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Axpert And Kodak Inverters And Solar Panel Queries


GerhardK83
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Hi All

I trust that you are all well.

I have the following questions regarding the Axpert King, Axpert MKS and Kodak King inverters.

A] With the Axpert King inverters in parallel and a couple of Lithium batteries in parallel how do you connect the communication cable from the batteries to the inverter so that the BMS can report the capacity back to the inverter?

B] Do you get lithium batteries which communicate via RS232 so that Axpert MKS inverters in parallel can communicate with the BMS of the batteries in parallel?

C] If I want to use the Kodak King in parallel where do I buy the parallel communications boards required or are the parallel communications boards already included with the inverter?

D] Which electrical parameters must be used for the calculation of the quantity of solar panels required for an installation STC or NOCT?

E] Does the solar panel ever exceed the STC electrical parameters with regards to the Voc as per the electrical parameter as provided by the PV panel manufacturer?

F] Is it a good practise to be as close to the maximum PV array power of the inverter or should there be a little headroom in case the PV array exceeds the STC electrical parameters and damage the inverter?

 

Kind Regards

GerhardK83

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1 hour ago, GerhardK83 said:

A] With the Axpert King inverters in parallel and a couple of Lithium batteries in parallel how do you connect the communication cable from the batteries to the inverter so that the BMS can report the capacity back to the inverter?

I've heard that paralleled Kings don't talk properly to the Pylontech BMS. In theory, you should just connect from the BMS master to any one of the Kings. Axpert MKS can't talk directly to the BMS, as they don't have the required RS-485 port, or the supporting firmware.

1 hour ago, GerhardK83 said:

B] Do you get lithium batteries which communicate via RS232 so that Axpert MKS inverters in parallel can communicate with the BMS of the batteries in parallel?

No. Not without some special gizmo to control the inverters, like a Pi running ICC.

1 hour ago, GerhardK83 said:

C] If I want to use the Kodak King in parallel where do I buy the parallel communications boards required or are the parallel communications boards already included with the inverter?

You get them from the same supplier that sold you the inverters. They used to sell inverters with the parallel boards already installed, but I've not seen that lately. You might also be able to buy them from resellers like MPPSolar that have a presence on EBay.

1 hour ago, GerhardK83 said:

D] Which electrical parameters must be used for the calculation of the quantity of solar panels required for an installation STC or NOCT?

NOCT are supposed to be more "real world", so you could use them, or work on 75% of STC. It's all a bit of a guess till it's actually installed and running.

1 hour ago, GerhardK83 said:

E] Does the solar panel ever exceed the STC electrical parameters with regards to the Voc as per the electrical parameter as provided by the PV panel manufacturer?

Yes. The Voc figure is for 1000 W/m², which is a high figure, but it can sometimes be exceeded. It's also at 25°C, and Voc increases with lower temperature. At 0°C, the lowest I'd see in my area (Brisbane, Queensland, Australia), a panel's Voc is typically some 7% higher than at 25°C.

1 hour ago, GerhardK83 said:

F] Is it a good practise to be as close to the maximum PV array power of the inverter or should there be a little headroom in case the PV array exceeds the STC electrical parameters and damage the inverter?

If the manufacturer gives a maximum PV power figure, you should stay under that, or not go over by more than a few percent. Unfortunately, Axperts rarely give this figure, only the maximum output. For example, typically 80 A maximum output will be quoted as 4000 W maximum, even though the battery voltage could be 10% higher than that. You don't have to aim for below the maximum output of the solar charger. Plonkster recommends not connecting more than 120% of maximum output in panel power; I've been saying 112.5% because for those few Axpert models that do have a maximum PV array size specification, it's typically 112.5% of the maximum output (so 4500W max panel power for a 4000 W nominal solar charge controller). 

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  • 10 months later...

I have a similar problem. y. Hi, I have 12 300w pv's on a 5k/4k axpert. 3S4P. I want to add 3 series pv's in parallel.
I'm afraid that I'm going to fry the inverter?

The axpert spec's are 4kw max and VOC is 145v. DC input current is 93A and charge current is 60A.
The pv's series voltage is 136.5v and parallel sc amps is 37.6 A. If I add another string the amps will increase to 47A.
Do I use the input current 93A as parameter? Can I do this.

 

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2 hours ago, Tokkiebod said:

I have a similar problem. y. Hi, I have 12 300w pv's on a 5k/4k axpert. 3S4P. I want to add 3 series pv's in parallel.
I'm afraid that I'm going to fry the inverter?

It's not too much total nominal PV power (4500W). So it won't fry the inverter-charger. 

2 hours ago, Tokkiebod said:

The axpert spec's are 4kw max and VOC is 145v.

Don't forget that the open circuit voltage in winter is about 7% higher than summer. And you get zero power at 145V.

2 hours ago, Tokkiebod said:

The pv's series voltage is 136.5v.

At that voltage, you're only getting 57% of rated power. Possibly less, because bucking from such a high voltage seems to overheat the solar charger.

You are probably better off rewiring to 2S6P, and not adding more panels. 

2 hours ago, Tokkiebod said:

 

 

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On 2021/03/19 at 5:31 AM, Coulomb said:

It's not too much total nominal PV power (4500W). So it won't fry the inverter-charger. 

Don't forget that the open circuit voltage in winter is about 7% higher than summer. And you get zero power at 145V.

At that voltage, you're only getting 57% of rated power. Possibly less, because bucking from such a high voltage seems to overheat the solar charger.

You are probably better off rewiring to 2S6P, and not adding more panels. 

 

The reason why I  want to add 3 pv's is eskom still takes 400kw and the sun pays 400kw. Now you gave me 2 answers. 1st I assumed you said yes for 3 more, then you said I must do 2s6p? Can I add 1  2s to make it 2s7p? 

I had it 2s4p when I change it to 3s3p , this configuration, gave me a better performance. I then added another 3s to make it 3s4p which gave me a bigger saving.

I have 9k4w pylontech battery setup. When the finance is ready,  I want to add another 3k5 battery. 

Thnks. for your  knowledge so far.

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1 hour ago, Tokkiebod said:

The reason why I  want to add 3 pv's is eskom still takes 400kw and the sun pays 400kw.

I don't understand the above. Are you saying that you are still using about 400 kWh per billing period (month quarter?), and the inverter generates a similar amount?

Quote

Now you gave me 2 answers. 1st I assumed you said yes for 3 more, then you said I must do 2s6p?

What I tried to say is that switching to 2S6P might give you enough performance increase that you don't need the extra panels at all. But your experience seems to contradict that; see below.

Quote

Can I add 1  2s to make it 2s7p? 

Yes, you could even make it 2S12P. But that would be the very limit for one inverter-charger, assuming it's an 80 A output model. Some earlier ones, including the ones I own, are 60 A output.

Quote

I had it 2s4p when I change it to 3s3p , this configuration, gave me a better performance.

I assume you mean it gave you better than 9/8th energy. That's interesting, as it is different to the experience of many others. Are they perhaps 60 cell panels? If that's the case, then you do have to wire them 3S. But 136.5 V open circuit sounds like 72 cell, and will be limiting your output until the SCC draws power from the panels. I worry that in winter, they might end up over 145 V, which is dangerous, and will never start. But hopefully the sun will heat them up, reducing the voltage, and it might start an hour or two later.

 

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19 hours ago, Coulomb said:

I don't understand the above. Are you saying that you are still using about 400 kWh per billing period (month quarter?), and the inverter generates a similar amount?

What I tried to say is that switching to 2S6P might give you enough performance increase that you don't need the extra panels at all. But your experience seems to contradict that; see below.

Yes, you could even make it 2S12P. But that would be the very limit for one inverter-charger, assuming it's an 80 A output model. Some earlier ones, including the ones I own, are 60 A output.

I assume you mean it gave you better than 9/8th energy. That's interesting, as it is different to the experience of many others. Are they perhaps 60 cell panels? If that's the case, then you do have to wire them 3S. But 136.5 V open circuit sounds like 72 cell, and will be limiting your output until the SCC draws power from the panels. I worry that in winter, they might end up over 145 V, which is dangerous, and will never start. But hopefully the sun will heat them up, reducing the voltage, and it might start an hour or two later.

 

Now that you mentioned it , I never measured the voltage.  I just added the voltages from the specs of the Pv's, in my argument. I only looked at the wats, which increased, from from under 2kw to a max of about 2k8W. 

My array also have a mixture  of 300w to 395W pv's. Over the last 3 to 4 years I increased my system with either battery or pv's,  courtesy of the tax returns. Each time I bought the pv's that was on special,  irregardless of the Wats. This didn't bothers me because I knew that I'm going to revert back to the lowest voltage

However I deducted from your reasoning that I'm  at my max . Now, how am I going to solve the problem of the 400kw eskom bill?

Must I change the inverter to a bigger one, go parallel or wat?

 

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2 hours ago, Tokkiebod said:

My array also have a mixture  of 300w to 395W pv's.

You can parallel panels, or strings of panels of identical power rating in each string, of different power ratings as long as the Vmp is within 5%.

How many different sizes do you have?

You probably don't need to replace your inverter.

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On 2021/03/21 at 10:46 AM, Coulomb said:

You can parallel panels, or strings of panels of identical power rating in each string, of different power ratings as long as the Vmp is within 5%.

How many different sizes do you have?

You probably don't need to replace your inverter.

I have 1 string of 300w, 2 of 310w  and 1 of 395W. Thus the voltages per string is with in  specs. 

Now how can I reduce my 400w eskom  power. Can I connect 3 more pv's? 

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6 hours ago, Tokkiebod said:

I have 1 string of 300w, 2 of 310w  and 1 of 395W. Thus the voltages per string is with in  specs. 

395W and 300W doesn't sound compatible to me. 

6 hours ago, Tokkiebod said:

Now how can I reduce my 400w eskom  power. Can I connect 3 more pv's? 

As I posted before, you may be able to add 3 more panels, assuming that the PV voltage isn't too high (I suspect that it is).

The rule of thumb that I use now is max PV power = 20-25% more than rated. If your model has an 80A MPPT (4000W), then you can attach 4800W of panels, absolutely no more than 5000W.

But by my calculations, you already have 3945W attached, so the next string should be 350W absolute max, preferably about 300W each.

The 93A DC that you mentioned is the maximum draw from the battery, nothing to do with PV. 93A x 46V = 4278W = 4000W + losses.

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