Off Grid Home Forums Technical Discussion Inverters for Computers

Viewing 15 posts - 1 through 15 (of 24 total)
  • Author
  • #63261

    Are Modified sine wave inverters acceptable for computers (and printers, scanners, ect )? Or would a pure sine wave inverter be a better/safer choice?

    Also is there any special/additional grounding recommended for the computer or inverter?


    Hello ttab, I use a modified sine wave inverter and have & use a laptop computer and all-in-one inkjet printer (printer, scanner combo) with no problems, I do not have any special or additional grounding.

    You would need a pure sine wave inverter if you are using a desktop computer or a laser printer.



    I have used modified sine wave with desk top computer for over 11 years. I use an inkjet printer. I also occasionally use a laptop.

    Of course it is all going into a power strip which is shut off after use. I will no longer use it in a thunderstorm, because I lost two from nearby lightning strikes, but that can happen even with grid power. It actually came in through the phone line(dial up once, and phone cable DSL once), which I now disconnect, also, during a storm.


    Any laptop can run off any type inverter since it has a battery that it runs off of.  Most Desktop computer can handle modified or sine if you use an UPS battery backup system it want care either.   Always use a surge protecter or power strip to protect your items.  Another hint is to insure you turn off the power strip to stop the vampire voltage in most electronics.   You actually waste more electricity with this than when the item is running.

    You can buy a small pure sine inverter to run sensitive items with (digital) and a larger modified sine to run everything else.   I have both and run Macbooks, IMacs, standard PC windows based laptops and desktop and the only thing I have found is the timer (clock) might be off a little with the modified sine. That is with the desktops.  The laptops and Macbook since they run off battery they do not lose time.

    If your recording TV shows with a digital clock recorder this is were the pure sine inverter comes into play.  Or you can just open up the time of recording 15 minutes each side if you dont want to spend the money on a pure sine inverter.

    Just my 2 cents worth of information.  Hope it helps


    I recently built a system using 6, 240watt panels and did a great deal of research before buying my inverter. Bottom line their is no black and white answer to which is better as for most things there are tradeoffs. Here is the pros and cons for each.

    Modified Sign Wave


    Low cost – a 400watt MSW inverter is about $40 at any Walmart.  Even a 2000watt inverter will cost around $200-$250

    Compatibility – Almost anything will work with them. There are a few things that will have issues but not many. Some clocks have trouble as they use the 60 cycle from line current as a time base. And my Kill-O-Watt meter would not work.

    The only real cons are that some CFL’s will hum as well as ceiling fans. But the biggest reason not to use one is that some items especially motors and other inductive loads will not run as efficiently requiring more power consumption and can shorten their lives somewhat.


    Now the pure sine wave inverters are much more expensive. I recently bought a 1000watt PSW inverter because as a total solar home I wanted the highest efficiency I could get as power is at a premium for me. The cost was $450 so not only did it allow me more reserve power, but I didn’t have to listen to the ceiling fan complain all night while trying to sleep. Oh, and my Kill-O-Watt meter works with it.

    However for the past few months I used a 400watt MSW inverter and powered my 15″ LED tv, media player, laptop, water pump and lights with no problems at all. So which is better? Well the Pure Sine of course, but the question comes down to what are your personal needs? You will not hurt anything by using the $40 inverter and will most likely never see any difference in most cases. If money is no object get the PSW, if price matters get the MSW and see how it works for you.


    Thak You all for the very good replies. I sincerely apologize for the great lenght of time that it has taken for me to get back to you. I’ve had a number of technical and personal difficulties.

    I should have stated in my original post that I was talking about a desktop computer. From your replies I think the general consensus  as far as desk tops are concerned is that MSW will work but…… The idea of putting the MSW to the UPS battery sounds like a good idea though. I hadn’t thought of that.

    Since a computer is a major investment to me I’m thinking that a pure sine wave inverter would probably be the better way for me to go.  Even if I change my mind later, I know I PSW inverter will be used later on. Probably next year I’ll be using a fairly good sized furnace blower in my heating system. I’m sure the PSW inverter will come in handy for that.

    Any thoughts on MSW for sattellite or wireless internet connection equipment? Any 12vdc connection equipment out there?

    Thank You,



    Hi ttab,

    OK, first of all most electronic devices today run on low voltage DC. The AC that you supply them is converted to 12v, 5v, 3.3v to power the IC’s on board. The power regulator in the device will drop the voltage and regulate it. Since most electronics today are very sensitive to voltage drops, the regulators have filter capacitors used to smooth out line noise so a MSW inverter is no problem.

    As for the furnace blower motor, that could be an issue. Either inverter style would work, but the thing to remember about inductive loads (motors) is that they have a heavy start up surge. If the blower motor is say 3/4 hp then the running wattage will be around 575 – 600 watts; however, the surge may be 2,000 watts or more. That is an expensive PSW inverter. And yes, a 1,000 watt inverter may claim to have a 2,000 watt surge capacity, but don’t believe it. Read the fine print for the specs, the surge capacity may be 2,000 watts, but the surge duration will be less than one second (if it’s listed at all). This is not long enough to start most motors. Now I’m not trying to talk you out of a PSW, just be sure you buy a large enough inverter to power your load. That is the only regret I have about my system, 1,000 watts is just a tad too small for some loads. I would like to run a small 700 watt microwave, but the 700 watts of cooking power requires 1050 watts to produce. A 1,500 or better yet 2,000 watt inverter is what I really would like to have. (It’s on my wish list now)

    An option to get around this is to get a DC motor for the blower. 12v and 24v motors can be had that run at 1,800 RPM to match the 1720 RPM of most AC motors. There is no surge issue with the DC motor since you don’t run it through the inverter anyway. The only down side to that is the wire will need to be a heaver gauge wire to handle the higher current load. But wire is a lot cheaper than inverters.

    One last thing, if I where you I would consider using a laptop rather than a desktop. Laptops use a fraction of the power of a desktop computer, and believe me, using 30 – 40 watts is much easier on your battery bank than a few hundred watts for the desktop. I don’t even use a laptop, I use a netbook. Granted the 10.1″ display is a tad small, but I can use it 24/7 if I wanted to as it runs at around 10 watts or less most of the time, and has never spiked over 26 watts when burning a DVD on the USB powered external DVD drive.




    I design and build modified and pure Sine wave inverters. In 8 years I have blown two DVD players, two desktop computer power supplies, and one directv DVR box using a Samlex inverter. When I ran tests on this unit I found the appliances running from it were using 10 percent more energy then they did on the pure sine wave unit. We run our main house on a Xantrex 4024 pure sine wave unit now.

    Power supply capacitors have a hard time with modified sine wave, but let me clarify. Some modified sine wave inverters use a softer waveform. They try and taper down the hard square waves into a more reasonable stepped pattern to make it easier on appliances to handle. Square wave forms that simply alternate between positive and negative are very hard on power supplies. You can test this for yourself by running even a simple desktop fan on both type of inverters. On the modified sine inverter you will notice the fan motor gets much hotter while running than it does on pure sine wave. This is because the square portion of the wave form is being absorbed by the windings and some of that is being turned into heat without adding anymechanical energy to the fan itself.

    The ironic thing is that from an electronics standpoint, it only costs the manufacturer another 15-20 percent in cost to build pure sine wave versus modified. So there is a large disparity between the two inverter types, which cannot be accounted for in price alone. Now that the chinese are dumping pure sine wave units onto the global market it’s a no brainer. These chinese units cost no more than modified sine wave units, however, they are not built very well. Then again, most of the modified sine wave inverters are not built very well either unless they are well known brands.  Many of the US brands selling modified inverters are now made in China anyways.



    Hi all

    My question is whether I can run my iMac on a 24V solar PV supply (without the need for an inverter)? I am guessing the 110-240V AC is stepped down to somewhere like 24V – I don’t see the point of going 24 to 240 to 24V

    Would a major mod be necessary or can i simply cut the plug off and connect it safely to the 24V ?





    Your Imac most likely uses a standard DC-DC converter since it allows an input of 100-240VAC. Typically these converters will take any DC or AC input in the range stated on the back panel. Since they rectify the AC to DC, then convert it down to 12 and 5 volts DC. Thus you would need to use 100 VDC to 240 VDC by running your panels in series then modifying the plug to hook up to the DC power. 24VDC from the panel would NOT work in this case.

    Of course there is a chance you could turn the Imac into a puff of smoke doing this as well, but it’s unlikely based on how these DC-DC converters work.



    Thank you for your replies. You have given me some things to think about.

    Zathris; I understand about the power surge needed by the blower motor. However I hadn’t thought of the surge duration. That problem hadn’t dawned on me at all. I agree that a 24VDC motor would be a better choice but actually finding one that will fit and mount correctly may be easier said than done . So I guess we’ll see how that works out …..

    I also agree that a laptop would better serve my needs. My reasons for using the desktop were (A) I already had it and (B) because of some vision problems I have the small screen on a laptop is very difficult for me to use. I need the larger monitors on a desktop. Of course since the desktop has gone belly up (A) is now a moot point. And funding has dried up for the present so I suppose I’ll be spending $5 worth of gasoline to get to the free computer at the library.

    Mr Energy;  I always suspected that some brands of MSW inverters were more ‘modified’ than others. But other than buying then testing  how is a person to know which brands are better than others? I could take the power supply filter coil and capacitors froon old tube type TV. Do you think that might help smooth out the MSW square waves? (At least on a circutt just for a computer.)




    The best way to know for sure is to get a screen shot of an oscilloscope output of the waveform. Most inverter manufacturers are showing the waveform output on their website. Here is one that I tested in the lab to show what a stepped modified waveform looks like.

    <embed width=”440″ height=”420″ type=”application/x-shockwave-flash” src=”″&gt;

    The above inverter company (PowerJack) now makes these inverters as true sinewave.  The plugs were universal plugs and not just euro plugs, as I was mistaken.

    Of course pure sine wave looks like this:

    Image and video hosting by TinyPic

    Waveform shaping can certainly be done with an LC filter. You will need to play with the values of the components but you can certainly soften the waveform a bit. As for filtering enough to get a pure sine wave from a modified, it would require alot of testing. A laptp can run a large LCD/LED screen off the port in the back. Laptops now come with both VGA and HDMI output on them to run large monitors or even TV’s from the output.




    Video of powerjack modified output on scope:

    [URL=]PowerJack PSW interver output[/URL]


    Please excuse the delay. My computer time is very limited.


    Thank you MR. Energy for taking the time to find those screen shots.  I have a background in electronics also but mine is from the dinosaur era.  My first impression from looking at the screen shots is that such a waveform would have to generate a lot of RF noise. Especially with a couple of hundred watts running through your house wiring . Your house wiring acting as a big antenna.  I would be surprised any one could use a an AM radio anywhere near such a thing.  I’m worried that a computer could (not nescesarily would but could) mistake some of the peaks of the noise for bits. That much power in the RF noise that close by would almost have to be induced in to the computer circuitry somewhere. Or at least so it seems. Yet many people use MSW with their computers with no problems. Quite baffling  So I guess it is time for me to try something and see whats happens.


    Thank you all.




Viewing 15 posts - 1 through 15 (of 24 total)
  • You must be logged in to reply to this topic.