PV voltage drops ~60% when connected to charge controller (Victron 100|50)

[sallaben]

Hello, I'm experiencing an issue with my new charge controller. I would like to ask the more experienced members of this forum for a sanity check, just to make sure I am not missing something simple.

- I have a small 12v LiFePO4 battery and many small panels, all the same model, ~22Voc, ~18Vmp.
- When I wire two such panels in series for example, I read a Voc of ~30 on a cloudy day like today from the ends of my PV wires.
- When I connect those exact same PV wires to my Victron 100|50 charge controller, I read a voltage of 13.2V from the PV connection terminals.

So, obviously PV voltage=Voc will only happen when the circuit is open. But why is my voltage dropping all the way from 30 to 13? This is far more of a voltage drop than I would expect from two of these panels in series. The one-way distance from panels to charge controller is only 2 meters. This change in voltage is observed simply by removing one PV wire from the charge controller, marking 30Voc, then plugging the same cable into the charge controller, and marking 13.2V.

I have checked, re-checked connections for anything that is loose or high resistance, but even with the PV leads jammed back into the terminal as far as they'll go, and clamped down to manufacturer torque specs, I get 13.2V. Would using a ferrule on the end of the PV leads help at all?

For another piece of evidence, consider this test. I put a piece of cardboard over one of the panels and plugged that sole panel into the charge controller. At the PV leads directly, I read 5V. From the charge controller, I read 5V. It almost feels like the PV voltage is being capped by my battery voltage (currently 13.3, but maybe that's just a coincidence).

Is this expected Vmp? Do I just need to wire more panels in series? Or is something potentially wrong with my controller. Thank you very much for reading this far

TL;DR: I'm reading 13V PV input as soon as I plug into my charge controller, whereas I read 30 Voc unplugged. Is this normal?

 

[SparkyJJO]

30 volts open circuit means zero amps. When you put a load on it, it can't push those 30 volts with any current. The MPPT targets the highest power it can pull down, so in this case it is pulling the voltage down to 17 to get the peak wattage.

Cloudy days suck, by the way. My 8400W of panels can get sometimes only a few hundred watts at high noon on a heavily overcast day.

 

[efficientPV]

If the controller is shorted, that will drag the panel down to battery voltage. What kind of current are you seeing?

 

[sallaben]

30 volts open circuit means zero amps. When you put a load on it, it can't push those 30 volts with any current. The MPPT targets the highest power it can pull down, so in this case it is pulling the voltage down to 17 to get the peak wattage.

Cloudy days suck, by the way. My 8400W of panels can get sometimes only a few hundred watts at high noon on a heavily overcast day.

I thought the same at first, but the controller is drawing zero amps at 13 (not 17) volts! :O

This particular MPPT charge controller requires battery voltage +5V from PV input, so it's not even turning on when it sees 13.2V PV.

 

[sallaben]

If the controller is shorted, that will drag the panel down to battery voltage. What kind of current are you seeing?

No current draw at all. This particular MPPT charge controller requires battery voltage +5V from PV input, so it's not even turning on when it sees 13.2V PV.

 

[SparkyJJO]

I Missed that. 0 amps? Ouch. Something isn't right. Unless it is just so overcast that you have no appreciable power available.

 

[sallaben]

I Missed that. 0 amps? Ouch. Something isn't right. Unless it is just so overcast that you have no appreciable power available.

The clouds aren't _too_ bad now, I see a little blue in the distance. ?️ Still reading 13.2V PV even though it's gotten brighter, so I am leaning toward a problem with the controller. If at peak sunlight time today it's still the same voltage, I'm opening a support ticket with the distributor. Thank you both for helping out so quickly

 

[sallaben]

I tried 3 in series just now for 45Voc and it still reads 13.2V on the input. Definitely the controller.

 

[SparkyJJO]

Well that sucks. At least you know.

 

[sallaben]

Well that sucks. At least you know.

At least it's under warranty

 

[MisterSandals]

and many small panels, all the same model, ~22Voc, ~18Vmp.

Just out of curiosity, how small are these panels? Isc?

 

[sallaben]

Just out of curiosity, how small are these panels? Isc?

100W. ~6A but I will never have them alone, was planning on strings of 2 in series but maybe 3 for use with MPPT, and several of those strings in parallel.

 

[MisterSandals]

I would like to ask the more experienced members of this forum for a sanity check,

100W. ~6A

The sure fire sanity check would be to test your panel(s) with a digital meter. Super easy, can be done in less than a minute.
Do you have access to a digital meter that reads both DC volts and DC amps?

 

[sallaben]

The sure fire sanity check would be to test your panel(s) with a digital meter. Super easy, can be done in less than a minute.
Do you have access to a digital meter that reads both DC volts and DC amps?

Yes! I have posted some voltage measurements in the original post, but I can take any new measurements that you think might help diagnose the issue.

 

[MisterSandals]

but I can take any new measurements that you think might help diagnose the issue.

If you can measure volts and amps, you can multiply the 2 to get watts. This is the number you seek, right?

Solar panel testing

I set the multi meter to dc amps red probe to the red wire in the connector and black probe to the black wire of the connector Well, that is why your reading is wrong, if you look at the meter probe terminals, you will use red and black probe wire when you try to measure current in uA only...

diysolarforum.com

 

[sallaben]

If you can measure volts and amps, you can multiply the 2 to get watts. This is the number you seek, right?

Solar panel testing

I set the multi meter to dc amps red probe to the red wire in the connector and black probe to the black wire of the connector Well, that is why your reading is wrong, if you look at the meter probe terminals, you will use red and black probe wire when you try to measure current in uA only...

diysolarforum.com

No, I'm not sure what you mean.

The problem is that my charge controller is stunting my panel voltage down to the voltage of my battery.

TL;DR: I'm reading 13V PV input as soon as I plug into my charge controller, whereas I read 30 Voc unplugged. Is this normal?

 

[MisterSandals]

No, I'm not sure what you mean.

The problem is that my charge controller is stunting my panel voltage down to the voltage of my battery.

If you measure the volts and amps, it may reveal why your charge controller is behaving as it is. My initial guess is that the amps are VERY low and the MPPT algorithm drops the voltage down trying to find a power sweetspot.
It may drop the voltage down as far as it can with hopes of finding the optimal volt vs amp mix.

With the measured volts and amps, we can make better guesses as to what the charge controller is doing.

 

[sallaben]

If you measure the volts and amps, it may reveal why your charge controller is behaving as it is. My initial guess is that the amps are VERY low and the MPPT algorithm drops the voltage down trying to find a power sweetspot.
It may drop the voltage down as far as it can with hopes of finding the optimal volt vs amp mix.

With the measured volts and amps, we can make better guesses as to what the charge controller is doing.

Three of these panels in series right now give me 42V (open circuit). When I plug them into the charge controller, the PV terminals read 13.27V and 0.02A.

 

[MisterSandals]

When I plug them into the charge controller, they read 13.27V and 0.0A.

But if we measure what the panel is producing, we may be able to see why the SCC is dropping the voltage down to 13.27V and 0.0A.

If you're not willing to measure your panel amps then you won't know much about what your panel is producing when your SCC says 0.0A.

 

[sallaben]

But if we measure what the panel is producing, we may be able to see why the SCC is dropping the voltage down to 13.27V and 0.0A.

If you're not willing to measure your panel amps then you won't know much about what your panel is producing when your SCC says 0.0A.

Sorry, I didn't understand what you were asking until now. I think that is the culprit rather than the charge controller. I read an astounding 0.05A from the panel itself when I read Isc with the multimeter. But when I tilt the panel to match the sun I get a much more respectable 5A.

I didn't expect a flat-laying panel to produce effectively 0 amps - it's turned into a mostly clear day with plenty of direct sun. Does this mean, crappy panels? Or is this true of most mono panels?