MPPT will not turn on

DIY
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1

I have four 200W solar panels connected in series. The voltage at the end of the cables read about 122V. I have them hooked up through a 15A breaker on the positive cable and then into the 150/60- tr. I have a Multiplus II, Cerbo GX, SmartShunt on the system. Multiplus, SmartShunt, Battery Protect and the Cerbo GX all seem to be functioning completely normal with no errors or notifications since the install. The system worked great for three weeks. On a clear sunny day last Thursday, July 23, 2026 (after great production until 2:00 PM), the MPPT stopped working while I was trying to get the MK3-USB working to open the VEconfig software. I was told the 150/60 was the problem so I upgraded today to a 250/60 - tr. Same results. I have checked the breakers (before and after the MPPT), redid and quadripple checked all the cable connections, the DVCC settings and have worked through the VEconfig software to get all the correct settings.

What the MPPT is actually doing:
With both breakers closed (PV input breaker and battery breaker), the PV input terminals read battery voltage (~12.2V) instead of the expected array voltage (~122V). The MPPT shows zero charging current. This is true on both the original 150/60-TR and the replacement 250/60-TR.

Diagnostics already performed with no change:

  • DVCC turned off — no change
  • MultiPlus-II turned off — no change
  • VE.Direct cable disconnected — no change
  • Settings reset on MPPT — no change
  • Static resistance PV+ to BAT+ (all cables disconnected): 250/60-TR = 1.7 MΩ, 150/60 = 0.4 MΩ — neither is a dead short

Firmware versions:

  • Cerbo GX: v3.63
  • MPPT 250/60-TR: v3.18 (pushed by Cerbo GX on first connection)
  • MultiPlus-II: v3.18
  • SmartShunt: v4.19

Timeline note:
The problem started on July 23 while attempting to connect the MK3-USB adapter to run VEConfigure. The MultiPlus-II was confirmed to have been on factory default settings (never previously configured) — those settings have since been corrected, but the MPPT issue remains unchanged.

Are there any other suggestions on how to get the MPPT to turn ON? I could use a quick answer because we have to leave the cabin tomorrow.

2

Assuming MPPT is a SmartSolar unit - try using VictronConnect to connect to it. It may have a message saying “why isnt it charging?” that you can click on.

Are all the cable polarities correct? It super easy to get that wrong when swapping out a unit.

3

Thanks for the reply! I have been using VictronConnect, vrm remote console and i have seen that info link. i have clicked and have chased the reasons they give, including polarities, loose connections, etc. No luck.

4

I noticed the new 250/60 has a PV relay reset now. i just pushed it after I disconnected the PV array. Now, I wait for the sun tomorrow morning. Praying it works!

5

No change this morning. So, I switched the input array to my 200W portable panels at 9:00AM (it is cloudy but the sun just came up). The panels are reading 22.5V at the ends of the PV + and - wires. When hooked up I get the same on both sides of the 15A e6 breaker. After switching open the 15A breaker and hooking the portable panels up to the system and then closing the 15A breaker, the MPPT does not start charging. The voltage at the PV terminals on the MPPY now reads 0.6V.

Any ideas?

6

Something is shorting the panel power between the breaker and the MPPT.

Are you sure that the new MPPT didn’t apply the protection relay to short the PV input when you had the original panels hooked up today just before you swapped to the portables? Maybe it stayed closed when you swapped panels to the portable ones?

7

I reset the relay again and reconnected the portable panels. Same result. The MPPT drops the voltage from 23V to 0.6V. If I connect the four 200W panels the voltage drop after resetting the relay is 122V to 12.3V as soon as I introduce power from the array. How do I know when the relay resets? I don’t hear anything and the screen stays the same.

I am not sure what else I can do. It is hard to believe that I have two failed Victron SmartSolar Controllers, especially the second one repeating the issue right out of the box.

8

Agree its unlikely to have 2 failures without an apparent cause.

Do you have a schematic and photos of your setup?

9

Yes to both.

Cabin Electrical Diagram.pdf (603.7 KB)

image
image722×915 219 KB

Cabin PV Array Diagram.pdf (306.3 KB)

10

I would love to know what could cause two MPPT’s to fail, particularly the second one with increased allowable voltage than the 150/60 and failing at the initial commissioning. The 250/60 never switched to ON and charging. Only read 0V for PV voltage at any time. If I disconnect the PV from the MPPT the voltage of the array goes to normal readings for two different arrays. One I have been using for the past week and months actually.

Any ideas, especially Victron engineers and Victron equipment installers that likely have encountered this problem before.

11

Classic reverse polarity behaviour.

Either its a protection behaviour.
Or you have clamped on insulation? Or the pv ‘breaker’ is the suspect definitely. I would take that out of the equation to eliminate it as an issue.

By commissioning what do you mean?
Programming and hardware commissioning?

Unrelated and a definite co incidence.

12

I’m not a licensed professional electrician, and it would be wise to hire one for a bit of help.

The schematic and photo are very concerning. There are numerous errors. Some problem areas:

The panel wiring in the schematic is at least confusing, and possibly drawn wrong and/or wired wrong - Panel 1,2,4 in series for 75V, put in parallel with Panel 3 @ 25V. The MPPT will not be happy with 3 vs 1 panel on the same circuit.

Page 2/4 - why is the Ground electrode connected to the system negative bus? AC safety grounds normally go from chassis ground connections (eg on the Multiplus II, any AC electrical boxes, AC disconnects and breaker boxes via heavy wire (6 AWG) to a pair of ground rods or a ground plate buried outside. Per your local electrical code requirements (eg NEC in USA, CEC / OESC in Canada, and Euro equavalients). This may be giving an unwanted DC electrical path.

Battery fuse - should be close to the battery common +, before the switch. The switch looks like a 275A, and yet your fuse is 400A, so the switch will melt and catch fire before the fuse blows.

Battery wiring - the photo shows hazards - skinny wire on the right battery, and I guess a 3rd battery off camera with skinny wire.

The 3 batteries should be right beside each other, with equal length connections as much as possible. That skinny wire can’t deliver the same current from the two right hand batteries to the MP, and might actually overheat and cause a fire. The leftmost battery will do most of the work.

It’s hard to tell from photo but the PV + wire looks like an unintentional Y between MPPT PV +, breaker, + Bus Bar. It should not go to the + Bus Bar.

See yellow circle:

PVplusshort
PVplusshort582×474 74.1 KB

Double check that, and then fix / check the PV wiring and verify polarity.

13

That image has made me twitch. Please get a professional to review it before something expensive goes poof, if it hasn’t already.
It pays to go back to basics when strange problems persist, with power electronics a problem can go seriously wrong quickly. Its not worth the risk.

14

Im a marine guy and I see many issues on a quick view. The dc breaker is probably not rated to over 100 volts dc. The layout is not clear and the breakers are always located at the power source in the marine world. Looks like its time to bring in a competent professional.

15

I eliminated the PV 15A breaker as a cause. I have continuity when closed and when open I have no continuity. I have also bypassed the breaker with the same results.

I was of the understanding that the mk3-usb was not necessary if I had a Cerbo GX. Once I knew it would be better to have it I ordered one late, but it did not arrive in time so I programmed all the correct settings in the Remote Console. The system worked great for three weeks and then it went down in the middle of the day when I came back with the mk3-USB. The MPPT turned OFF and would not turn ON.

16

There is no Y that is the same cable. The panels are connected in series (+ cable emanating from Panel 1 and the - cable emanating from Panel 4. The + and - cables run to the 15A breaker. Also, the system also does the same think with my portable panels so that pretty much eliminates the array and the cabling from it as the problem. The 2/4 drawing shows the ground as a dotted line. It is not connected directly to the negative bus. It goes to the ground and ultimately to the ground rod buried in the ground. Also, the three batteries are geographically very close. I also verified the correct polarity for the MPPT.

17

I happened to be a licensed professional engineer who has worked for the last 50 years in nuclear engineering and forensic engineering. I am not your typical DIY’er.

18

With respect, take the various comments onboard. That installation wouldn’t pass muster by generous diy standards. It is constructive criticism that is worth considering.

19

Agreed. But the advice that the photo causes him to twitch is not helpful by itself. A lot of engineering time went into this design while working with a licensed electrician who actually did the entire installation.

20

Forgive the humour. The attention that has gone into your project and the desire for guidance is well appreciated and understood.
When helping from afar on strange issues we can only use the information we have access to and it would be difficult to look at that image and not consider that there may be a devil lurking in that detail somewhere.
The intention is not to be unkind nor flippant.

I had a strange mppt issue at a site. One strand of each connection had not made it into the connector and were just close enough to create a problem that eventually cascaded into something more serious. It was not visually obvious to a critical eye. Small things can sneak through far too easily.