Why Would the Charge Controller's MPPT Tracking be Set to Disabled?

Michael57

I purchased an off-grid cabin a few months ago, and have been spending a fair bit of time learning about the system and it's configuration with hopes of being able to properly manage and maintain the system.  My understanding is that the system was setup and configured at install time about 4 years ago, and no changes were made since then.  I've noticed that the configuration has had some sub-optimal settings and so far have been able to improve things a bit, based a lot of what I've learned from reading this site, so thanks! 

One item that I could use some help on, is why the configuration for the charge controller has the MPPT tracking disabled with a reference voltage of 53 volts?  I haven't been able to find much info on why you would change/disable the tracking setting, or if you did, what value you'd use for a reference voltage.

The array is 4 Sunmodule SW 300 watt panels.  The charge controller is the Conext MPPT 60 150, charging a 48 volt 435ah battery bank.  Also on the system is a Conext SW+ inverter, AGS, SCP, a newly installed Conext Gateway, and a Cummins 13kW propane generator.

Dave Angelini

Probably someone made mistake and hit enter.

The reason one would use a different mppt voltage is if they were troubleshooting the mppt and trying to decide if the mppt was tracking correctly. We tweaked the mppt voltage when Schneider was doing a field test here. you might get a better power for a 15 second period but over a minute or two it was much faster at reacting to solar conditions. Much Faster!  That is an excellent mppt and I have never seen one have any tracking problems in probably 50+ installations.

Michael57

So you'd recommend to flip it back to auto and let the MPPT do it's thing?

mike95490

How are your panels wired, what is the PV input voltage into the controller ? 

If the panels are not high enough voltage to activate the MPPT circuit, that could be why it's disabled.

  What's the Vmp and Voc of the panels ?

NANOcontrol

I use fixed voltage power point in some of the equipment I build. Some track with panel temperature.  Fixed minimum power point allows you to use a second controller on the same panels.  Personally would like to see a fixed minimum voltage option in MPPT as sometimes MPPT gets lost in shading and doesn't recover without removing panel voltage. 

Michael57

mike95490 said:

How are your panels wired, what is the PV input voltage into the controller ? 

If the panels are not high enough voltage to activate the MPPT circuit, that could be why it's disabled.

  What's the Vmp and Voc of the panels ?

Here are the panel specs:
Pmax: 300W
Voc: 40.1V
Vmpp: 31.6V
Isc: 10.2A
Impp: 9.57A

According to the controller's history, the highest voltage that the array has produced is 114V.

mike95490

How are your panels wired ? 

If all 4 are in series, you should show 160V (death to the controller)
2 in series , 2 in parallel  should only be 100V unless you are really getting cold snaps.  So you should be in the MPPT range, I can't explain it.

Michael57

Oops, sorry I forgot to type that in.  Yes, it's 2 in series, 2 in parallel. 

So the 114 volts is what the Controller displays for "Max Array Volts" on the LCD.  Per the manual for that setting:
"Records the maximum input voltage from the array during the lifetime of the solar charge controller.  You cannot reset this screen."

As I purchased this cabin a few months ago and the system is a few years old, I really don't have any additional context so maybe it was caused by something weird prior to my ownership?  I'm not sure what you mean by "really cold snaps", this array is in WA state at a little elevation so it does get well below freezing and every now and then into the single digits, but I don't know that this location has ever been below zero.

Dave Angelini

The 114 volts is for warranty or to deny warranty. You are fine as that is a typical number I have seen on many -60 controllers. It has not gone up in voltage so forget about it, unless you rewire. Turn on the tracking and you are good to go.

Michael57

NANOcontrol said:

I use fixed voltage power point in some of the equipment I build. Some track with panel temperature.  Fixed minimum power point allows you to use a second controller on the same panels.  Personally would like to see a fixed minimum voltage option in MPPT as sometimes MPPT gets lost in shading and doesn't recover without removing panel voltage. 

I wonder if I ran into that situation today, and if so, it would explain why MPPT had been disabled as being far too unreliable. 

I turned on the MTTP algorithm last weekend and everything seemed fine.  We came back to the cabin last night to do some work through the weekend, and this morning I noticed that the charge controller didn't seem to "wake up".  It locked in at an input of like 74.1v and 1.4 amps (~100Watts) and the output was fluctuating between 9W-12W so basically nothing.  We had beautiful clear morning skies, and looking back at last week for comparison, which was much hazier, it was already way behind on the output.  I gave it until about 11am and it never budged.  At 11 I put the controller on standby for a few seconds then flipped it back to Operating, and immediately started producing ~650Watts.  

I'm guessing it is an issue with the MPPT algorithm, so I'll likely disable it again.  I much prefer reliability and consistency over the gain in efficiency it may provide.

NANOcontrol

And I thought that only happened on really cheap controllers.

Michael57

Also, I am running the latest firmware (1.08) which I upgraded too about a month ago using a new Gateway.  Doing a diagnostic check via the Gateway and everything under Xanbus PGN Status shows as OK.  

Dave Angelini

Sounds like you have damage to the mppt. Is there an SPD in the battery and solar circuit ? Surge protection is required to prevent or help to prevent this kind of thing. The algorithm in this controller is rock steady, so either the wiring/solar is bad, or you have a unit that needs replacement.

Seriously, I have never seen this happen to this controller (over 200 used)  unless it got zapped. Any controller, cheap or expensive needs to be installed correctly with SPD's

Gateway is firmware 1.07 BTW not 1.08.  Good Luck

Michael57

I was referring to the charge controller's firmware version, since that's the device that had an issue.  I'm not sure on the SPD, I'll have to check.  In the meantime since it has been running for some years just fine with MPPT disabled, I will revert back to that setting.

mcgivor

@Michael57
Being that you're dealing with somebody else's installation settings, I would be inclined to default the controller and start from scratch, assuming you're confident in doing so, all it takes is a single setting to upset the algorithm. Perhaps before doing so try a cold reboot to see if that makes any difference, if the controller works some of the time it would be logical, to me at least, that there is either a corruption in the logic or a invalid setting which causes the algorithm to become confused.

Dave Angelini

Definitely try a dark restart of the mppt. Make sure the DC voltage gets to zero volts on the battery and solar sides.
You can also reset to factory defaults.
Definitely not the Firmware!  I did the beta field test for Xantrex. The firmware has been unchanged since 2006. Changes since then have nothing to do with basic operation and have been to add new devices like the battery monitor, housekeeping, and combox.
Most users have no idea about this setting as the unit works and tracks mppt in less than a second.

mike95490

I've found glitches in all the algorithms in the Midnight MPPT controllers, except their "Basic Solar".   the other algorithms would hang with changing cloud conditions.  Not sure how they could even ship that way, but they did.

Michael57

Thanks for the suggestions, I may try the reset or the dark restart.  Yesterday, with MPPT still enabled, everything worked fine and the system started producing in the morning like I would expect.  I didn't get a chance to address it before I had to head back home, so the MPPT algorithm is still enabled. 

My main concern with the controller not recovering like that is really when I'm gone from the property, which could be for many weeks at a time, especially in the winter.  In that situation, everything is shutdown so the only draw on the batteries are from the devices in the power shed. I have the Gateway, SCP, AGS, XW Inverter, and the Charge Controller which would still be online while I'm gone.  Now I know they use very low wattage, but if the solar is only producing 10 watts per hour and only when there is sun, over time that would drain the batteries and the generator is offline too.

Overall, I'm not really sure what the MPPT algorithm is doing for me.  Is it just more efficient at running the array?  If that's it, I may continue to troubleshoot it while I'm at the property, but always turn it back off before I left.  Is it even worth the trouble?

NANOcontrol

I have extreme shade and and a 60V array.  This problem was so bad with my controller, I built a disconnect for the array into my house micro.  If the array drops below 40V for more than two minutes, It disconnects the panel for ten seconds. You might have shading problems like this guy.   https://www.youtube.com/watch?v=r-BJ8S7HfNA

Dave Angelini

You should just buy another controller if the testing does not confirm anything. Cheap insurance for sleeping at night.
Most mppt's are best with clouds. I know the one you have is. I think you would know by now that there is no surge protection. You should definitely add that as an XW+ is not cheap. Good Luck!

Michael57

Oh right, that is correct.  I know very little about electrical systems (though I'm learning), but I do not see any SPDs connected.  The only thing between the array and the charge controller is the combiner box, but there is no SPD inside, just the breakers.

BB.

Good Surge Suppressors are not small or cheap:

https://www.solar-electric.com/search/?q=surge+supperssors

-Bill