Pure Sine Wave vs. Modified Sine Wave Inverter

[wakerider09]

I am looking to put an inverter on my 25' Doral pocket cruiser. I'll primarily use the inverter to run a 21" LED TV and also to power an HD antenna (when on the hook). The TV is 30watt consumption and the TV antenna i'm sure is significantly less but am unsure exactly.

I would be powering the inverter with a deep cycle 210 min reserve interstate marine battery - I also have a second 1000 cranking battery isolated for engine starts (single screw). I am aware of the fact that a pure sine wave inverter is 'better' in that it more accurately replicates pure AC, but my question is:

1.) is a pure sine wave necessary for the application i'll be using? I've read that a mod. wave can exhibit a grainy or snowy appearance on the tv... or is this such a subtle difference one could hardly notice? Anyone have experience here?

Thanks.

 

[bobdec]

I've run a small flat screen, on a Tivo or DVD player in my conversion van with just a 150W cig lighter adapter inverter w/o any quality issues. Usually any device like a TV, PC, etc. that converts incomming AC to DC or multiple DC voltages does not need pure sine wave.
As far as battery load your TV 30 watts / 12 volts = 2.5 amps do the same for your antenna amp add the wattage then figure a 20-30% efficiency loss through the inverter. EG if your for a load requirement is 50 watts, add 20-30% loss of 10-15 watts = 70-75 watts total load. I'd use a minimum 100-150 watt inverter and it would draw about 70/12= 5.8 amps from the deep cell house battery.. That's 5.8 amp hours per hour, a fully charged house battery w/o any other loads should last many hours between charges.

 

[thumpar]

It probably depends on the quality of the circuits inside the devices you want to run whether it would have an effect or not. If it is not a pure sine wave there is "noise". If the power circuit in the device it better it can take the "noise" out. The antenna is probably more susceptible to have issues if there are any. It is kind of like a cheap car stereo that has a whine with the engine speed but a quality one doesn't because it has a better power circuit that takes the noise out.

 

[Texasmark]

The power supply in today's electronics is much better adapted to power line spikes, high and low voltage variations and such due to the sensitivity of the chips and digital circuitry. Usually there are noise filters at the front end of the power line and once through that the rectifiers pass the dc voltage along to maybe an LC or PI filter that pretty much makes whipped cream out of line noises. So, personally, I wouldn't worry the least about it.

Mark

 

[4now04]

I installed a Xantrex 1800W modified sine wave inverter in our Four Winns 268. It works well and will power most AC accessories. There are two limiting factors. An inverter that is producing a 1000 watts, give or take, can go through battery power rather quickly. The other issue with modified sine wave inverter power is that some AC appliances may be affected and not perform perfectly. I have noticed that a squirrel cage fan will hum, a microwave may take longer to heat something with the inverter than on shore power, and when we connect the TV audio to a new stereo we get a buzz or hum. Having said that, it is still better than not having one.

 

[Texasmark]

Agree on the motors as the change in frequency, the frequency of the non uniformity, and the inductance of the motor are at odds in lay terms.

 

[Chris1956]

The way I understand it, pure 60Hz sine waves are necessary for brushless AC motors like refridgerators and other items. I would think other electronics would tolerate square wave or non-60Hz frequency better. Newer TVs are mostly digital, so they will have some tolerance. Not sure about microwaves, but expect they would like sine waves...

 

[amanphoto]

Modified sign is fine for Tv's and X boxes and computers. But if you want to run something with a heating element like an espresso machine or a microwave you need a pure sign inverter.

To find the size of the inverter. Volts x amps = watts.

 

[KD4UPL]

I build off grid solar systems for a living. Just about everyone has an inverter. MSW inverters have all but disappeared from use in these applications. The PSW units are very competitive on price and eliminate all the questions of "will this work or be damaged".
Heating elements don't care. Incandescent lights don't care. Microwaves will hum loudly and take longer too cook on MSW. They don't have heating elements by the way. Any many motors will hum, especially ceiling fans.
Some electronics will exhibit bad behavior like hum in the audio, lines on the TV, etc. Some electronics will be damaged. I had a customer destroy the electronics in two gas ranges despite my warnings. Apple computers will also be damaged. One of my employees plugged his Apple laptop into my MSW inverter even after I warned him of the danger. He had to buy a new computer. Electric blanket controls are also often damaged with MSW power.
As for your TV and electronics, it's hard to say. It just depends on the quality of your components and the quality of the inverter. At the low power levels your talking about PSW inverters are so inexpensive it's not worth wondering about in my opinion. Get a PSW unit and you won't have to watch fuzzy lines on your screen.

 

[H20Rat]

You guys are all about doing this the hard way!

For $100 to $200, you can have a 21" class TV with a built in DVD that runs on DC (or AC) natively! No need to convert DC, to AC, just to have your TV convert it back to DC... And the amplified antenna has a wall wart that converts AC to DC also, you can get universal DC->DC adapters with different power pins that can be changed.

<---- Firm believer in the KISS approach when it comes to boating! The fewer pieces of electronics gear to fail, the fewer that WILL eventually fail.

 

[thumpar]

You guys are all about doing this the hard way!

For $100 to $200, you can have a 21" class TV with a built in DVD that runs on DC (or AC) natively! No need to convert DC, to AC, just to have your TV convert it back to DC... And the amplified antenna has a wall wart that converts AC to DC also, you can get universal DC->DC adapters with different power pins that can be changed.

<---- Firm believer in the KISS approach when it comes to boating! The fewer pieces of electronics gear to fail, the fewer that WILL eventually fail.

I didn't even think about that. Great idea. For the antenna a straight 12v to the plug that the wall wart goes into would be fine without any conversion.

 

[BRICH1260]

I agree with the 12v TV.I had one in a remote, of grid cabin. Uses much less amps as you do not have to power the inverter.