Two Xantrex MPPT60's don't auto-track.

MaxThrashMaxThrash Registered Users Posts: 5
I have 2 Xantrex MPPT60 CC’s, 2 XW6048’s, 735Ah 48V AGM battery bank, 27 each 230W PV panels, 6.21 kW plus a generator. I’m grid tied with sell back.

The two Xantrex MPPT60 charge controllers do not work properly when auto-tracking is enabled. One controller has 5 strings of 3 panels each and the other controller has 4 strings of 3 solar panels each. I’ve tried 4 different charge controllers.

If the PV input breakers are turned off and the controllers turn off with 'low light' and then the breakers are turned back on the two controllers appear to work correctly with input voltages auto-tracking closely for a minute or two as the system power goes steadily upward then the controllers go their separate ways and the system output drops 1500-2000W. One of the charge controllers will then incorrectly display lower input power than output power. Never both controllers. Just one or the other. It appears the Xantrex firmware cannot maintain auto-tracking synced between two controllers.

Xantrex MPPT Auto-tracking does not come close to producing maximum power. The charge controller voltages do not stay together and get up to 40 volts or more apart. I believe they lose sync and constantly hunt. If I disable the auto-tracking and enter a manual reference voltage for the controllers the system output goes up by 1500-2000W. Setting the controllers back to auto-tracking enabled drops the system output back down again. The manual reference voltage I enter seems to work best on country music radio station settings. Actually any random manual setting works much better than the so-called Xantrex MPPT Auto-tracking feature.

To me this all indicates that this is a Xantrex firmware/hardware problem that the manufacturer has been trying to get right for years or why else keep 'upgrading' the firmware and changing the tracking algorithm. As I recall the latest released firmware for the controllers installed with the latest and greatest MPPT algorithm actually did not work with the latest released firmware for the inverters and that one of the Xantrex support people emailed my installer an unreleased version of the inverter firmware that supposedly did work. Did not help.


Is anyone else out there having similar problems with two MPPT charge controllers? Anyone have a system with two controllers that actually work together?

Is there a better charge controller to use in this system?

Suggestions welcome!

Comments

  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: Two Xantrex MPPT60's don't auto-track.

    Some thoughts:

    There is no linking of the mppt functions between charge controllers, they independently track there own arrays, it sound like maybe you have got negative leads reversed so the current of one array is getting connected through the second controller?

    If you have the sell voltage to high, at higher power levels you do induce this type of issue, you should be using a sell of @ 52V ( compensated )

    Make sure you have your grounding correct, the XW-Mppts are true 4 wire controllers, if you have combined negative leads somewhere, it will cause the controllers to perform in odd ways
  • MaxThrashMaxThrash Registered Users Posts: 5
    Re: Two Xantrex MPPT60's don't auto-track.

    My sell voltage is set at 53V right now. I'll try lowering it to 52V and see what happens.

    I don't know where I got the idea that the two charge controllers would track together. I guess it was from watching the input voltages starting off together and then diverging so much with a resulting significant fall off of the system power.

    I'll have to think about the best way to check for any cross wiring of the negative inputs. Back to the combiner boxes.

    I appreciate your help. I'll let you know how things go.

    Thanks.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: Two Xantrex MPPT60's don't auto-track.

    Sounds like that's your problem, remember, you have to have both the positive and negative leads go back to a single charge controller or put it another way, the two arrays must be 100% isolated from each other
  • MaxThrashMaxThrash Registered Users Posts: 5
    Re: Two Xantrex MPPT60's don't auto-track.

    Solar Guppy,
    You were right on the mark concerning the wiring causing my problems.

    My installer did an excellent job on this system with tremendous support after the install for which I am very grateful. I can't say much for Xantrex technical support help. They just did not seem to know their products very well.

    The system installer did a very thorough back check of the wiring from the two combiner boxes into the charger controllers. All grounding was correct. There was a cross connection between the two arrays' negative polarity wiring that was causing the charge controller problems with MPPT enabled all along exactly as you said. I'm truly surprised the system actually worked at all even in it's chaotic fashion.

    The installer also put in a much better grade of commmunication cable, made the connectors for the Xanbus, tested them and all the communication drop outs went away. Even though the original cables were properly installed the xanbus always had problems with loss of comunications from day one. Guess Xantrex shipped cheap cable with cheap pre-installed connectors. There is also a limit stated in the manuals of eight devices maximum on the bus I have seven now. I have no clue how the xanbus could support three inverters, 3 controllers, a SCP, an AGS and a gateway. Guess if I ever expand I'd have to drop the gateway and hard wire to my router or computer with an interface of some sort.

    My next question is concerning the sell back current limit setting. With the inverters cascaded making any change on one inverter sell back current setting changes the setting on both inverters. Is this setting a combined total current setting or does it apply individually to each inverter? Say the setting is 10A. Does this limit the sell back to 10A total or 20A total? Xantrex does not elaborate on this. A Xantrex tech rep told me to set it at the max, 27A. This seemed greater than the inverter 6000W continuous rating.

    My last question is the setting for the grid supp voltage. The xantrex manuals say very little concerning this except that the batt voltage must be greater than the sell back setting in order to sell power to the grid. The default setting was 54V. My setting was 53V but the installer changed this to 58.2V. My battery voltage is always around 53.3v. It seems like this would prevent any sell back to the grid at all but the system is happily selling away to the grid. What gives with this setting?

    Xantrex just does not put out much technical information. I guess most users would not care as long as everything was working or would fail to understand technical info if it were available.

    I appreciate your input and help with my problems.
    Thanks.
    Max
  • BB.BB. Super Moderators, Administrators Posts: 30,640 admin
    Re: Two Xantrex MPPT60's don't auto-track.

    Setting the sell voltage is basically setting the float voltage for the battery bank (the grid tied hybrid inverters are basically just shunt loads for the battery bank).

    Setting your sell voltage >> float voltage either lets the solar charge controllers set the battery bank voltage (which could limit their harvest)--or you run the charging of the battery bank at the "absorb" voltage all the time... Hardly needed since the batteries are not really cycled when the XW system is running in "GT Mode". I don't see a reason for your high voltage setting????:confused:

    As I understand (not an expert)--if the SW Inverter sees the battery voltage drop below the float voltage (basically, battery bank is discharged for some period of time), the XW will go through the normal bulk, absorb, float charging algorithm before it starts selling again.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,231 ✭✭✭✭✭
    Re: Two Xantrex MPPT60's don't auto-track.
    MaxThrash wrote: »
    Solar Guppy,
    You were right on the mark concerning the wiring causing my problems.


    Max

    And the installer does not seem to know what he is doing here no matter how pretty all the wires look! The charge controller has to wired correctly! It is in the manual. All the setpoints need to be correct. You paid this person right?
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • MaxThrashMaxThrash Registered Users Posts: 5
    Re: Two Xantrex MPPT60's don't auto-track.

    Dave,
    I intially watched the test of the positive and negative cabling from each array and everything was good. The two arrays were isolated 100%. What I speculate happened after that was a different person terminated the negative cables to the charge controllers and to the PV input breakers and ran the load side connections from the breakers to the wrong controllers. Two 2-ft. pieces of cable swapped. Since I did not have the utility meter changed out at that time I had the grid sell back disabled and only light loads on my interior panel being driven by the PV arrays. Things seemed to work fine. When I got the utility to install their new meter (they don't stock these meters because so few customers have a grid tie system, only 5 in the state) and the load went up considerably the charge controllers went off the deep end. Once I got the distribution panel cover taken off and both leads disconnected from each controller the problem was pretty obvious.
    Thanks.
    Max
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,231 ✭✭✭✭✭
    Re: Two Xantrex MPPT60's don't auto-track.

    Max,
    Cool! My point is there is always plenty to knock on a huge corporation like xantrex. Following wiring diagrams and their implementation is not their problem! Glad you have it going. By the way the 2 controllers will go thru the charge process and the first one to hit the set-point will xanbus the others and they will be in sync. Not sure about how that interacts with the grid tie as I only go off the grid.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: Two Xantrex MPPT60's don't auto-track.

    Set your sell to 54V, if you start having issues @ high power levels, lower as needed

    58V is nuts, you will cook the battery's and have all sorts of tracking issues as the battery's are needed to reduce the AC current ripple.

    As for the max sell amps, not sure as I have never run a pair of inverters, I'd read the manual front to back cover to get familiar with your system, but I don't understand why you even set that value .. with grid tie, the goal IS to sell all the harvest
  • MaxThrashMaxThrash Registered Users Posts: 5
    Re: Two Xantrex MPPT60's don't auto-track.

    Solar Guppy,
    Xantrex manuals have about two sentences on the max sell amps for a single inverter and nothing about when using two or three inverters. It basically states this sets the max limit on how many amps go back to the grid. I'm reasonably certain that with the inverters cascaded and changes to one inverter automatically changing the other inverter amps the current setting actually applies to the inverters individually. I simply set a low value and watched the AC1 currents for both inverters total exceed the setting.
    There is even less information on the sell to grid voltage other than stating that only when battery voltage exceeds the sell to grid voltage setting will power go out to the grid. With that 58.2V sell setting both inverters outputs constantly slowly cycle up and down like a roller coaster seveal hundred watts over about 8 -10 seconds then repeats. this is noticable when there is high power output because the cycle range is greater. I initially though the utility impedance must be cycling continuously but the two inverters did not hit the highs or lows at the same time. The problem lessens as the sell to grid voltage setting is decreased and at 53-54V that seems to pretty much go away.
    Anyway thanks again to everyone.
    Your knowledge and help have been of great benefit to me.
    I've finally got a system that works as it should!!!
    Max
  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: Two Xantrex MPPT60's don't auto-track.

    There are more than one manual for the XW and its components, for the SCP

    http://www.xantrex.com/web/id/920/docserve.aspx

    Also, when your using the SCP to set values, you should enter tha advanced mode to see all the options. With the SCP you select every device indivudually and configure it, for most things related to GridTie, you need to be in the advanced mode ( I beleive you hold the three left most buttons at the same time when you have selected a device ).

    Xantrex has the number one inverter out there and has many options, so many, you really need someone with training to configure and install a XW system. Sounds like your installer really isn't familiar with the equipment, as shown by not even following the wiring diagram to connect the charge controllers.

    Down load and read every manual, cover to cover, use the SCP and go through all the devices, settings and screens and that should get you to the point you can be self sufficient.

    One note, if you less than 400ah battery bank per inverter, you will need to lower the Sell Voltage so the battey's buffer more of the AC ripple. I have 660ah and at high power levels its board-line on effecting the chargers ability to do mppt tracking
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,231 ✭✭✭✭✭
    Re: Two Xantrex MPPT60's don't auto-track.

    As Mr. guppy said there is a ton of info out there and a shame that alot of it disappeared with their forum. The door on your power panel should have been left with the basic system operation (I always do) for you. The installer is suppose to add value to the system by taking it from the world of monkey's to your world.

    Definitely pay attention to the battery capacity as they dropped the ball on that one assuming that people would always use a large enough battery for a battery based inverter. I may be with them on that one but I keep scratching my head every time I hear this story. Good Luck!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • XWGuyXWGuy Registered Users Posts: 15
    Re: Two Xantrex MPPT60's don't auto-track.
    MaxThrash wrote: »
    Solar Guppy,

    My last question is the setting for the grid supp voltage. The xantrex manuals say very little concerning this except that the batt voltage must be greater than the sell back setting in order to sell power to the grid. The default setting was 54V. My setting was 53V but the installer changed this to 58.2V. My battery voltage is always around 53.3v. It seems like this would prevent any sell back to the grid at all but the system is happily selling away to the grid. What gives with this setting?

    Max

    When an XW inv/chg is on the same Xanbus network as a XW MPPT, the sell voltage will either be the voltage that it is set to via the Grid Supp Volts setting, or it will be the Battery Charge setting that the XW MPPT is currently following - which ever one is less will be used. The battery charge voltage setting on the XW MPPT will change as it goes through the bulk/abs/float charge cycle. So if the XW inv/chg has been configured for Grid Support at something like 60V, and the XW MPPT is in Abs mode where the voltage setting may be 57.6V, then the XW inv/chg will use the 57.6V setting as it's sell voltage. Once the XW MPPT goes to float mode and the charge voltage drops to 54V, the XW inv/chg will change follow this change and sell energy from the batteries to bring the battery voltage back down to around the 54V level. (Note that the XW inv/chg actually regulates the battery voltage to about 0.5 to 1V lower than the actual charge setting that the XW MPPT is trying to charge the batteries to).

    This scheme allows the system to experience a proper charge cycle, while still allowing excess energy to be sold back to the grid. For customers that are not concerned with having their batteries go through a full charge cycle every day, they can set their grid support voltage setting on the XW inv/chg to 53 or 54V and the XW inv/chg will regulate the voltage to that point by selling all the excess energy from the XW MPPT.

    I hope this information clears this up for you.
  • XWGuyXWGuy Registered Users Posts: 15
    Re: Two Xantrex MPPT60's don't auto-track.
    MaxThrash wrote: »
    My next question is concerning the sell back current limit setting. With the inverters cascaded making any change on one inverter sell back current setting changes the setting on both inverters. Is this setting a combined total current setting or does it apply individually to each inverter? Say the setting is 10A. Does this limit the sell back to 10A total or 20A total? Xantrex does not elaborate on this. A Xantrex tech rep told me to set it at the max, 27A. This seemed greater than the inverter 6000W continuous rating.
    Max

    The Sell current setting will set the sell current for each XW inv/chg, so if you set it to 10A, it will be 10A for each inv/chg that you have. I recommend you set this value with the amount of PV on your system in mind. You have a total of 6.2kW of PV, so you do not need to sell more than that amount. I would suggest that you set your sell current to around 12 or 13 amps for each inverter. This will allow you to sell up to about 6kW total. Also keep in mind that the sell current limit ensures that you don't pop your breaker by trying to push more current back to the grid than it is rated for. So make sure you don't set the sell current to a value that is higher than your breaker current rating.
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,231 ✭✭✭✭✭
    Re: Two Xantrex MPPT60's don't auto-track.

    Exceptional advice! I only wish those guy's at Schneider would figure a way to set my sell current offgrid. You would think they would have done this by now!;)
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

Sign In or Register to comment.