Buying a New Inverter

Point1Point1 Registered Users Posts: 1
   This is my first post and I want to say a huge thank you to all of the knowledgeable people who donate their time to make this forum such a great resource! I have been researching and reading for weeks and have learned a great deal thanks to you.

   However, there are a few questions I haven't been able to find answers to...
   The general consensus is that buying a good quality inverter is worth the investment, and I would like to take that advice. However, my application is an off-grid one-room cabin and the inverter and batteries are in the living space. I might have guests who could be bothered by the hum of the inverter, so I thought it would be best to buy a high-frequency, switching type that doesn't have the big transformer. I read somewhere that most of the noise comes from the transformer and that the high-frequency ones are quieter. However, it would appear that the better inverters are generally the low-frequency type.
   After all my sizing research, I concluded that a 3000W inverter would be a good size, give or take. Most of the time, the loads won't be more serious than things like coffee maker, toaster, hair dryer, laptops, vacuum, and a TV. The fridge and stove will be propane, and no washer/dryer. The biggest concern is the well pump which is currently 24VDC. Its pushing the limit with the total head, but it does manage to fill the pressure tank to 50 PSI or so. However, the flow isn't great and down the road I may need to upgrade to a 1/2HP or 3/4HP pump on 120 or 240VAC. If the inverter I buy now can't handle the surge for a normal well pump motor, it looks like I might be able to get a Grundfos soft start pump to work. My other idea is to buy an inverter with stacking capability, so that I could add another one later to get 240VAC if needed.

Here are my questions:
1) Is my concern about the inverter noise valid? If you were sleeping 8 feet from your inverter, would you go the high-frequency route? (Turning it off probably won't be an option. It will probably need to be in search mode at least.)

2) What are the best brands of high-frequency inverters?

3) In general, are high-frequency inverters more efficient with low power loads (laptops & lights) than low-frequency inverters?

4) The only high-frequency inverter I have found with stacking capability is the Cotek SD3500-124. Is Cotek a decent brand? Does anyone have this inverter and like it? Does the paralleling/stacking feature work as expected?

5) If I had two stackable inverters, I should be able to combine a 120V leg from each inverter to get 240V for the well pump and still use the 120V legs to power house circuits, right?

Thanks for any help!


  • EstragonEstragon Registered Users Posts: 4,451 ✭✭✭✭✭
    Personally, I think fan noise would be more of an issue for me than transformer noise.  I have an autotransformer living in the main area of the cabin which makes a loud-ish boing noise starting up, but otherwise doesn't bother me.  Intermittent fan noise from an inverter might though, and I think pretty much any inverter that size will have a fan.

    Cotek is fairly well regarded here AFAIK.  Two series stackable inverters would give you 240v for a pump, and 2x120v legs for 120v loads, though each leg would be limited to the individual capacity of each inverter.  Another way to do it is with a single (or parallel stack with a 120/240v autotransformer.

    If a bigger 240v pump is a possibility, I'd highly recommend considering 48v DC system.  At 24v, currents get pretty big.  Even a single 3500w inverter could be ~145a, with higher surge current even higher, meaning hefty wire etc.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • parbob1parbob1 Registered Users Posts: 40 ✭✭
    I just purchased a Schneider Comext sw4048.. it runs quite however when my 240 water pump ( same size as yours) kick on there is a noticeable hum/vibration/bang for the short time.. after the first few times it’s not an issue.. the bigger issue is the search mode if I was sleeping near the inverter.  The search cycle made me turn off search when I’m there.
     SW Conext 4048
    Combox & Conext battery monitor 
    16- 235 6V batteries 
    Honda 6500 gen
  • 706jim706jim Solar Expert Posts: 298 ✭✭✭
    I put my inverter and batteries in a shed 15' away from the cabin. No inverter noise at all. And this season, my 24 year old Trace ran 24/7 for six months faultlessly.
    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 27th year.
  • petertearaipetertearai Solar Expert Posts: 416 ✭✭✭✭
    yep my first inverter was a xantrex ps1800 . Ran well,but during the night when fridge started the fan also started for a short time on the inverter . i didn't like that .
    Present inverter outback fxr 2kw  got the sealed one hoping to have less noise .  No fan noise except when runing it hard on power tools. .... But there is a continual hum from TX .It is in the garage with a door to living area . Acceptable but still audible .I think a power shed is the answer.    +1 on the 48 volts if you can .
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . victron battery monitor . 24 volts 450 ah surette batterys . off grid  holiday home 
  • parbob1parbob1 Registered Users Posts: 40 ✭✭
    My first Inver was 24.  48 is double the fun
     SW Conext 4048
    Combox & Conext battery monitor 
    16- 235 6V batteries 
    Honda 6500 gen
  • littleharbor2littleharbor2 Solar Expert Posts: 1,482 ✭✭✭✭
    parbob1 said:
    My first Inver was 24.  48 is double the fun
    Double the fun at only half the amperage =)

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • ScoobyMikeScoobyMike Registered Users Posts: 37 ✭✭
    A couple of things to consider:

    1 - An inverter with GFI ouput will not work with any GFI outlets in the cabin.
    2 - Big inverters come with big idle power consumption and can drain a small battery bank overnight, even with nothing running.  Throw in a rainy day or two and   How big are your batteries and solar system?

    I enjoy living off grid and realized early on that trying to make my off-grid home as convenient as my grid tied home is financially daunting.  Instead of using a large inverter have you considered investing in a quality generator for the coffee maker (or use a stove-top unit), toaster (or use stove top camping toaster), hair dryer and vacuum? 

    1.2KW off grid system; 2 strings of 2ea 305W 60 cell panels on a redneck ground mount;  MNPV3 combiner feeds a MN Classic 150 located 100' away;  12V 460AH FLA battery bank powers a cabin-wide 12V DC system as well as a Cotek 700W PSW inverter; Honda EU2000i  and IOTA 55A charger bridge cloudy days and a Champion 3800W generator for short duration, power hungry appliances.

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