We have recently added 3 more panels to our existing 12 panels. 2 were added to one string and 1 to the other string. All the panels are 50v and 455w each. 
Since adding the extra panels the indication in the screen from the solar panels with switch off at dusk indication no volts, amps or watts. But they then switch back on work an audible sound a few hours later and will continue this process for a few hours. All it shows is a voltage reading under 90v with 0amps and 0w. Is this a problem or would resetting the parameters on the inverter help?  Any assistance would be appreciated

1 hour ago, Guy P said:

We have recently added 3 more panels to our existing 12 panels. 2 were added to one string and 1 to the other string. All the panels are 50v and 455w each. 
Since adding the extra panels the indication in the screen from the solar panels with switch off at dusk indication no volts, amps or watts. But they then switch back on work an audible sound a few hours later and will continue this process for a few hours. All it shows is a voltage reading under 90v with 0amps and 0w. Is this a problem or would resetting the parameters on the inverter help?  Any assistance would be appreciated

Please give more details. Do you now have 8 panels in series on 1 string and 7 on the other string? 

Are these 2 strings in parallel? 

Rather post a picture of the big label on your inverter. This will help. 

3 hours ago, Scorp007 said:

Please give more details. Do you now have 8 panels in series on 1 string and 7 on the other string? 

Are these 2 strings in parallel? 

Rather post a picture of the big label on your inverter. This will help. 

 

Thank you for your reply. This is the label on the side of the inverter. We do have 2 strings as you have stated. They are both connected in series and then each string is attached to the inverter via the 2 MPPT connections. There is no parallel connection between the two strings

Measure dc voltage on mppt's input at the inverter with a Dmm when the sun is out and post both readings.

1 hour ago, TaliaB said:

Measure dc voltage on mppt's input at the inverter with a Dmm when the sun is out and post both readings.

So far this evening both strings are zero on all readings and are not showing up on the inverter screen. If it should change I will measure the voltage and post results here. Thank you very much for assistance 

Does the inverter display any error or fault while the alarm is sounding?

If possible measure if there is any current flowing between the solar panels and the inverter.

If there is voltage present and there is current flowing then the array power can be calculated.

Also check on the inverter while the sun is shining if the unit display U3, at the moment the unit should not display any info for U3.

16 hours ago, GerhardK83 said:

Does the inverter display any error or fault while the alarm is sounding?

If possible measure if there is any current flowing between the solar panels and the inverter.

If there is voltage present and there is current flowing then the array power can be calculated.

Also check on the inverter while the sun is shining if the unit display U3, at the moment the unit should not display any info for U3.

There is no error or fault. The noise is what the inverter makes when the panels switch on in the morning. 
We cannot see any U3 on the display