At work we've got an 8 panel single string set up, going into a 3000w inverter via a double pole DC isolator.
The AC goes supply > isolator > meter > inverter.
Obviously the DC usually comes from the roof, into the DC isolator, into the inverter where it's converted to AC which then goes back to the consumer unit.
Never had a problem with this and we've done thousands of them.
Today however, i came to commission the set up and the inverter wasn't recognising the modules. So i did some testing; DC correct polarity coming into the isolator, and when the isolator is turned on the load side is showing voltage, as are the MC4's from the load side of the iso to the inverter.
Tried re-making off the MC4's and their cable ends, tried changing the isolator, tried using different terminals on the iso, but to no avail. Then i realised when i was turning it off it was starting to smell like burning plastic and then i noticed the inside of the DC isolator was arc flashing every time it was turned off under load (so if plugged into the inverter or if the pos-neg were plugged together).
I chucked a fluke continuity tester on the isolator and when the MC4's are plugged into the inverter, the continuity tester is detecting AC power at the DC isolators connections.
On the display, the inverter was showing a two way feed and supply between the inverter and the grid.
Any ideas? Seems like the inverter is backfeeding AC into the DC supply which leads me to believe the inverter is playing up.
The AC goes supply > isolator > meter > inverter.
Obviously the DC usually comes from the roof, into the DC isolator, into the inverter where it's converted to AC which then goes back to the consumer unit.
Never had a problem with this and we've done thousands of them.
Today however, i came to commission the set up and the inverter wasn't recognising the modules. So i did some testing; DC correct polarity coming into the isolator, and when the isolator is turned on the load side is showing voltage, as are the MC4's from the load side of the iso to the inverter.
Tried re-making off the MC4's and their cable ends, tried changing the isolator, tried using different terminals on the iso, but to no avail. Then i realised when i was turning it off it was starting to smell like burning plastic and then i noticed the inside of the DC isolator was arc flashing every time it was turned off under load (so if plugged into the inverter or if the pos-neg were plugged together).
I chucked a fluke continuity tester on the isolator and when the MC4's are plugged into the inverter, the continuity tester is detecting AC power at the DC isolators connections.
On the display, the inverter was showing a two way feed and supply between the inverter and the grid.
Any ideas? Seems like the inverter is backfeeding AC into the DC supply which leads me to believe the inverter is playing up.