a beach house. It's not like it has water dripping on it or sloshing around its interior. Also, no matter how much the boat moves, I have a difficult time believing the interior wiring is moving and work hardening.

A lower power microwave means longer cooking times. There is no free lunch on that, and the use of a good inverter makes the conversion losses pretty negligible for the short time it is in use. I don't see any advantages of a 12V microwave.

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Old 28-12-2014, 10:06   #22
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Re: Inverters; Pure versus Modified Sine Wave

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Originally Posted by nimblemotors View Post
Isn't it about time for someone to say how things not designed for a marine environment will not last in a marine environment..
Sorry for breaking this up into two parts. I don't think one can generally make that statement. We have computers, TV's, stereos, cameras, phones, tablets, guitars, small inverters, etc on board that were not designed for a marine environment, and none of them have been harmed by being in one. Some of them are 16yrs old, having spent their entire lives on the boat.

It is true that some things may not be desirable in this environment - but those usually involve really cheap consumer items, or things with mild steel cases, etc that just look and feel bad in a marine environment.

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Old 28-12-2014, 10:55   #23
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Re: Inverters; Pure versus Modified Sine Wave

There are so many different loads today compared with 20-30 years ago that it's hard to build a decent inverter that will support anything and everything. But in general, pure sine wave inverters are "more compatible" with "more stuff" than modified sine wave inverters. But even pure sine wave units can be challenged by certain devices and often it's the case that a MSW unit can work for a device where a pure sine won't. There is no hard and fast rule either way. No mater what, you may find some device doesn't like the inverter. A "trick" that sometimes works is to connect a space heater or hair drier on low heat when running a troublesome device. It wastes power but if you absolutely need to run something it will often work. This trick often works with small generators too.

The reason microwave ovens don't like MSW is their high voltage power supply has a high leakage transformer and the high voltage diodes respond to the peak AC voltage. A MSW has lower peak voltage than pure sine. This screws up the frequency of the magnetron in addition to producing much less power. That's why Mainesail measured less power consumed by the microwave. This can also overheat the magnetron collector and leads to reduced life span. If your microwave cooks slower on the inverter than shore power you are likely killing the magnetron.

Transformers generally don't care about MSW or pure. It's what is on the secondary of the transformer that cares.

The most common problems are caused by bad installations. Too small wire to an inverter that is too far from the battery. Also, the battery cables should be run right next to one another directly from the battery to the inverter separating only to allow the addition of a fuse and disconnect switch. This reduces inductance and inductance hurts inverter performance. Keep the DC cables short and make them bigger than you think is necessary. Don't size the DC cable based on the inverter terminals unless the wire is really short. You may need a terminal junction close to the inverter to use a smaller short connection to the inverter. Assume the DC current is equal to 1.5 times power divided by nominal battery. A 1000W inverter on 12V should be wired for 1.5*1000/12=125 amperes at 3% drop. 5% drop may be ok but 10% voltage drop wire sizing will usually cause problems.
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Old 28-12-2014, 11:36   #24
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Re: Inverters; Pure versus Modified Sine Wave

I should probably start a new thread for this but here goes. To the OP. I have a Magna 2000 inverter charger (modified sine wave) and it runs everything I have thrown at it including my 1000 W microwave. My question is this. If you really find something you need pure sine wave for couldn't you get a computer UPS at any electronic store. Charge that with your modified sine wave inverter and run your device with the backup UPS.
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Old 28-12-2014, 12:19   #25
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Re: Inverters; Pure versus Modified Sine Wave

Mark, that's not a bad idea. But a small 400W pure sine inverter will do the same job and it does not require another battery like the UPS. The small inverter may be less expensive as well since it does not need a charge function.
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Old 28-12-2014, 12:41   #26
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Re: Inverters; Pure versus Modified Sine Wave

OK, I get it: different inverters, different wave shapes, different results in use. I now accept that some, possibly most, MSW inverters are indeed the devil's spawn and should be avoided. But I still object to the statement that MSWs will not work doing this or that when mine does work. How about saying that SOME MSW inverters will not work?

Now the operative question: when considering purchase, is there any way other than carrying a portable scope around to the shops and testing to determine what the output wave shape from an inverter is? This includes both MSW and alleged pure SW designs. I'm actually thinking about buying a smallish 240/50 inverter to add to my 110/60 unit. It is a PITA when one spends most of one's time in 240 volt lands to be restricted to electrical stuff imported from the states.

Cheers,

Jim
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Old 28-12-2014, 12:53   #27
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Re: Inverters; Pure versus Modified Sine Wave

Watts and Volt Amps – What’s a KVA and how is it calculated?


Have you ever wondered why some power ratings are expressed in WATTS, some in AMPERES or AMPS, some in VOLTS, and some in KVA? This page will explain in simple terms the difference between the power ratings and describe when each should be used in your data center and network architecture planning.
A KVA is simply 1,000 volt amps. A volt is electrical pressure. An amp is electrical current. A term called apparent power (the absolute value of complex power, S) is equal to the product of the volts and amps.
On the other hand, a watt (W) is a measurement of real power. Real power is the amount of actual power that can be drawn from a circuit. When the voltage and current of a circuit coincide, the real power is equal to the apparent power. However, as waves of current and voltage coincide less, less real power is transferred, even though the circuit is still carrying current. Differences between real and apparent power, and thus watts and volt amps, arise because of inefficiencies in electrical transmission.
The resulting inefficiency of electrical transmission can be measured and expressed as a ratio called the power factor. The power factor is a ratio (a number from 0 to 1) of real power and apparent power. In the case of a 1.0 power factor, the real power equals the apparent power. In the case of a 0.5 power factor, real power is approximately half that of the apparent power.
Deploying systems that have higher power factors result in less electrical loss and can help improve your Power Usage Effectiveness (PUE). Most Universal Power Supply (UPS) units will list the average power factor and real-time load capacity of the UPS, in addition to the KVA.
Example: You own a 500 KVA UPS unit (apparent power) with a 0.9 power factor. The resulting real power is 450 kilowatts.




So you see Jim, PF of the device will also effect how it runs on a Modified Sine-Wave. Also not all MSW Inverters have the same wave form, some have lower peak voltage and some have more square wave. It also depends on the quality of the transformer in the inverter it's self.


Lloyd



Quote:
Originally Posted by Jim Cate View Post
OK, I get it: different inverters, different wave shapes, different results in use. I now accept that some, possibly most, MSW inverters are indeed the devil's spawn and should be avoided. But I still object to the statement that MSWs will not work doing this or that when mine does work. How about saying that SOME MSW inverters will not work?

Now the operative question: when considering purchase, is there any way other than carrying a portable scope around to the shops and testing to determine what the output wave shape from an inverter is? This includes both MSW and alleged pure SW designs. I'm actually thinking about buying a smallish 240/50 inverter to add to my 110/60 unit. It is a PITA when one spends most of one's time in 240 volt lands to be restricted to electrical stuff imported from the states.

Cheers,

Jim
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Old 28-12-2014, 12:54   #28
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Re: Inverters; Pure versus Modified Sine Wave

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Originally Posted by Jim Cate View Post
OK, I get it: different inverters, different wave shapes, different results in use. I now accept that some, possibly most, MSW inverters are indeed the devil's spawn and should be avoided. But I still object to the statement that MSWs will not work doing this or that when mine does work. How about saying that SOME MSW inverters will not work?

Now the operative question: when considering purchase, is there any way other than carrying a portable scope around to the shops and testing to determine what the output wave shape from an inverter is? This includes both MSW and alleged pure SW designs. I'm actually thinking about buying a smallish 240/50 inverter to add to my 110/60 unit. It is a PITA when one spends most of one's time in 240 volt lands to be restricted to electrical stuff imported from the states.

Cheers,

Jim

The only thing I can think of is to look for online reviews of the unit, specifically if it works well for the devices you want to plug into it. I've sure saved a lot of grief by checking Amazon reviews or just doing a google search for the item.

I'm still amazed by the weird, niche websites where people discuss all kinds of odd topics. Just read one an hour ago devoted exclusively to hacking or modifying action cams. Talk about a small niche!

If you don't need a powerful unit, perhaps a pure sine wave unit would be the safest choice if it's not too expensive. Seems like they're getting cheaper.
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Old 28-12-2014, 14:27   #29
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Re: Inverters; Pure versus Modified Sine Wave

When I buy anything like this I read reviews first then I call their customer service to ask some question about what I want to buy. Depending on how long it takes to answer or return a call, and the kind of treatment I get, and the knowledge of the staff. I make my decision. That is why I went with the Magna charger inverter, Based in Wa state.Raymarine electronics & Emtrak AIS receiver I bought. they are based back east and that,s where they answer the phones
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Old 28-12-2014, 14:38   #30
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Re: Inverters; Pure versus Modified Sine Wave

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How about saying that SOME MSW inverters will not work?
I don't think that is the issue. I think it would be more appropriate to say that SOME devices will not work with MSW inverters - which covers the differing experiences with them.

In our example of a very high quality and well-regarded MSW inverter, many things worked just fine, but some very specific things did not. Interestingly, most of those devices that did not work were newer electronic designs. Microwaves will never work as well with MSW because of the peak power issue.

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