inverter sine wave vs modify sine

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System
System Posts: 2,511 admin
in Solar Beginners Corner #1
i noticed the modify sine is cheaper and has higher watts.
which one is better for an off grid system

thanks.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #2
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    Re: inverter sine wave vs modify sine

    the inverter you buy should be determined by what you are going to power ie a saw, fridge, or ???


    Eric
     
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
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    Re: inverter sine wave vs modify sine

    Read the Inverter FAQ for the basic comparisons...

    And there is the HomePower Mag inverter article from 7 years ago...

    Basically, my 2 cents... If you just need an inverter to power the occasional drill, TV, etc... It is hard to beat the price on a Mod-Sine/Square-wave inverter...

    However, if this is an off-grid situation for long term use--and you don't want to risk expensive and/or occasional unplanned failures do to us of MSW inverters--get the True Sine... Or get a smaller True Sine for your "home/electronic/Fridge/Freezer stuff" and get a big MSW for the old well pump/table saw usage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #4
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    Re: inverter sine wave vs modify sine

    Eric,
    i will use inverter to feed power thru the household electric panel for lights, computer, small fridge. Power tools when use will plug direct to the generater.

    bill,
    thanks for the link.

    westbranch wrote: »
    the inverter you buy should be determined by what you are going to power ie a saw, fridge, or ???


    Eric
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
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    Re: inverter sine wave vs modify sine

    Couple other issues with MSW inverters...

    Do not ground the Neutral connection in the electrical panel (like normal NEC code would require) when running MSW inverters... I believe that some (all?) will get a case of input to output short circuit when the DC battery input is grounded and the AC Neutral is grounded...

    Also, if you are using transformers (220 for well pump and such)... MSW inverters will waste about 20-25% of their output in waste heat (in transformers and motor windings)... So--you will have to oversize your inductive devices if intended for continuous loads/operation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
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    Re: inverter sine wave vs modify sine
    BB. wrote: »
    Couple other issues with MSW inverters...

    Do not ground the Neutral connection in the electrical panel (like normal NEC code would require) when running MSW inverters... I believe that some (all?) will get a case of input to output short circuit when the DC battery input is grounded and the AC Neutral is grounded...

    Also, if you are using transformers (220 for well pump and such)... MSW inverters will waste about 20-25% of their output in waste heat (in transformers and motor windings)... So--you will have to oversize your inductive devices if intended for continuous loads/operation.

    -Bill

    Bill is absolutely right on this one,,,I know from experience!

    Many of the smaller true sine wave inverter also suffer from the floating neutral problem. The only small tsw (under 500 watts) inverter that I know of that you can ground the neutral is the MorningStar Ts 300. As has been suggested consider what you are really going to do with any inverter. If it is going to be a "permanent" install consider the true sine wave.

    Tony
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  • System2
    System2 Posts: 6,290 admin
    #7
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    Re: inverter sine wave vs modify sine

    Also, unless you have lots of spare power, seriously consider, as was mentioned earlier, a smaller inverter that perhaps could be always on, for lights and misc small loads, and a bigger inverter for the bigger loads. Reason? The bigger the inverter, the bigger the "idle" power draw from your battery system.
    Do you really want to waste 20 or more watts continuously, just to run a 7 watt CF lamp for the evening? Fine of you have lots of excess power, but most off grid systems do not.
    By the way, I've been running 2 of the Morningstar 300 Pure Sine inverters for a year now and find them A-1. VERY pleased with them. One is on 24/7 for lights etc and the other for a dedicated load. I do have bigger inverters for bigger loads too, but they only come on when needed.
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  • wxh3
    wxh3 Solar Expert Posts: 70 ✭✭✭✭
    #8
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    Re: inverter sine wave vs modify sine
    icarus wrote: »
    Many of the smaller true sine wave inverter also suffer from the floating neutral problem. The only small tsw (under 500 watts) inverter that I know of that you can ground the neutral is the MorningStar Ts 300.
    Tony

    I believe my Exeltech 250W TSW inverter also has AC neutral grounding. The manual states "The AC neutral lead is internally bonded to chassis; chassis must be bonded to earth ground through the external ground connector located on the unit."

    My Samlex 300W TSW inverter AC neutral is not bonded to chassis ground and the manual suggests you follow national/local electrical codes regarding grounding. At least it doesn't say to not ground the neutral.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #9
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    Re: inverter sine wave vs modify sine

    whx3,,
    I stand corrected, I think I have heard of the exeltch being able to be grounded. I would take a look at the Samlex however. While the manual suggests installing to "code' it doesn't specify how. I would contact the manufacturer and see what they say about bonding the neutral,

    Tony
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