Bypass/Blocking diode failure

[cinderella]

Has anyone maybe experienced a problem with the diodes failing on the solar panel.
I have two 24V 250W panels connected in parallel, and then connected to an MPPT charge controller/Inverter combo.
The system shows the panels providing about 120 Watts in the morning, but at midday, the wattage drops to around 9Watts and the batteries are only about 1/3 charged.
The panel input then disappears off the controller display and only reappear in the late afternoon.
Can the diodes be causing the problem.
Any help appreciated.

[sensij]

What are the specs of your panels, and are you charging a 24 V battery? With an mppt controller, why aren't the panels in series? It sounds like maybe as the panels warm up, the panel voltage is dropping below the battery voltage and you lose the ability to charge.

[inetdog]

And, no the diodes are not causing the problem.

[Mike90250]

Few modern panels use Blocking Diodes anymore. Many panels use bypass diodes to reduce partial shading loss. Neither would cause the panel voltage to drop to 9V.

[cinderella]

Hi, Thanks for the response, The panels are 24 volts 250 watts fed into a 3Kva Mppt solar charge controller/inverter combo and charge a 24v battery bank.
If I wired them in series, would that not raise the voltage too much for the charge controller?
My problem started after a lightening strike took out my inverter which I replaced.
The system worked reasonably well after that but was never the same.
I cant seem to get my batteries to charge fully, even by running a 6.5Kva generator into the utility input of the inverter and d I had it running for about 6 hours.

[littleharbor]

If your 250 watt panels are of the 60 cell type they really aren't 24 volt nominal (as in 24 volt battery charging) panels. 60 cell panels are intended for grid tie applications. Their voltage isn't high enough. A 72 cell panel would be considered a 24 volt "nominal" panel. 60 cell panels may be used for battery charging with a TRUE MPPT charge controller and your panels wired in series as long as your maximum open circuit voltage remains below the max voltage allowed by your controller.