On Keeping LFP Warm

wild01

Solar Enthusiast
I'll second 14c seems really high. 2-4c should be fine. I have my bms set to disconnect at 2c and reconnect at 4c.
 

ken morgan

Solar Addict
14C seems like a high cut off for charging. Or is this for initial testing?

Is that ambient temperature or battery temperature?
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°.
 

Horsefly

Solar Addict
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°.
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....
 

ken morgan

Solar Addict
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....
yes the magnum inverter with its battery monitor system.

To those interested: I couch the following as I think, I have no proof as of yet, but once I get a wifi hotspot to land line conversion figured out so that I can export data in real time and record data I will be able to possibly answer this better.

Two weeks ago I added 12 panels for an additional 2.4kw to the roof of the shop (total 6.4kw) and since I fired them up, once a day for the last eight days has shown a fault history where it is at high voltage surge of 69-71ish volts. To date it has occurred between 1330-1430 and I think it represents when the morningstar charge controllers disconnect due to high voltage.

the SCC is set as 54.4 charge, with a 54.1 VDC 1 hour absorb, and then it drops to a 54.0 float for 3 hours. no temp compensation, a high voltage disconnect of 56 volts, and a reconnect of 54.6 . it also has a setting called maximum regulation limit which honestly I don't understand the need for as it acts as a total cap on voltage output. I set that to 56 the same as the HVD.

it has not shut down the inverter, nor the BMS so it must be very brief and with no actual current to speak of. I know it has not shut down neither of the two for two reasons the Magnum does not show a shutdown in conjunction with the fault, and if the inverter or BMS did shut down then my split pack unit in the house would have shut down as well. (and not restarted.) (split pack is run on timer from 1000-1400 to dry out the house during the damp seasons).

I think the sudden termination by the SCC causes a brief transient surge. this happened once before that I noticed and at the time I had just suffered a BMS failure so I thought it might have something to do with that. (now I do not think so). it has happened daily since I added the extra panels.

one other thought that just entered my pea brain is that it could be when the a/c shuts down at 1400 hundred and the panels are cranking out juice to charge the pack and power the hotel loads including the a/c. possibly the shutdown of the a/c on timer might for a brief microsecond allow the SCC to race up to hit the maximum voltage regulation set point??? too many questions on this one and not having internet I cannot monitor and log them unless I am there. (and last time I was there is was heavily overcast, batteries hovered between 60-70 percent the entire time.)

anybody have an idea on if there are any routers that can take the wifi signal from a portable wifi hotspot and send it out a normal ethernet cable? the magnum and the tristars need an ethernet cable to a modem. I figure there has to be a way to do this. a pocket wifi would cost me like $30/month and I could then monitor my solar charge controllers, my inverter and even my bms via the internet...

Regards

Ken
 

ken morgan

Solar Addict
also as I am sure someone will ask this... the Morningstar Solar charge controllers do not offer a temperature controlled charge parameter other than if you are using them for temp compensation on FLA or AGM batteries.

what I have is a separate temp controller that is wired in series with the Tristar's RTS. the temp controller opens the circuit on the RTS which then stops the SCC from charging until the RTS is reconnected.

Interrupting the circuit is a Morningstar approved way of preventing/stopping charging for any reason that you can build a circuit for. So in my case I use the same style temp controller as I use on the battery heater and I set the little temp controller to 14° and it will open the RTS circuit until the temp is above 14°. once it rises above the setpoint the SCC takes a few seconds to check its status and then it will start charging (or in the case of an interrupted charge, resume it).

many thanks to @Mcgivor for that tidbit about the TS MPPT and TS series SCC and the RTS.
 

FilterGuy

What, me worry?
I have been considering an install of a large set of cells in an attached but un-insulated garage. They would be on the concrete slab floor of the garage. We rarely get freezing so I am not too concerned about that. (but I will have a low-temp disconnect). My big concern is it being too hot in the garage. Over the past few weeks I have been running an experiment with a logging thermometer covered with an insulating towel on the concrete floor and another logger on the bench above it (in the open air). I did not have a logger outside, but during this time the outside temp was into the 90s (F) on several days.

1631489365964.png
As I expected, the concrete slab has a tremendous buffering effect on the temperature. What I did not expect is that the temperature on the bench did not get higher.

This is enough data to convince me I wont' have a problem if I put an insulated box over the cells that are sitting on the concrete slab. However, I will keep the experiment going for two reasons: 1) We often get an extended hot spell in September and I want to see what happens. 2) Even though we only occasionally get overnight frost in the winter, I still want to see what happens in colder weather. As I get any interesting data I will post it here but I suspect there won't be anything worth posting till Jan or February and we have had a few cold spells. Even then, it does not get super cold here so it might not be very interesting.
 
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FilterGuy

What, me worry?
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.
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.

 

Sojourner1

Itinerant
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.
 

FilterGuy

What, me worry?
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.
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.

It would be interesting if someone in a more sever-winter location did a similar experiment.

BTW: This is what I am using for my logging thermometer.
 
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