PV voltage too low to charge

[Gordon Mayer]

Hi— I’ve got a Victron system at 48v and about 720Watts of panels (on my canal boat). Everything had been working great. But now…

When the sun starts coming up the MPPT reports over 60v from the panels (perfect) and charging begins.

But within about 30 minutes my reported panel voltage drops to about 50v and charging stops.

Any ideas?

 

[binky]

Clouds .

does it stay off after 30 mins , or come back to life?

 

[Gordon Mayer]

I wish it were clouds. Then it is just me being stupid

Sunny days. It stays off for the entire day. It’s reported voltage floats around 50v. I’ll get a volt meter tomorrow & I can check the individual panels and the actual voltage into my MPPT.

It all worked perfectly a year ago. The only change is that I had a person install a Victron Cerbo GX (for remote monitoring) over the winter. It is possible that he inadvertently did something that affected things. But I can’t think of what it might be.

 

[binky]

check all the connections, sounds like you are only seeing the voltage off 2 panels - I'm guessing you have around 3off panels @ 240W, which should be around 30V each VoC . As such the stalled voltage is 60V, dropping to 50V as the inverter tries to get power from them but failing due to faulty connection. I would guess in the -Ve line somewhere.

 

[Gordon Mayer]

I have 6 panels. My recollection is that they are 120W each. They go into a Victron MPPT. Tomorrow when I get my meter I’ll check the connections on the roof and I’ll check the actual voltage at the MPPT.

 

[binky]

quick google of 120W panels suggests VoC (that's voltage open circuit) should be around 20-25V, look half way along the panels, you should be getting something like 120-150V VoC - turn off inverter / isolate panels from inverter before pulling connections, or you might get a little surprise arc flash.

 

[Gordon Mayer]

Thanks—I’ve got to get more info, because... …I just went on the roof. Two of my panels wire into one connection box, and they’re wired in series. The other four panels go into another connection box, and those 4 are wired in series. All the 4 main wires (two out of each connection box) disappear into the roof. At my MPPT there are just two incoming PV wires. It is possible that somewhere the 4 main wires are also wired in series. But that doesn’t make much sense to me, as that would be 6x 20-25V = 120 - 150V, right? Yet my battery bank is 48v. I could understand it if my 6 panels were wired in 2 groups of 3. I think I’m not understanding something properly

Years ago I had a masters degree in electrical engineering. Imagine.

 

[binky]

Thanks—I’ve got to get more info, because... …I just went on the roof. Two of my panels wire into one connection box, and they’re wired in series. The other four panels go into another connection box, and those 4 are wired in series. All the 4 main wires (two out of each connection box) disappear into the roof. At my MPPT there are just two incoming PV wires. It is possible that somewhere the 4 main wires are also wired in series. But that doesn’t make much sense to me, as that would be 6x 20-25V = 120 - 150V, right? Yet my battery bank is 48v. I could understand it if my 6 panels were wired in 2 groups of 3. I think I’m not understanding something properly

Years ago I had a masters degree in electrical engineering. Imagine.

the Victron will control what goes into the battery itself. Check the junction boxes, I'm not quite sure what voltage you would see with that setup, but 2 panels is 40-50V, 4 panels 80-100V. Boat electrics aren't my strong point

 

[Gordon Mayer]

More info—I figured out the wiring. All 6 panels are wired in series. I should see about 120v. Today is reasonably sunny. I’m measuring 50v at the MPPT which is what it is reporting. Went on the roof & disconnected the panels from the MPPT. 50v. Then I disconnect all the panels & measured them individually. I’m getting 20v from 2 of the panels (perfect), 10v from one panel, and 0v from 3 of the panels.

Is it possible that I have 3 dead panels and one that is dying? This seems quite impossible (they are 3 years old). What am I missing?

 

[binky]

Could well be 3 dead panels, although unusual for that to happen in such short time. Possibly badly handled when installed, have a look at the front for any signs of damage, odd marks like burnt spots etc. Maybe worth opening up the junction box on the back of the panels and testing for volrages across the bypass diodes

 

[offgridAndy]

I'd check the connectors on the + and - on the back of the panels. Many crappy connectors out there. I have seen them completley melted away.

 

[binky]

I'd check the connectors on the + and - on the back of the panels. Many crappy connectors out there. I have seen them completley melted away.

Bosch panels, you could pull the wires out