Hope this helps somebody in the future. This has got to be the most difficult troubleshooting I’ve ever had to do with this inverter. Now, having solved it, the solution seems so simple.
Short version
If you found and fixed all the faults and the inverter still shows the 3701 or 3501 error messages and will not start on its own, go into the settings of the inverter via a web browser and delete the codes as described at the bottom here.
Long version
So back up to several days ago. The Sunny Boy threw the error codes at noon on a sunny day. They are insulation resistance error codes meaning there’s possibly a short somewhere on the DC side. So I checked out the connections and discovered some corroded terminals and wires. Also found an MC4 connector with water in it. Fixed all those parts, but the inverter still threw the same error codes. The red and the blue lights were on the inverter also. So did more checking. Took one string out at a time and still nothing worked. I hooked up an older Sunny Boy to the solar panels, and everything worked fine. The older Sunny Boy was producing power on both strings. I also connected a known good string to the 7.7, but the 7.7 still wouldn’t start. Put in a temporary DC cable from the panels to the inverter and still nothing worked. The Sunny Explorer menu kept showing that it was trying to connect to the grid, but wouldn’t because of the fault. The DC voltages were showing up in the DC side but nothing was showing up on the AC side. Probably because the inverter wasn’t on yet. I also checked the insulation resistance with an insulation resistance meter that I got on Amazon ($50) and everything was still showing OK. The MEGGER is a handy tool for finding shorts. It sends voltages up to 1000 V DC through a line and checks whether the insulation is OK or not. It also has a permanent on feature so you can check leakage overtime. But I digress. One set of DC wires that I knew was bad also showed up as bad in the MEGGER insulation resistance tester. It showed a dead short to ground. One of the many things I learned is that in checking for these faults you check positive to negative voltage on the panels. You also check negative to ground and positive to ground when everything is disconnected from the inverter. Voltage should be the sum of the in the string. If you have a higher voltage in either positive or negative to ground you can divide it by the panel voltage to see exactly where the fault is. I.e. between the second and third panels or fourth and fifth, etc. Normally, voltage on both should be close to or at 0 V to ground. In an SMA video, they mentioned that anything between 12 and 15 V was OK. They called it a capacitive discharge or something like that. Anyway, voltage does not have to be exactly 0.0 Vdc. When measuring, I measured some thing like 20 or 30 V going down rapidly to 15 V, then 12 V, then 10 V, and finally ending up at 1.5 V after a minute or two. Those numbers are ok.
So it’s pretty certain that the panels themselves are OK and don’t have any faults. You certainly don’t want high voltage when testing positive or negative to ground. That indicates a potential fault. Another thing I found out was that when you connect and disconnect the MC4 connectors, you should never see any sort of arcing under normal conditions. An arc generally means a fault somewhere. So not having arcs when disconnecting stuff is a good indication that things are OK. Course you should always follow safe procedures when handling any sort of DC or even AC wires. I generally like to do DC work at night because then there’s little voltage to worry about. I have put tarps over solar panels and regardless of how many tarps I put on, there was all ways DC voltage high enough to be troublesome. So I just switch to doing that type of work at night. Made it a lot easier. The MC4 connectors also make it quite a bit safer than dealing cable with bare wire ends. Anyway, lots of testing, lots of swapping of parts, I even used a temporary DC connection from the panels to the inverter and still the inverter wouldn’t turn on. I.e. it would not connect to the grid. Same error codes. In desperation, I even considered and called an electrician for help only to find out that it would be a two month wait for an appointment. Of course, knowing what I know now the electrician wouldn’t of helped at all. I talked to SMA they had me do a bunch of voltage checks and again everything checked out fine. Then finally, I just replaced all the DC cabling with new cables and MC4 connectors, and went directly from the panels to the inverter, and still nothing worked on the inverter. How can that be? Same error message. So having talked with SMA and we having found out that the panels were OK and with new DC cabling, what could the problem be? I kept asking them if there would be something in the inverter after all, but they kept looking at the DC side of the cabling and panels. In the end the SMA tech said there was a sort of a trick that we could try also. Well, deep in the settings menu, there’s some settings you can change for the Sunny Boy to get rid of all error messages and start fresh. I did that and lo and behold, the inverter started up just fine! Back in business! As usual I ended up doing a whole bunch of things I certainly didn’t need to do but learned a whole lot. Hope this helps somebody someday. Ground faults can be very difficult to diagnose and identify. Once you found the fault and things are not working, if the inverter still doesn’t start up, go to the settings and delete all the codes then it might start up. Procedure for deleting the codes as below. In this case, even though all the faults were cleared, the inverter wouldn’t start up until the codes were actually cleared. Not an obvious solution or the first thing you think of but that’s what solved it.
Note: you have to log in as the installer, not user. If you log in as a user, you can only see the settings and data but you’re not able to change any of them. Logging in as the installer lets you edit settings and parameters. You can either login through Sunny Explorer or by typing the IP address in a web browser.
Sunny Explorer
Select the inverter you want to work on.
Click the "Settings" tab
Click on the "Device" tab
Go to the bottom and select "Edit"
Go to the "Operation" section.
The last line of the operation section says "Reset operation inhibition."
There is a drop-down menu in that section when an event is recorded. Select the second from the bottom option.
Save data.
Click Events tab.
Reload data from that day. If successful, reset event should be recorded.
Inverter should start up in a few minutes.
Short version
If you found and fixed all the faults and the inverter still shows the 3701 or 3501 error messages and will not start on its own, go into the settings of the inverter via a web browser and delete the codes as described at the bottom here.
Long version
So back up to several days ago. The Sunny Boy threw the error codes at noon on a sunny day. They are insulation resistance error codes meaning there’s possibly a short somewhere on the DC side. So I checked out the connections and discovered some corroded terminals and wires. Also found an MC4 connector with water in it. Fixed all those parts, but the inverter still threw the same error codes. The red and the blue lights were on the inverter also. So did more checking. Took one string out at a time and still nothing worked. I hooked up an older Sunny Boy to the solar panels, and everything worked fine. The older Sunny Boy was producing power on both strings. I also connected a known good string to the 7.7, but the 7.7 still wouldn’t start. Put in a temporary DC cable from the panels to the inverter and still nothing worked. The Sunny Explorer menu kept showing that it was trying to connect to the grid, but wouldn’t because of the fault. The DC voltages were showing up in the DC side but nothing was showing up on the AC side. Probably because the inverter wasn’t on yet. I also checked the insulation resistance with an insulation resistance meter that I got on Amazon ($50) and everything was still showing OK. The MEGGER is a handy tool for finding shorts. It sends voltages up to 1000 V DC through a line and checks whether the insulation is OK or not. It also has a permanent on feature so you can check leakage overtime. But I digress. One set of DC wires that I knew was bad also showed up as bad in the MEGGER insulation resistance tester. It showed a dead short to ground. One of the many things I learned is that in checking for these faults you check positive to negative voltage on the panels. You also check negative to ground and positive to ground when everything is disconnected from the inverter. Voltage should be the sum of the in the string. If you have a higher voltage in either positive or negative to ground you can divide it by the panel voltage to see exactly where the fault is. I.e. between the second and third panels or fourth and fifth, etc. Normally, voltage on both should be close to or at 0 V to ground. In an SMA video, they mentioned that anything between 12 and 15 V was OK. They called it a capacitive discharge or something like that. Anyway, voltage does not have to be exactly 0.0 Vdc. When measuring, I measured some thing like 20 or 30 V going down rapidly to 15 V, then 12 V, then 10 V, and finally ending up at 1.5 V after a minute or two. Those numbers are ok.
So it’s pretty certain that the panels themselves are OK and don’t have any faults. You certainly don’t want high voltage when testing positive or negative to ground. That indicates a potential fault. Another thing I found out was that when you connect and disconnect the MC4 connectors, you should never see any sort of arcing under normal conditions. An arc generally means a fault somewhere. So not having arcs when disconnecting stuff is a good indication that things are OK. Course you should always follow safe procedures when handling any sort of DC or even AC wires. I generally like to do DC work at night because then there’s little voltage to worry about. I have put tarps over solar panels and regardless of how many tarps I put on, there was all ways DC voltage high enough to be troublesome. So I just switch to doing that type of work at night. Made it a lot easier. The MC4 connectors also make it quite a bit safer than dealing cable with bare wire ends. Anyway, lots of testing, lots of swapping of parts, I even used a temporary DC connection from the panels to the inverter and still the inverter wouldn’t turn on. I.e. it would not connect to the grid. Same error codes. In desperation, I even considered and called an electrician for help only to find out that it would be a two month wait for an appointment. Of course, knowing what I know now the electrician wouldn’t of helped at all. I talked to SMA they had me do a bunch of voltage checks and again everything checked out fine. Then finally, I just replaced all the DC cabling with new cables and MC4 connectors, and went directly from the panels to the inverter, and still nothing worked on the inverter. How can that be? Same error message. So having talked with SMA and we having found out that the panels were OK and with new DC cabling, what could the problem be? I kept asking them if there would be something in the inverter after all, but they kept looking at the DC side of the cabling and panels. In the end the SMA tech said there was a sort of a trick that we could try also. Well, deep in the settings menu, there’s some settings you can change for the Sunny Boy to get rid of all error messages and start fresh. I did that and lo and behold, the inverter started up just fine! Back in business! As usual I ended up doing a whole bunch of things I certainly didn’t need to do but learned a whole lot. Hope this helps somebody someday. Ground faults can be very difficult to diagnose and identify. Once you found the fault and things are not working, if the inverter still doesn’t start up, go to the settings and delete all the codes then it might start up. Procedure for deleting the codes as below. In this case, even though all the faults were cleared, the inverter wouldn’t start up until the codes were actually cleared. Not an obvious solution or the first thing you think of but that’s what solved it.
Note: you have to log in as the installer, not user. If you log in as a user, you can only see the settings and data but you’re not able to change any of them. Logging in as the installer lets you edit settings and parameters. You can either login through Sunny Explorer or by typing the IP address in a web browser.
Sunny Explorer
Select the inverter you want to work on.
Click the "Settings" tab
Click on the "Device" tab
Go to the bottom and select "Edit"
Go to the "Operation" section.
The last line of the operation section says "Reset operation inhibition."
There is a drop-down menu in that section when an event is recorded. Select the second from the bottom option.
Save data.
Click Events tab.
Reload data from that day. If successful, reset event should be recorded.
Inverter should start up in a few minutes.
Last edited:
