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Old 05-15-2008, 09:40 PM   #1
Join Date: Apr 2008
Home Port: Stockton, MO
Vessel Name: Ceilidh
Posts: 160

When it comes to sensitive electronics the traditional advice has always been to choose a True Sine Wave Inverter over a Modified Square Wave but many of my friends seem to have had good luck with their less expensive Modified Square Wave Invertors and don't recommend spending the extra money. Probably the only sensitive electronics ours will run are a laptop that is somewhat filtered through the external power supply and a convection/microwave. What do you have on your boats and how does it work for you?


s/v Friendship

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Old 05-15-2008, 10:47 PM   #2
Join Date: Oct 2004
Posts: 3,067

Hello David , Good question!

I extracted the following comments from an article provided by a long cruiser Bob Brooks - Catamaran "Cathouse" I posted the article somewhere a long time ago - it must be in the archives.



* Electronic inverters are not all the same, there are two basic types

on the market.

* SQUARE WAVE INVERTERS are by far the cheapest, most rugged, efficient,

and repairable. On the down side, this type is not well voltage

regulated nor is it's operating frequency very stable but many modern AC

powered devices just don't care. For example: power tools, sewing

machines with brush motors (not the processor controlled types),

computers, TVs and other multi-volt electronic equipment will operate

very well.

Square wave inverters Will NOT work with induction or

capacitor start motors like household fans and refrigerators (motors

with brushes, like your power tools, are ok). Also on the down side this

type generates HF radio noise, has higher idle (no load) current and is

not load sensing to automatically turn on, you must manually switch to

power up AC when you need it.

* The MODIFIED SINE WAVE type inverter is a sophisticated, expensive,

and irreparable (the mfrs. will not provide a schematic and active

components have the identification erased) piece of equipment that is

easily zapped by near-miss lightning. The advantages of most of this

type is that it will sense you plugging-in or turning on your appliance

to power itself up and provide accurate regulated frequency and voltage.

* Combined INVERTER/CHARGERS for marina queens, a lot of money for that

charger function and they radiate HF radio noise that screws up your

radio and everybody else's on your dock.

* The Heart inverters, 120V and 240V

120V inverter and the 240V inverter powers only the microwave, blender,

and power tools.

All of our other appliances are now efficient direct 12V operating. The last

to go were the 19" TV, the computer monitor, and the amplified speakers.

All replaced with a Samsung 15" LCD video/TV/PC monitor, does it all for

only 2.2amps at 12V and a picture quality that must be seen to believe.

The LCD in your laptop fades only a few degrees off axis, this thing is

still viewable 80 degrees off axis.

* You won't find square wave inverters at West Marine. Try looking for

USA made TRIPP LITE on the net. Or, if you're in Thailand, SPECTRUM has

a line of VERY affordable square wave inverters.

MMNETSEA is offline   Reply With Quote
Old 05-15-2008, 11:09 PM   #3
Join Date: Apr 2008
Home Port: Stockton, MO
Vessel Name: Ceilidh
Posts: 160

Thanks Richard,

I did some other research and may yet have to go with the True Sine Wave due to the fact that our Convection/Microwave is digitally controlled and is the largest draw on the inverter. There are many other options today that were not available until recently... Small inverters in the 300 watt range are now available in true sine wave for under $200.00 US. An assortment of dedicated smaller invertors for specific appliances can both save you money and provide redundancy. Unfortunately I have found that digital circuits prefer true sign wave as other wise some of the semiconductors can become overheated to to the lack of efficiency of the modified sine/square wave compared to the true sine wave. While space is limited in our boat I like redundancy where possible, but if the size of the invertor is determined by the largest load and the largest load needs True Sine Wave then I expect to pay for the cleaner energy production. We have a back-up generator aboard that is true sine wave through an inverter, so other options are already available to us and redundancy is already handled.

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