My ccgx shows a wildly fluctuating Pv wattage and an unsteady charge to the batteries. I suspect that this is because the voc and the operating voltage of the MPPT are too close, 148voc and 150v mppt.
What is the MPPT actually doing in this scenario is it being damaged is it protecting itself is it damaging the batteries???
Another thing to consider is the VOC of panels is rated at 25°C if you are colder it can be much higher. There is also cloud edge effect as well.
There does need to be headroom.
If you need more square meterage covered to pick up more solar in poor irradiance conditions you add more strings also to the max of the input current limit.of the mppt. Or add more charge controllers.
Check it up on the mppt calculator by Victron.
Much too close.
Disconnect your panels immediately and reconfigure them to reduce the voltage.
Your batteries should be fine, but your charge controller is possibly damaged. But you will not know until the panels are correctly configured below that PV VOC limit.
What fails "catastrophically" when exceeding the maximum Voc at the input? Is it some capacitor, or an IC that can't handle the voltage? I would expect that there would be some overhead build-into the charge controller.
Asking the above question, because I just connected three panels in series to boost the Voc since it will be much too cloudy and snowy for a few days here and I really HAVE to keep a particular installation alive. Tried with 2s2p but the charge controller wouldn't produce enough power. 3s works much better, due to the higher voltage. Problem is, I am running 3 49.89Voc in series on a 150/30 SmartSolar, which means that if the sun shines through a hole in the clouds, and the battery is full, I will be having issues.
Any other ideas, apart from upgrading to a 250V Voc controller? Is there any way I could lower the Voc just a bit? I thought of adding diodes in the series connection, but diodes don't add a voltage drop, unless there's current going through. So, under the above conditions, the controller would still register a too high input voltage.
What would fail would be the MOSFETs in the input stage.
These Voltage limits are the limits of the actual semiconductor devices. If you consult the datasheets for MOSTFET devices there is a parameter called "Vds", which is the Drain to Source Breakdown Voltage and is usually advertised as an "Absolute Maximum" rating. Above this limit problems should be expected, so do not do it. Always design overhead into your system to keep below this limit.
Why are the MPPT controllers available specifically with "75V", "100V", "150V" and "250V"? This is because there is the widest choice of transistors available from different manufacturers at these specific Vds Voltages. Selecting one of these Vds Voltages when designing a product will give a designer a lot more to choose from the other required parameters. Transistors are available with Vds Voltage limits in between these, but your choices are limited.
