Tapping a pure sine wave into a modified system

santaigo
santaigo Registered Users Posts: 22 ✭✭
in Off Grid Solar & Battery Systems #1
[IMG][/img]Powerboard.jpg

I posted this photo of my board 5 or 6 months ago and now have it up and running in my place in Baja. A number of my cohorts have brought down small freezers and using a control module that home brewers use, turn the chest freezers into very efficient refers. (In the hot humid months of the summer, the propane refers don't really keep the beer cold - not good.)
My concern is that the Xantrex inverter is a modified sin wave but I can get a small, pure wave inverter pretty cheap just to run the fridge/freezer. Anyone see a problem in attaching the pure wave inverter to the 12 volt input leads at the Xantrex?
edit: I forgot to mention that many fridge/freezer motors will burn out on modified wave systems.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Tapping a pure sin wave into a modified system

    There is no problem with running more than one inverter of the same Voltage off a common battery bank. Just be sure the bank can supply all the power needed and that each inverter has its own fuse/breaker protected wiring.

    What you can not do is connect the AC outputs of two or more inverters unless they are specifically designed to do so (stacking). (Just making sure in case someone reading this wonders.)

    Another potential problem is the use of the word "small" in reference to the pure sine inverter. You may find you need a 1kW unit to start any type of refrigeration unit. It all depends on the particular motor. One of the forum members has managed it with a 300 Watt Morningstar, but it took some doing (and just the right 'frige).
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Tapping a pure sin wave into a modified system

    "Anyone see a problem in attaching the pure wave inverter to the 12 volt input leads at the Xantrex?"

    yes, i see a big problem with putting the sinewave output to the 12v input of the modsine inverter. it can create magic smoke making your modsine inverter disappear from your panel as it will become junk.

    my advice is for you to get 1 good sine wave inverter capable of all of the loads you intend to put to it and keep the modsine inverter as a spare.
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  • santaigo
    santaigo Registered Users Posts: 22 ✭✭
    #4
    Re: Tapping a pure sin wave into a modified system

    I didn't mean to connect the output side of the pure sine wave to the input side of the modified.:blush: That would be nutz.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #5
    Re: Tapping a pure sin wave into a modified system

    I think best practice woul be to attach at the battery. I suppose it the cables going to the Input of MSW was heavy enough it would work but the safer situation is a battery attachment.
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  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    #6
    Re: Tapping a pure sine wave into a modified system

    Prices have come WAY down on PSW inverters. I bought a Xantrex Prowatt SW 2000 Inverter for $349 at Camping World (on sale). Rated at 1800W continuous.

    It'll easily run both my full sized refrigerators, lights, TV, fan, computer, etc. But it does take a substantial battery bank, and fat wire, to supply enough current to run it anywhere near the max rating. I have mine connected to a 900AH battery bank, with 4/0 cable. Some people have reported issues with these inverters, and after doing a little research, they lacked the necessary batteries or cables to do the job. The inverter wasn't the issue. I mention this since I only see two batteries in your setup.

    I do have several paralleled inverters, but they don't share the feed cable. I have my battery bank tied to solid copper busbars, and the inverters are each tied to that. This allows full current to each inverter, and they can be individually taken off-line via Blue Sea battery switches.

    buss2902.jpg

    I agree with the comment about using your MSW inverter as a spare. Buy a decent sized PSW inverter. The smaller ones aren't much cheaper, and it's better to have too much capacity, rather than too little.

    FWIW, both my fridges each draw about 150W with the 1/4HP compressors running. Next to nothing with the compressors off, and ~600W during the defrost cycle.

    It compared very well to my more expensive, and older, Prosine 1800W inverter.

    dscn4928.jpg

    dscn4933.jpg
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: Tapping a pure sine wave into a modified system

    even though i am not certain of what you were actually asking, but i think i agree with 2mtoyz to just get a larger psw sinewave and as was said make the modsine inverter as a spare. you could use a good dc switch like the blue sea model 9001e,
    http://www.solar-electric.com/basw1300amp.html
    to even switch between inverters. i'd suggest having more capacity in the batteries to run several large items at once.
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