What appliances will not work with Modified Sine Wave inverters?

SolaRevolution Solar Expert Posts: 410 ✭✭
How can you check to see if an appliance will work when powerd by a modified sine wave inverter?

Trial and error can get expensive. Is there a cheaper way?

What happens when an appliance can't handle it? Can the "smoke" be put back in?



  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: What appliances will not work with Modified Sine Wave inverters?

    It's quite a guessing game because not all MSW inverters are alike. Some are really just square wave and some have enough steps and smoothing to be near sine-wave quality.

    As for what will/won't run on them ... That's the second half of the game.
    The more complex the power system in the device, the more likely it will run. Computers have no trouble, for instance. Things powered off wall warts often do (the power supply heats up, burns out). Battery chargers are notorious for not working; in some cases they literally burn up, in others they just don't recharge properly because the line Voltage appears low to them so the reference is off.

    With bigger appliances like refrigerators and washing machines beware of those with electronic controls. Not lot of thought gets put into the power supplies for them, so they "see" low Voltage and don't work right. Usually it doesn't hurt them, at least not right away. They'll either work or won't. Motors will draw more current, start harder, and have a shortened lifespan.

    Now someone is going to come in and tell me I'm wrong, ignoring what I said in the very first paragraph.

    The first thing you have to do is try to get accurate specs on the inverter involved, including its THD. Manufacturers are not keen on giving this info because it tends to make the product look bad. Who wants to buy an inverter that has RMS Voltage of 97 and THD of +/-18%?

    The second thing is to get info from the appliance maker: a direct answer to the question of if they know it will work on a power source with the specs provided by answer #1. Good luck on that too, as most of the time they won't have the faintest idea.

    Not very helpful I know. Sorry. :blush:
  • BB.
    BB. Super Moderators, Administrators Posts: 33,478 admin
    Re: What appliances will not work with Modified Sine Wave inverters?

    It is hard to say...

    Generally, anything built "cheap"... Wall mount transformers and AC/DC converters will usually overheat if loaded to near their rated capacity.

    One of the major tool companies that makes consumer battery powered tools and chargers--Was a report here that as soon as the charger was plugged to an MSW inverter, it stopped working. Later versions were supposed to be OK.

    Things with larger transformers will probably work OK--You can watch their temperature and if they get too hot (start to smell hot), you still have time to disconnect.

    Anything resistive (electric heaters, filament bulbs, etc.) will be OK.

    Brushed motors (AC/DC electric drills) usually work fine too (although, variable speed versions may have problems--vary speed may not work, could overheat).

    Larger induction motors (relative to load), will usually fine... Smaller induction motors/motors that are sized to their loads and/or with poor cooling (such as fridge compressors) may run quite a bit hotter and have a shorter life overall.

    One way that I used to check computer/electronic power supplies... In general, Power Factor Corrected supplies work fine on MSW inverters. I would take a Kill-a-Watt meter and measure the power factor. If it was >0.9, it probably would work fine (although, one thread here had a PFC supply fail on MSW inverter). You can also look at the VA and Watts consumed on Grid Power and MSW and if either goes up a lot on MSW (say +20% or higher vs grid power), then the heat has to go somewhere (usually heating components).

    I have several laptops... The older/larger ones have PFC bump in cord power supplies and same brand but smaller netbook computer is non-PFC. I have not tried the netbook on a MSW inverter--but I would avoid it except for emergencies (PFC is required for larger power/appliances in Europe--But not required for lower wattage AC powered devices).

    In the end, probably 80% of the stuff you plug in will work fine, 10% will fail pretty quickly, and the other 10% it will be difficult to tell.

    For emergency use at home--An inexpensive MSW inverter is probably going to be OK... If something fails, you replace it. Remember that virtually all consumer and most smaller UPS's for computer systems are MSW (although, they are designed for ~15-30 minutes of run time--just enough to save your work and shut down)>

    For a remote cabin/critical application, I would push TSW inverters. Or, at least a smaller TSW inverter for critical/expensive loads. And a large MSW to run the power saw, pumps, etc... You don't need something to fail 100's of miles and days away from replacement parts.

    All About Inverters
    Choosing an inverter for water pumping

    Remember heating is typically the I2R type... So if something "doubles" the current, the amount of waste heat will be 4x as much.

    Roughly, MSW Inductive motor loads will use about 20% more power (wasted energy from square waves). 1.2*1.2=1.44x more more (44% more heat to dissipate).


    PS: Should add--Some electronic timers get their time sync from the AC wave form... MSW wave forms may confuse the electronic timers (run 2x as fast, etc.). Second, MSW inverters have lower peak voltage vs sine wave--Some devices (like florescent tubes) may have problems starting with MSW inverters.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: What appliances will not work with Modified Sine Wave inverters?

    as to what bill said here,
    "You can also look at the VA and Watts consumed on Grid Power and MSW and if either goes up a lot on MSW (say +20% or higher vs grid power), then the heat has to go somewhere (usually heating components).",
    do not think if the % is under 20% that you are ok or safe. extra power being dissipated is extra heat being generated and appliances, parts, etc. can all react differently depending on design, quality, specs, etc. even one item that has more metal to heat sink the extra power or more ventilation may outlast another that has the exact same makeup otherwise.

    there's no definitive answer and msw will not operate optimally in comparison to sine wave ac for certain unless it is a resistive load. in other words, it will be worse than sine wave, but will vary in its degree of being worse with the exception of resistive type loads.