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MPPT 75/15 Stats not changing to next day at night

Hi

I've been having a problem with one of my MPPT controllers displaying the days stats. Looking at VRM portal, the other MPPTs reset about 9pm at the moment, but this one changes about 10am the next morning, therefore including part of yesterday's stats.

I've found the problem to be a CCTV camera with an IR illumination that keeps a voltage of about 15v coming out of the panels all night. If I switch off the IR on the camera, it does drop to nearly zero.

I've read various posts on here about streetlights, and putting a resistor across the input, but the values quoted mean I would need about a 10W resistor for when the panels are generating full power.

I can't relocate the CCTV camera, or shield it's beam.

I'm running it all using a Raspberry Pi and Venus OS Large. I would have thought there would have been a way of sending a reset day command to an MPPT controller at midnight maybe, but cannot see anything, even in Node-RED. The MPPT controller has no user changeable threshold levels for detecting day changes as far as I can see.

Hopefully I'm missing something

Thanks for any help

Steve


MPPT Controllers
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kevgermany avatar image kevgermany ♦♦ commented ·

I think you're probably going to have to live with it. These MPPTs are automatic.

But you may be able to trick it by turning it off (disconnecting the panels & battery), but read the manual - somewhere there's a section on how it sets its clock.

I tried to find the details, but couldn't.

From memory, it uses panel voltage to determine dawn and dusk, then calculates midnight from them. You might be able to simulate by covering the panels for a night or two.

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JohnC answered ·

Hi @Mopatops

You say you're looking at VRM Portal. Just set your location/timezone there and the mppt's won't have to guess.

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mopatops answered ·

Hi John

I have now set my time-zone correctly on VRM, but I'm not sure how this effects the MPPT's. 3 of the 4 always report correctly on VRM, but these panels aren't effected by the CCTV camera.

If I understand correctly from other posts, the MPPT's reset themselves to the next day when they see a period of darkness, and I was guessing the one that's showing incorrectly is the one that has the CCTV IR illuminating it. Does VRM interact with the MPPT's?

You can see from the Yield graph below for today that the orange trace didn't reset until 10am.

capture.jpg

And yesterday's shows the the 3 MPPT's resetting at 9pm, but the Orange trace gets carried into the next day.

capture.jpg

Thanks for your reply John, I'll see if setting the time-zone sorts it out, but I'm curious to know how this works.

Steve

PS I have reset the MPPT's when dark but after a couple of days this one reports wrong again. I have also tried a new MPPT and this does the same.


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kevgermany avatar image kevgermany ♦♦ commented ·
I checked my system. MPPT values align perfectly with time zone set.

@JohnC thanks, yet again I've learnt from your experience.


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JohnC avatar image JohnC ♦ commented ·

@Mopatops

Not sure what Widget you're looking at there, but I suspect Custom using PV Yield Today. So I had a look at mine..

1671934519607.png

Reset at 1:14am. Hmm, so I looked at the yesterday plot, which also reset at the same time, but just a flatline after that. Sorta understandable given this is normally a flat value by each day, and the only progressive value available is for the current day. The 1:14 reset time might be just VRM easing the load on their server from the midnight peak +/- an hour for daylight saving issues. The VRM guys would know that an accurate reset time for the mppt doesn't really matter, as long as it's deep in the night.

My conclusion is that one shouldn't necessarily read gospel into these things, some pragmatism may be in play. So take care, and Merry Christmas too.

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mopatops avatar image mopatops JohnC ♦ commented ·
Hi John

Sorry, I didn't mention it was a custom graph. You're right, it's the yield of the 4 MPPT's I'm running all on one graph.

It's not just VRM that this is happening with. The stats on the MPPT itself are incorrectly timed as well. If I have a really overcast day the day after a sunny day, this MPPT still reports a good day's solar carried over from the day before.

I also run Node-RED, and grab the Yield every day from each MPPT and put it into a database. I then have a routine that lets me know if there is much discrepancy between the MPPT's. This always reports an error with this specific MPPT.

I know it's not the end of the world, but I find it fun playing around and learning with this stuff. I blame Victron for giving us access to all these stats ;-) I've tried the resistor trick seen in another post, so will see how that works out.

Thanks for your reply John, and Merry Christmas to you too.

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mopatops answered ·

Hi

A quick update to my tinkering.

I didn't want to try too low a resistor value across the PV input as suggested in this post Strange DC at MPPT input at night as I was worried about the power requirement for the resistor.

A 1K resistor at 75v would dissipate around 6 watts, which would ideally have to be a lot higher than that so as not to get too hot.

I had about 25v on the input when totally dark, so I thought I'd start with 100K. This would only need to dissipate 60mW, and to my surprise this reduced the input to 4v. I'm going to run with this for a couple of days and see if this sorts out my problem.

Steve


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mopatops answered ·

Hi

Quick update - It looks like wiring a 100K resistor across the PV input has sorted my problem. The 4 MPPTs are changing to the next day at exactly the same time now. Obviously the residual voltage caused by the CCTV illuminator was confusing one of the MPPTs. As stated above the 100K resistor dropped the night time voltage from 25v to 4v. Thanks for the replies. Steve.

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