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PeterDawson

Axpert - strange behaviour (Potential MPPT issue)

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Hi All

This is my first post, but I've been a long time lurker, so first off, thanks to the creators of PowerForum and to all the contributors for making this a truly great information resource.

Background:

In Oct last year I installed a small off-grid system in the SA bush.  

  • Axpert MKS 5kVA.
  • 9 x 260W panels (3x3).
  • 1 x Huawei ESM-48100 battery (48V, 100Ah, 4.8kWh).
  • Generator connected to AC in, but only used to charge batteries very infrequently.
  • ICC with BMS-702 used for monitoring and remote setting adjustments.

90% of the time the house is vacant and only the fridge draws power from the system.  

For the most part the system has worked very well.  There are however some strange behaviours from the Axpert (and I suspect the MPPT) that I have not been able to iron out.

The first of these strange behavious is illustrated in Fig 1 below showing the charge period of the battery in the morning.   The SolarWatts (blue pen) shows the fridge's compressor periodically switching on and off.  Batterywatts (orange/yellow pen) shows the power flowing either into or out of the battery.  Notice how the pvwatts (green pen) sometimes drops right off when the fridge starts up.  This behaviour is not consistent as can be seen at 08:15ish.  Any ideas?

image.png.0d25806e570ea600731fbd45713e5a5d.png

Fig 1. PV power drops to zero when fridge compressor switches on.

 

The second, and more annoying behaviour is illustrated in Fig 2 below.  Sometimes, the MPPT seems to shut down and the inverter switches to battery mode.  The panel voltage jumps to Voc (103V for panel Voc of 36V), and the current drops to zero.  The trend in Fig 2 shows this happening at the same time the fridge compressor switches on.  This is also not consistent.  Fig 3 shows it happening when the fridge compressor switches off. It does however seem to always be associated to a change in inverter load, but the size of the load does not seem to matter.  Its not worse when the draw is higher, say when the dishwasher element or the kettle switch on or off.  Sometimes things resort to normal in a few minutes or hours, but typically only the next morning when the sun comes up.  If I happen to notice that the MPPT is not drawing any power from the panels, I can log onto the RPI remotely and bump the Bulk Charge Voltage setting by .1 and that kick starts the MPPT again.  

This behaviour does not seem to correlate with battery SOC nor with the panel output.  Sometimes we can go for weeks without it happening.  Today it has happened twice, once early this morning when panel power was 175W (Fig 3 @06:57), and then again just after I bumped it back to life with panel power output at 1,300W (Fig 4 @09:37).

image.png.b7a5f195e8ed44a185417eaeb0306390.png

Fig 2. MPPT seems to switch off completely and inverter switches to battery mode when fridge compressor switches on.

 

image.png.52b2bcfe67db002b3937504ba46ee762.png

Fig 3. MPPT seems to switch off completely and inverter switches to battery mode when fridge compressor switches off.

 

image.png.5c2c675a0f64c3e7f7651f921cdd747b.png

Fig 4. MPPT seems to switch off completely and inverter switches to battery mode when fridge compressor switches on and panel power at 1,300W.

 

I'd be very grateful for any ideas or advice on solving this.

Thanks

Peter

 

 

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Hallo Peter

I am experiencing the same issues with my Axpert King (5K) Inverter.

image.png.f36635cd0fa23e8a934c5f4dc8136a79.png

Freezed twice today but due to fairly constant monitoring rectified it quick enough not to loose to much PV Watts.

As you mentioned it dips normally with load change (Normally when the load drop) and it is annoying to say the least.

Busy with the Inverter supplier but not much luck as they are only Suppliers and repairers and not installers.

Please keep me updated should you find a cure and I'll do the same.

Jaco

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On 2019/05/21 at 7:08 PM, PeterDawson said:

I'd be very grateful for any ideas or advice on solving this.

It's quite strange. Your problem and Jaco Venter's seem quite similar, yet they are quite different models.

The only thing I can think of is that they have introduced some change to the hardware and/or firmware recently, and it affects all the PF1 models after a certain date.

It seems difficult but hopefully not impossible to convince them that a problem exists, and to get them to fix it. Keep hassling your suppliers, I guess. It's up to them to pass on the information to the manufacturer.

One minor point, you say when the SCC stops completely, the inverter switches to battery mode, but isn't it in battery mode all the time? I guess you mean that the battery is forced to supply the load on its own. Do you hear a relay click when this happens? This may suggest a change of mode, but in reality I would think it's the SCC output disconnecting from the battery, indicating that it's completely off, possibly having had its controller reset. This may be a little different with the Kings, which may control the SCC from the main DSP.

Edit: thanks for the detail and graphs, it certainly makes a clear case that there is a problem. That the puny load change of the fridge compressor switching off can cause the comparatively large PV power to crash to zero is striking on that graph. 

Edited by Coulomb

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Thanks for the replies Jaco and Chris (I hope I got that right).

Quote

One minor point, you say when the SCC stops completely, the inverter switches to battery mode, but isn't it in battery mode all the time? I guess you mean that the battery is forced to supply the load on its own.

you're quite right here.  I cant say that I have ever been standing next to the unit when its stopped charging, so have not heard whether there is a click from a relay.  That said, you've given me an idea.  I'm not exactly sure how the charger works, but I know when I change the bulk charge voltage parameter, there is some clicking from relays, possibly the charger unit switching off, parameter change takes place and then the unit starts again. Does this sound like normal behaviour?  If this is the case, there should be two relay clicks, off, and then on again.  So the next time that this happens, and when I use the bulk charge parameter to bump things back to life, I'll listen to hear if there are two clicks or just the one on click.

Here is the trend of the PV voltage and current during one of these trips.

image.png.8ff77de0e15d9bcd340e7f4cf4690229.png

Cheers

Peter

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1 hour ago, PeterDawson said:

If this is the case, there should be two relay clicks, off, and then on again.  So the next time that this happens, and when I use the bulk charge parameter to bump things back to life, I'll listen to hear if there are two clicks or just the one on click.

Brilliant! Yes, I agree that should work, as long as you can hear the faint click(s) over the fans and everything else. Note that if it's two clicks, they could be up to some 30 seconds apart. The SCCs don't rush things starting up.

1 hour ago, PeterDawson said:

Here is the trend of the PV voltage and current during one of these trips.

There seem to be two different kinds of trips there. The first is from about 7:00 to 9:30 am, where it just couldn't quite get started; one of the lower dips was at a PV voltage of 60 V. That should have been enough to  get started, especially that early in the morning. The PV current was then zero.

The second is from about 11am to sunset, where the PV current didn't go to zero, it just oscillated from 2 to 4 amps. Was the battery perhaps full by then, and the load not very high? If so, that's nothing to worry about. But if this is another dip, it's a different kind, where the SCC seems to be "fibrillating" 😮

It certainly shows that you have plenty of PV voltage during the dip(s), and it's nowhere near too high in voltage.

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The 07:00 to 09:30 is when the SCC was in its "tripped" state.  The 11:00 to sunset is as you suggest, full battery and solar is merely running the fridge and the float of the battery.

Here is another example of the SCC "tripping".  It went down at about 11:33 when the washing machine element switched off.  Fig 2.  

It then stays down until I noticed at 14:30ish and got it going again.  Notice that I ran the generator to charge the battery up from 16:00 to 18:00ish.

image.thumb.png.a315ff0134917c626fea687f977a211c.png

Fig 1. Whole day with relatively heavy system use.

image.png.c690619730335964fc01a3f3725ceda0.png

Fig 2. Showing trip as washing machine element turns off.

 

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Hallo Peter

Where did you buy your Inverter from?

What is your supplier's feedback regarding this issue?

I'm busy with Mustek to try and solve the issue but with not much luck.

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Hi Jaco.

I bought it from a supplier in Middelburg.  He's been great so far.  We've exchanged a few ideas on the issue for a few months now, trying various setting changes, but nothing has helped.  

I've sent this thread to him to follow and depending on what we learn here he'll take it up with his supplier.  

I guess this is what makes the extra cost of the Victrons worth it ;)

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I'll just add that @SnoopySniper seems also to be experiencing the freeze here. He hasn't mentioned (so far) the dips.

@PeterDawson, are you also running main firmware version 74.30? SnoopySniper's screenshot did not reveal his SCC (secondary, U2) firmware version, as the PV power was zero at the time (presumably, SCC frozen).

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On 2019/05/23 at 2:39 PM, Jaco Venter said:

Hallo Peter

Where did you buy your Inverter from?

What is your supplier's feedback regarding this issue?

I'm busy with Mustek to try and solve the issue but with not much luck.

I have exactly the same issues with several late 2018 and 2019 Mecer PF1 units. Currently 2 units at Mustek and a few still in the field. As you suggest, it must be a new batch / Firmware issue. Older units still performing as they should. "Expert Technician" at Mustek not knowledgeable at all - says he will liaise with Taiwan for advice. 

Mustek supplied a replacement unit which does exactly the same.

 

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Hi @DaveSA I also bought my inverter from Mustek.

I had the first unit replaced and the second one is still doing the same.

Also busy with Mustek at the moment (Trevor and Lubo) but with no luck.

We need to put more pressure on Mustek for them to put pressure on their supplier.

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Yes @Jaco Venter, also speaking to those two. They replaced the MPPT charger on a unit as well, but it did not resolve the issue. I had Luba on site to see for himself as they did not have similar PV source at Mustek to simulate the problem.

I will be on their case first thing tomorrow.

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I’m surely going to mention your name to them as well, for them to understand the problem is only to become bigger as more units are installed.

I am experiencing the freezes normally one or two times a day. I’m also experiencing PV dips throughout the day, and it is irritating to say the least. (Refer to previous trend posted)

on paper the Axpert King is one of the best inverters due t the ability to share loads between powers sources but with the current issues I’m experiencing I would not recommend these inverters to anyone.

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Hi,

I have also noticed this strange behaviour on my Mecer MKS 5kW. I have been running in utility mode for a couple of weeks as I was busy installing my PV panels and didn't notice anything funny during this time.

Last night I finally go to a point where I could connect my panels to the inverter, so was quite excited to see how they perform this morning. Everything started out well and I could see the PV Voltage rise as the sun came up and eventually current started flowing.

At some point when the PV Voltage was fairly constant at around 80V, the PV current/Watts dropped away and the battery charge stopped as well.  

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17 minutes ago, Pipes said:

I have also noticed this strange behaviour...

OK, so the problem is not isolated to a few cases. Recent installers, please get around to checking your graphs, as you too may be affected.

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Sure sounds like the same issue. 

Quote

I'm not exactly sure how the charger works, but I know when I change the bulk charge voltage parameter, there is some clicking from relays, possibly the charger unit switching off, parameter change takes place and then the unit starts again. Does this sound like normal behaviour?  If this is the case, there should be two relay clicks, off, and then on again.  So the next time that this happens, and when I use the bulk charge parameter to bump things back to life, I'll listen to hear if there are two clicks or just the one on click.

Would you potentially be able to carry out this test above?

Maybe change the bulk charge voltage when the inverter is running fine and confirm that there are two clicks.  Off and then on again.

Then the next time that the system freezes and PV watts drops to zero, change the bulk charge voltage by 0.1 and listen for how many clicks you here.  My suspicion is that there may only be one click, the on click, since the SCC is already off.

Thanks in advance.

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6 minutes ago, Coulomb said:

OK, so the problem is not isolated to a few cases. Recent installers, please get around to checking your graphs, as you too may be affected.

Hi @Coulomb, also noticed this would happen at another installation when the battery achieved the set Bulk voltage it would cut all PV and not switch to Float nor power the load (home). PV would then restart again whist Battery is used to supply the Load. While restarting PV,  the Battery depletes by 0.01%. Solar then revives and supplies Battery and load, until Bulk Voltage is achieved - about a minute later, then disconnects all PV again.  So it cycles this way approx every 2 minutes. Load of approx 1.5kW, Bulk set at 54V

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Hi @DaveSA

I changed the Bulk Charging Voltage from 53.5V to 54.1V at 13:16 and I must say I saw an improvement on the dips. Not sure how long it will last but for now it is surely better.

See trend below

IMG_0563.thumb.PNG.2fa159200f01875f8059e9ffb2622280.PNG

The last few dips were caused by load change.

IMG_0564.thumb.PNG.e5aa772ee8daa74c0d503e2d6e2d0739.PNG

For now I'm excited, but not sure if this is the root cause of the problem.

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Good Morning Guys

I only had a chance now to read the thread. I'm 'glad' i'm not the only one suffering from this problem. I really hope this can be resolved soon.

It is seriously annoying and impractical to monitor the system every half an hour to make sure is operating normal.

I've played around with bulk and float charge voltage. yesterday my bulk charge voltage was set to 54.5 and sadly this morning it went offline again(09H58).

I changed the float charge by 0.1V just to get the system going again. 

In terms of the panels dipping during load change i've gone so far as to have a normal Eskom plug for the iron. Although the iron only pulls a 1500W the quick on and off 

of the iron really messes with the system and it leads to the panels basically staying off for the whole duration of the iron session.

I hope there is a solution soon. I follow the thread attentively.

Good luck to everyone.

image.thumb.png.a3e413edca25c757b51e46ebe1a62870.png

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Hi Guys

just a quick update. After a PV freeze on Friday i changed my bulk charge To 54.8V and float charge to 54.0V. 

The system did not freeze for Saturday and Sunday. Will monitor in the coming week as well. 

The pv dip momentarily still happens when load is added or taken away. 

Greetings

 

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