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Axpert 5KVA Relationship between charge parameters and Solar output


Valken
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Hi All,

I hope someone can shed some light for me on this?

First my setup: Axpert 5KVA inverter with 4X Energizer 105Ah batteries and 10 X Renesola Vii 300W panels.

 

Now i would like to know if someone has a similar setup? Because i would like to know how you get your full potential (3000W give or take) from your solar panels when you should not be charging your batteries (4 X 105Ah) at more than 10 amps??

See, when you set your total charging on the Axpert to 10 amps, it seems that the maximum output from your PV is also limited to this figure? I could not understand why i couldn't get more that about a 1000W from my 3000W panels. Then i noticed that when i change the maximum charging to say 60 amps, my PV output also jumped and i could get the full 3000W??

The problem now is that my poor old 105Ah batteries are being charged during the day at a way too high current and looks like they are not really charged fully.

Is there something wrong with my inverter or am i missing something?

Thanks.

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Nope, you are spot on.

I HATE to do this(!!!)  but IF I am correct, your batteries are the leisure types, i.e. Valve Regulated Lead Acid Batteries, the maintenance free ones?

If so they are good for UPS'es, not solar applications, but IF you have to use them, you need a few more to bring them in line with your array.

Why?

What I have been taught is that the load dictates the batteries, the batteries dictate what array you require to charge them at 10-13% of the total battery AH.

You have 4 x 105ah at 48v right? That is a 105ah bank.

Here are the off-grid solar sums, if you have 3000w array, 48v system, with all the losses included, you need on:
5% loading: 786AH bank - good for weekend use, whole week to charge the batts.
10% loading: 393AH bank - good for daily / off grid use.
13% loading: 302ah bank - Min bank you can install.

And to power your load:
178w max load will last you 12 hours up to 50% DOD, with one day reserve.

Batteries are a wee bit expensive so we get very clever here, but 105ah is a wee bit out of the scope for a 3000w array.

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Hi Valken. The minimum recommended battery is 200Ah for the Axpert 4kW MKS. So another 4 batteries. I would  get any load you can lay your hands on pool pump aircon geyser (a good bet witha 1500 W element)  whatever you have to hand. Otherwise you are wasting potential of your installation. My system is similar to yours (battery bank 260Ah) but the rest is essentially the same. My batteries would be in float mid morning and we would idle the day away. Now I put 1500W through an electric geyser and and have the added advantage of not buying gas as we use to heat water with a gas geyser but the gas geyser now run 5% of the time and my batteries are charged late afternoon.

For you first step would to be ensuring that your battery bank was 200Ah or larger and secondly finding elective load that you can add or subtract from the system.

Remember that you only approach 100% of PV capacity for a short period each day. The system should be over 2.2kW for several hours if there is a load big enough to draw the power.

 

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Ah, so I need to enable the Solar Power Balance? Was wondering what exactly that does. (Tnx viper_za)

Thanks all. And yes I agree I need better batteries. If only I knew what I know now I would have spent a lot more on batteries and less on panels....

I have very small loads during the day.. (Except for these hot days when my Air conditioners run all day)

Ps: Any good suggestions on batteries and where best to source them? Any experience on the Narada / SonX RA 260AH batteries?

 

Thanks again for all the feedback.

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  • 2 weeks later...

Ok..I really need some advice here now as i think i am going crazy with this. So i enabled the Solar Balance to make use of the full 3000W PV power (Sun permitting of course)

But now i find my solar just cutting out and some strange behavior? Just before i started typing this my batteries were on 100% and my house was on a load of 1300W. Now, however my settings are on Solar first (I have tried it on SBU also) There is not a single cloud in the sky but my solar only outputs about 250W (It does this for about 30 seconds the cuts out and seem to cut in again at around 250W for about 30 seconds again. NOW - when i switch of the power from eskom to the inverter, it happily gives out about 1500W and stays there??? So now the house is pulling the 1300W from the solar plus a bit for keeping the batteries on float. But the moment i switch the grid back on and the load increase slightly the solar cuts out and switches back to grid (Note that batteries still on 100%) and the same process repeats again. If i switch of eskom feed it works fine again?

Now im not sure if i understand this wrong but should it not pull some power from the batteries should the load exceed the PV output i.e The House draws a 1500W when a small cloud comes along....Now the PV drops to 1000W. Should the batteries not provide the other 500W? And up to what point will it keep providing that 500W as i understand in "Solar First" mode it does not take into account the voltage settings?

 

Then one last thing. I connected my BMV 702 - But the readings on voltages and capacity are in line what AICC tells me. The only thing that is way off is the SOC? And the fact that my battery voltage would be down to 47.2 V but the BMV states my SOC is still over 95% This cant be right?? 

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@Valken

I still want to know how you are wiring up 10 panels.

To run 3 strings you would only need 9, sounds like you have 2x3 strings and 1x4 string or 2x5 strings and this(2x5) would sometimes put you under the startup voltages needed for the MPPT letting the inverter think PV is not available.

 

The SOC on the BMV needs to syncronize before it gives you a accurate reading (Normally after one full charge cycle it should sync)

 

Thys

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If you go to grid the only draw on solar is the batteries hence the low solar production. Solar production is based on load until you exceed max available. So if you are plodding along you not drawing enough. Panels can be likened to a carthorse. It won't canter unless you make it.

Sent from my SM-G925F using Tapatalk

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The inverter cuts out when the scc hits a speed wobble. Often for instance whilst ironing as the iron stops drawing the scc cannot adjust fast enough. My inverter draws from battery while the scc adjusts. Under variable load the SCC starts over again drawing about 20W before the MPPT kicks in.

Sent from my SM-G925F using Tapatalk

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1 hour ago, viper_za said:

@Valken

I still want to know how you are wiring up 10 panels.

To run 3 strings you would only need 9, sounds like you have 2x3 strings and 1x4 string or 2x5 strings and this(2x5) would sometimes put you under the startup voltages needed for the MPPT letting the inverter think PV is not available.

 

The SOC on the BMV needs to syncronize before it gives you a accurate reading (Normally after one full charge cycle it should sync)

 

Thys

Hi Thys,

Yes they are wired up 2 Together 2X5 (ReneSola Virtus II 300W) so i get a VoC of 44.8V X2 

I know if it drops below 60V the MPPT disconnects but this is the problem...There is perfect weather and the MPPT voltage does not drop below 60V??

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35 minutes ago, Valken said:

Hi Thys,

Yes they are wired up 2 Together 2X5 (ReneSola Virtus II 300W) so i get a VoC of 44.8V X2 

I know if it drops below 60V the MPPT disconnects but this is the problem...There is perfect weather and the MPPT voltage does not drop below 60V??

I suspect this is your problem.

Heat will cause your voltages to drop.

Someone told me once that their is a +-0.13v rise in panel voltage for every degree below  25oC and I'm pretty sure the opposite counts for higher than that and this is the only reason I can think of why they would drop out like that.

Open circuit voltage (44.8V)is not the voltage you should be looking at you need to look at Voltage at Max Power as that is what the MPPT uses and for your panels this is 36.6V. Now take in account how hot your panels get on the roof and any voltage drops that occur over your cables this still makes the most sense to me. Voltage given by the Axpert is after the MPPT modified it

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Valken, so you have 5 strings of 2 panels per string, 89.6v coming in per string.

The 10th panel, how is that one connected?

Then you have 4 x 12v 105ah battery bank connected for 48v giving you 105ah battery bank. You will damaged them quite quick if you use them to power your load.

You have too many panels for the battery bank so you will damage them if you charge them too fast.

On top of this the 105ah Energizer batteries are sealed maintenance free batteries which means they are good for camping and UPS'es. Not for solar systems. 

First fix the batteries then tjune the system for your needs, is my suggestion.

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6 hours ago, The Terrible Triplett said:

Valken, so you have 5 strings of 2 panels per string, 89.6v coming in per string.

You should not use open circuit voltage, voltage at max power is 36.6 x 2  = 73.2v

6 hours ago, The Terrible Triplett said:

The 10th panel, how is that one connected?

Panels are connected in 5 strings of 2

 

6 hours ago, The Terrible Triplett said:

You have too many panels for the battery bank so you will damage them if you charge them too fast.

This is not true, why should you only have just enough panels to charge your batteries and not to carry your load also on top of that?

You simply adjust the Axpert to limit the charging current to what your batteries require and use the rest of the PV output as needed.

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Thank you Viper...

That makes sense i suppose. So would it be better if i add two more pannels (12 in total then) and do a 4 X 3 rather? this will then push up my voltage to 109.8V instead of the current 73.2V (But also the PV would now be 3600W) which should handle voltage drops better during those little clouds pasing by every now and then?

And yes @TTT I agree and i will change my batteries soon. These were also just during my testing phase. (I am also limiting the charge to 10amps) The thing is that these same batteries with the same panels worked perfectly with my 3KVA Axpert MKS Plus?

Now one last question TTT- You say i have too many pannels for the battery bank? Is this not the idea to use as much as possible power from the sun during the day?(Not from batteries) Or is there some kind of relationship between the PV power and ammount of needed battery power?

Thanks for all the advise so far guys!

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Valken you do not have to many panels. All you do is set the max charge current to 10 amps. Then you will not overcharge the bank. You also then drive your loads in the day. You want your volts as high as posible. Did Johan not hook up your panels for you ? Best config is sets of 3. 

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Viper, I have been taught to use Open Circuit volts in calculations, as all panel calculators do, i.e. my panels are 36.3 Volts at max power. Open circuit is 45.35. Have seen them reaching 46v infrequently. All solar calculators from i.e. Victron, Morningstar and Outback take that value into consideration with temps. So, if you NEVER have a cool / cold day with clear sunshine, go for 3 per string, for at the lower calcs it is 109.8v, with the MPPT at wot, 115v, max open voltage of 145v? 

It all really depends on how the Axpert controller will handle IF you go above 115v coming in on cool sunny days. Will it switch off till volts drop?

Valken. It has been said here that min bank is 200ah for the 5kva Axpert (?).

Yes, to charge 105ah batteries you set the MPPT to charge at 10amps, 15 amps max (13% charge rate is best). Problem is your batts are sealed so they do not like when they bubble when charged at higher rates. Been there, done that. 

Now, maybe the Axperts are clever i.e. even though the MPPT is limited to 10amps to charge batteries, it can increase the draw from the panels to max amps coming in to power the load? That will be quite cool I think.

I have been taught you match your batteries with your load, then panels to charge the batteries at max 13% of their AH rating, using as little batteries as possible i.e use larger amp hour batteries, then you have a lot less problems and worries. If you juggle that a bit, the more the load, the slower the batts will charge, which is ok. If the balance is too far out, you are straining the batteries.

And then, to not having to buy the full set we all require, we use clever tricks to switch back to Eskom at a set DOD, to not go below the magical 20% or 50% DOD, depending on our preferences for our set of batteries

  5% charge rate - good for weekend use, whole week to charge the batts for weekend use - so max power to load, limited battery use daily.
10% charge rate - good for daily / off grid use.
13% charge rate - ideal for off-grid use.

But, you need to know I do not use Voltronic devices. Charge controller is separate from the inverter and I cannot charge my batts using Eskom, only solar. But, I have the min amount of batts for my panels, for I switch back to Eskom at set DOD to save the batts at night so that I can re-charge as quick as possible each morning, without damage to the bank.

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23 minutes ago, The Terrible Triplett said:

Viper, I have been taught to use Open Circuit volts in calculations, as all panel calculators do, i.e. my panels are 36.3 Volts at max power. Open circuit is 45.35. Have seen on them reaching 46v infrequently. All solar calculators from i.e. Victron, Morningstar and Outback take that value into consideration with temps. So, if you NEVER have a cool / cold day with clear sunshine, go for 3 per string, for at the lower calcs it is 109.8v, with the MPPT at wot, 115v, max open voltage of 145v? 

You normally have to use both, the MPPT charge controller requires you to stay within both of them.

The 60v he was talking about is the minimum voltage the MPPT requires to start up and for this specific one you need to work with Voltage at max power from your panels

see spec below

temp.JPG.463325076a15a174a474cc6edbfd239

23 minutes ago, The Terrible Triplett said:

It all really depends on how the Axpert controller will handle IF you go above 115v coming in on cool sunny days. Will it switch off till volts drop?

According to the Australian forum it should

23 minutes ago, The Terrible Triplett said:

Now, maybe the Axperts are clever i.e. even though the MPPT is limited to 10amps to charge batteries, it can increase the draw from the panels to max amps coming in to power the load? That will be quite cool I think.

They do see below

 

On ‎3‎/‎7‎/‎2016 at 6:31 PM, viper_za said:

temp settings.JPG

 

23 minutes ago, The Terrible Triplett said:

I have been taught you match your batteries with your load, then panels to charge the batteries at max 13% of their AH rating, using as little batteries as possible i.e use larger amp hour batteries, then you have a lot less problems and worries. If you juggle that a bit, the more the load, the slower the batts will charge, which is ok. If the balance is too far out, you are straining the batteries.

This I think is your problem, why always depend on the batteries or maybe you should consider thinking of it this way.

Spec your batteries to your essential loads that always need to run

Spec your panels on charging the batteries at required % of AH + enough to carry your essential load while charging, then on that you add panels for additional loads as needed for day time use (this will help out charging your batts also even on cloudy days)

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2 hours ago, Valken said:

That makes sense i suppose. So would it be better if i add two more pannels (12 in total then) and do a 4 X 3 rather? this will then push up my voltage to 109.8V instead of the current 73.2V (But also the PV would now be 3600W) which should handle voltage drops better during those little clouds pasing by every now and then?

Yes if you add more panels you will be able to see the supported maximum of +-3000w even on hot days when your panels don't work as efficiently.

(on another post I said that my 1800w array makes only +- 1550w on hot clear days)

If there is more than 3000w available on cloudy/cold days the MPPT will only use up to a maximum of 3000w and the rest will not be useable, however we are not clear on if it will use the amount above 3000w to maybe charge the batteries (saw something about this on the Aus forum too)

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3 hours ago, jdp said:

Valken you do not have to many panels. All you do is set the max charge current to 10 amps. Then you will not overcharge the bank. You also then drive your loads in the day. You want your volts as high as posible. Did Johan not hook up your panels for you ? Best config is sets of 3. 

Hi Jaco..Lol. Can you really have too many pannels. Because i had 10 X 300W (Not 12 X 250W) panels i could only wire them up in 5 X 2

The charging is fine now and the Solar balance now seem to work corectly. I suspect the issue to be firstly the fact that the MPPT drops out the moment the voltage drop below 60V - This should be fixed when i add two more panels which will alow me to wire them in a 4 X 3 setup which will give it a higher voltage. I was just not sure if you could actually go over the rated max of 3000W for the 5KVA.

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1 hour ago, viper_za said:

Yes if you add more panels you will be able to see the supported maximum of +-3000w even on hot days when your panels don't work as efficiently.

(on another post I said that my 1800w array makes only +- 1550w on hot clear days)

If there is more than 3000w available on cloudy/cold days the MPPT will only use up to a maximum of 3000w and the rest will not be useable, however we are not clear on if it will use the amount above 3000w to maybe charge the batteries (saw something about this on the Aus forum too)

So adding two more panels (Total PV will then be 3600W) should not be an issue.

I must say i have actualy seen more than 3000W on my panels a few times. So i know they are very capable ;-)

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1 hour ago, viper_za said:

Spec your batteries to your essential loads that always need to run

Spec your panels on charging the batteries at required % of AH + enough to carry your essential load while charging, then on that you add panels for additional loads as needed for day time use (this will help out charging your batts also even on cloudy days)

Back in a time when there where no Voltronic devices with MPPT's and batteries where quite a bit more expensive than Eskom, I did it like I did to power loads daytime, with batts as backup in case. The lessons learned stands to date if you are off-grid and no high end Voltronic device.

Going off-grid with Eskom available is very expensive for a household of 6 adults. Grid tie is the only real way to go cost effectively, but I am not going there.

And, I may have to admit that maybe I could be a little bit impressed that the upper level Voltronics models can adjust to small battery banks, yet use all the power the panels can produce and not destroy the batteries in the process.

But, if the sun has set or a very cloudy day and Eskom does go off again (and it does seem it is not going to happen soon), then a very small bank is useless. So it is perfect way to learn.

Flip side, with batts nearly at Eskom charges per kWh (on the back of a paper napkin), the smaller bank is again a waste for if one has the panels, store the energy and run the loads 24/7 off solar. Maximum savings as you all are enjoying.

I stand by what I said: The 105ah leisure batteries are too small, and are incorrect being sealed. :D 

Valken has said that he will sort that when he can. So now he has a lot of info, from more sources than just Voltronic users. 

Ps. I still feel the idiot for asking: " The 10th panel, how is that one connected? " (facepalm)

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The way the Axperts work is not like the old inverter / charge controllers. The power does not go via the battery bank. So if you set your max charge current it will only send that to the bank. The rest goes to the load. So even if you have 6 inverters all with 9 panels each and have one small bank of 4 x 100ah. You will be fine by setting the max charge current to 10amp on one and 0 on the rest. 

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23 minutes ago, jdp said:

The way the Axperts work is not like the old inverter / charge controllers. The power does not go via the battery bank. So if you set your max charge current it will only send that to the bank. The rest goes to the load. So even if you have 6 inverters all with 9 panels each and have one small bank of 4 x 100ah. You will be fine by setting the max charge current to 10amp on one and 0 on the rest. 

Just when i think i got this down Jaco comes and throw a spanner in the works...lol (thats why you got rain today on the beach ;-p )

Ok, on another note, on the settings side Jaco, when using the software (AICC) to switch between Grid and Solar.. Does switching to Solar put the inverter in SBU mode and switching to Grid into Grid only?

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