Inverter question(s)

FrxddyFrxddy Solar Expert Posts: 113 ✭✭✭✭
Here's a brain teaser that I've been contemplating. and would like thoughts and opinions from anyone.

Pure sine wave inverters are preferred, even necessary, for a lot of things. Of course they are more costly. Often times we think a certain size will be what we need, but then discover that we need a larger one just to start the item that we want to run.... let's say a refrigerator or stereo. Then of course the larger one is out of our budget. So, here is the brain teaser..... what if we had a pure sine wave inverter that would run the item, (but not start it), and using a time relay, have a modified sine wave start it. So, when we turn the item on, for 2 seconds it starts and runs on modified, then switches to pure sine wave.
Hmmmm? Hmmmm? *smile*

Comments

  • drew4justicedrew4justice Solar Expert Posts: 36
    Re: Inverter question(s)

    Wouldn't that technically create a theoretical brownout? I guess if the switch was fast enough, eh?

    I clicked your signature link. WOW MAN! What a setup you have!!!
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Inverter question(s)

    I've seriously thought of doing that with my earlier fridge and freezer. Start them on a MSW that had no trouble doing that job, then after a few seconds have a DPDT relay instantly switch it over to, say, a Morningstar 300. Never got that far, although I do use something similar on my present fridge and freezer. Along with adding capacitor start on the compressors, I use an autotransformer which drops the voltage to about 95, and in the process, makes more amps available (from the morningstar 300) which is just enough to start the compressor, then after it's up and running, a relay kicks out the auroteansformer and connects the running compressor directly to the inverter. Been working perfectly for my fridge and freezer for over 3 years now, so I see no reason why it wouldn't also work as you describe.
    In my case, the TS300 can't start the compressors directly connected, but reduce the voltage a bit and increase the available current and away we go. :p
    Your way sounds a lot simpler.
  • 2manytoyz2manytoyz Solar Expert Posts: 370 ✭✭✭
    Re: Inverter question(s)

    No longer necessary. A decade ago, the prices of a PSW inverter were rather high. Last year I bought a Xantrex 2000W PROwatt SW inverter at Camping World, for $349 on sale. Rated at 1800W continuous. The waveform looks great on my o-scope, and easily powers the appliances I've tested with it.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Inverter question(s)

    No you don't want to do that. To do that the two inverters need to be syncronized in phase.

    Without phase syncronization the phase will be random at switchover. If happens out of phase there will be a large current surge. It is a little like throwing your car in reverse while driving down the road.

    Modified sinewave inverters with transfer switch like old Xantrex DR series units syncronize the modifed sinewave inverter to AC grid sinewave phase before doing an immediate relay crossover when grid loss is detected. When grid comes back on they slew their inverter phase to rematch grid phase before releasing relay back to grid power.

    Sinewave grid interfacing inverters like Outback FX, Xantrex XW and old SW syncronize phase and voltage and run their bidirectional inverter in parallel with grid. They can go back and forth on their voltage transfer ratio which goes from charging batteries to producing AC output.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Inverter question(s)

    if you are willing to start the appliances with the msw inverter then you might as well just keep it all msw as it isn't just the running part that makes sine wave necessary. i seriously doubt you could switch from one to the other fast enough to make it a smooth workable transition anyway.
  • arghhharghhh Registered Users Posts: 18
    Re: Inverter question(s)
    RCinFLA wrote: »
    No you don't want to do that. To do that the two inverters need to be syncronized in phase.

    This is very important. Switching from one source to another out of phase will trip breakers and blow fuses. I don't think there is any equipment for small scale that will do this.

    I also have the Prowatt SW2000 and the AC looks better than my utility on my scope. They are cheap enough where you could put motor loads on their own inverter.
  • mike95490mike95490 Solar Expert Posts: 8,373 ✭✭✭✭✭
    Re: Inverter question(s)
    arghhh wrote: »
    This is very important. Switching from one source to another out of phase will trip breakers and blow fuses. I don't think there is any equipment for small scale that will do this.....

    Naw, the motor windings just jump off the armature and turn it into an mangled snarl. The inverters don't blow the fuses fast enough.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • arghhharghhh Registered Users Posts: 18
    Re: Inverter question(s)
    mike90045 wrote: »
    Naw, the motor windings just jump off the armature and turn it into an mangled snarl. The inverters don't blow the fuses fast enough.

    I deal with larger inverters usually, exciting way to let the magic smoke out of a 250KW inverter. :cry:

    Either way, probably not good for the fridge!
  • FrxddyFrxddy Solar Expert Posts: 113 ✭✭✭✭
    Re: Inverter question(s)

    < edit>

    Oh gosh... I just realized... when a pure sine wave inverter starts, there's a few seconds of lag... so, it finally hit me why this won't work. Thanks for chatting though!

    <what I wrote before the edit> :

    This "matching phase".... I can understand that if both inverters were "on" at the same time, but with a DPDT relay it would be one, followed by the other. For a split second, there would be no power. As the terminals inside the relay transfer from normally on to normally off, while the points are in the air, they are not connected to either inverter. IF it's the mere fact that the motor is spinning, then I'd understand.

    I do think a good point is made that pure sine wave inverters are cheap enough now. I guess I asked because I happen to have inverters and relays "in stock", and a friend that needs to start more than the pure sine wave will do.

    You think if I tried it could/would do more harm than just blow an inverter fuse? It's not a fridge we're starting, it's a blower motor.


    Drew4justice...thanks for the compliment on my solar array. It's only been on line for 2 1/2 months, but so far, we love it!
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