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Thread: Can I stack inverters with different wattage?

  1. #1
    robertas9 Guest

    Default Can I stack inverters with different wattage?

    Hello,
    I am thinking about alternative energy and I have questions. First of all, I see that I can get used inverters a lot cheaper than new and that is great. But finding two same wattage inverters are different. So can I stack different wattage inverters?

    Secondly, I am curious about grid tie systems. How does current chooses where to come from? From the grid or from inverter? I saw system diagrams and inverters are connected straight to the grid system.

    Also, how does inverters synchronise them self then stacked?

    Thats all for now.

    Best regards,
    Robert

  2. #2

    Default Re: Can I stack inverters with different wattage?

    Stacked inverters must be units designed for that application; you can't tie together any two inverters and get anything other than smoke, sparks, and fire. So two Outback 3524's, yes. One Samlex and one Magnum no. Likewise they should be of the same Wattage. In theory two different Watt but compatible units could be connected, but when the load goes up the smaller unit will be over-taxed in comparison to the larger one. Stack-compatible inverters synchronize by having one "Master" inverter from which the "Slave" inverters take their cue for frequency synchronization and power output. Mis-matched units would probably result in confused synch info. I don't know exactly because I don't build the things and I'm not going to try any such experiment!

    Don't know if I'm explaining this well.

    Grid-tie inverters function in a similar fashion, viewing the grid as a "stacked inverter".

    There are experts in this field here who can give you quite a detailed explanation, if you wish.
    Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  3. #3
    Join Date
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    Default Re: Can I stack inverters with different wattage?

    I agree with Marc--For various reasons, you really should only "stack" identical brand/model of off-grid inverters.

    And there are two types of stacking--one where you can add power (2x 2000 watt inverters for 4,000 watts at 120 VAC) and another where you can take two 120 VAC inverters and get 120/240 VAC split phase. They are not the same.

    If you are asking about "stacking" Grid Tied inverters of different capacities--Yes you can do that. The inverters synchronize with the Grid / Utility Power--And they output power based on how much solar energy is available and each inverter's own limits.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  4. #4
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    Default Re: Can I stack inverters with different wattage?

    "Stacking" basically means tying the inverters together (as already described).

    If you are asking about "tapping" a battery bank with multiple inverters - then yes, you can certainly do that.

    An example would be to tap off the battery with say a 300w pure sine wave inverter to feed sensitive electronics, and also tapping off a 2000w modified square wave inverter to feed power tools. That's a relatively common thing to do.

  5. #5

    Default Re: Can I stack inverters with different wattage?

    ok i will bite.. WHY buy 2 seperate inverters to be stacked and lets say that both ate 2500 watt inverters to achieve a 5000 watt capacity. Why not just buy a 5000 watt inverter?
    3-120 watt panels, 1-125 watt panel AND 8 15 watt panels--5000 watt inverter, ts-60 controller, Midnite combiner with lightining resister and 4-cr395 batteries. Still working on the job though.

  6. #6
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    Default Re: Can I stack inverters with different wattage?

    Quote Originally Posted by VanDeusen View Post
    ok i will bite.. WHY buy 2 seperate inverters to be stacked and lets say that both ate 2500 watt inverters to achieve a 5000 watt capacity. Why not just buy a 5000 watt inverter?
    Because some stacking kits let inverter # 2 sleep till inverter #1 is at 75% capacity. That saves you the standby losses of 2 inverters, till the 2nd one is actually needed. Not burning 30 or 40 watts 24/7 becomes a big thing in winter (short sun)
    http://tinyurl.com/LMR-Solar
    http://tinyurl.com/LMR-BigLug
    http://tinyurl.com/LMR-NiFe

    Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
    Powerfab poletop PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe battery | 15, Evergreen 205w "12V" PV | Midnight ePanel || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT

  7. #7

    Default Re: Can I stack inverters with different wattage?

    Quote Originally Posted by mike90045 View Post
    Because some stacking kits let inverter # 2 sleep till inverter #1 is at 75% capacity. That saves you the standby losses of 2 inverters, till the 2nd one is actually needed. Not burning 30 or 40 watts 24/7 becomes a big thing in winter (short sun)

    GOOD answer, I also have ONE 2500 msw stackable inveter that just sits in my basement BRAND NEW and collecting dust. I bought it because at one time I was going to stack and thought why bother when I can just get a 5k. Now I know I will never use the thing and it will probably be listed for sale to get some of my 300 bucks back.
    3-120 watt panels, 1-125 watt panel AND 8 15 watt panels--5000 watt inverter, ts-60 controller, Midnite combiner with lightining resister and 4-cr395 batteries. Still working on the job though.

  8. #8
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    Default Re: Can I stack inverters with different wattage?

    you may sell it here if you wish to, but leave the bulk of correspondence via pm. you should specify some things online like make, model, when bought, etc.
    NIEL

  9. #9
    robertas9 Guest

    Default Re: Can I stack inverters with different wattage?

    Thanks for replays,

    You mentioned main and slave inverter, does this mean, that there is one main grid off inverter and one grid tie inverter? Also maybe there is place to read about inverter connections and everything. I am searching web but found only basic information.

  10. #10
    Join Date
    Sep 2006
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    Default Re: Can I stack inverters with different wattage?

    Stacking inverters is specific to each model. You can't mix 'n match, they have to be designed to work stacked with each other, and sometimes need a controller module added.

    Stacking for 240V , both inverters would be on all the time.

    Stacking in parallel @ 120V, for additional load capacity, one is master, and one is slave, to save standby losses, or both could be on 100%.

    Grid Tie does not need to stack, each inverter just feeds the grid, monitoring the grid health on its own.
    Battery based, the inverters communicate somehow with each other, either directly, or via a control module.
    http://tinyurl.com/LMR-Solar
    http://tinyurl.com/LMR-BigLug
    http://tinyurl.com/LMR-NiFe

    Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
    Powerfab poletop PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe battery | 15, Evergreen 205w "12V" PV | Midnight ePanel || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT

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