SMA inverter & Discover AES Battery

BobK · October 2021

Back in 2015 I started a thread about plans to eventually add more solar panels, better inverters and a battery bank to have a grid-free system. The adding part is pretty well complete, but the local electricity grid provider is trying to run off people who have solar panels. Because of this I’m trying to finally go off-grid

What I’m not sure about at this point is the hooking all of the new equipment together part. See the new equipment below. Part way through the process my installer took a new job working for Tesla. For that job he moved from Louisiana to Colorado. We occasionally talk on the phone, but that is not enough.

I have the original system that was installed by a professional installer in 2014. That system has been working for seven years and includes:

24 265W solar panels

2 SMA Sunny 3000 grid-tied inverters

12 Tigo optimizers

This was supposed to and pretty well does provide 2/3 of my electricity

What I have added:

24 300W solar panels

2 SMA Sunny Boy 6.0 1SP US 40 PV inverters

2 SMA Sunny Island 4548 off-grid inverters

2 Discover Energy Corp LiFePO4 48V battery packs. These batteries have an internal BMS that is more efficient than using the inverter BMS (according to the battery maker).

1 Discover LYNK Gateway to facilitate communication between the SMA SI4548 inverter and the Discover battery modules that are connected in parallel.

1 Discover edge card that enables the SMA SI4548 inverter to work with the Discover LiFePO4 batteries.

1 feed through breaker box that will house AC breakers associated with the solar panel/inverter setup. This breaker box, which is 120 feet from the house, will eventually lead to a new house breaker box that is not connected to the grid.

Yes, I do have a good reason for going off-grid even though I am currently connected to the grid. No, I am not using the original installer who installed our system in 2014. He wants $100,000 that I do not have to do the job.

I connected one SB6.0 inverter to one SI4548 master inverter. The SI4548 inverter was then connected to the battery via the LYNK Gateway. While I was attempting to commission the SI4548 inverter following directions in the inverter installation manual something went wrong. The SI4548 and a DC-DC Converter (a part of the Discovery LYNK Gateway) were destroyed. A 150A fuse on each battery module was also blown, but after replacing the fuses the batteries are working good.

The destroyed SI4548 inverter has been replaced (so far at SMA expense, but the jury is still out on that). As soon as I receive the new DC-DC Converter I will try to commission the SI4548 inverter again. As soon as it is working I will then commission the SB6.0 inverter using the SI4548 master as the local grid.

First I will install a circuit breaker between the SI4548 and the Discover LiFePO4 battery packs. My installer that took the new job in Colorado suggested a 240A DC circuit breaker between the inverter and battery modules. Because the battery packs are connected together in parallel a 240A charging current should not be a problem for the 150A fuse in each battery pack because only 120A will go to each battery pack. He also recommended one 30A AC circuit breaker in the breaker box for each of the two 120A outputs from each of the two SB6.0 inverters (4 30A breakers total).

My questions at this point.

Do these circuit breakers sound good and reasonable?
What else am I missing?
Another thing is that SMA does not consider Discover Energy Corp LiFePO4 batteries as approved for use with their inverters. Both Discover Energy Corp and Northern Arizona Wind & Sun (from whom I bought the batteries) have told me that they have many customers using this battery/inverter combination successful. Neither Discover or Northern Arizona Wind & Sun have supplied any component connection information that has resulted in successful connection of Discover batteries with SMA inverters. Yes, I should have bought different batteries, but it is too late for that.

Why will they not provide installation connection directions? That sounds like a reasonable thing to do for items that they sell. A representative from the battery company says that their engineers have “worked extensively with SMA engineers to develop an edge card that allows communication between their battery and an SMA Sunny Island inverter.” That cooperative work produced the very information that I am asking for, but have not received.

Dave Angelini · October 2021

Installation instructions are often not supplied because of liability or the store feels that a licensed installer should be involved. It is their business! Also SMA and Discover are not UL9540 certified and this is a building department issue for code compliance. This may be another reason that you are not having success. I have to supply that UL Doc to an inspector in a home that is insured. My .02

mike95490 · October 2021

Mixing and matching components is a bit risky, as you discovered. If I was doing this, I'd get 4 group27 deep cycle batteries ( cheap, costco, sams club, bj ) and make a sacrificial battery bank, about $150 total, batteries & cables. Wire the whole thing up and test with the lead acid batteries. Add the 2nd inverter. power up the 2nd charge controller after the batteries are full, it should just go to FLOAT

BobK · October 2021

I can’t say that I’m surprised about the comments above so a bit of my history. I learned a lot about electrical systems while serving as a Combat Engineer in the Army. I served nine years in the Army. Later while living in a home in Aiken, South Carolina I replaced a lot of wiring that had been chewed up by mice, and circuit breakers that no longer worked in the breaker box. After moving to Louisiana my wife and I spent evenings, weekends and holidays building our house, starting in late 1996. We did not hire a “professional” carpenter or electrician to do the work for us. I wired the whole house from breaker box to outlets and switches. From 1997 (when we moved in) to now there have been no problems. Recently I removed an old water heater, and replaced it with an on demand, tankless system. Later I added two 50A breakers and ran wiring to a NEMA 14-50 outlet for charging our electric car.

In 2015 I installed four solar panels, a Morningstar charge controller, a Magnum inverter, a shunt, a Bogart Engineering battery monitor and two Lifeline AGM batteries on our RV. That installation is still working good. Anytime that I was uncertain
about anything I contacted the places where I had bought the parts, and they were always willing to provide guidance. They never seemed to worry about my training in solar & inverter installations. They just wanted to help insure that the products that they sold were working correctly. But then when I bought each item it had much better instructions than what I received with the items I purchased for going off-grid. Yes, they were informed that I was going off-grid. I am not a newbe to electric wiring or electronic equipment.

As for why I want to go off-grid, my local electric company has informed all of their customers that they will no longer accept new customers who have solar panels. No new net meters will be used, and those of us who already have solar panels and net meters are grandfathered in for a short time. When that time ends we will lose our net meters. Without a net meter any excess electricity produced will go to the electric company at a full cost to me. When we first had solar panels installed in 2014 we were charged full price for all surplus electricity that we produced until the net meter was installed.

While wiring the SMA inverter and the Discover AES batteries I followed the installation instructions that were provided. When I attempted to commission the SMA SI4548 inverter I was following the directions on pages 69 and 70 of the operating manual.

I did not include all of this information in my previous post because that post was already too long.

BobK

Dave Angelini · October 2021

Well Bob, with your experience you can also see that when inverters,150A fuses, and low voltage electronics are "blown", some folks are going to be skeptical. I can't speak for the store here but they are not in the installation business. They have people like me who I know really well that do installation. If you want to DIY, it is not a problem as long as you know the install / owner manuals backwards and forwards.

An old forum member Photowit would say to you that you should not buy anything until you are up to speed and well beyond. This is extremely important for someone with the grid and a home that has a Fire Insurance policy on it.

Post some pictures and a diagram if you want folks here to give input.

BB. · October 2021

Bob, don't worry about long posts (I am the "king" of long posts there--I keep having to make the max post limit larger so I could have "room").

More information helps. And you are welcome to post links to your products (or something you are thinking of purchasing). And photos too.

Using circuit breakers instead of fuses... Can be very nice. Large Amperage fuses (and holders) are not cheap. And good quality breakers also make handy ON/OFF switches.

My own personal suggestion... Rate the wiring and fuse/breakers for 1.25x larger than the max continuous current (NEC continuous current derating).

120 Amp (say charging current which can be for hours in a discharged battery bank) * 1.25 NEC derating = 150 Amp (or round up to next standard size) for wiring and breaker(s).

In North America, the typical fuse/breaker will not trip at 80% or less of rated current... And will (eventually) trip at 100%+ of rated current.

-Bill

SMA inverter & Discover AES Battery

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