Good morning, Wrenches. This is an article I'm working on that addresses this topic... It's not done yet, as I'm still working on it between the normal calls and emails we get. It's centered on our LFP batteries but can be used more broadly, and it's based on the experiences I've seen with some of the legacy inverters out there.
Configuring Legacy Inverters with LFP BatteriesOpen-Loop Integration – Field Experience and Recommendations My experience with LFP batteries and legacy inverter/charger equipment has been mixed. Some equipment works reasonably well, while other equipment presents challenges that require careful configuration and ongoing customer involvement. In many cases, these systems can be configured to work with LFP batteries in an open-loop configuration. However, there are limitations, particularly with charging algorithms, voltage regulation, battery monitoring, and maintaining balance between parallel batteries. The following recommendations are based on my experience working with these systems in the field. ------------------------------ 1. Magnum Configuration Requirements With Magnum equipment, we haven't encountered many issues connecting LFP batteries in an open-loop configuration, as long as you take a few precautions. 1. *Remote Display:* You must have either the Advanced Remote or the Advanced Router Remote. 2. *BMK (Battery Monitor Kit):* Do not use the BMK. I've found that it barely works reliably with lead-acid batteries, specifically when configured with default settings. With LFP, the errors and warnings it generates will cause more headaches than they're worth. 3. *PT-100 Charge Controller:* If you're using a PT-100 with a Magnum inverter, you cannot link the inverter charging settings to the charge controller settings. Disable this feature in Menu 02E. 4. *Battery Programming:* Program the system using Custom Battery settings. I've found this necessary even when a Lithium setting is available. Most preprogrammed lithium profiles are designed for 15-cell-series batteries rather than 16-cell-series batteries. 2. Charging Configuration I generally recommend the following charging configurations: - *Solar Charge Controllers:* Two-stage charging. - *Inverters/Chargers:* Three-stage charging. Absorb timer settings are particularly important. As a general starting point, allow at least 20–30 minutes of absorb time per parallel battery in the system. For larger systems with relatively low charging current (less than 8–10% of the bank's C20 capacity), you may need to increase absorb time to up to one hour per parallel battery. *Important: Do not terminate charging based on End Amps or SOC%. Terminate charging only after the programmed Absorb Done timer completes.* End Amps and SOC% accuracy are not sufficiently reliable in many of these systems to use these features for LFP charging. We have found similar limitations when using them with lead-acid batteries. 3. Battery Temperature Compensation (BTS) Disconnect the BTS from the inverter and charge controller. Do not allow battery temperature compensation to operate. Even with the BTS disconnected, Magnum's output voltage regulation can introduce overvoltage errors with LFP batteries. Slightly reducing the absorb voltage target can help minimize these errors. However, there is a trade-off: lowering the charging voltage can make it more difficult for the batteries to reach a full charge and balance properly. This can increase voltage and SOC differences between batteries, potentially requiring additional manual balancing of the battery bank. 4. Low Battery Disconnect Settings Set Low Battery Disconnect at or just above nominal battery voltage. This setting depends on the specific battery manufacturer and the number/voltage of cells in series. Recommended starting points for Surrette LFP Batteries. System Voltage Low Battery Disconnect 12V 12.2–12.4V 24V 24.4–24.8V 48V 48.6–49.0V 5. Routine Battery Monitoring and Maintenance Customers should periodically check the SOC% and individual battery voltages of all parallel battery stacks. We recommend performing these checks every 30–60 days, preferably after the system has completed a full 100% charge. Pay particular attention to the following: - SOC% differences between individual batteries. - Resting voltage differences between individual batteries. If SOC% is more than 5% out of balance, or resting battery voltages differ by more than 0.3V, separate the batteries and charge them individually to 100% to rebalance the bank. The objective is to prevent small differences between batteries from developing into larger imbalances over time. ------------------------------ 6. Other Legacy Inverter and Charger ManufacturersOutBack Power We have found that the OutBack FM60, FM80, and FM100 charge controllers can be configured to work with LFP batteries. *OutBack GT Inverters:* These do not work particularly well with lithium batteries. Their battery charging algorithm changes based on how quickly battery voltage rises. This can lead to inconsistent charging and balancing issues. *OutBack Radian Inverters:* These can be programmed to work with LFP batteries. However, we have also found that pre-2008 Outback inverters, for some reason, just don't like lithium batteries. Something in the firmware appears to cause the inverters to bypass absorption, which can lead to balancing issues. Schneider Electric Schneider equipment can also work with LFP batteries. We generally configure the charging much like the Magnum recommendations: - Charge controllers operating in two-stage mode. - Inverter/chargers programmed for three-stage charging. - User-defined battery settings. - Carefully configured absorb voltage and timers. Victron Energy Victron equipment generally works well with LFP batteries. I would again recommend using a user-defined battery profile and disabling adaptive charging. The Magnum configuration outline above provides a good starting point for programming and maintaining these systems, although individual equipment settings and capabilities will vary. Trace Engineering and Heart Interface Some older Trace Engineering and Heart Interface inverters can work with LFP batteries, provided you can control the absorb timer settings. Inverters such as the older UL, UX, DR, and Heart 458 models do not provide adequate control over absorb timer settings. This can lead to inconsistent charging and battery balancing issues. ------------------------------ 7. Battery Monitoring Equipment The battery monitoring equipment I've had the best experience with includes: - Victron BMV-712. - Victron BMV-712 Smart. Traditional battery monitoring equipment from Magnum (BMK), Schneider, and OutBack (FNDC) is not ideal for LFP applications. These products were largely designed around lead-acid battery characteristics. Their SOC calculations and monitoring algorithms are not necessarily suited to LFP batteries. I've encountered inaccurate SOC readings, along with numerous errors and warnings, particularly as battery SOC drops below 50%. For this reason, I generally prefer monitoring the battery manufacturer's individual battery data and voltage readings rather than relying exclusively on the inverter's battery monitor. ------------------------------ 8. Summary If you have a customer willing to work with you, learn the equipment, and do basic system monitoring and maintenance, you can configure much of this legacy equipment to work with lithium batteries. However, if you have a customer who isn't willing to learn the system, or simply doesn't have the ability or interest to monitor and maintain it, we strongly recommend a closed-loop system. Another consideration with much legacy equipment is charging voltage regulation. Many of these older inverters and charge controllers simply do not regulate their charging output particularly well. Their output can be electrically noisy and can generate high-voltage errors and warnings with LFP batteries. The pulse-width modulation (PWM) of the charging output can produce voltage fluctuations that trigger annoying high-voltage errors and warnings in the battery management system. This is also often exacerbated by the smaller capacity of an LFP battery compared with a lead-acid, FLA, AGM, or GEL battery bank. Open-loop systems require more attention, more customer education, and a better understanding of the equipment's limitations. Closed-loop systems generally provide a much more straightforward installation and support experience. *Steve Higgins* *⋅* *Technical Services Manager* *t* +1.902.597.4020 <(902)%20597-4020> *m* +1.206.790.5840 <(206)%20790-5840> *f* +1.902.597.8447 <(902)%20597-8447> *e* [email protected] ------------------------------ CONFIDENTIALITY: The information transmitted herein is intended only for the addressee and may contain confidential, proprietary and/or privileged material. Any unauthorized review, distribution or other use of or the taking of any action in reliance upon this information is prohibited. If you receive this email in error, please contact the sender and delete or destroy this message and all copies. ------------------------------ On Tue, Nov 3, 2026 at 7:06 PM Zeke Yewdall <[email protected]> wrote: > I have used a number of newer magnum inverters with lithium batteries > pretty successfully with custom absorb/absorb time/float settings (newer > being 5 to 10 years old or so), on both 24 and 48 volt systems. I have > heard that some of the older ones, however, just cannot work with them, > even with custom settings. I can't remember what the issue is, but it's > something that just doing custom settings cannot fix (or maybe it's that > they can't take custom settings?). I konw that the standard DIP settings > on the PT100 don't work, so if you don't have a magnum inverter and ME-ARC > to do custom settings, the PT100 won't work well with lithium batteries. > > I am interested in seeing what the lithium settings on the new Magnum card > is. I recently ran into a different inverter (AIMS) which the lithium > rotary switch setting had an absorb of 57.6 which is okay for some 16 cell > LFPs, but a bit too high for others -- I've run into a lot that shut off > the BMS at more like 56.5 or so. I could not determine what the absorb > time was, which isn't good. And the float voltage was also 57.6, which is > really bad. So, just because an inverter has a lithium setting, doesn't > necessarily mean it will work with a particular BMS for a particular > lithium battery. > > Zeke > > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > > List Address: [email protected] > > Change listserver email address & settings: > > https://lists.re-wrenches.org/mailman/options/re-wrenches_lists.re-wrenches.org/ > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/[email protected]/ > https://lists.re-wrenches.org/pipermail/re-wrenches_lists.re-wrenches.org/ > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > http://www.members.re-wrenches.org >
_______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: [email protected] Change listserver email address & settings: https://lists.re-wrenches.org/mailman/options/re-wrenches_lists.re-wrenches.org/ There are two list archives for searching. When one doesn't work, try the other: https://www.mail-archive.com/[email protected]/ https://lists.re-wrenches.org/pipermail/re-wrenches_lists.re-wrenches.org/ List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: http://www.members.re-wrenches.org
