thanks.
Two Outback GVX4836 ; 7.2Kw total
Flex 80 Charge controller
Flex 60 Charge controller

Haven't bought gas in 23k miles.

All my critical loads are backed up. Well pump, fridge, freezer, phones, lighting, computers.

Thank you!

Logan thanks for the input.
I originally designed the system with BMS in mind but the Outbacks are so good that I don't need it. I cycled through a few charges running all my critical loads. with no problems.

What I did was to set max voltage to the bank at ~3.400v per cell. The data sheet shows the batteries to be very stable at under 3.600v so I even took an extra measure of safety. Also I cut the batteries off at ~3.00V cell which is well above critical. Internal battery resistance is very stable at these voltages. In fact the differential is under 40mV for the 16 legs.
LiFePo4's are the best batteries around for off grid and backup, really bullet proof.

I agree on both your points, the Outbacks are awesome and so is the chemistry of the cells.

Lets think of an insurance policy for your system. Do a Contactor with a voltage controlled switch. That way IF the controller hangs because of a hardware or a software issue you will be protected. Cheap insurance.

On my DIY system I protect both the High side and the DOD. It is cheap insurance. I have seen many controllers from several major brands do crazy things especially if networked into a "System".

One day Ill be able to post my DIY battery on here.

Regardless Great battery bank!

Cheers!

instagram .com/wlbryce

Might be time to jump on here and make a thread about my solar with battery back up.... but to answer the battery question asked above: I like simple phi lithium iron phosphate battery’s. Three of them make 10.5kw. At 10,000 cycles and built in BMS they work great for load shifting and back up. I paired it with a Schnider xw+ so I could ac couple to my grid tied inverter. If I did it again I would look long and hard at Sol-ark for its many more features and modern design.

Weather Spotter; As far as new installs we have installed over 500 Kwh of Fortress batteries. The price point is extremely competitive and come in large formats.
I also like the Sol-ark. We have installed several. The onboard dual channel MPPT makes for a easy and clean install.
One important issue that needs to be identified. If using Lithium you must insure that the battery is NEVER removed from the Sol-Ark when the chargers are charging hard. If you do, it will blow up the chargers. Sol-Ark now has a warning to this problem (also is a issue for other 600V charge controllers not just Sol-Ark, ask how I know! LOL). So, if the BMS trips the battery offline for some problem when the charger is charging it can kill the onboard charger.

On my system I built a 40f super cap bank that will hold the charger power long enough for the Fets to shut off the charging.

Just a Lithium FYI, or a LA issue if you trip the breaker somehow.

Logan

instagram .com/wlbryce

I have not used the sol-arks yet, last year at this time when I installed my system they did not support ac coupling. Mid January they did and I kicked myself :(. I wonder if the issue of lithium battery’s you are talking about would apply to my xw+? Tech support was saying that they have built in capacitors on the dc side.... which was why the xw+ needed the battery monitor add on to properly read battery voltage.... the caps make a voltage lag or something....

What are fortress battery’s?

In AC capacitance circuits current lags voltage.