sunnyboy SB7.7 -1Sp-US-41 error 6404

Dear Members: I could really use some assistance, I do not know what else to do at this point, I cannot find my problem, and am so far getting no where's with sunnyboy tech support. I have not heard from them since Thursday morning. Sept 28th. I wrote them on the 29th with no reply.

My Inverter has been down for a week now, since Sunday 24 September. I am not getting useable help from Tech support. The system was commissioned June 2nd 2022. It has been running okay until last week when I got the 6404 Error. I have reset the inverter by shutting it down over night to no avail.
I have 26 panels on 4 separate strings going into the inverter. They are Canadian solar 250W panels. CS6p-250PX Open circuit voltage 37.2V
As per Sunnyboy Tech I have taken the following measurements.
AC side L1/N 120.9V L2/N 117.7 V L1/L2 235.6 V
DC strings taken in the evening.
String A +/- 191.8V +/PE 68.3V -/PE 67.1V
String B +/- 183.6V +/PE 60V -/PE 95V
String C +/- 110-125V +/PE 65V -/PE 92.5V
String D +/- 228.8V +/PE 92.8V -/PE 118.8V
I also ran the solar on only string D and on only string A I still got the error 6406.
I cannot believe I have 4 bad strings in my system.
What DC voltages should I see on a good string? The strings are bone dry, no obvious water can be seen in the solar panels. It has not rained here for many days now.
I am at a loss now what to do. I cannot afford a new inverter as a test, and sure cannot install all new solar panels.
I would greatly appreciate some advice as I am apparently not getting anything out of sunnyboy. They have been dragging their feet so long. I have to hound them for a response. The last message from them, they wanted my address(which they already had by the way) in case they may have to do a replacement. I have heard nothing since.
Thank you
_stampee

According to SMA


Event 6406
Hardware threshold for overcurrent at the relevant DC input (A) has been exceeded.

So assuming this covers your inverter then its amps you need to look at not volts.

kommando said:

According to SMA

SMA - Customer Community

Event 6406
Hardware threshold for overcurrent at the relevant DC input (A) has been exceeded.

So assuming this covers your inverter then its amps you need to look at not volts.

Click to expand...

Thank you, but how can a solar panel/string put out to much current? Also I disconnected all strings and tried running on single strings to no avail.

Cold panels with good sunshine will output more power than during the summer and higher than the rating, I have seen my 270W rated panels reach 330W on a cold day with intermittent clouds when a cloud has just passed by. You have not posted the panels spec for amps or the inverters spec for amps so a calc of the different strings potential amp output can be calculated to see if there is an issue with the panels.

However based on what you have done its likely to be the an inverter fault but post the panel and inverter amp specs first for greater certainty.

Thank you. It fails early in the morning when there is barely any sunshine and in the 60's Fahrenheit.

• Inverter Type: Grid-Tie String Inverter
• Maximum/Peak Efficiency [%]: 208V:97.1% / 240V:97.5%
• CEC weighted efficiency @ 240V [%]: 97
• Transformer / Transformerless: Transformerless
• DC Power Rating [W]: 7950
• Nom. DC Voltage [V]: 600
• Max. Input Power [W]: 10905
• Max. Input Voltage [V]: 600
• Max. Input Current [A]: 30
• Min. DC voltage / start voltage [V]: 100 / 125 V
• Min. DC voltage / start voltage [V]: 100 / 125 V
• Number of DC String Inputs (Inlets): 3
• Number of MPP Trackers: 3
• Max. Input Current per MPPT [A]: 10
• Voltage Lower Limit for MPP Range [V]: 100
• Max. AC Power [W]: 6660W @ 208 VAC / 7680W @ 240 VAC
• AC voltage range [V]: 208V: 183-229V / 240V: 211-264V
• AC grid frequency [Hz]: 60
• Max. output current [A]: 32A
• Nominal AC Voltage [V]: 208V / 240V

Canadian solar panels cs6P-250PX nominal 250W Optimum current 8.3Amp
2 strings of 6 panels and 2 strings of 7 panels.
I am getting no place with SMA sunnyboy. I haven't heard from them since Last Thursday.
-Stampee

I should have also stated, I haven't been able to get the system online at anytime of day for a week straight now.

Try following the instructions in this thread


I note you have 4 strings and 3 MPPT's, which strings are connected to which MPPT's and how many panels in each string.

Kommando: Thank you for the assistance and I apologize for my slow reply. I had ceilings coming down in 2 rooms from to much rain recently. That and over time has had me very busy.
SMA sunnyboy finally got back to me and shipped me a new inverter a few days ago Thursday. I installed it, and the solar came online fine Friday all day. I stopped it once to commission the wifi and get it connected to my internet, it came back online the 2nd time fine as well.
Today Saturday is heavy rain, at this time solar is online and producing 370 watts. Not alot, but with rain and heavy overcast it is normal production. The main thing is I have no errors, or GFCI faults.
Thank you once again. I will continue to monitor the system and see how stable it is.
-Stampee

No problem, I would check the potential peak amps on the mppt you have 2 strings attached to. Total amps limit is 30A but each mppt is limited to 10A, so it's possible one of the mppts with the 2 strings has high amps on good output days.

Thanks, it is confusing, and i may be reading it wrong. Sunnyboy combines 3 strings onto 2 mppt inputs. Then i have a separate string on the final 3rd input.
My panels are rated at 8.3amp output. So three of those strings in parralel give 24.9 amps, but then divided over 2 inputs that gives 12.45 amps per input. The sunnyboy spec says Max input per mppt is 10 amp, so yeagh it looks like i am over amperage.
I have two 6 string circuits and two 7 string circuits. 26 panels total. It looks like i would be better off making longer strings and raising the string voltage to keep the amperage lower. Apparently i got away with the higher amperage for awhile, but i dont want to keep pushing it. The inverter may be clipping higher amperage also on high days. I also may be better off using 3 strings instead of 4 just to make things simpler. I still would be well under the maximum voltage per string.

-stampee

Seem like that would be a simple change, that is, if all your panels face the same direction and mounting angle.
Series connect one 7s string to one 6s string and connect to one MPPT input. Same for the remaining two strings and one more MPPT input.

13s would be about 480 volts at 25c and should still be below 600 volts when it's cold.

Wow, yeagh that would be very simple to do. I dunno why I didn't think of it. I kept thinking i needed 3 strings,but i don't.
. Thank you