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dax021
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I have a couple of questions regarding my Axpert , which i'm hoping someone can help me with.  Model is "SOL-1-AX 3Mplus48".  I have 4 x 300W panels connected in 2 parallel strings of 2, and 8 x 100Ah batteries, connected in 2 strings of 4.  Lister 4KW for backup, and completely off grid.

1.  I very rarely see the panel input wattage go higher than 350-400 with the volts sitting around 70 - 80.  Would it be better to remove one panel and just have 3 in series to get the higher voltage, as it would seem to me that the system isn't using the full panel capacity anyway?

2.  The last few days have been pretty overcast and I got a low battery warning for the first time.  I tried to charge the batteries via generator power, but after an hour it didn't seem to have made any difference.  My load was only about 500W while the genny was running, so thought there would be plenty of juice going into the batteries.  There was a trickle of panel W coming into the inverter.  Reading the manual, I'm getting the impression that the genny will only supply power once the low battery level is reached or there is no solar input.  In other words, I can only make use of the genny at night or if I disconnect the panels.  Am I interpreting this correctly?  Also, will the excess genny power not being drawn by loads, go to charging the batteries?

Thanks in advance.

Peter

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3 hours ago, dax021 said:

Model is "SOL-1-AX 3Mplus48".

Good day, Can you please confirm that this is the correct manual. 

http://www.solarwholesale.co.za/Axpert MKS-MKS PLUS 1-5KVA Manual on 20140306.pdf

Please take a screenshot of all the settings available to you as well as the values you have chosen for each. 

3 hours ago, dax021 said:

1.  I very rarely see the panel input wattage go higher than 350-400

What is your output at this stage. If your load is 400watt  your PV will only produce 400 Watt (plus losses). If you are home around mid day,  please use a load bigger than 1200 watt, kettle maybe, just to see what the panels will bring in. You can expect around 80% of your combined panel capacity. In your case about 960Watt. 

If you dont get that, it might point to a string problem. If you do get it, the Axpert Experts around here would want to see your settings to make sure your system setup is correct. 

 

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3 hours ago, dax021 said:

Would it be better to remove one panel and just have 3 in series to get the higher voltage, as it would seem to me that the system isn't using the full panel capacity anyway?

No, not in my opinion. 

3 hours ago, dax021 said:

I tried to charge the batteries via generator power, but after an hour it didn't seem to have made any difference. 

This might be a setting issue. 

What is the value of setting 2 and 11 on your inverter?

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Hi @dax021

My suggestions follow, but @Chris Hobson is probably best qualified to answer Axpert off grid questions on the forum.

If completely off grid with genny backup then I recommend that [Menu 01] is set [Uti] this will ensure that when the genny is running it will be used to supply the loads, also [Menu 16] should be set to [Cut] for a similar reason regarding charging of your batteries.

The default for [Menu 02] of [60A] should be good, and similarly [Menu 11] default of [15A] as these are the highest available as far as I know.

I believe that you should have 1x 300W panel per 100Ah battery for a well balanced system, your PV input seems a bit low.

As @Jaco de Jongh said you will not benefit from going to 3 panel strings, in fact you may risk over-voltage to your MPPT under cold+bright conditions.

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Hi Peter - good advice so far.

Program 1 => UTI so that the load is being supplied by the gennie. The Axpert cannot charge your batteries unless it is in utility mode.

Program 2 => We have no idea what your batteries are and have no datasheet so we will start off conservatively and say 20A.

Program 3 => Try UPS but in my experience generally there few gennies (including my own) that can supply power clean enough for the Axpert's UPS setting. If it keeps switching back to solar/battery use the APL setting.

Program 16=> SNU. This allows to to use both solar and utility to charge the batteries.

A list of your settings and a datasheet for your batteries will be helpful.

 

 

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22 minutes ago, Chris Hobson said:

Program 2 => We have no idea what your batteries are and have no datasheet so we will start off conservatively and say 20A.

I think with 4 panels the charge current would struggle to reach 20amps (1kW), which is only 10 amps per string of batteries (too low for Sinetech 100Ah batt's which want 20amps minimum per spec).

So 60amps (30amps per string) may be a bit high without further info - but 20amps per string (40amps total) would be pretty safe but that would require an additional 4 panels - and still seldom get there.

I believe that the 3kW+ has a 3000W MPPT but I may be mistaken.

 

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6 minutes ago, pilotfish said:

would be pretty safe but that would require an additional 4 panels

Depending on the VOC of his panels. With 4 extra panels I would lean to 4 strings of 3 series in parallel..  

1411790475_Axpert2.PNG.0695fe327f696615466ea3f2c3485df2.PNG

 

@dax021 Can you please take a picture of the label on the side of your inverter to clarify the exact model you have. It will also indicate your max MPPT voltage. 

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3 minutes ago, Jaco de Jongh said:

With 4 extra panels I would lean to 4 strings of 3 series in parallel.

Yes this has been discussed a number of times. With 250W panels (60 module) you can comfortably install 3 panel strings, with 330W (72 module) you are getting VERY close to Max open circuit voltage of the MPPT and may very well exceed it under cold bright conditions and with cloud edge effect. The consensus has been that it is not worth the risk.

On my own system I tested 9 panels 3s3p and 10 panels 2s5p and saw a small improvement with the 2nd setup - thus my opinion that it is not worth the risk with 72mod panels.

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Just now, pilotfish said:

and saw a small improvement with the 2nd setu

This was done with 2 inverters in parallel and at the same time - so as close to scientific as can be. I now have 10 panels on each inverter in a 2x[2s5p] arrangement (I would go to 12 each but no more roof space on the building being used).

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15 hours ago, dax021 said:

Reading the manual, I'm getting the impression that the genny will only supply power once the low battery level is reached or there is no solar input. 

You can set it up so that as soon as the generator is on, it will supply loads and charge the battery. This is normally how you'd want it set up when completely off-grid. But the inverter doesn't know if you are off-grid or not. So you have to change some settings.

Quote

Also, will the excess genny power not being drawn by loads, go to charging the batteries?

Again, you have to make sure the settings are right before this will happen. It will depend on the battery voltage as well as settings. Others have indicated what settings need to be changed.

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Hi, thanks for all the replies.  Attached is a spreadsheet of my settings.  I see a few of them are not as recommended, so will make the changes.  I take note of all the all the advice on more panels etc., and agree entirely,  but unfortunately this aint going happen owing to budget.  I pretty much live hand to mouth at the moment.  Reading another thread prompted me to check each bty V independently, and found I have 1 in each string down to 11.6V.  I presume this is causing a problem .  I have been in contact with Chris R, and as soon as I can, I will be purchasing 2 x HAO2's from him.  

My bty's are Willard Solar 105's, but are actuallly only 90Ahrs at the 20C rating.  I survive on this system by really watching my loads.  Fridge draws 100W while running, lights maximum of 100Wh, microwave over 1000W, but I only use for about 10min/week and only when the sun is shining. Laptop and Cell chargers, I'm guessing at 200W/day and I also try to keep to sunshine hours. 

Thanks again, and sorry for the belated reply.  The weather has been so shit for the last 3 days that even my cat refuses to go outside and I have basically shut my inveter down and am operating on my backup 12V system for lights at the moment.  the rain is pelting down on my tin roof so hard that I can't hear myself think. As soon as i can concentrate, I will go through this thread again and make changes as recommended.

Axpert Prg Settings.xlsx

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You need to do something to balance your batteries fast or you can expect a costly meltdown - maybe swap highest and lowest in each string for now and monitor until you are able to get the HA-02's.

TTT has a theory about the 1st batt in each string being going low, he may be on to something from your answer.

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Thanks to all for the great advice.  I have gone through it all and deduced (not sure if correctly) that the unbalanced batteries are pulling the bty bank down and confusing the Axpert, hence the premature low bty warning.  Will take pilotfish's advice and rearrange for now.  Panels are working fine.  The sun is shining again, at last, so switched on the microwave and observed 1.14Kw feed from the panels at 09h00 this morning.  I have changed prg 1 to "uti" and although not tested with the genny, am pretty sure this will cure my charging problem.  Will test during the next cloudy period.  At the moment the Axpert reports the bty's at 53.6V and in float.  Panels supplying 135W, my laptop is charging and fridge is running.  Thanks again, Peter

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On 2018/09/06 at 4:16 PM, Jaco de Jongh said:

In your case about 960Watt. 

 

25 minutes ago, dax021 said:

1.14Kw feed from the panels at 09h00 this morning.

Great, so your string is fine and the panels produce what is expected of them.. 

Please just for interest sake. Can you still supply the VOC of your Panels as well as.. 

On 2018/09/06 at 9:25 PM, Jaco de Jongh said:

Can you please take a picture of the label on the side of your inverter to clarify the exact model you have. It will also indicate your max MPPT voltage. 

 

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1 hour ago, dax021 said:

Will take pilotfish's advice and rearrange for now.

This is what I would truly suggest while you wait for your HA-02's;

  • allow your bank to charge fully until they go to float,
  • measure individual voltages and label them with number (1/2/3 or4) and the voltage on masking tape,
  • if unbalanced then remove one string from service and connect them in parallel, allowing them to balance naturally,
  • then put a 12v charger on those batts to top them off while connected in parallel,
  • wait until 48v string is float again and then swap so that you can do the same with other string,
  • if you notice a pattern (eg. #1 is low and 4 is high) then install in reverse order when put back into service,
  • monitor individual voltages periodically to ensure that your batt's are not damaged.

You want to do this in a fine weather period.

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Hi Jaco,  inverter is a Mecer branded 3kva plus model.  Bit difficult to get a camera in there to photo the label because of the way it's mounted, but have double checked model #, as per the decal it is "SOL-1-AX-3MPlus48".  The manual you mentioned earlier is the correct one with a couple of minor differences, I guess different prints only.  Axpert can definitely take 3Kwp with V range from 60-115V and  VOC of 145V, so same as the 5Kva model.  Panels are ReneSola JC295M-24Ab, 295W with 44.7VOC.

Pilotfish, that's a good idea.  I can remove 1 string and connect in parallel to my standby PWM charger.  This seemed to balance them nicely previously when connected as such.  Batteries are probably fubar anyway as I was given them when they stopped holding charge on the landlady's 24V Microcare system.  After having them on my PWM for some time I had them tested at a battery place and they insisted that they were 100%

After I've robbed my local bank I will invest in a couple of Pylontechs 

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Just been rereading the whole post.  To Chris H,  the 3KvaPlus can't do "snu" in prg 16, it is not an option for some reason.  The genny seems to work fine in either APL or UPS mode.  It is a SR2 with Hoffberg alternator and seems really smooth.  I'm too dof to connect a scope or such to check waveform.

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2 hours ago, dax021 said:

.  Axpert can definitely take 3Kwp with V range from 60-115V and  VOC of 145V, so same as the 5Kva model.  Panels are ReneSola JC295M-24Ab, 295W with 44.7VOC.

 

On 2018/09/06 at 9:34 PM, pilotfish said:

With 250W panels (60 module) you can comfortably install 3 panel strings, with 330W (72 module) you are getting VERY close to Max open circuit voltage of the MPPT and may very well exceed it under cold bright conditions and with cloud edge effect.

@pilotfish, I wanted to ask this question for a couple of days now. The inverter supplier states the inverter can handle a string with a combined VOC of 145Volt. In this case 3 panels will give 134.1Volts while not connected to any load. Under normal loads that should easily drop to 120Volt and even lower under heavy loads. The panel supplier rates his panels Max VOC at 44.7 Open circuit volts.

My Question:

  1. Cloud edge effect will normally happen under load conditions, what is the chances that the connected panels will ever exceed open circuit values?
  2. Will the supplier rate his product to a certain value without taking something like that into consideration, and will there be no safety factor already build in to compensate for events like you mentioned?
  3. What VOC will you recommend for a 75/15 MPPT for example? I know for a fact it will handle 75 volt, and up to 25% bigger in Array size because its got a 25% build in safety factor. Even if Voltronic only allow for a 10% safety factor in their products, the chances of that being exceeded is slim at best....  
  4. Is 134.1 Voc to high for a system rated at 145Voc with some kind of safety factor still above that. 
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Hi @Jaco de Jongh

To be clear I share the opinion of @Chris Hobson that is a risk not worth taking as the Axpert 5k MPPT doesn't appear to benefit from 3S as apposed to 2S when using 72 module panels (verified from my personal test), if using 60 module panels then this doesn't apply as your safety margin is greater. I'm not saying that it will cause damage, only that you are very close to max ratings and it MAY cay damage under certain conditions.

1 hour ago, Jaco de Jongh said:

Cloud edge effect will normally happen under load conditions, what is the chances that the connected panels will ever exceed open circuit values? 

If you monitor ICC you will find that when running on PV and a load kicks in that the inverter cant sustain then the system will often switch to grid for a while (with panel voltage going to Voc) then switch back to PV when the load drops - on a cold day with cloud edge effect your Voc could exceed 145V which may or may not result in damage, but I don't want to be the one to find out that it will and I similarly don't want to advise others to do something that I am not prepared to do myself.

Here is an example from Tuesday

1081153749_GridSwitching.thumb.png.0d606ccf579f6e3ee3236d396cc1575d.png

I had staff at home using DW/TD/Iron/lawnmower at the same time causing the system to switch to grid, when this happens the MPPT shuts down for a while and then boots back up again (I guess to prevent an overshoot as the load requirement suddenly drops to battery charging only), If this timing coincided with cloud edge effect on a cold spring day like today then you would be at risk.

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12 minutes ago, pilotfish said:

when running on PV and a load kicks in that the inverter cant sustain then the system will often switch to grid for a while (with panel voltage going to Voc) then switch back to PV when the load drops

Thanks now I understand your position. I have only used  2 different Infini models and being Hybrids, I was never faced with the switching back to grid part leaving my panels at VOC. My panels are always in use and seldom reaches 80% of VOC.

Thanks for Clarification, now I will remember the Axperts opperate differently, and I can agree the risk is pretty high for a Axpert user. 

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6 hours ago, dax021 said:

  To Chris H,  the 3KvaPlus can't do "snu" in prg 16, it is not an option for some reason.  The genny seems to work fine in either APL or UPS mode.  It is a SR2 with Hoffberg alternator and seems really smooth.  I'm too dof to connect a scope or such to check waveform.

I had forgotten that I have programmed a friends 3kVA and remember that is one of the quirks. If your inverter will run on UPS use UPS. I have a SR3 witha Compton Greaves and it is not smooth enough.

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