I'm asking in response to this thread: https://community.victronenergy.com/comments/58148/view.html
The Spec sheet for pylontech US3000 states 3552Wh capacity, but useable capacity 3200Wh. This would mean discharging all the way to 10% Depth of Discharge. Wouldn't that seriously ruin the lifespan of the batteries? I thought all LiFePo4s should only go to 20% DoD.
With LiFePO4, better watch the cell voltage.
Do not discharge under 3.0V (cell voltage under load).
Do not charge above 3.6V (absorption voltage).
These are the safe extremes. You can restrict them further, for longer lifespan. Keep in mind that cell voltages in a battery are not exactly the same, so account for this.
Pylontech "48V" batteries have 15 LiFePO4 cells in series.
It looks like the compatibility manual suggests setting inverter parameter to:
"DC input low shut-down - 44V"
Wouldn't that mean the damage had already been done.
The 44v allows for voltage sag under load and voltage drop across cabling.
If you are using DVCC and your voltage is being measured directly at the battery it is possibly worth monitoring your system and seeing what normal loads drop the voltage down to.
With Lithium having a fairly flat discharge curve it can be difficult to determine the best voltage cutoff without restricting your usage of the battery.
A better solution is to have the SOC from the battery cut the inverter off and only rely on voltage as a fallback.
They do what they say they can do. Stick to the Spec sheet and you will be fine. Pylontec are usually damaged more by over current charges and discharges. So always size the pack correctly and use the recommended settings. The guarantee on their products will stand as that is what is says it can do.
https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom
Their pouch cells as Seb71 mentioned make them a little different to the other batteries.
The Pylontec BMS system keeps the battery from full discharge in any case - cuts if off in the right place so you as the user does not need to worry about that. The big brains at the company have worked it all out for you, and have designed a bms to manage the cells.
"The guarantee on their products will stand as that is what is says it can do."
That's okay if you live next door to a distributor,and have money to burn, but for most it's a question of convenience and economics . I'd prefer to have batteries running at or above the published cycle life than have to figure out how warranty service works.
I'm not too familiar with the tech. Is there something about pouch cells that allows them to maintain their lifespan at 90% discharges relative to other kinds of cells?
Pouch cells are similar to the ones in your cell phone or tablet. They dont like high charge and discharge currents.
When they say 3200wh usable you can use the range. They say 5000 to 7000 cycles which if you did everyday will get you over 13 years. I wont say they recommend it - just their product can do it. I think they guarantee 12 years (most suppliers less though, I guess they don't want to carry that).
There are many long discussions as to what a cycle actually is on a battery is, so I cannot answer that even if you only shallow discharge it. I only know a few systems that have had Pylons in the field for about 3 years now some light DOD some heavy. There seems to be no difference between the installs so far.
Besides the known issues listed in the FAQ part of the Victron page the only ones I have seen fail are the silly installs where someone put one battery on a 5kva - (not a Victron and poorly sized bank) and the pouch cells blew up like balloons from the high discharge currents. (so user/installer error) and popped open the case.
And yes I am in the same school of thought as you I prefer running my batteries between 50 and 100%, so I have sized my battery bank accordingly based on night usage of power.
wow 50% that's crazy. Almost treating it as if it were lead acid...Yet, from what I've heard, that will give the greatest longevity.
Personally, I was thinking going down to 15%, which would give me 12kwh useable storeage. I've got 4 US3000.
So, I'm running a Multi 48/5000, which can handle 10,000W surge...but it seems the pylontechs could handle more. I think the manual says each may sustain 100A for 15seconds. Which would be 100A x 48V = 4800W.
With my four batteries = 19,200W. That sounds like my setup is good for running welding equipment and water pumps simultaneously.
Don’t stress about it. It does what it says. The Pylontech BMS will shut down when it wants to. My neighbour’s ran at 12% for the much of the day due to grid failure and rainy weather. It shut down at the end of the day.
The battery state of health was still good at 100% after this incident.
