Testing....14C seems like a high cut off for charging. Or is this for initial testing?
Is that ambient temperature or battery temperature?
Sounds like a good set of experiments @ken morgan - before you commit for the winter!\Testing....
Currently my BMS is set to stop all charge at 5°. I have my solar controllers set to stop at 14°
as I am in testing mode, and will keep that parameter until I have thoroughly tested the battery heater and feel comfortable with it. The battery heater should keep battery between 8 - 15°C I set the SCC point at 14°C for the time being as I am a three to four hour drive from my cabin during the week and as yet cannot remote monitor.
At worst, setting it at 14°c just means it cannot charge in the early morning hours for this time of the year.
Until I have directly observed the performance & behavior of my home brewed battery heater over several cycles and can show empirical proof of it following the predicted performance parameters, I am leaving nothing to chance. the idea here is to not be the guy whose batteries spectacularly die from a case of hopes and wishes.
once I have seen the battery warmer in action and am satisfied that it as well as the backup systems all work correctly I will remove the limit of the above mentioned 14° , and lower the Solar charge controllers to 8° and the BMS to 4°.
yes the magnum inverter with its battery monitor system.Sounds like a good set of experiments @ken morgan - before you commit for the winter!\
I'm really curious about the 70V fault on your Magnum. Is that the magnum inverter? I think you said you have morningstar SCC's.
I have an all-Schneider system (with some regrets) but I get some odd faults that don't seem to match to reality. Strange....
I had the same problem with my hunting cabin. When I leave, the battery is disconnected from everything and the BMS balance harness is unplugged. However, it is in the Mt Mountains were it can get extremely cold. I built a well insulated box and added this independent warmer to it and everything seemed to work just fine over the winter.So my issue is how we handle an LFP battery when the cabin is unoccupied for 5 months or so. If we have to carry them out for the winter, that could be a deal-breaker, and I may be stuck with AGM. In this case I'm not sure a small load periodically is an option.
Yup..... the concrete slab temp is being buffered by the earth it is sitting on. It will be interesting to see what actually happens, but my expectation is that the floor temp won't get much below 60F even on the coldest nights. If it gets down to 50F I will be quite surprised. According to a google search, the typical temperature 15ft underground is 50-60F and usually varies only a few degrees year around. My slab is on top of the ground so it will vary more, but it will probably still stay in a relative narrow range.Your concrete floor experiment is sort of like my setup in the 5th wheel front compartment. Thread in this section. https://diysolarforum.com/threads/12v-heating-pad.2468/
The metal floor during the colder seasons worked like a heat sync drawing heat from the cells cooling them off. I have no dought that during the cold months it will do the same, it might not be a problem if it doesn't get to extreme freezing. During the summer it probably helps as you see with the earth under the concrete keeping it cooler than the ambient air.