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Its fine to use as long as you keep it away from surfaces that need to be conductors. ie: use conductive antioxidant between battery and terminal, then coat outside of terminal with dielectric grease to prevent moisture damage.

If the system voltage has been high that should show up in the diagnostic trouble codes of the body module as a history code. That will be separate to the failed component codes.

I imagine one battery 2P4S (two cells in parallel, connected together four in series), the other is just four in series. If that is the case then they are OK to parallel as long as the chemistry is the same (eg both LiFePO4)

Yes, it will work fine as long as they are the same chemistry and series cell count.

Nobody really knows for sure yet, as simulations of <.5C current cycles have to be done in real time. Above that it is literally a different chemical reaction in the cell. The first cells I know that have been constantly gently cycled (3.0 - 3.45V) at maximum 0.5C were commissioned in 2007...

I’m completely off grid in South Australia and have been for over 12 years. I started off with a SMA Sunny Island, which is now CEC approved as a grid tie hybrid. Compatible with SMA Sunnyboy grid tie inverters, and most commonly available batteries. I recently purchased a second hand grid...

I remember seeing a lot of those cells on the market around seven years ago. When I dug a bit deeper they were all coming from cell brokers that were known to deal with factory seconds and refurbished cells. Fully charge that battery, then subject it to the highest load you can and measure...

My LiFePO4 battery is over 12 years old now. It often goes all winter without being fully charged or activating balancing. I wouldn’t worry about it if I were you.

With my LiFePO4 that doesn’t have inverter comms I set my BMS cell LVD to 3.0V, and my inverter LBCO to 50.0V This seems very conservative, but I regularly run that system to inverter shutdown and get over 80% of battery capacity, so I see no reason to stretch the cells any further.

There are zero engineers / chemists that recommend parallel charging LiFePO4 cells to upper knee voltage until current reaches zero. Sadly, too few youtube heros and the sheep that follow them realise that.

Of course it is an accurate method. I’d say over 99% of batteries have their cells balanced by individually charging to a known setpoint.

My advice - ask your cell manufacturer (not reseller), how they balance and match their cells and follow what they say.

That packaging is awesome 🤩

In Australia, private company’s own the power distribution. If you want to participate in their distribution you follow their rules. Our government simply obeys its corporate masters. There is always my preferred option of going off-grid. Unfortunately there is no complete escape as a...

Maybe, but in 2012 when I set up my primary off grid system I chose an SMA Sunny Island. In 2024 I would choose the same inverter.. Some things change - some stay the same.

My system isn’t grid connected.

Yes, in theory it does. That is the worst case scenario and puts 0.8C into a battery that can handle 1C for a couple of seconds. I haven’t seen that cause problems.

I’ve set up dozens of systems with SMA that have between 2 and 4 kw PV / 100ah of LiFePO4. There have been zero issues to date. The way the REC-BMS works with the Sunny Island means that there cannot be a scenario where the battery is full AND fully charging, the Sunnyboys are well ramped...

My experience working in Automotive manufacturing led me to use the open barrel crimp i pictured. I’m not sure why you think closed barrel is a better option?

Use an open barrel butt splice. Same thing used in automotive wiring looms so proven reliability in harsh conditions. Make certain you use the appropriate sized crimp for your wires, and the correct tool. Cover with UV stable sealant filled heat shrink.

A well done butt splice crimp covered in sealant filled UV stable heat shrink is all I use for PV connections, inside or out.

Sure, the inverter has to have a slightly higher voltage than grid, and will push all the current it can unless told otherwise. When charging batteries the grid tie inverter has to be told to reduce current. It’s default is maximum current possible. The Sol-Ark is a hybrid inverter, different...

I think you are solving a problem that doesn’t exist. It is a cool solution though.

No, a grid tie inverter will produce maximum output unless told otherwise.

Yes. Most of the feed in source is utility controlled though, overproduction raises voltage, if the utilities are slow to adjust their own production down, they can bump off customer production.

Yes utilities regularly use this function - yes it is accepted practice and not a hidden feature. The sneaky thing is utilities deliberately raising grid voltage so they can shut off grid feed inverters and not have to pay people for feed-in. (this is obviously denied by utilities).

In Australia, all grid tie inverters have to have the ability to be remotely disabled by the utility provider. They are switched off during times of peak production to stop grid over-voltage.

Have you had issues with your BMS disconnecting due to cell high voltage? I think you have a good solution, but haven’t actually seen anyone else with your problem. With my BMS, when the first cell reaches balancing voltage, the current is already limited so the AC coupled frequency has...

DIY isn’t for everyone. I see some people building their own inverters / charge controllers / BMS from discrete components. That is over my head. Assembling a battery is within my capabilities, and the savings are huge. People forget that commercially available batteries typically have a...

I appreciate the time you have put into this, and am trying to get a better understanding. Thanks.

That is over my head sorry, just replying to bump your thread and say that your system looks very neat. There are a few batrium users on this forum - hope someone can make sense of it.

I’d be curious to see the inrush current trace of that inverter - i’ve never bothered with precharge for 12V inverters.

The REC precharge module in combination with a contactor is what i use for automatic operation. It is a significant added expense for a FET based BMS though.

My take on balancing. I charge to 55V with up to 0.5C current (depending on availability of PV) If no cell goes over 3.5V before 55V pack voltage the charger switches to 54V, and no balancing occurs. If a cell reaches 3.5V, the voltage is held at 55V until it is reached, but current is...

It will reset itself to 100% SOC, otherwise you can manually set SOC in the REC to 100%, follow instructions in the manual, from memory it is command SOCS 1.00