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Old 17-03-2010, 17:03   #1
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Pure Sine Wave vs Modified Inversion

What's the difference between a pure sine wave and a modified sine wave inverter?
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Old 17-03-2010, 17:06   #2
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Modified sine a square wave that is stepped up like a stair. Pure sine wave is smooth.

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Old 17-03-2010, 17:09   #3
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What's the difference between a pure sine wave and a modified sine wave inverter?

Some items, such as variable speed motors in tools or battery chargers for tools, razors, cameras etc. may not run on a MSW inverter. Pure sine wave is the same wave form you get in your house.
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Old 17-03-2010, 17:16   #4
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There has been a lot of discussion on this and what is and is not affected by modified verses true or pure sine wave. We have used both extensively over the years and have seen no difference in performance or longevity from tools, electronics, appliances or anything else between the two despite all of the theories. We find that rechargeable batteries and chargers do not work to full capacity using either and need 110 volt from a shoreside source to work. WG
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Old 17-03-2010, 17:19   #5
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Both are generated using oscillators & filters. The modified sine wave inverter uses cheaper/simpler filters. While this reduces cost, it can also reduce efficiency in the systems you're trying to power. It can especially be a problem for sensitive electronics, since the filters they have to rectify the AC signal to a clean DC voltage are optimized for a smooth 120V 60Hz sine wave (or 240/50Hz, etc).
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Old 17-03-2010, 17:47   #6
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Basically if you want quality you should buy a pure sine inverter.
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Old 17-03-2010, 18:08   #7
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.........We find that rechargeable batteries and chargers do not work to full capacity using either and need 110 volt from a shoreside source to work. WG
Uhhh, no, not quite. The power from a quality sine wave inverter -- like the Victron, Mastervolt, etc. -- is exactly like that from your household mains, i.e.,. 120VAC RMS 60 cycles pure sine wave. There's no reason a battery charger or rechargeable batteries shouldn't work exactly as they do at home. This is NOT true for modified sine wave inverters, however, Some electronics do not work right -- or at all -- with the MSW inverters (which really should be called modified SQUARE wave inverters, 'cuz that's what they really are!).

Here's what the 120VAC sine wave looks like:

Click image for larger version

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Old 17-03-2010, 18:09   #8
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Basically if you want quality you should buy a pure sine inverter.
Simply buying a pure sine wave inverter does not guarantee quality. There are poor quality pure and modified sine wave inverters. For a boat the inverter should probably be designed for the marine environment as inverters made for the RV industry and for other uses can have issues when installed on a boat. A lot depends on the complexity of the installation. If you are usuing a simple inverter to connect to a 12 volt source, and run small items it probably would not matter. But if this is a more permanent install a marine inverter should be the first consideration. WG
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Old 17-03-2010, 18:14   #9
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Uhhh, no, not quite. The power from a quality sine wave inverter -- like the Victron, Mastervolt, etc. -- is exactly like that from your household mains, i.e.,. 120VAC RMS 60 cycles pure sine wave. There's no reason a battery charger or rechargeable batteries shouldn't work exactly as they do at home. This is NOT true for modified sine wave inverters, however, Some electronics do not work right -- or at all -- with the MSW inverters (which really should be called modified SQUARE wave inverters, 'cuz that's what they really are!).

Here's what the 120VAC sine wave looks like:

Attachment 13940

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Not being an engineer Bill, I can only report on our experiences, using both on our cruising boats for several years. We switched over to pure sine wave inverters and our laptop, cell phones, hand held VHF, hand held GPS and others would still not charge fully with the pure sine wave. Granted, it was not a Victron, but is was a good quality unit. On shore power, there was never an issue. WG
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Old 17-03-2010, 18:21   #10
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WG,

I believe you, but without the ability to put a scope on those "sine wave inverters" it's impossible to say what was going on.

Modern sine-wave inverters have come a long way in design, efficiency, reliability, and lower cost. There really shouldn't be ANY difference discernable between their output and what you've got with shorepower or house power (except that the output of the inverters might be better regulated 120V 60 cycle AC than many shorepower installations!).

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Old 17-03-2010, 18:25   #11
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If you are using a simple inverter to connect to a 12 volt source, and run small items it probably would not matter. But if this is a more permanent install a marine inverter should be the first consideration. WG
Unfortunately we fall somewhere between these two, small boat, small budget but serious intent to stay away from "prosumer" items. Can anyone recommend a relatively inexpensive model that would be suitable for running a laptop, charging a cell phone, or running some tools?
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Old 17-03-2010, 19:00   #12
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Some electrical items will run on modified sine waves and some have trouble. I once used an electric blanket to warm up the bunk before getting into it on a cold winter night away from the dock. The temperature control unit fried and actually started to smoke. Later I read in my inverter documentation that it was not to be used with thermostatically controlled devices such as electric blankets and that a fire could result. I have found that some things don't work as efficiently on the inverter. We have a drink fidge/ice maker that will keep things cold, but will not make ice on the inverter. Plug into shore power or turn on the generator and the first ice cubes come off in about 20 minutes. The microwave seems to work ok, but seems to take a bit longer to do things. It seems I have to give things about 25% more time. I plan to replace my current inverter witha true sine inverter/charger before I go cruising full time. If you can live with the limitations you'll save quite a bit of money going the modified route though prices for the true sine units have started to drop dramatically.
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Old 17-03-2010, 19:59   #13
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(except that the output of the inverters might be better regulated 120V 60 cycle AC than many shorepower installations!).

Bill
No kidding. I run a Monster Cable power conditioner at home now. Spikes during a power outage several years ago damaged my DVR & my DVD recorder.
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Old 17-03-2010, 20:11   #14
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Yes, since modsine does AC in steps, at border it is more prone to produce spikes and those eventually find their way through appliances. Nowadays, mostly laptop, celphone, etc ... charges does use a very robust filtering method that prevent most of the worse, and that's why majority don't find any problem using mod-sine inverters. Try it using a delicate electronics circuitry like your Hi-Fi, and you'll "hear" spikes. Another difference is the power generated, since such power can be "seen" as the sq. area under the waveform, pure-sine does provide more area per same Hz cycle, so the power factor is higher.
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Old 18-03-2010, 07:23   #15
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To emphasize the "spike" description above; I have put an o'scope on the output of a ubiquitous 2.5 kw MSW inverter/charger and observed spikes >300V at the start of every cycle.

I cruised 8k miles with this unit and never had a problem other than, as noted above, microwave took approximately 25% more time to cook.

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