Need some help with an issue. I have a MUST 5 kW hybrid inverter (this is probably a Voltronic white labelled inverter) and its MPPT range is 64-130 V, 9 x 375 W Fivestar solar panels connected with 3 strings (so 3 x 3), and 4 x 200 Ah Gel batteries. I noticed earlier this year (as I can monitor the system remotely via a WiFi card setup) that randomly, the PV voltage spikes to between 125 and 131 V. When this happens, the charge power from the PV drops to 150 W odd and the charger current to 3 A. This can happen randomly during the day and can sometimes stay at these levels for up to an hour or so and hence the load is not being fulfilled by the solar even though there is plenty of sunlight. Does anyone know how to resolve this issue? I understand the PV is going to the top of the MPPT range but how do I prevent it from doing this. It seems much worse now i.e. its happening more often than it was earlier in the year.

Do I need to reconfigure the setup of my panels to a different combination to reduce the PV voltage etc., or what do I do to maximize production without the voltage spiking and effectively killing the charge power? I am not super technical so would appreciate a layman response on this.enter image description here


1 Answer 1


It appears that the Voc (open circuit voltage) on your PV panels is 44V or so. When you put then in a string of 3 in series that make the total Voc to be 132V. This is outside the MPPT range of the inverter and I suspect it's trying to protect itself by interrupting power generation.

Why don't you use 2 PVs in series which will give you a Voc of 88V which will be well inside the MPPT range?

One issue is that you have 9 PV panels and there is no way to use all of them in a 2X string without either adding or deleting one PV panel.

  • \$\begingroup\$ Can i use 3 x 2 in series and 1 x 3 in series? or will that end up being unstable? also the max solar voltage (VOC) on the inverter says 145VDC but the MPPT range is 64-130VDC i see that on the panels it actually says open circuit voltage (VOC) of 47.2V which means 3 x that will be 141.6V what is Vmp for the panels mean = 39.8V \$\endgroup\$ Aug 12, 2021 at 15:10
  • \$\begingroup\$ If your inverter has more than one MPPT input then you should be able to do that. But if your strings are all in parallel into one MPPT input then no, you cannot do that. \$\endgroup\$
    – jwh20
    Aug 12, 2021 at 15:13
  • \$\begingroup\$ currently its setup as 3 in series x 3 in parallel so not sure how its done into the inverter - im not that technical so unsure \$\endgroup\$ Aug 12, 2021 at 15:15
  • \$\begingroup\$ Do you have a link to the installation manual for the inverter? Or even a model number? \$\endgroup\$
    – jwh20
    Aug 12, 2021 at 15:25
  • \$\begingroup\$ Model number is PV18-5048 VHM - its a 5kw inverter - also wanted to add that this issue is adhoc and some days no issue like today but yesterday there was. Also normally the PV voltage ranges between 115 and 125 but then randomly spikes up like in the pic i sent. \$\endgroup\$ Aug 12, 2021 at 15:29

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