Horsefly
Solar Wizard
Greetings folks! This is my first post, so go easy on me.
I've been reading as much as I can here (what a great resource!), and learning lots.
I've got a 24V off grid cabin system, with a 4000W inverter, 1700W of panels, and a 60A MPPT charge controller (the electronics are all Schneider). I designed and installed the system in the spring / summer of 2017. We used AGM lead-acid batteries, as that seemed like the best choice at the time. At the time I was very interested in LiFePO4 for the future. I've got two hurdles to get over before I can go with LiFePO4: Max current draw, and temperature.
My nominal load on my inverter is pretty low, but I do have two bigger loads: An 800W microwave (draws about 45A from my ~25VDC battery) and a 0.5hp well pump (draws about 55A from the battery). Neither of these is used more than about 10 minutes per day, and the chances of both being on at the same time is almost zero. The bigger issue is that the well pump is an old induction motor, and it pulls close to 34A@115VAC for a fraction of a second when it starts. That translates to something like 160A@25VDC pulled from the battery.
The cabin is at about 9000 ft elevation, so yeah it gets cold. I've got a temperature logger up there through this winter, but it will be May before we can get up there and see how cold it gets in the basement of the cabin. Until then I've been thinking through strategies for my future LiFePO4 battery. Although I'm experimenting with some ways to heat them in an insulated box (and would love to hear from anyone here with some experience in that), my main thing is preventing my charge controller from killing the cells by charging when the temp is below 32°F.
So I think I need a BMS that can handle 200A, and I need it to have a low-temp cut-off so that I don't kill the cells. I've read that the low-temp cutoff doesn't work as advertised for lots of of the available BMS's. I've read great things here about the Overkill BMS, but the 24V version only goes to 100A. Does anyone have some experience with another BMS that FOR SURE has a working low-temp cutoff?
Thanks in advance for your thoughts!
Steve
P.S. I've got an email off to Overkill to see if a 200A 24V version is in their future, which would solve my problem!
I've been reading as much as I can here (what a great resource!), and learning lots.
I've got a 24V off grid cabin system, with a 4000W inverter, 1700W of panels, and a 60A MPPT charge controller (the electronics are all Schneider). I designed and installed the system in the spring / summer of 2017. We used AGM lead-acid batteries, as that seemed like the best choice at the time. At the time I was very interested in LiFePO4 for the future. I've got two hurdles to get over before I can go with LiFePO4: Max current draw, and temperature.
My nominal load on my inverter is pretty low, but I do have two bigger loads: An 800W microwave (draws about 45A from my ~25VDC battery) and a 0.5hp well pump (draws about 55A from the battery). Neither of these is used more than about 10 minutes per day, and the chances of both being on at the same time is almost zero. The bigger issue is that the well pump is an old induction motor, and it pulls close to 34A@115VAC for a fraction of a second when it starts. That translates to something like 160A@25VDC pulled from the battery.
The cabin is at about 9000 ft elevation, so yeah it gets cold. I've got a temperature logger up there through this winter, but it will be May before we can get up there and see how cold it gets in the basement of the cabin. Until then I've been thinking through strategies for my future LiFePO4 battery. Although I'm experimenting with some ways to heat them in an insulated box (and would love to hear from anyone here with some experience in that), my main thing is preventing my charge controller from killing the cells by charging when the temp is below 32°F.
So I think I need a BMS that can handle 200A, and I need it to have a low-temp cut-off so that I don't kill the cells. I've read that the low-temp cutoff doesn't work as advertised for lots of of the available BMS's. I've read great things here about the Overkill BMS, but the 24V version only goes to 100A. Does anyone have some experience with another BMS that FOR SURE has a working low-temp cutoff?
Thanks in advance for your thoughts!
Steve
P.S. I've got an email off to Overkill to see if a 200A 24V version is in their future, which would solve my problem!