Inverter undersized?

vtoffgridvtoffgrid Registered Users Posts: 2
I built a small house in rural VT, decided to go off grid and purchased a 3.7kW array of 12 panels, 4 Kilovault 3600 batteries, and a prewired Schneider Conext 4048 SW with a Midnite 200 charge controller through AltE. I don't have much experience with electrical and hired a local guy who hooked it all up for me. Everything works pretty well but I've had a couple issues... I have a 420' deep well and my well pump has a pretty big start up surge. It's a 1hp pump and I haven't been able to see exactly the surge goes up to but it's normally at about 2000 watts when it's running, so I would imagine it gets to around 3x times that, (my inverter is rated for 6800 surge watts for 30 seconds). It's never shut the inverter off but sometimes the inverter makes a horrible grinding noise when it kicks on sounds like it's about to break. If it never shuts the inverter off is it appropriately sized? and is the grinding noise normal or something I should be worried about? When the well pump runs it makes the lights flicker really badly, and when I have a small load ~100 watts the lights will also flicker pretty intensely. After some research I'm wondering if my house isn't grounded properly, I saw my electrician shove a 6' or 8' rod into the ground but I am worried it's not working correctly and if that could be the cause of the flickering and possibly the bad noises from the inverter? Thanks in advance for any info!


  • VicVic Solar Expert Posts: 3,112 ✭✭✭✭
    Hi vtoffgrid,  Welcome to the Forum.

    My guess about that grinding sound,  is that it is one of the relays in the CSW 4048.   This can happen when there is not battery surge current available for the load on the Inverter.   This can be because the large load causes the battery voltage to drop low enough that the inverter can shut off momentarily.   This causes the relay to drop out,  removing the load on the inverter.  This causes the battery voltage to rebound,  and the process begins,  anew,  a number times per second.  With a very large overload on the inverter,   it will Fault off,  and need resetting.   The pump load may not be large enough to cause this fault,   and so on.

    Am not familiar with the batteries that you are using.   Perhaps the batteries are not getting a full charge  ...   or   ...

    Just a drive-by.   Good Luck,   Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    edited November 2020 #3
    Tell us more about your batteries (flooded cell. AGM, GEL, Li Ion, xxx AH, etc).
    Length and awg or mm wire diameter?
    Have you placed a voltmeter on the AC inverter's DC input terminals under heavy load?
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    edited November 2020 #4
    I should add, I don't think the ground rod is an issue... Ground cable wiring could be an issue.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,028 ✭✭✭✭✭
    I would guess you are correct on inverter size. CSW should be running a soft start well pump. An XW would not have this issue, I think from what you have written.  How does the pump do with a genset? I ask this because you could also not have CSW gen support configured.

     Not a bad LFP battery/size but you need to have it full and charging when starting the pump. Is that what you are doing?  You also may need to list the battery cable size and distance as Bill asked.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • vtoffgridvtoffgrid Registered Users Posts: 2
    Thanks a lot for the info everyone, much appreciated! To answer the questions, my battery cables are 2/0 and are 10 feet long with 13 inch cables connecting the batteries. I have four batteries and they are LiFePO4 lithium ion batteries. I haven't placed a voltmeter during a load yet, the inverter is set to shut off at 48v as per the battery manual. I haven't used the pump with a genset yet, I am still in the process of getting a generator for the winter. I have a 30 gallon pressure tank that is filled automatically by the well pump when it reaches a certain level of emptiness, it seems to kick on after about 5 gallons or so have been used, so right now I'm just using the well pump whenever it kicks on. Is it possible to add a soft start to a 3 wire well pump? Some sort of VFD or something? I've been trying to find more info on that but haven't had much luck with mr. google. Thanks again!
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,028 ✭✭✭✭✭
    i was thinking that you were just filling a large tank during the day, like most offgrid folks do. What you are doing is going to be a bit harder.

    You need the model number of the pump and make. Really what you need to do is get a pump like grundfos SQ. I also would shorten the battery cable by 5 feet. Good Luck.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • mike95490mike95490 Solar Expert Posts: 9,358 ✭✭✭✭✭
    Running a pressure tank water system, and having that pump cycle on-off several times an hour is very energy demanding.  The starting surges are much larger than you believe - they are 10x the running power, but just for 2 seconds.
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • MichaelKMichaelK Registered Users Posts: 215 ✭✭✭
    I would say your system is just marginal in terms of capability.  You didn't do your homework when you were designing your system.  I also have a 1hp submerged pump, and before designing my system I measured both the starting and running current that my pump demanded.  Those numbers were 10A and 38A respectively.  To determine the starting current you need a clamp meter that has "in-rush current" capability, like this one.
    So, 38A at 240V turns out to be 9120W.  Looking at the spec sheet of your Conext, you can see it has a max current of 41A (100ms) and 7000W (5 seconds).  That's assuming that it can pull enough current out of the batteries to produce the 41A.

    I have a bigger battery bank, more panels, thicker 4/0 wire to the inverter that's only 2' long, and a Schneider XW+ inverter.  It starts my 1hp pump without any fuss any day of the week.  You have a couple of options.  Get a second Conext 4048, and connect them in parallel.  Coupled with a second battery bank and more panels, the pair will have ample power to start the pump.  Alternatively, replace the 4048 with Schneider"s XW+ 6848, along with added panels and a larger battery.  You can make it work, but start with the numbers first, and proceed from there.

    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
  • jtdiesel65jtdiesel65 Solar Expert Posts: 239 ✭✭✭
    edited December 2020 #10
    I'd find out what kind of pump and see if you can get a soft start one.  That's what I did years ago.

    Also, are your lights LED?  Some LEDs will flicker no matter what. I just got some new ones to replace some older CFLs which are terrible and flicker all the time. I have others that don't flicker at all.
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