TRAP: FNS / Sacred Sun LifePo4 3U & 5U Solar Batteries

This is a continuation of my post yesterday about Growatt SPF inverter/chargers. Why? They have the same Chinese parent company (FNS) and share a common problem.

So let me start off with a compliment to the company and what they are trying to accomplish. As I understand it FNS was a battery company located in China. They then bought an inverter manufacturer also located in China. I think that is a great concept…a single company that makes the inverter/charger side of a solar system and also the batteries. Makes perfect sense…the system is better suited to work together, the components are compatible, and the inverter/charger is able to communicate with the LifePo4 battery BMS (battery management system) making it more efficient.

Last summer when a neighbor had to upgrade his solar system he asked me to handle it for him. No problem, I like helping neighbors and I do pretty decently with solar systems. Yes, he saw my system that I built and had confidence in me I could build him a good system as well.

In the market place today, and yesterday, there has always been great charge controllers and inverters. I am partial to Victron. The problem for several years now has been reliable, decent quality, lithium batteries that are priced affordably. In 2019 I started that quest for good LifePo4 batteries that I could afford…that is a story for another day. For my neighbor I had no idea what brand of batteries would fit the requirements; reliable, decent quality, and affordable. Off to visit my buddy who owns a solar company.

He had just brought on a new line of equipment…FNS. He explained the FNS inverter/charger and battery relationship. Sounded right…and they met the system requirements and they were very affordable.

I put together a plan for a 6kw, 240vAC, 400Ah, 4.8kw of PVs system that also included an FNS battery cabinet that is really sweet. PVs went up, and I started tearing out the old system. Installed the new system with all new wiring, lightening protection, etc. Then fired it up…problems right off the bat with the batteries. The FNS 3U batteries would simply not function. Two days and 5 phone calls to the battery company later we found out there was a problem with the battery’s BMS software. Took the batteries in to the technician…one battery failed to update, burned another one out.

Another couple of days worth of phone calls with the US office, then phone calls and emails with the techs & managers in China. They had to rewrite the battery BMS software, download it to the US, and then the tech here loaded it into the battery. It worked. But there was still a problem with the batteries talking with the inverter. A week later the software was available to download into the inverter. It worked.

However, about the time you think it is a sunny day once again…ah, no. The batteries were still not performing up to standards…low full charge voltage and discrepancy between the battery charge indicator lights, the actual voltage reading, and the tech spec.

The low full charge voltage problem was explained after about a month from the first purchase…it was a 15 cell battery not an industry standard 16 cell battery. And since each cell is 3.2v, missing a cell was the discrepancy in voltage. And for along time no one in the supply chain knew it was a 15 vs 16 cell battery…and that difference also explained the competitive price point. No one in the company (FNS) was ever able to explain the discrepancy between the battery charge indicator lights, the actual voltage reading, and the tech spec.

AT the time the local dealer assured me they would stand behind the batteries, but, in the subsequent months they have also discontinued selling that line of batteries.

So the FNS 3U & 5U LifePo4 batteries are a “DO NOT BUY!” if you are looking for a trouble-free, industry standard 16-cell LifePo4 battery for your solar system. If you are tech savvy or have a solid working relationship with, and warranty from, your system installation company then they are a decent alternative.

I wouldn’t install them in my system based on what I know and the fact that there are better alternatives out there.

note: Sacred Sun batteries are made by FNS, Sacred Sun is just a private label.

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3 thoughts on “TRAP: FNS / Sacred Sun LifePo4 3U & 5U Solar Batteries

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