Hi everyone,

I have a weird issue that I'm not sure exactly how to classify or interpret it. Now, I can't speak for this happening every day as I am back at work and it only seems to happen during the peak heat of the day, but my PV supply seems to fluctuate wildly with supply. This is after batteries are charged.

The PV will be supplying the load of lets say 2kw, then in a second it will drop to 20w, then a few seconds later, 1.5kw, then again a few seconds later 600w. This causes the source of power to fluctuate quickly between PV, battery and grid to supply the load which is stable. 

I have a video clip of this happening but I'm not sure where to upload it to for someone to view.

I'd like to find out why this is happening, and how to rectify it, as surely its not good for the electronics to be constantly between the various sources of power?

Thanks so much!

PV in general is not necessarily stable. Even if you don't change anything, it could fluctuate with the load (eg. as a washing machine changes actions through its programmed cycle), or with a passing cloud causing shade over the panels (and causing the load to exceed available PV).

It could take the MPPT a few seconds to adjust the PV output to the change, at which point the inverter could be switching to the grid to pick up the slack briefly, especially if it's not an inverter that can blend power from different sources.

One would need to know more about which inverter, the connected loads or the amount of PV connected to form a better picture, but so far my 2c is that it sounds like it could still be fairly normal.

 

Edited January 12, 20232 yr by GreenFields

Not what one would want to hear but also look at the connections making bad contact between panels as you confirm the load is stable. 

Is it on some parallel strings to the MPPT? 

The load is stable with a pool pump and normal loads (no washing machine) of about 1.5kw. This may fluctuate by 10w or so, but not close to 1000w which the PV supply seems to do.

Again, it's only in the afternoon that this happens. Between midday and say 4pm.

It's an 8kw Magneto (Deye) inverter with 18x 455w panels, 9 per string in series. My nominal voltage is around 385v that max's out at ±405v.

A picture says 1000 words so a video must say even more! Here is a link to the video I took: https://youtu.be/9KSCOp9ZOCg

8 hours ago, Gavin286 said:

The load is stable with a pool pump and normal loads (no washing machine) of about 1.5kw. This may fluctuate by 10w or so, but not close to 1000w which the PV supply seems to do.

Again, it's only in the afternoon that this happens. Between midday and say 4pm.

It's an 8kw Magneto (Deye) inverter with 18x 455w panels, 9 per string in series. My nominal voltage is around 385v that max's out at ±405v.

A picture says 1000 words so a video must say even more! Here is a link to the video I took: https://youtu.be/9KSCOp9ZOCg

That is not normal, you need to ask your installer to investigate this. There can be lots of causes, it seems to be happening with both strings where the amps just falls away completely which is telling me the circuit is somehow incomplete.

One of the most common problems is loose MC4 connectors (this can also be a fire hazard), poor wiring etc. It might also be the MPPT that is broken, but it is unlikely that both will be damaged. It can also be loose connections in your junction box or a problem in your fuse holders

 

Thanks for your input, @I84RiS. I also suspected this to not be normal or good for the system overall to be so erratic. Frankly, the installer and I are not on good terms any longer after I had to force them to remove 2 panels from my setup due to the voltage being too high (as per the flipping spec of the system) and him outright ignoring them. 

Perhaps someone on the forum here would be able to assist me with a site visit, or recommend someone that could just go over the system to see where the issue might be. Of course I don't expect this to come free of charge and will happily pay for the assistance!

Does that also happen when the battery is low and taking charge? I suspect it is due to the export limitation being on.

1 minute ago, P1000 said:

Does that also happen when the battery is low and taking charge? I suspect it is due to the export limitation being on.

No sir, not that I can tell. The batteries are always charged fully before 12 midday and it happens after that. Which setting should I check or rectify?

4 minutes ago, Gavin286 said:

No sir, not that I can tell. The batteries are always charged fully before 12 midday and it happens after that. Which setting should I check or rectify?

Then I would leave it. It's probably because the export limit function has a slow feedback loop. Possibly worsened by a fluctuating load.

21 minutes ago, P1000 said:

Then I would leave it. It's probably because the export limit function has a slow feedback loop. Possibly worsened by a fluctuating load.

Should I post some pics of the settings? The inverter is exactly the same as a Deye if that helps...

No, it won't be an export limitation. In the video you actually see it happen during loadshedding, grid is "0", and then the battery supplies the shortfall when the PV generation collapses. Other times as per the description it could be that it's switching to grid as backup.

Checking the panel's connections & circuit sounds most plausible. Otherwise the MPPTs could be damaged from earlier over-voltage? Just speculating.

6 minutes ago, GreenFields said:

No, it won't be an export limitation. In the video you actually see it happen during loadshedding, grid is "0", and then the battery supplies the shortfall when the PV generation collapses. Other times as per the description it could be that it's switching to grid as backup.

Checking the panel's connections & circuit sounds most plausible. Otherwise the MPPTs could be damaged from earlier over-voltage? Just speculating.

Thanks for your input. I preferred P1000's comment as it was better news 

I know for a fact that my undercounter lights in the kitchen pulse when this is happening, so I'm sure it's also affecting every electrically connected device which is the entire house. 

What would the process be to check (disconnect and re-connect) the MC4 connectors? Will it be enough to just turn off the PV switch on the inverter?

17 minutes ago, Gavin286 said:

What would the process be to check (disconnect and re-connect) the MC4 connectors

If power is steady when the batteries are charging, it's not your MC4 connectors.

I think I'm going to decrease the charge rate of the batteries so they take almost the whole day to charge, and see if this happens over the course of the next few days. 

Note also that it only seems to happen during hot days - if that's also another possible contributing factor.

28 minutes ago, Gavin286 said:

I think I'm going to decrease the charge rate of the batteries so they take almost the whole day to charge

that would be my recommendation, aim for a full charge by 1500 to 1600 local time... but it still sounds like there may be a problem, which could be an actual fault somewhere in the system as a whole, or... maybe a software issue/settings glitch...

There are plenty of Deye/Sunsynk and now Magneto's around the countryside and what you are experiencing sounds really off and not correct to me...

For what its worth, I have an 8kw sunsynk and have the same thing happens to me. I thought that it was due to me having a high inductive load kicking in such as an aircon but after seeing yours do the same thing with less load.. now I am not sure.

14 hours ago, SteveP said:

For what its worth, I have an 8kw sunsynk and have the same thing happens to me. I thought that it was due to me having a high inductive load kicking in such as an aircon but after seeing yours do the same thing with less load.. now I am not sure.

I changed my charging schedule to only finish at around 14:30 or so, and also now have a fan blowing into my pantry where the system is set up. Between both changes I haven't seen it happen for the last few days. I'm beginning to suspect that the MPPTs are getting too hot and trying to regulate themselves again the higher temps. Note that my fans DO kick in and function as normal, but perhaps the ambient temp is just over a threshold...

@Gavin286 possible. Although we are not talking very high loads given that the mppts are rated for 10.4kW.. I guess more testing is needed. With that said, I have not had my system run through a winter cycle so it could very well have something to do with temperatures given how hot it is and the fact that it has only happened to me when running my 30k BTU non-inverter aircon - because it is so hot XD

Edit: I initially suspected the issue was due to the very high inrush current caused by the old aircon toggling on and off during its cooling cycle but again, more testing required.

Speaking to my installer, he said that he has seen a similar thing in a factory that has a large non-inverter aircon on a 12kW sunsynk so theres that..

Edited January 19, 20232 yr by SteveP

is it not possibly clipping with a high MPPT input voltage.

6 hours ago, razzor13bt said:

is it not possibly clipping with a high MPPT input voltage.

The inverter used can go up to 450V so no worries here. 

Every inverter type and model has his own way of handling floating charge situation. Some appear weird. Basically higher battery capacity provides more stability thanks to reduced battery voltage drop due to sudden load. I experienced this. After adding a 4th pack floating operation became much more stable and satisfactory.