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Axpert VM II 5KVA Inverter - max levels?


Rulf
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I have a DIY Solar Solution which include

  • Axpert VM II 5KVA Inverter
  • 3 strings each with 4 * 360W Solar Panels (Total 12 panels)
  • Polyntech 2.4Kw + 3.5Kw batteries

This is very much a DIY build system.

My question is how can I push this a bit further. The thinking is adding more solar panels and batteries. The questions here is to where can I push the Inverter:

  • Can I add another 4 * 360w solar panels. @ 80% it looks like one should be able todo 16 panels (perhaps even a few more)
  • Can I add another battery? What is the cap on batteries that can safely be added?

Do someone have experience, what is the max possible with the Axpert VM II inverter, and what configuration of panels & batteries will work best?

Thanks

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Hi Rulf

According to the documentation the limit for your inverter is 5000w, 500vdc max open circuit.

This information should be on the side of your inverter.

You have 4320w of panels installed. Your voltage per panel should be about 47vdc  so each string is 188vdc.

Operating MTTP range is: 120vdc-450vDC.

I would like to ask why are there 3 strings in parallel of 4 in series for any special reason?

To be be more efficient  it would be wiser to only have two strings of 6 so that your voltage is increased and the amps lowered as the MTTP cutoff is 120vdc.

 Youi could add one or two panels to the the two parallel strings. 

2 X 6 (360w panels) = 282vdc  4320w (12 panels). -13.6%

2 X 7 (360w panels) = 329vdc  5040w (14 panels). + 0.8%

2 x 8 (360w panels) =  376vdc  5760w ( 16 panels). +15.2%

2 X 9 (360w panels)  = 427vdc 6480w (18 panels).  + 39.6%

I am not sure about the 16+ panels and you will need to verify this but it should be safe. I will make no sense to use more than 16 panels as you will only be able utilize 5000w.

You can add more batteries however you should check if the charging currents with different capacities which you have.

It is advisable to add batteries of the same capacities and age and most importantly the same type.

 

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26 minutes ago, Peter Topp said:

Your voltage per panel should be about 47vdc

If you have Voc with [email protected]°C shouln't you take also temperture coeffiant in your calculations e.g. -0.2V/K. If your temperature falls down to 0°C, you have to add another 5VDC, with 9 panels (47V) in series, this make another 45VDC, therefore 423VDC + 45VDC = 468VDC?

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Hi

The voltage is an approximate voltage as I do not know the make of panels  and was not given hence the question I asked.

Also for the amount of panels used it would make little difference as the voltage is well below the max of 500vdc. 

Temperature definitely does make a difference however this is the figures given is purely for aprox specs for this installation.

I doubt very much if this installation requires 18 panels.

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20 hours ago, Rulf said:

I have a DIY Solar Solution which include

  • Axpert VM II 5KVA Inverter
  • 3 strings each with 4 * 360W Solar Panels (Total 12 panels)

I would strongly recommend only 2 strings of panels with these inverter-chargers. There seems to be a strict 18 A PV current limit; that's about two strings.

As indicated above, 2 strings of 6 is about right. 2 strings of 7 is only slightly over the limit, and should be OK. The SCC is only capable of supplying 4 kW (80 A at 50 V output, perhaps a bit more towards the middle of the charge, when the battery voltage is a little higher). I would not attempt 2 strings of 8 panels, mainly because of the overshoots.

Edited by Coulomb
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Thanks for all the inputs. I am using Canadian Solar Panels. The 3 string of 4 panels is very much related to how the system grew over the past few months. To reconfigure and run a 2 string 7 panel configuration is going to be a bit of a challenge (just how my wiring is done), will test a 2 string 8 panel configuration. If this can work I need very little rewiring.

Currently 10 of my 12 panels face east, only 2 is north, Will aim to get some more north panels when I expand but my roof limits me a bit. Will also explore to add another battery that the midday high can be stored for evening use.

Will do the panels in the next month or two and update on results.

Thanks

 

 

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