EG4-6500s as Charge Controller and Battery Charger with separate 48V inverter?

[Tom Funchess]

When I bought my system, my primary objective was to ensure that my commercial refrigerator and freezer would have 100% power at all times, at least for long enough for me to get home and start up a generator in case of a power outage. Living in the South, we have multiple weather related outages each year due to thunderstorms, tornadoes, etc. My secondary objective was to reduce Utility power consumption and reduce my electricity bill.

The freezer pulls about 1500W and cycles every 22-minutes or so, while the refrigerator pulls about 1000W and cycles every 15-minutes or so. Occasionally they will start up at the same time, and the peak load can be over 4000W. With 0W of PV input, I will go through my 30KWh of batteries in less than 12-hours, so if weather is bad, I need to have AC Input to run the loads and charge the batteries.

I have two EG4-6500s running in 240V split phase with (6) LifePower4 batteries, with two 60A 120V AC Input circuits, one to each inverter. The system runs fine in SBU mode, using the EG4 BMS communications with a rare Error 61 alert that may beep twice and then go away. Both inverters are now on the newest firmware, 79.61/61.10.

My work occasionally takes me away from home for days at a time, and my original plan was to be able to use Solar Assistant to remotely control the mode between SBU, SUB, and USB as needed based on approaching weather systems, extended cloudy days, etc. When 100% battery backup was thought to be needed, I planned to switch from SBU mode to SUB or USB, give up the solar power generation temporarily, and then maintain the batteries at 100% in case Utility power goes out. If I could do that, it would give me about 12-hours to get home with the current battery bank, and up to 2-1/2 days if I were to max out my battery bank with sixteen LifePower4 batteries. That would be workable if it all ran flawlessly.

The problem that I have run into is that the inverters seem to have a problem operating between Solar and Utility, in both SUB or USB mode, when the batteries are at near full charge and the solar power generation is low and intermittent. This occurs mainly in the morning as the sun comes up, in the evening when the sun goes down, or when the sky is dark and gloomy. As the inverters try to switch between Utility and Power over timeframes that might range from 15-minutes to an hour or so, while running in SUB or USB mode, I have seen inverters shut down, GFCIs trip, equipment connected to the system not start back up, etc. These are issues that you can't restart or recover from remotely, so that doesn't meet my initial expectations.

I have upgraded firmware and have been testing the system for several days, and at one point I had decided to just pull the EG4-6500s down and replace them with something like a Schneider XW Pro system (keeping the LifePower4 batteries, but replacing everything else). The problem is that that option is very expensive (and a lot of work)!

Looking at the modular design of the Schneider XW Pro system, it got me to thinking about taking the inverter functionality away from the EG4-6500s and running a separate 48V inverter for the loads. I would keep the EG4-6500s installed as solar charge controller and battery charger using AC Input (with the BMS communications between the EG4-6500 and LifePower4 batteries), but I would use a separate Tier 1 inverter for 48V to 120V/240V loads (Schneider XW Pro, Victron, etc.).

It not only takes away the switching between modes in the All-In-One unit, but it also brings the possibility of better-quality, pure sine AC output to run my equipment. The EG4-6500s could then charge the battery from PV or AC Input as needed, and the extra inverter would run the loads at the same time, independently.

Has anyone else looked into doing this? Are there any reasons why it would not work?

Does anyone else have other thoughts on how best to achieve 100% uptime in a system using the batteries as a battery backup for fairly large critical loads, in a fix-it-and-forget-it configuration?

 

[Quattrohead]

The LV/SP6548 seem to be much more reliable than the EG4 version, what's up with that ?
But yeah, I was using a Solark 12k just to charge the batteries from my panels for a while with the pair of SP6548 powering the big loads of AC, HWT and dryer.
The Solark is a great single box option that could work for you.

 

[Tom Funchess]

Thanks. I'm thinking I want to get away from All-In-One, and I'm trying to figure out how to use my existing pair of EG4-6500s just as solar charge controllers and battery chargers with the AC Input. I would keep the communication between EG4 inverters and EG4 batteries, but would not use the inverter function if that's possible.

I would then add a 48V standalone inverter to run the 120V/240V loads (Victron Quattro, Schneider XW Pro, or other Tier 1 inverter, preferably one with a transformer).

 

[wheisenburg]

I don't see any reason this wouldn't work. Transitioning between different modes is always a little dicey. Sol ark claims to do it faster than others. On my system there is at least a little flickering of lights when transitioning. This could be enough to mess up some sensitive equipment. With a single Schneider running in inverter mode all the time, it should easily power the loads you describe. You may want to get some readings on the LRA startup current of equipment, but the Schneider inverters will generally handle surges very well. If your two EG4 inverters can handle it, I believe a single Schneider should do just fine. This configuration will of course be less efficient because of the multiple conversions that will need to happen. That is not a show stopper if reliability is your primary concern.

Also, if you do use a generator as a backup, this solution will insure that the generator is only used to charge the batteries. Smaller generators that are not inverter based will have power quality issues. Voltage sags and surges, harmonic distortion, frequency deviations will all occur as large loads are switched on and off from a portable generator. When you supply an inverter with generator AC in, it switches to pass through mode so the circuitry can be used to charge the battery. All the dirty generator power will just flow into the loads. Here your main inverter is always supplied with DC and will output clean power all the time.

You might consider getting a large capacitor placed across the main DC battery bus to prevent ripple current from being pushed and pulled from the batteries. I don't know that this is needed, but some people that are running fully off grid, will do this to prevent possible wear and tear on the batteries.

I know one person on this forum from PR has power quality issues and is planning to setup separate inverters to handle charging vs inverting so grid power is never fed into the house.