Jump to content

PV intermittently dropping to almost 0 W


Vijen
 Share

Recommended Posts

My 5kVA Mecer inverter has started dropping the PV input while the sun is still shining brightly outside and the load fairly constant. The PV input drops to almost 0W then in picks up again to the value it was before the drop. It does this at least twice within 30 seconds and then seems to settle down again. My system runs in SBU mode, with solar only charging and max current set to 30A. Its seems like the MPPT controller is faulty.

This started after I shut down the system to put my batteries on a stand. I followed the procedure in the manual for shutdown.The system was off for at least 2 hours and when I started up I had to set all the settings again as they had returned to defaults. I have since shut down the Mecer again and restarted to see if removes the issue but it still does it.

Has anyone experienced this with a similar inverter or any ideas what the problem could be?

Link to comment
Share on other sites

Thanks Coulomb - I read through the thread

It appears one solution was the replacement of batteries - did I miss any other possible solutions?

My system was fine before moving the batteries - will have a look at all connections again - maybe a bad battery connection has started this.

Fortunately, I do not experience the freezing - that would really suck!

Link to comment
Share on other sites

21 hours ago, Vijen said:

Sorry forgot to mention that I experience same drop when I make a changed to battery setting. When the solar controller resets it cycles solar power on/off a few times before it stablises.

That part is normal. The DSP (main processor) is sending a reset packet to the Solar Charge Controller's processor, so that it can read the new settings. Only changes related to battery charging have this effect. The reset causes the SCC relays to come off; they take a while to come back on, then a while longer for any current to flow, then a while longer for the ramp up in current. I recall about 15 seconds for each of these phases, so a full minute before full PV power is restored.

Are you saying that the PV power dropping to zero sounds exactly the same as after you make a battery charging related settings change? If so, that sounds like you've disrupted the PV wiring. The Solar Charge Controller is powered solely by the PV input; if that is intermittent, then the SCC will be restarting all the time from zero with those delays.

Link to comment
Share on other sites

  • 3 weeks later...

Hi Coulomb

Yes, the PV power drops the same as when I make a battery charger change. I expect the delays but it also oscillates a few times before it settles down. Its like the controller overshoots and then drops to 0 and then overshoots again. From my control system background its like an unstable controller after a change.

I have found that the problem is the worst if I set the charging current low to 20A and disappears as i increase the current through to 40A.

Link to comment
Share on other sites

  • 3 weeks later...
On 2020/03/09 at 3:27 PM, Vijen said:

My 5kVA Mecer inverter has started dropping the PV input while the sun is still shining brightly outside and the load fairly constant.

Did you manage to solve the problem, and if so what did you find?

I had a 20A PV fuse blown, about 2 months ago on my 4KW Axpert, so I did not have a spare fuse so I took a few thin strands of copper wire and built my own temporal fuse, Everything worked perfectly and I knew in the back of my head when I go to a electrical shop again I need to get that fuse fixed, so now with lockdown over easter weekend I had the perfect storm, I thought I’d use the extra unused wasted solar pv and switched on underfloor heating +-1200W so the load at the time was about 2KW ( that includes my general load of about 700W) my inverter handles this with ease. 

But my wife decided to switch on the oven to bake and she switched on dish washer and the kettle. So I think this added up to about 7KW of load on a 4KW Axpert. 

With my inverter being in the garage I did’nt hear alarms or notice any problems only my son who later told me there was a dip in power, thats when I realized what happened. I checked the inverter and it had shut itself down. 

After reset from this point onwards I had my pv solar dropping, almost as Vijen experienced. I checked my fuses on the roof at the pv junction box and found my home made fuse installed 2 months before had a hot connection and slight burn marks. I replaced that home made fuse with another home made fuse and sofar the system is working again like before, So what I am trying to say is check your solar pv connections and check fuse holder contact points for loose or hot connections as this can be a cause for pv falling away.

 

 

Link to comment
Share on other sites

Possibly not relevant to these posters, but I thought I'd add a comment that at least in some cases, unexpected reductions in PV power have been tracked back to the "solar balance" setting. On many models, this is setting 31, but on Axpert Kings, they have this value but there is no setting 31. So after a firmware update, it's possible for the solar balance to "silently" be disabled. So then when you battery is charged, and you have plenty of load and plenty of sunshine, the inverter refuses to use the PV power because solar power balance is disabled. You can turn the solar balance back on with a PSPB1 command, or by resetting to factory defaults (there is a command for that, or Watchpower can do it).

When solar balance is enabled, maximum PV power is load power plus the power required to charge the battery. When solar balance is disabled, the maximum PV power is only that required to charge the battery. Why you would want this disabled is beyond me.

If interested, details are here.

Link to comment
Share on other sites

Hi Gerrie

Problem is still there but much more prominent if I set my max charging current to 20A. At 30A max charging it happens very seldom and at 40A not at all. My max current that PV can supply is just under 50A. It seems like when it has to reduce charging current more the problem is worse.

I have checked PV fuses and holders since reading your post and all seem fine.

Link to comment
Share on other sites

Overcurrent event perhaps. I don't know the MPPT in these units that well, but I know that it is pretty typical for an MPPT to 1) have overcurrent events, and 2) to deal with them by resetting and starting over.

Overcurrent events happen when your solar conditions change suddenly (eg level of insolation increases sharply due to cloud flare effect), and the control loop can't pull back fast enough. It's normal and MPPTs handle them in one way or another. Cheaper MPPTs handle them in software, they simple reset and start over.

The other reason would be if the MPPT limiting the current, and then the load increased and more power was called for. This prompts the MPPT to increase power, and if the power increase is sufficiently large they have to scan for the maximum power point. Again, the cheaper ones restart from zero when they do a scan, while higher end stuff will scan from where they are.

Edited by plonkster
Link to comment
Share on other sites

7 hours ago, plonkster said:

Overcurrent event perhaps

Or an over-voltage event, perhaps. @Vijen, do you perhaps have 3S of 72-cell panels, and a Solar Charge Controller with the 145 V max? (And power derating from 130 V).

I can imagine that if you had that situation, when you have your charge current set low, the panels do less work, so their voltage rises, making a power ramp down due to excess panel voltage more likely.

My feeling is that Voltronic Solar Charge Controllers never set the output to zero just because they are scanning, or even from an over-current event. With over-current, they'd be more likely to just ramp down the current, and not worry about a temporary exceeding of the maximum current rating. They seem to have plenty of current rating for the silicon, the limit is more that they don't have enough cooling to allow more current continuously.

Link to comment
Share on other sites

4 hours ago, Coulomb said:

My feeling is that Voltronic Solar Charge Controllers never set the output to zero just because they are scanning, or even from an over-current event. With over-current, they'd be more likely to just ramp down the current, and not worry about a temporary exceeding of the maximum current rating. They seem to have plenty of current rating for the silicon, the limit is more that they don't have enough cooling to allow more current continuously.

That is possible. With the Victron chargers, the smaller ones reset if there is an overcurrent event, the larger ones have a hardware clamp of some sort and don't reset. When it needs to find the MPP they sweep from the current position in three sweeps (so you see three dips). I recall that we discussed this before, but that was years ago, that the Voltronic chargers do have a tendency to restart from zero. That is not necessarily a bad thing, from a software perspective such a simplification might be the right thing to do, especially if you can find the MPP fast enough. If this is the intermittent zeroes the OP speaks of... they will be at most a few seconds in duration.

Link to comment
Share on other sites

Hi Coulomb

I have the 145V max solar charge controller hence panels are in 2S config so no chance of overvoltage. It also does not drop all the way to zero but does what Plonkster says happens on Victron. Usually 3 rapid drops to slightly increasing values and then returns to normal operation. As I said before, its like the charge controller overshoots (extra current) then drops quickly and goes up and down once or twice more until its at the correct charging current and voltage. 

Link to comment
Share on other sites

3 hours ago, willietes said:

Clear skies 1.8kw load and suddenly if switches PV off running on battery 10 Minutes later back on PV. I am baffled.

Next time when it happens again test the incoming dc voltage from PV panels at the inverter to confirm the incoming solar voltage is reasonably stable, It should not fluctuate allot. It should be within the inverter min and max voltage. If their is a bad connection somewhere on the pv than the voltage will suddenly drop or shoot up.

 

Link to comment
Share on other sites

4 minutes ago, willietes said:

 

I was there when it happened voltage was at 90V

When it reengaged, it went down to 77v

 

I think that normal as long as it’s not dropping low like below 40’s or something like that.

Link to comment
Share on other sites

  • 4 months later...

I experienced the same problem. I just installed my system with an Axpert MKS 5K and 9 330W panels. I installed also a remote control panel in my home office including a cable for battery monitoring. Since I'm still in tuning phase I observed this phenomena when the battery is fully charged. It even after some time remained in PV cutoff mode and discharged the battery below 90%. So I cranked the floating charge voltage (27) up to 54.5V but left the bulk charge voltage (26) at 54V. That seems to have solved the problem. When battery is full it maintains approx 51.5V by alternating in short intervals between charging at sun power and zero current.

Link to comment
Share on other sites

I must correct my previous post. I was kidding myself. The setting of 27 to 54.5V did not solve the problem.

The problem remains that when battery is full and reaches around 52V the inverter first reduces charging current, then switches the PVs off and on again several times in some 15 seconds intervals. It does this for a while and then it remains in PV off condition until it reaches approx 90% of charge. I vent trough the manual over and over again but cannot find any clue. Is there anybody that can help?

Link to comment
Share on other sites

There is a firmware for MKS II models that is supposed to mostly fix this problem; see this topic. That doesn't help directly with your model, but it means that Voltronic have at least a partial fix for this, and could apply it to the firmware for your model. You could pester your supplier for a firmware update equivalent to 71.82 for MKS IIs.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...