Error 6406 "Interference device" on Sunny Boy SMA SB7.7

[phx]

The proper "commissioning" of Sunny Boy SMA SB7.7 or turning it on after the maintenance is connecting the AC, and then turning on the DC solar disconnect switch. That's according to the instruction.

If I do that early morning or late afternoon when the sun is low, there are no issues, and the inverter starts as normal. However, when I do that close to noon at the solar peak power, the inverter is trying to start. But during the starting sequence, it produces an error with the same number and two following descriptions:

6406 Self-diagnosis
6406 Interference device

The latter error is the most frequent while the first error might never show up. Then the inverter keeps sitting with 6406 on its display in permanently disabled status failing to produce any AC power. Even the SPS doesn't work.

I found a workaround on how to bypass that problem:

• Initiate "Rapid Shutdown" via a "Kill Switch" with Tigo TS4-O and Tigo CCA. That individually disconnect each PV module bringing its voltage to zero and the entire string to zero as well.
• Turn on the AC to the inverter and wait until it begins the start sequence.
• Turn on the DC switch on it. However, there is no DC yet due to the Rapid Shutdown status.
• Turn off the "Rapid Shutdown." In such a case the DC voltage grows gradually when more and more PV modules activate, and it reaches the full voltage of 500-550V within 10-15 seconds
• Inverter starts and operates as normal for months never showing any issues until the next grid power outage.

Such "Slow DC" start when DC grows gradually instead of suddenly jumping to 550V idle preventing the error 6406.

I Googled a lot and found nothing on that issue. Please help if somebody has any ideas on what's that and how to fix it.

BTW, I have another inverter Sunny Boy SMA SB6.0 connected to a similar PV string with the same voltage. It never had those issues and it starts as normal, when the entire 550V DC is instantly applied to it.

 

[enzeno]

Hello phx,
I wanted to follow up with you on this - I am having the same issue on my Sunny Boy 5.0 purchased in 2016. Are you still using this work around? For years I have dealt with the issue by simply turning the unit off for 24 hours or so, and it would work for a few weeks until this message came back. And now, it would seem that it has gotten worse, resetting it no longer works, it gets this message every time. So I am wondering if yours ultimately failed as well and how it went with SMA dealing with that.

I also tried your method - basically trying to get it to feed in when the solar DC voltages were lower, but this did not work for me. It would seem that this is also how it would be as the sun comes up - very low voltages at feed in.

Of note - this Interference device is fault code 6406, and it happens whether its in grid-tie or SPS power mode (so regardless if it is connected to AC power or not).

I am in communication with SMA about this - I believe they are going to be sending me a warranty return for it - but so far communication with them is lackluster. I can also follow up to this when I hear back from them.

Thanks for reading!
-enz

 

[Hedges]

I've been able to get support from SMA, but it can be a very long time before first response. Subsequent responses to same help request are somewhat faster.

550V sounded pretty high to me, could exceed 600V limit on cold day.

I've only done brief testing of SB 7.0 -41 so far. No Tigo connected yet, using a ground mount array and just switch on the DC switch.

Since voltage seems related to the problem, try shortening the string by a few panels.
If that makes a difference consider changing array from say 12s to 6s2p.

 

[Kuma]

Had a 5.0-US-41 that would not work with SMA RSD's. SMA replaced it with another 5.0 inverter and its been working. Tigo RSD's put out .6~.7vdc, SMA RSD's out put 1vdc. Not saying that is a problem or not. Sunspec does require specific voltages to function. You should measure at least 6vdc, a min of 6 SMA RSD's per string, at the inverter inputs with DC disconnected. I think that putting strings in parallel could also reduce the RSD's voltages at the inverter. Again, just be mindful of what Sunspec requires.


Other considerations:

"NOTE1: Only SMA-branded TS4-R devices connected to SMA model inverters are fully supported by the SMA Serviceline."

https://my.sma-service.com/s/articl...les-for-SMA-US-Model-Inverters?language=en_US

https://my.sma-service.com/s/article/FAQ-for-JMS-F-SunSpec-Rapid-Shutdown-Devices?language=en_US

 

[enzeno]

Hello phx,
I wanted to follow up with you on this - I am having the same issue on my Sunny Boy 5.0 purchased in 2016. Are you still using this work around? For years I have dealt with the issue by simply turning the unit off for 24 hours or so, and it would work for a few weeks until this message came back. And now, it would seem that it has gotten worse, resetting it no longer works, it gets this message every time. So I am wondering if yours ultimately failed as well and how it went with SMA dealing with that.

I also tried your method - basically trying to get it to feed in when the solar DC voltages were lower, but this did not work for me. It would seem that this is also how it would be as the sun comes up - very low voltages at feed in.

Of note - this Interference device is fault code 6406, and it happens whether its in grid-tie or SPS power mode (so regardless if it is connected to AC power or not).

I am in communication with SMA about this - I believe they are going to be sending me a warranty return for it - but so far communication with them is lackluster. I can also follow up to this when I hear back from them.

Thanks for reading!
-enz

I just wanted to update to my posting, SMA did come through with good support it just did take a couple days for them to initially respond. They simply replaced the inverter based 6406 error messages that I was getting. I have already received the replacement and installed it. General consensus seems to be that these "interference device" error messages merit replacement of the inverter. Now considering adding another 10 years to the warranty.

 

[Kuma]

I just wanted to update to my posting, SMA did come through with good support it just did take a couple days for them to initially respond. They simply replaced the inverter based 6406 error messages that I was getting. I have already received the replacement and installed it. General consensus seems to be that these "interference device" error messages merit replacement of the inverter. Now considering adding another 10 years to the warranty.

Good to know. I applied for the 10 year extended warranty. Prices went up recently from $500 to $530 for 10 year. Still good value imho if one plans to remain in the same house for 10+ years.

 

[Hedges]

I've thought about that, but I've seen used and even NOS 10 year old models at $0.10 or $0.20 on the dollar.
If you only have one, that changes the game.
I had 5x SWR 2500U, one replaced under 5 year warranty, one failed out of warranty. Something like 32 or 34 years MTBF over my 17 years using them.

 

[Kuma]

Another consideration for purchasing the 10 extended warranty now with the new pv system is taking advantage of the 30% tax credit. And, having SMA support help troubleshoot any issues for 20 years. Also, SMA ships replacement units within a couple days. My only concern is SMA being viable in the USA 10, 15... years from now and providing the same level of service and support. SMA market share has diminished the past few years.

 

[Hedges]

They've been around for decades, probably makes them longer than virtually any other brand (as oppose to those bought out.) Share may have diminished but probably sales have grown.

SolArk has positioned itself as a competitor being installed professionally for home systems.

SMA also has big stuff, MW scale for solar farms.

I think there will continue to be a market for their premium quality. They just have to maintain that. With available 25 year warranty for Smart Energy, they are showing confidence in it.