Strange PV input voltage behavior on Midnite Classic 200

[darinheath]

Hello all. I purchased my first Midnite product, a Classic 200, just recently to replace an Outback FM60. Its only been in service for a week or two, and I'm noticing some strange PV input voltage behavior on the Classic 200. It will start by recognizing the entirety of my PV voltage input (140-150v) and then immediately start falling to 110v on the display. It will hover there for about 6-8 seconds, then the Classic will start cutting off the PV voltage / wattage input until it gets below 18v, then the process starts all over again with the Classic 200 jumping back up to actual full PV input.

To try and troubleshoot the issue, I checked the amps and volts on all my panels separately; they are all working properly. When I have all 1200 watts in series, they also measure correctly (140-150v and 10 amps).

It almost looks like the Classic 200 is doing this on purpose for some reason, like its trying to formulate a charge profile or something, but there is always a chance that there is something wrong with it as well. I have used three separate circuit breakers between the panels and Classic 200, as well as simply running without a breaker considering I only have 8-10amps running along that wire anyway. (The breaker is only for convenience).

I followed the basic LifePO4 setup for my bank concerning charging settings from Midnite Solar instructional videos, nothing else weird or unrelated was messed with yet in the menu. I haven't even gone in to turn off the main display backlight which is apparently on by default.

The Classic 200 I have may have been doing this the whole time and I just now noticed. It will charge at a respectable 68ish amps into my bank when it accepts all 140-150v from my 1200 watts of panels, but just for about 5 seconds of every 60, then that trickle down to 110v, then 18v process kicks in over and over and over for the remaining 55 seconds of every minute.

Any ideas? Troubleshooting steps?

Thank you in advance for any help.

[darinheath]

It seems to have stopped for now, it hovers and stays at around 110-113v. I will keep an eye on it. I'm still open to any ideas.

[darinheath]

Sigh.. Unfortunately it started again when I checked on it this morning. I will watch to see if this PV voltage / wattage suppression continues all day.  As a reminder, I am getting solid current and voltage rate from the panels, there are no clouds, direct sunlight on all panels.

[boB]

Gee !  Sorry you are having this trouble !  Not fun !

Could you take a really short video of the status screen so we can see all of the numbers as they change  ?

That really helps to debug.

If you just replaced the FM60 with the Classic, then all should work OK if the FM60 was working OK.

Sometimes these things can be just a loose connection.   

What is your battery voltage ?   When running, the PV input voltage will usually not go below the battery voltage is the sun is out and connections are good.

boB

[darinheath]

I'll take a video tomorrow after work.

The Outback controller never did this. This is a new phenomenon. I watched it all day, it never ceased to follow the pattern I outlined, wherein it artificially prevents the Classic 200 from using the wattage and voltage its being provided at a steady rate, going to full PV input for a second, then trickling down to 18v, then starting over again. I am starting to think this Classic 200 is scrap and I need to return it. It was on sale when I bought it from a vendor a few weeks ago, which means it might have been a return from another customer and they just resold it. I've checked all the connections multiple times. It makes no sense that if it can absorb full PV voltage for a second, it should be able to for more than that, so its' not the connections. My battery voltage is 12v, I charge it to 14.2-14.4 as they are LFP batteries. The sun was out most of the day, but this up and down pattern persisted. Thanks for reaching out regardless. I opened a trouble ticket and hope to hear from Midnite Solar tomorrow.

[boB]

Our customer service guys should be able to see the history, if any, of that Classic by the serial number.

[darinheath]

I received a prompt response from Midnite Solar. They gave some recommendations for me to try when I get home after work and I will update the results of any testing or alterations to this Classic 200 they suggest. Thank you.

[darinheath]

Hey guys.

So I finally had a chance to bleed my bank with a heavy load while the sun was up today. When the battery bank is topped off, of course this isn't an issue. Once the Classic 200 attempted to switch to Bulk MPPT to start filling them back up, the strange PV and wattage limitation cycle started again. It ran like that for hours, so I just had to turn my PV input off and call it a day.

I'd love to upload a video to show you, but the one I took is 2 mins and 95mb, which unfortunately exceeds the forums (and the ticket systems) limit. I will stand by for more assistance from tech support, likely Tuesday.

[Vic]

Hello Darin..,

Had been waiting for your report on the results from your conversation with MN Tech ...

At the very least,  check in the Mode menu,  and see what Mode is set.  You should probably be in Solar.

If you have not done so, you should probably just restore the Classic to the Defaults.

In the MN Local App,  (which runs on PC computers),  you can save your settings for Absorb,  Float,  etc.

Since there is a possibility that the Classic had been previously used,   check the Firmware version for the Classic,  and MNGP  --  what are those numbers?   The Local App will show these version numbers,  or,  from the main Status screen on the MNGP,  push the small round grey button on the left,  >EDIT: seven times,  from the main Status screen.    The Classic version number and the MNGP version numbers are on that screen<

MN Tech probably mentioned the above,  and many more things  ...   Just to try to keep you from getting bored.

A couple of still pics of the status displays might help.  Good Luck,   VIc

EDIT>  Also,  is it possible that any BMS system for your LiFePO batteries is causing some of this behavior ??  I know nothing of these batts,   VB<

[darinheath]

Thanks Vic:

So far the tech has asked me to verify the mode was set to "solar", which it was, and to set the LMX to the "off" position.

None of those two options made any long term difference, although I had some hopes for a short while. Although I am just now reading your message, I did already try resetting the Classic 200 to default settings. I tried it with just the defaults, same result. Then I made the normal LFP modifications to the charge profile (setting float, absorb, etc to as close together as they can get), and same result. Then I set the LMX to the "off" position. It did hit 150ish volts (actual PV input voltage) for a split second, then it settled in at around 120v with about a 48 amp charging output to the batteries. It stayed there for about 20 mins, and I thought something maybe was finally working, albeit inefficiently, but alas, the vicious up and down cycle started again after all of those troubleshooting steps.

My battery bank is six Lion UT 1300 LFP batteries. I tried the same bank with another charge controller recently when this issue was first discovered. That charge controller reacted normally. I routinely swap around the primary battery in my parallel chained bank just to keep them all as balanced as possible long term. Moving one of my batteries up to the "number one" position made no difference, hence my dismissal of the "bad BMS" suggestion, which would still not explain the Classic's desire to limit wattage and voltage input on its own.

I am now awaiting further guidance from Midnite solar. I have a feeling at this point they are going to want to swap out the controller for another and take a look at mine. I am respectably experienced with this stuff and have tried to examine all my behaviors, equipment, attached peripherals, etc.. I don't believe I have done anything that would necessitate failure with this device or damage it. NO lightning, everything is grounded to the chassis properly, no strange settings were modified in the Classic. I am at a loss.

[Vic]

Hi Darin..,

OK,  thanks for the added info.

When you saw the Classic PV input voltage go to about 150 V,  momentarily,  then go to 120 V in,  you were probably seeing it measure the Voc.   Normally in good sun,  these CCs run PV input voltage at about 80% of the measured Voc (unless this value is changed on a Menu)  when in MPPT charge stages.

Will let MN Tech and others here,  give guidance.

There was/were early version/s of Classic Firmware,  that had some Sweeping issues,  IIRC,   but that was probably before the advent of CL 200 & 250s.

The only other comment,  is that your battery V is 12 V,  and the STC string Vmp is probably around 140-ish volts,  and this,  plus,  running Li batteries,   may be a bit of an uncommon configuration.  So,  the experience-base might not have too many such configurations.  Am not saying that your config is out of range of Classic 200 specs   ...

Thanks for the info,   Good Luck,   Vic

[littleharbor2]

Just a longshot here but with such a high Voc I wonder if you have added any additional solar since you switched from the MX-60?  Possibly you have a wiring/polarity issue.