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2x11kw Mecer inverters


Grant P

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Hi guys

we have just installed 2x Mecer Sol-I-AX-11M inverters.

each inverter has a 10.2kwh LV Topsun battery.

Each inverter is connected 2 two strings of 5 Ja solar 540w panels facing North.

My issue is the max the panels give out is 3500w sometimes a little more, so it works fine most of the time, but if I’ve had loadshedding at say 8 in the morning and the batteries have drained to say 50% unless I have excess solar power the batteries will not charge.

I have the battery charge priority set on Solar and utility and the output priority on Solar Utility Battery.

I can get it to charge off utility by putting off the solar or setting it to Utility Solar Battery but I would rather not use that setting.

please see attached screenshots of what I’m experiencing and hope someone can help me.

thanks I’m advance.

 

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EA19B005-E735-42F6-8DE8-0CEC588F464D.png

83D01903-DCA1-4AE2-A143-1DCC82AA3120.png

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Not sure i am understanding the issue here. From the images it shows you have 2.x kw being generated by the panels but the house is using more than this. So the extra is drawn from either the grid or the batteries. The system seems to be working as intended unless I missed something

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Ah ok - i get you now - It is probably how those settings are used by the Inverter. Are there other charging options available for you that you could use? Maybe the Solar>Utility setting will only revert to grid if there is no solar at all

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13 hours ago, Grant P said:

Ya it’s confusing as on the charge source priority SNU it says utility and solar will charge the batteries simultaneously ,but the batteries will not charge unless either the solar disappears or the solar is more than the load. 

Frustrating  

As mentioned only when solar falls away would grid charge take over. If you change setting 16 to UTIL charge only will the grid charge even if solar is available. This way you can force it to charge if battery charging is needed during high LS stages.

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Hi @Coulomb this one is an interesting scenario for me.

If we have SUB priority with solar available, then it appears the DSP prioritizees the pv energy to load, then only to battery.  Having a 'half duplex' birectional flow path, the grid cannot flow down to the battery while the pv energy flow up to the loads. So USB mode change will have to suffice if battery charge is a priority? 

Edited by BritishRacingGreen
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1 hour ago, BritishRacingGreen said:

Hi @Coulomb this one is an interesting scenario for me.

If we have SUB priority with solar available, then it appears the DSP prioritizees the pv energy to load, then only to battery.  Having a 'half duplex' birectional flow path, the grid cannot flow down to the battery while the pv energy flow up to the loads. So USB mode change will have to suffice if battery charge is a priority? 

Very interesting the way it is put forward and why. 

This is where an external MPPT comes handy. In this way PV can flow to battery while grid is also charging? 

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21 minutes ago, Scorp007 said:

Very interesting the way it is put forward and why. 

This is where an external MPPT comes handy. In this way PV can flow to battery while grid is also charging? 

Yes, the bidirectional gridtie topology makes up for an good solution at reasonable cost. But one sacrifice is there is no more a seperate grid charger.  

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8 hours ago, BritishRacingGreen said:

Having a 'half duplex' bidirectional flow path, the grid cannot flow down to the battery while the pv energy flow up to the loads. So USB mode change will have to suffice if battery charge is a priority? 

SUB is only available on high PV voltage models (for reasons that are not totally clear to me). Let's take an example, keeping an eye on my handy block diagram:

file.php?id=4538&sid=658db1cfc75a9cd58e6

For SUB to work, we have to have the high PV voltage solar charger, so the green path not the blue path. The red AC-DC converter doesn't exist as we're not talking about a King here. Both switches are on.

Let's say solar is weak, 1 kW; load is moderate, 3 kW. If I understand correctly, MAXs and the like pull 2 kW out of the battery to make up the shortfall, even though the utility is standing ready (we'll pretend that there is no load shedding for the purposes of this example). So 1 kW of PV is boosted to the DC bus, as is 2 kW of battery power, and all 3 kW flow left to right through the DC-AC converter, balancing the load, so that the AC input has nothing to do. That's despite the fact that U comes before B in SUB.

But we don't have to push all 3 kW through the DC-Ac converter. Let's drop it 2 kW to 1 kW. Now only 1 kW of load is countered, so the AC-in has to supply 2 kW. All of the DC-AC's needs are supplied by the PV, so there is no drain from the battery. It seems to me that this is how SUB mode should work, and maybe it is and I'm misunderstanding.

But the DC-AC converter is bidirectional. We can smoothly change the power level, through zero if we want, as easily as an electric car transitioning from power to regenerative braking by smoothly letting pressure off the accelerator pedal. So let's drop the DC-AC's power by another 2 kW, from 1 kW to -1 kW. In other words, now 1 kW is flowing from the AC-in/load connection backwards to the DC bus. This power has to go somewhere; the firmware will arrange for 2 kW to also flow backwards through the DC-DC converter to the battery. The 1 kW from the DC-AC converter (now running in reverse as an AC-DC converter) joins with the PV's 1 kW to provide the 2 kW needed by the DC-DC converter. If the firmware stuffs up and doesn't balance the power properly, the DC bus voltage will quickly head up too high or too low. Remarkably, despite fairly poor control of things like battery voltage when charging, the firmware seems to be able to keep the DC bus within bounds. Anyway, this is now the situation that you want: The AC input is supplying 4 kW: 3 kW for the load, and 1 kW through the DC-AC converter in reverse. 2 kW is now charging the battery. The battery is being charged by solar and utility at once, while also supplying the loads.

Despite my singing the praises of Voltronics' firmware, maybe the reason that they don't do the above is that they tried and couldn't get it to work because their control systems are too poor. Possibly that old bugbear I keep harping on about: integral wind-up.

If I've misunderstood the situation, please correct me.

I'll finish by noting that older models (like the two I run here) have no trouble charging from utility and solar at once, but of course, that requires far less juggling prowess from the firmware, since the solar charge controller connects directly to the battery, and the battery has way more storage capacity than the bus capacitors. So a little overshoot or undershoot doesn't cause much of an issue. In the simultaneous charging scenario I painted above, I'm assuming a nice steady 3 kW load, and steady 1 kW of PV power to keep the arithmetic simple. In reality, loads and PV power change dynamically, and even the mains voltage changes a few percent from moment to moment as large loads come on and off the grid. Still, that's one of the inverter's jobs, to cope with all that.

Edited by Coulomb
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Wow! Now I know how little I know.

I wish I understood what you guys are saying.

from my limited knowledge what you are saying is that I have to run on USB even though I have the charge source on solar and utility? That’s not great as we not going to get much savings as it will prioritize utility even when there is solar, or will it utilize the solar being made as well as the utility ?

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15 minutes ago, Grant P said:

Wow! Now I know how little I know.

I wish I understood what you guys are saying.

from my limited knowledge what you are saying is that I have to run on USB even though I have the charge source on solar and utility? That’s not great as we not going to get much savings as it will prioritize utility even when there is solar, or will it utilize the solar being made as well as the utility ?

Not sure if I understand. On the one hand you want to save by using solar for the load but then you also want to use solar to charge the battery. For this reason with the amount of solar available you set the way the 3 sources would be used for the load under setting 1 and then combine it with how you want to charge. 

IMG_20230426_212248.thumb.jpg.9b13c9ec92b877b5f9096bc61b01d3b4.jpg

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7 hours ago, Scorp007 said:

Not sure if I understand. On the one hand you want to save by using solar for the load but then you also want to use solar to charge the battery. For this reason with the amount of solar available you set the way the 3 sources would be used for the load under setting 1 and then combine it with how you want to charge. 

IMG_20230426_212248.thumb.jpg.9b13c9ec92b877b5f9096bc61b01d3b4.jpg

That is  correct I have it set to snu, solar and utility charge, but it will not charge via utility.

I know I can’t have it all but would like to use solar to help power the loads but also on cloudy days would like the utility to help get the batteries full, so that when loadshedding happens my batteries are able to last the duration.

but it seems like that is not possible.

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2 hours ago, Grant P said:

That is  correct I have it set to snu, solar and utility charge, but it will not charge via utility.

I know I can’t have it all but would like to use solar to help power the loads but also on cloudy days would like the utility to help get the batteries full, so that when loadshedding happens my batteries are able to last the duration.

but it seems like that is not possible.

Yes it is a shortcoming of the Axpert and some newer models have a timer that can be set so that one can choose what times to bring in grid charge when needed and not wait for no solar to start. 

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4 hours ago, Scorp007 said:

Yes it is a shortcoming of the Axpert and some newer models have a timer that can be set so that one can choose what times to bring in grid charge when needed and not wait for no solar to start. 

That’s makes sense, do you know if it’s possible to add a timer to the system?

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23 hours ago, Coulomb said:

SUB is only available on high PV voltage models (for reasons that are not totally clear to me). Let's take an example, keeping an eye on my handy block diagram:

That is interesting . SUB mode to me would be typically important   when I do want to use solar when available , but keep battery cycles at a minimum , eg. when solar is poor , and of course  during night time (only use battery when  grid is off) .  I think the fact that with high voltage MPPT connected to DC bus as opposed to low voltage models connect directly to battery , makes up a rather shift in paradigm regarding what the former has available to offer.

 

23 hours ago, Coulomb said:

Let's say solar is weak, 1 kW; load is moderate, 3 kW. If I understand correctly, MAXs and the like pull 2 kW out of the battery to make up the shortfall, even though the utility is standing ready (we'll pretend that there is no load shedding for the purposes of this example). So 1 kW of PV is boosted to the DC bus, as is 2 kW of battery power, and all 3 kW flow left to right through the DC-AC converter, balancing the load, so that the AC input has nothing to do. That's despite the fact that U comes before B in SUB.

If you referring to SUB mode here  , then  no ,  when U is available  the load requirement is fulfilled by the blend of AC to the S shortfall. So a definition of SUB would be as follows (a) if there is enough of S then load will be  fulfilled by (see also note 1) .  If S has a shortfall (or if S is 0)  then next up is U to add the extras , the S shortfall is made up by ac blending.  The B is only applicable when U is not available (load shedding!) , then the S shortfall is recovered from  B .  I assume that with the availability of U , that U will always provide the S shortfall , so that a full-on S-U-B  is never realized in practice when U is available.

Note 1 :  I have performed additional tests today at my own site in order to confirm that S will prioritize the load and not the battery. So if the battery is flat , grid is available , load is 3kw and S is 2kw , that full 2kw supports the load . Only when there is excess (spare) S power , then that balance will be skimmed off to the battery.  I have also proved that in SUB mode  when U and S are both  available , the grid cannot flow to the battery even if grid charging is enabled by menu setting

23 hours ago, Coulomb said:

But we don't have to push all 3 kW through the DC-Ac converter. Let's drop it 2 kW to 1 kW. Now only 1 kW of load is countered, so the AC-in has to supply 2 kW. All of the DC-AC's needs are supplied by the PV, so there is no drain from the battery. It seems to me that this is how SUB mode should work, and maybe it is and I'm misunderstanding.

Yes and that is  how it works  . Again when U is available , it provides for the S shortfall , via blending in the AC domain (the grid tie).

 

23 hours ago, Coulomb said:

But the DC-AC converter is bidirectional. We can smoothly change the power level, through zero if we want, as easily as an electric car transitioning from power to regenerative braking by smoothly letting pressure off the accelerator pedal. So let's drop the DC-AC's power by another 2 kW, from 1 kW to -1 kW. In other words, now 1 kW is flowing from the AC-in/load connection backwards to the DC bus. This power has to go somewhere; the firmware will arrange for 2 kW to also flow backwards through the DC-DC converter to the battery. The 1 kW from the DC-AC converter (now running in reverse as an AC-DC converter) joins with the PV's 1 kW to provide the 2 kW needed by the DC-DC converter. If the firmware stuffs up and doesn't balance the power properly, the DC bus voltage will quickly head up too high or too low. Remarkably, despite fairly poor control of things like battery voltage when charging, the firmware seems to be able to keep the DC bus within bounds. Anyway, this is now the situation that you want: The AC input is supplying 4 kW: 3 kW for the load, and 1 kW through the DC-AC converter in reverse. 2 kW is now charging the battery. The battery is being charged by solar and utility at once, while also supplying the loads.

Yes ,  that's the reverse gear  in operation of the bidirectional flow path. But with S available , we must explicitly set the mode to USB  .  This relieves S to supply loads and all its energy can go to battery .    . And if the charge priority setting includes U , then U will flow down via the DC-AC converter and join the S in the DC domain , from where they combine forces to charge battery (the DSP will of course throttle AC contribution according to grid current setting in menu , and at the same time throttle the total current as well according to setting).

This will answer the OP's (  @Grant P  ) question , he will need to make mode changes to affect charging from grid when required during the day where S is available .  SUB mode will block grid charging , USB mode is required to allow that.  EDIT : I have been informed also  by @Steve87 that if at night S is 0V  , then U will be allowed to flow reverse and charge the battery , even if in SUB mode. Which makes sense, because the DC-AC converter direction from S to loads doesn't mean a thing when S is at 0V.   ( you will know better than me , but this infers that the DSP firmware algorithm  is a complicated beast).

 

23 hours ago, Coulomb said:

'll finish by noting that older models (like the two I run here) have no trouble charging from utility and solar at once, but of course, that requires far less juggling prowess from the firmware, since the solar charge controller connects directly to the battery, and the battery has way more storage capacity than the bus capacitors. So a little overshoot or undershoot doesn't cause much of an issue. In the simultaneous charging scenario I painted above, I'm assuming a nice steady 3 kW load, and steady 1 kW of PV power to keep the arithmetic simple. In reality, loads and PV power change dynamically, and even the mains voltage changes a few percent from moment to moment as large loads come on and off the grid. Still, that's one of the inverter's jobs, to cope with all that.

Noted ,  the fact the low voltage models connects MPPT output directly to battery , as opposed to high voltage model which connects MPPT direcly to DC bus, will make for fundamental functional differences.  in low voltage case , in doesnt matter what the DSP does ,  if battery demands charge it will suck it off the MPPT directly (it can limit the current of MPPT yes , but it cannot stop the current flowing to battery) . in high voltage system its a different ballgame.

It is my firm belief and opinion  that the Voltronics hardware and software is very well designed , but the various modes are not clearly and user-friendly explained out there in the wild.

Edited by BritishRacingGreen
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