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Wednesday, October 18, 2017

When To Pure Sine Wave And When Not To - Is It Really Needed?

Ready To Travel!
    The 12 Volt system in any RV takes care of most of our camping electrical needs. Lights, Fridge controller, Furnace fan (and sometimes ignition), water pump, etc. That being said, having 120 Volt house style electrical power is very useful. I've written all about having a big, Heavy Duty inverter for supplying electrical power to outlets in the coach, but mine is a "modified sine wave" model. It works fine and dandy. There are a few gotchas that could happen, but haven't to me...yet. For instance, I have heard that microwave ovens work at much less efficiency and harder when fed with modified sine wave 120V AC. Maybe. I know some laser printers just won't work at all. The same with some old style chargers for drills and the like. And inductive loads like motors. As with everything, your mileage may vary (YMMV.) So what to do if you are nervous something could get damaged? Read on!


Modified Sine Wave Example
First, the main concern. The power we have coming into our homes is 115-120 Volts (mostly) and 60Hz. It looks like an ocean wave in shape. Very old school analog. Newer, Pure Sine Wave inverters replicate this wave so it's indistinguishable from house electricity from the grid. Older (and cheaper) inverters take 12 Volt Battery power and change it to be 120 Volt (or so) and kind of a 60Hz wave. Kind of? Well, since they are a digital device, they can't really perfectly replicate an analog waveform. So they simulate it by producing one that has jagged edges (multiple on/off cycles). It usually works fine as is. In fact, higher quality inverters have so many steps that unless you look at the waveform closely, they look purely analog. Just like your new-fangled TV is made up of tiny squares or dots, the closer you get the more "jaggedness" you can see. The trouble happens when sensitive electronic items cannot cope with the stair-step quality and begin to malfunction and/or overheat.

My Inverter (Right) & Solar Charge Controller (Left)
I have tested everything I can think of on my regular modified sine wave inverter. I have a Xantrex 1800 Watt (continuous) one. It has run everything I've thrown at it. When I installed my new digital media players and the experimental OTA Satellite system (Stay tuned for an article on that thing!) I figured it couldn't hurt to have that stuff powered by its own Pure Sine Wave inverter. I mean, it's not consuming a large amount of power, and pure sine wave inverters have dropped dramatically in price, so...why not?

I picked up a quality 300 Watt Pure Sine wave inverter and wired it directly to the main 12 Volt fuse panel in the RV. Since 300 (350 Max) Watts / 12 Volts = about 30 Amps maximum, I made sure the wiring was heavy enough and the fuse was at least a 30 Amp to protect everything. It was still wired through the energy monitor, so I could keep track of energy usage as well. Yes, it's made in China, but tested on the workbench it puts out very clean power. For just over $100 USD online, it was economical to purchase.

I really don't see any difference and my "big" inverter doesn't really use that much power when in standby, so I'm not sure I've gained anything. At least now I have an option. Who knows, I may come across something that requires pure sine wave power...I did want to put an old Okidata LED "Laser" printer on board and I KNOW that hates modified sine wave power...Where can I find THAT antique!

Be Seeing You...Down The Road,

Rich "The Wanderman"
www.thewanderman.com

14 comments:

  1. Electric toothbrushes and electric blankets both require pure sine wave inverters. We damaged one of each using a modified sine wave inverter.

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    1. How about heating pads? Do they require pure sine wave?

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  2. I enjoyed your comments on pure vs modified sine wave. I've had a Cobra 5000/2500 watt modified sine wave inverter in my trailer for almost 20 years (moved from our old 1997 trailer to our new 2012 trailer). I've cautiously tried using it for everything from computers, cell phone chargers, camera chargers, microwave (which we RARELY use!), wifey's hair dryer (a real plus, believe me!) and everything else you can imagine. So far, no problems. Given the amount of time, I don't foresee anything going wrong - knock on Formica. This is not to say something CAN'T go wrong, but I'm a positive thinker - ha. We basically use it to run our Dish box, which we use 95% of the time for the music channels. I've toyed with 'upgrading' to a pure sine wave unit but think, "Hey, if it's not broke, why fix it?".

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    1. Mr Tommy,
      My initial installation was based on cost. PSW was MUCH MUCH more pricey than regular old MSW. Like you, I haven't had any real issues at all.

      Rich "The Wanderman"

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  3. Destroyed my laptop battery and could not recharge my b/o drill with my modified inverter. No problems since converting to a pure sine wave. Nice to have that peace of mind,

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    1. Anonm
      Always better to err on the side of caution!

      Rich "The Wanderman"

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  4. Using Cobra modified-sine-wave for many years, no issues. Microwave, hair dryer, MANY laptops, cell phones, vacuums and other battery devices charged many times with no ill effects. Flat-screen TV, DVD player, etc. etc. I'm totally convinced that "modern" switching power supplies are immune to the 'chunky' waveforms. (Electronically speaking: After all, they all simply rectify it before use.)

    G.

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    1. Unknown,
      I agree...as technology marches on..things should get simpler.

      Rich "The Wanderman"

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  5. Very interesting, as my new 2017 Forest River came with a 2K pure sine inverter, well at least it said it did in their fancy brochure. I was having an issue with a GFIC breaker tripping when I changed over from shore/generator to inverter. After months of BS from the dealer & Forest River & everyone doing their finger pointing, it was discovered that it actually had a modified one! Finally the inverter folks (Magnum said hey our inverter works as designed). Long story short answer, seems the GFCI breaker needed 110 volts to function & the modified didn't supply that when it was just waiting to be used (don't know the proper electric term) somewhere around 105 volts. That also effected the bathroom GFCI, as when you tested it, it wouldn't reset for the same reason. Forest River did replace it with a pure sine wave inverter, but I never had a clue that I didn't have what I paid for. I suppose what I'm saying is more about what you thought you bought & what you actually get on your RV. Basically the are lying & cheating you out of your hard earned dollars. Frankly they are CROOKS & get to say that some item may not be as described, but really my brochure had 11 such items. I'm with Chuck, it's time to stand up the RV industry & tell them enough is enough!
    Thanks for letting me vent!
    Dave

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    1. davtel,
      Very interesting story, it pays to do your research and call out unscrupulous folks whenever possible!

      Rich "the Wanderman"

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  6. Way cute rig! I too am using a Xantrex 1800. It's my add on for kitchen appliances, works fine for microwave, coffee pot, electric skillet and toaster (one at a time!) but does not power up the Nuwave induction hot plate.

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    1. Anon,
      Hmmm..my induction "burner" works great on inverter power, but I wouldn't really use it that way as it's a power hog.

      Rich "The Wanderman"

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  7. Rich, Thanks so much for sharing this really interesting article with us. I have a small older 400W inverter that I installed to run the TV, which is new and it works fine. We have a new this year TT and have been going quite a bit, now lately I've been thinking about a larger inverter in case I want to nuke a quick breakfast sandwich or something, now I'll just stick with the MSW inverter which I can afford! Thanks again! Walt

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    1. Walt,
      My pleasure. Enjoy the freedom and lack of generator noise a larger inverter will afford you!

      Rich "The Wanderman"

      Delete

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