Sensitive electronics running on msw Inverter for cheap.

[eXodus]

just made an interesting discovery:

I bought an 115-230 step up tranformer ($6 amazon) for my electric razer which i brought from germany, it was not working on the 115v of my msw inverter. Even it worked at home.

i plugged it in the transformer and the buzzing was gone.

My hd tv reciever was not working on my inverter, it just didn't power up. but was loud buzzing. So i did read the label of the reciever 100-240v so I'd give it a try and plug it into the transformer. Now it's working and not humming anymore.

I'm guessing that the trafo smoothes out some of the Msw wave form. maybe one of the geeks here could dig deeper into the topic. the step ups available in 50w and 100w. so it's only a fix for small stuff. and you have to check if your devices are good for 230v

[HamRad Mobile]

Good morning, eXodus; 

     Yes, there can indeed be problems when trying to run things off a "MODIFIED SQUARE WAVE" inverter.  Those simple things should in no way be allowed to use the phrase "sine wave" in any published literature about them.  It may be a multiple step square wave, but it is not a "sine wave," and the harmonic content of that square cornered waveform is still impressively high.  Madison Avenue got to us again. 

     Yes, using a transformer will indeed help to smooth out and round off the corners of the square waveform those things put out.  The coils of the transformer windings with their inherent inductance that resists the change in the flow of a current through them is what is helping you.  It is a little bit like a mechanical flywheel where the inertia of the flywheel will resist any fast changes in the rotational speed of the mechanical system to which the flywheel is attached.  Similarly, the inductance in those windings and the magnetic field around the windings will resist any fast or abrupt changes in the current flow through the coil windings. 

     There are a lot of electrical things that really do like a real sine wave being fed to them.  A modified square wave type waveform with its high harmonic content may not be something they want to digest.  It upsets their tummy. 

     While they may be more expensive, the only thing I would trust is one that is clearly labeled and described as a "true sine wave" or "pure sine wave" or "real sine wave" or something similar that shows that the maker has made some real effort to give you something that really does make electrical power with a waveform that looks like a rotating field electrical generator or a single phase alternator. 

          Enjoy; 

          Ralph 
          Latte Land, Washington 

[eXodus]

Thank you ralph for the explanation.


i did learn to be an electrician two decades ago, and we never had something more about the topic in school. No one needs a waveform when you crawl throug channels and dig in cables.


a true sine wave would be great but awful epensive at the moment. they will come down in a couple of years, but i did need a 2000w to run my fridge now, as Msw you pay 50$ as true sine it's more like 400-600.
this will change fast. but for the moment I stick for the 50+6$ transformer solution.

[HamRad Mobile]

Good morning, eXodus; 

     When looking at the efficiency of RV refrigerators, the gas absorption cycle types are still the most efficient in comparison with the energy consumed.  When we factor in the other conversion losses to bump up and convert (invert?) the 12 VDC from the batteries up to 120 VAC to run a "household" type compressor operated refrigerator,  the old gas absorption type really does look pretty good, and they are also available in a "three way" powered form that uses the propane gas, 12 VDC directly, and 120 VAC.  They are more expensive, yes, but if 120 VAC power is not available, it is kinder to your batteries to operate it directly off 12 VDC than to go through an inverter to bring the coach 12 VDC up to 120 VAC 60 Hz to run the refrigerator. 

     I do agree that the gas absorption type does ask that the coach be level when it is parked and the refrigerator is on, while the compressor types are quite tolerant of being operated up to 30º off level.  This attitude requirement of the gas absorption type does not seem to be a great disadvantage when driving, and the makers do say that this is permissible operation without any great effect on their system. 

     However, you already have the 120 VAC 60 Hz type refrigerator in your motor home.  That does mean that the idea of a good sine wave inverter is still a good thing, both for the mechanical parts of the refrigerator and for the modern electronic control system in the refrigerator, along with all the other electronics in your motor home.  One good point is that once it is cooled, the refrigerator will not be running all the time, and it will cycle on and off as the inside temperature rises due to the insulation heat losses.  Anything you can do to reduce the heat input into the refrigerator will also improve the efficiency. 

     One thing that I am doing with my gas absorption type refrigerator is to place a covering of adhesive bright reflective sheeting on the outside wall of the motor home in the area of the refrigerator heat exchanger ventilation shaft where the refrigerator condenser coil is located to reduce the amount of solar radiation that will warm that outside wall of the vent shaft.  When I have all the cables run up to the roof through one end of the heat exchanger vent shaft, then I will know how much space will be remaining at the very top end of the vent shaft so that I can make the size panel that will hold three small 12 VDC operated "muffin fans" with a thermostatic control to turn the fans on to improve air flow through and up the vent shaft when needed.  There are enough solar panels on the roof to make this fan system a practical thing to do.  This will be better than the existing convection air flow system. 

     OK.  While I cannot really tell you what you should do for your system, at least I can tell you about what I am doing to improve the efficiency of mine. 

          Enjoy; 

          Ralph 
          Latte Land, Washington