Lithionics has discovered a potential issue with High Capacitive Inverter Inrush with 3000W and above inverters. If you have a Xantrex or Kisea 3000W inverter, a simple firmware update on your battery and making sure you have an on/off switch between your battery and inverter is sufficient.

Lithionics is the first battery company to discover and address this issue and start sending out firmware updates and suggested best practices to avoid damaging your batteries. If you have any other brand of lithium batteries, such as Battle Born, Dragonfly or Lion Energy, we suggest contacting the manufacturer to see what they are doing to address this issue.

If you have a Victron 3000W inverter, these have double the amperage of capacitor charging, and could be even more of an issue. More documentation is to come on the Victron inverter InRush situation.

If you have a Xantrex or Kisea 2000W inverter, there is no issue and nothing needs to be done (however an on/off switch between inverter and battery is always a good idea).

If you have a 3000W Xantrex or Kisea inverter, the firmware upgrade and the installation of an on/off switch between battery and inverter is highly suggested to keep your Lithionics BMS safe.

If you own a Lithionics 315ah battery, the firmware upgrade is available in your Lithionics App.

Below is the synopsis from Sandra Johnson, who is a DIY installer of a huge Lithionics system in her Leisure Travel Van. She has dual Lithionics 315ah batteries and duel Kisea 3000W inverters. The advice below is her take on the subject, and you should still do your due diligence when it comes to installing electrical components.

After carefully studying this new Lithionics white paper on their Explanation of Inverter DC Capacitance and Inrush Current, I realize that the inverter capacitive in-rush occurs at the moment the batteries are connected to the inverters using my inverter battery switch.

That means that both of my 3000w Inverter's capacitors are loading at the same time putting the maximum stress on both battery BMSs. The beauty of a dual battery system is that they equally share everything. Given the high capacitive in-rush current of a 3000W Inverter it would be better to turn each inverter on separately via dual inverter battery switches, this allows the batteries to equally share the peak in-rush current, further reducing the stress to the MOSFETs/Internal BMSs.

So I ordered a Marinco Pro 400a battery switch which I will add to the Kisae inverter, my second inverter that powers everything but the air conditioner and refrigerator. Then when I turn on my Blue Sea ML-RBS main inverter battery switch it will connect first my Xantrex inverter to the dual Lithionics 315 batteries and then later I can flip on my new Marinco battery switch to the Kisae inverter to connect that to the dual batteries.

It just takes milliseconds for the inverter capacitors to load and then they remain loaded until such time as you disconnect the DC power from the inverters using their battery switches. Then overtime of being disconnected they bleed off their power and will recharge again next time you connect them, separately, to the batteries.

I personally like to disconnect my inverters when storing my Leisure so there is no parasitic draw on my batteries, but since the inverter capacitive in-rush only happens when the DC power circuit is switched on (inverter is initially connected to the battery), not when the inverter itself is turned on at the control panel for use. I could leave the inverters connected with their control panels off, and the capacitors would stay charged, and I could rely on my solar to make up any small parasitic loads like it does for the other small parasitic draws of the rest of the items connected directly to my battery's busbar.

Adding an inverter battery disconnect switch is important for a number of other reasons besides just controlling when you connect the inverter to the battery. My Lithionics batteries have an exclusive battery on/off switch so I always need to disconnect the inverters if I ever want to power my batteries off and then back on. You must keep the inverter battery disconnect switch off until after the battery powers on because you don't want the inverter trying to charge its capacitors at the same time your battery BMS is at its most vulnerable trying to come on.

This same concept applies to other brands of Lithium batteries with a BMS. If you have manually disconnected your batteries from the coach you definitely want a way to keep the inverter isolated/disconnected from the batteries until you have connected them back up, then reconnect the inverter to them.

I had my inverters experience shutdowns and throw codes that can only be addressed by a hard reset, which means disconnecting all power to the inverter for more than 30 minutes. A battery switch makes it easy to disconnect the DC power otherwise you'll need tools to pull the positive battery cable to disconnect the DC power from the inverter. Additionally a switch meets electrical safety code requirements by giving you a means to completely isolate the inverter if you need to work on it or something abnormal happens.

So adding an inverter battery disconnect switch makes good sense on a number of levels. I encourage everyone to understand this new information associated with larger inverters and their high capacitive in-rush current and re-evaluate their system to ensure you have an inverter battery disconnect switch.

If anyone is interested in a summary of the Lithionics white paper here are the key takeaways for me are: 
-Lithionics Battery engineers are making continuous hardware and firmware improvements to the BMS design as larger inverters become more popular in motorhomes and customer’s power needs continue to grow. 

-The inverter capacitive in-rush only happens when the DC power circuit is switched on (inverter is initially connected to the battery), not when the inverter itself is turned on at the control panel for use. If the inverter is turned off from its control panel and then on again, while the DC inverter disconnect switch remains on, there is no inrush in that situation as the DC capacitors remain charged even when the inverter is turned off at the control panel.

-Any system with an inverter above 2,000W should have specific ways of limiting in-rush current, such as estimation of circuit resistance, and above 3,000W should consider designing greater resistance into their overall system or adding an External BMS with an included pre-charge function.

-In practical terms we only care about in-rush peak current and how fast it drops below critical level. This is where the subject of switching speed, switching devices, and switching sequence becomes important.

-A solid-state switch, such as the MOSFET transistors (Metal Oxide Semiconductor Field Effect transistors) inside the internal BMS when the battery’s ON/OFF button is used to enable battery power is a premium function included in all Lithionics batteries, but it has an inherent limitation of switching speed imposed by the nature of the MOSFET transistors used in Internal BMS batteries.

-Using an Internal BMS as a power switch during inverter cold start imposes maximum stress on the BMS and if the peak inrush current is high enough, it could damage the BMS. It also means that a mechanical switch should be the preferred method of inverter cold start and use of high-quality switches capable of high in-rush is also important.

-The correct cold start sequence is important to reduce the stress on the BMSs, and is especially important in systems with multiple parallel batteries, particularly if using the smaller batteries, such as Lithionics 130Ah Group 31 batteries.

-The inverter battery switch should be off (open), before the battery(s) are turned on first by the Lithionics battery on/off switch, then turning the inverter battery switch on (closed) handles the entire inrush current. The MOSFETs/Internal BMSs are already fully conducting with lowest resistance, so there is even less stress on them using this cold start sequence. 

-Using this cold start sequence for 3000w and larger inverter systems using multiple batteries in parallel, particularly the smaller 130ah batteries, is even more critical because a single battery can’t handle the entire inrush current. Multiple batteries turned on together before the inverter switch is turned on (closed), allows the batteries to equally share the peak in-rush current, further reducing the stress to the MOSFETs/Internal BMSs.  

-At the end of 2021 an improvement was developed and deployed in a Lithionics battery firmware release to reduce the risk of in-rush related damage, but the minimum resistance requirement still applies for correct system operation.

-Another small improvement was recently completed in the Lithionics BMS hardware design to break up the inrush period into shorter pulses, which reduces the risk of damage when coupled with Victron inverters, which have a much larger capacitance and longer in-rush time period. However, this only addresses the time element of in-rush, managing the peak current based on circuit resistance is still needed in the overall system design.

For me the last part of this last sentence is very important, "managing the peak current based on circuit resistance is still needed in the overall system design." I appreciate that Lithionics would rather build the extra resistance into the system through wire size and length, fuses, bus bars, switches, etc. instead of added resistance to the internals of their battery. Resistance builds up heat which reduces the performance and power efficiency of the overall internal system, and the life of the battery.

I am impressed that Lithionics has lots of batteries in the field that have over 4000 cycles and counting. That is nearly 11 years of operation. I appreciate everything Lithionics does to improve the performance of their batteries and they can pass that learning on through firmware updates to the batteries already in the field via the Lithionics APP. The Lithionics approach to test, to apply knowledge, and to control their applications through engineering gives me a much greater level of confidence that I will have a great performing battery for the lifetime of my Leisure ownership.