Solar power problem

[Budawang]

Hello CF Brains Trust. I'm trouble-shooting my 150 watt solar panel. The panel is outputting 22 volts and normal current but at the end of the cable it's only producing 20 volts and my multimeter isn't registering any amps at all. I assume there must be something wrong between the panel and the end of the cable where it connects to the MPPT. The only thing I can think of is what looks like a capacitor in the attached photo. Would there by any problem bypassing the capacitor or is there a good reason to have one?

[Emmalina]

Its a diode not a capacitor. Used to stop return current at night. Your mppt controller should do this for you if your panel hasn't got its own diode. Remove it and see.

[smac999]

if you are measuring "normal" current exiting the panel. and no current entering the controller. the only explation is the solar panel wires are shorting to themselfs or something else...

more likly you are measuring something wrong...

[Budawang]

Originally Posted by smac999

if you are measuring "normal" current exiting the panel. and no current entering the controller. the only explation is the solar panel wires are shorting to themselfs or something else...

more likly you are measuring something wrong...

It seems strange that I'm recording voltage but no current....

[newhaul]

Originally Posted by Budawang

It seems strange that I'm recording voltage but no current....

are you hooked up to a depleted battery?
Hook up to a battery needing charged and retest.

[GILow]

The diode would account for the observed voltage drop.

[GILow]

Originally Posted by Budawang

It seems strange that I'm recording voltage but no current....

Not really. Open circuit due to blown fuse or fried controller will explain that observation.

Does the controller have a fuse on the panel side? Many do.

[GILow]

Originally Posted by Budawang

Would there by any problem bypassing the capacitor diode or is there a good reason to have one?

It would help to know the make and model of solar controller. Most good controllers don't need a diode to prevent power drain. Some older controllers might... but geez it has been a LONG time since I met one of those.

[Budawang]

The controller is a newish Victron MPPT 30 amp

[GILow]

Originally Posted by Budawang

The controller is a newish Victron MPPT 30 amp

Hmmmm.... right, well, no fuse then. (I've seen reference to an internal fuse on the Victrons, but I don't know if that is true, and either way, not easy to replace for an end user.)

The next step is to disconnect the panel from the controller and measure the short circuit current it can generate. If it generates close to rated short-circuit current, and the observed 20 volts open circuit is close to spec, then you have to assume the controller is fried, or the wiring to the controller is faulty.

Baby steps.

[Budawang]

No current (just voltage) is getting to the MPPT so logically the problem has to be with the cable or most likely the diode.

[GILow]

Originally Posted by Budawang

No current (just voltage) is getting to the MPPT so logically the problem has to be with the cable or most likely the diode.

Yes and no.

Current doesn't really "get" to the controller. What "gets" to the controller is voltage, then the controller permits current to flow, or not.

The diode will only permit current to flow in one direction, so check it is correctly oriented, or better still, remove it for the moment to eliminate that
variable.

This sort of thing is a good test of your trouble-shooting methodology.

-To be clear, are you measuring voltage on the panel side of the diode, or the controller side?
-Is the voltage you are measuring on the wires at the point where they supply power to the controller?
-Where did you measure short circuit current? At the panel, or the controller end of the wires.

If I were doing this, the order I would follow would be:

1. Measure voltage at the wire ends where they connect to the controller, but with them disconnected from the controller.
2. If voltage was ok, I'd measure short circuit current at the same point. If not, I'd check voltage at the panels. (I think you've effectively done this step.)
3. If short circuit current was ok at the supply point to the controller, then I'd check the controller can see the battery bank. (use the app if you can). If short circuit current at the controller supply point was no good, then I'd check short circuit current at the panel end. This tells you if you have some extremely high resistance in the wiring.

Others may have a different sequence, but those few steps pretty much cover all combinations of panel/wiring/controller faults that I can imagine. My order of preference is mostly dictated by the fact that I have very easy access to the mppt controllers, while going outside to the panels would be a cold and miserable job today.

[Budawang]

Originally Posted by GILow

-To be clear, are you measuring voltage on the panel side of the diode, or the controller side?
-Is the voltage you are measuring on the wires at the point where they supply power to the controller?
-Where did you measure short circuit current? At the panel, or the controller end of the wires.

If I were doing this, the order I would follow would be:

1. Measure voltage at the wire ends where they connect to the controller, but with them disconnected from the controller.
2. If voltage was ok, I'd measure short circuit current at the same point. If not, I'd check voltage at the panels. (I think you've effectively done this step.)
3. If short circuit current was ok at the supply point to the controller, then I'd check the controller can see the battery bank. (use the app if you can). If short circuit current at the controller supply point was no good, then I'd check short circuit current at the panel end. This tells you if you have some extremely high resistance in the wiring.

Thank you (and everyone else) for your advice.

I have measured voltage/current at the panel end (22 volts and 5 amps) and the controller end (20 volts and 0 amps) with the wires disconnected from the controller. The diode is somewhere in between the two ends.

The controller is receiving and outputting some voltage/current from two other much smaller panels, just no current from the big panel. I can see the current produced by the two small panels using my multimeter and from my battery monitor. I, therefore, have no reason to suspect a problem with the controller. I'll bypass the diode tomorrow when there's hopefully some sun out and I can test it.

[GILow]

Sounds promising.

[Budawang]

Update: I removed the diode and my solar panel is now charging my batteries correctly. Problem solved. Many thanks to all who contributed to this thread.