Need help with a Xantrex SW4048

This inverter is about fifteen years old. I installed it around '07and it's been powering my homestead full-time since. It's a little noiser than it used to be but just keeps chugging along. Today though I finally hooked up my AC1. The supply isn't good for more than twenty amps but it's always running and will be a whole new chapter... Except it won't stay synced, the meters menu on the inverter shows the voltage for AC1 fluctuating been 120 and 80VAC. But it's not, the multimeter shows a constant 118VAC at the lugs, and even with a 15A load (a compressor running on the line right before the inverter) the voltage doesn't drop below 115VAC. Is there a way to calibrate the voltage on AC1 or do I have some faulty hardware? Thanks in advance. 


  • BB.BB. Super Moderators, Administrators Posts: 31,433 admin
    Besides the usual of checking internal connections (rock the connectors to clean contact surfaces), look for bugs (as in really dead bugs and dust on electrical circuits), look for signs of running hot/overheating (brown/black), corrosion, loose hardware, and such)... Also look for "bad capacitors", electrolytic (fluid filled) can dry out over years, you may see leakage, swelling, or even a burst end or pressure release valve with dried fluid at the opening...

    One thing I read about years ago was the current sense transformers. They have very fine wire that attaches to the circuit board--And sometimes a wire can break...

    And here is a post with a bunch of inverter repair facilities that I have combed from the forum (just an FYI--No personal knowledge, and many links may have gone stale over the years):

    And 15 years from power electronics, not a bad service life... May be time to look for a replacement (and if you do get the old one repaired, just keep it as a spare).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    edited August 2020 #3
    On the small relay board there are two small AC voltage sense transformers.  It is just a small transformer with hair fine primary winding on 120vac and secondary of 12 vac.  There is one on AC1 (T4) and one on AC2 (T8).  The secondary 12vac is what is fed to controller board to read ACin voltage and phase. Without the sense voltage it thinks there is no ACin.  Check output of small transformer has the 12vac.  Fairly easy to access this board, just be careful as the AC inputs hookup up here.  Primary side winding resistance is 1.2k , secondary 98 ohms.

    You can try connecting grid to AC2 input to see if it works okay.  If it does then it is pretty surely the sense transformer.

    On mine, the AC1 grid took a lightning hit and blew open the primary side of voltage sense transformer.  Luckily the fine wire fused open between the small transformers PCB solder post and as wire went into winding bobbin.  It had about eighth of inch of wire sticking out from bobbin.  I was able to solder a small lead from terminal post and short stub of wire sticking out of bobbin.  Has been running over 10 years since that incident.  While I was at it I soldered an MOV surge protector disk across PCB pads at sense transformer primary side.

    It is likely an ordinary 120vac to 12.6vac transformer.  If you have to replace transformer you might have a slightly different AC voltage reading.  There might be a calibration pot on controller board but I am not sure which one it is.

    At least to get it working on grid you could swap the AC2 sense transformer to AC1 position.  When you take AC2 sense transformer out it would be good to hook up 120vac and measure 12vac output and take dimensions for transformer so you know what to look for to replace it.

    Attached is schematic of relay board
  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    edited August 2020 #4
    Re-reading your statements it also may be AC1 relay contacts getting bad.  In the schematic I enclosed is the relay manf. part #.  They may be hard to find.  You can also try to burnishing the contacts with fine emory cloth sand paper (5000 grit) to see if you can breath new life into them.

    Again, you can try putting AC on AC2 port to see if it acts normal.  It is a 12v coil so you could substitute.  The original relay is 3 pole contacts rated at 30 amps each contact put in parallel.  Not what I would call a proper way to get a 60 amp relay but it got pass U.L:. 

    If you decide to pull out the relay board make sure you mark the two large wires from the power transformers. One comes from smallest xfmr and one comes from largest xfmr and if I remember they both have the same color. You don't want to get them reversed when you screw them back together.

    I enclosed relay spec.  I think I have seen them recently for sale on ebay.
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