I too have that problem.
New MPT Solar controller with 4 panels a one battery.
App shows that battery voltage initially is ok, but connection of the panels drops the approx 18v down to zero. Yes, polarity is right.
App still indicates no PV activity.
I have checked all wire connections, tested all breakers and double checked the polarity of the wire connections. They’re all good.
I have plenty of voltage (138v) reading when I test the ends of the of the solar panel wires but as soon as I touch the positive and negative wires to the positive and negative PV input ports on the charge controller the voltage goes to zero.
It is possible that its an issue with the charge controller? However, if the charge controller was bad then shouldn’t the voltage coming out of the solar panels be good all the way up to the PV input ports where the wires connect to the controller?
It seems like the charge controller is eliminating the voltage coming from the panels as soon as it is connected.
Any thoughts as to why this voltage goes away as soon as it is connected to the controller?
The the positive and negative wires coming from the end of my solar panel string were reversed at the terminals that connect to the combiner box.
I reconnected them properly at that location but I am STILL getting zero voltage when I connect the output wires of the combiner box to the charge controller.
It now seems to me that this reverse polarity connection mistake has either damaged the breaker or surge protector inside the combiner box, blown the internal fuse inside the charge controller or damaged the circuit board.
Now, I must determine what if any damage has been done by this reverse polarity mistake.
I know that the housing on my Victron charge controller cannot be easily removed (it is glued on to the unit with some sort of resin) for some inexplicable reason.
Is there a way to test this Victron 250/ 100 charge controller to see if the fuse has blown or the circuit board has been damaged?
The blue Bulk light on the controller is still blinking on and off every four seconds and the Victron Connect App is still able to communicate with the controller which gives me hope that the controller has not been damaged.
Is it possible that the breaker and/or surge protector (which neither one was tripped off) inside the combiner box were damaged instead of the controller because of the reverse polarity mistake?
If your battery was connected in the correct polarity, it will survive reverse connection on the pv. (as long as you stayed within the max isc of the model.)
