Unattended system during rainy season

[BigBrosMo]

I am offgrid in Thailand. I have a new 280ah EVE LiFePo4 bank that I built with JK 8S BMS. I am here 3 to 6 months of the year and everything is packed up while I am away the other 9 to 6 months of the year (eg. the rainy season). Up until this year I have had Deepcycle Lead Acid cells and always kept the SCC running and charging while away. I've also packed up the 3000w pure sin inverter during this time.

This rainy season when I leave, my plan was to discharge the bank to 70%, disconnect the BMS so it doesn't drain the battery, and then store it inside the house (the store room where my SCC is can get quite hot)

However, now I think I want to install some IP cameras and motion activated lights while I am away so I will need to run a router, the cameras themselves and then of course the lights. Therefore I think I'll have to keep an inverter running. Here are my questions:

1. Should I run my main 3000w inverter 24/7 or would you install a cheaper 500w DC modified sin wave one? I don't think I need a pure sin wave one, and I don't want my big one to die, and think storing it is better than running it unattended for so long. If a cheaper one dies, I am not so bummed, and I could have someone replace it relatively easily for me.

2. Currently I charge my battery to 90% and then float it there as it's always under a small load during the day (I have a fridge etc). In the morning it's down to about 70%, then charges to 90% again, float, repeat. While I am away, with just router and camera, lights etc, usage will be minimal. Should I adjust my setup so the battery is charged to 90%, allowed to drain to 20%, and then allowed to charge again? Or am I better to keep it just as is always charging to 90% daily (maybe just disabling float)?

3. Since the solar shed gets quite hot while I am away (+40c I think), would it be beneficial to simply blow a fan on the battery box during the day? I know this isn't the most efficient but would it be useful at all for helping the life of the batteries?

4. What's the best way to monitor the JK BMS while away? It's Bluetooth - not WiFi

Appreciate all your thoughts.

 

[Supervstech]

If you choose a smaller inverter to leave running, I would get pure sine wave. Electronics do not like MSW.

 

[Supervstech]

I am offgrid in Thailand. I have a new 280ah EVE LiFePo4 bank that I built with JK 8S BMS. I am here 3 to 6 months of the year and everything is packed up while I am away the other 9 to 6 months of the year (eg. the rainy season). Up until this year I have had Deepcycle Lead Acid cells and always kept the SCC running and charging while away. I've also packed up the 3000w pure sin inverter during this time.

This rainy season when I leave, my plan was to discharge the bank to 70%, disconnect the BMS so it doesn't drain the battery, and then store it inside the house (the store room where my SCC is can get quite hot)

However, now I think I want to install some IP cameras and motion activated lights while I am away so I will need to run a router, the cameras themselves and then of course the lights. Therefore I think I'll have to keep an inverter running. Here are my questions:

1. Should I run my main 3000w inverter 24/7 or would you install a cheaper 500w DC modified sin wave one? I don't think I need a pure sin wave one, and I don't want my big one to die, and think storing it is better than running it unattended for so long. If a cheaper one dies, I am not so bummed, and I could have someone replace it relatively easily for me.

2. Currently I charge my battery to 90% and then float it there as it's always under a small load during the day (I have a fridge etc). In the morning it's down to about 70%, then charges to 90% again, float, repeat. While I am away, with just router and camera, lights etc, usage will be minimal. Should I adjust my setup so the battery is charged to 90%, allowed to drain to 20%, and then allowed to charge again? Or am I better to keep it just as is always charging to 90% daily (maybe just disabling float)?

3. Since the solar shed gets quite hot while I am away (+40c I think), would it be beneficial to simply blow a fan on the battery box during the day? I know this isn't the most efficient but would it be useful at all for helping the life of the batteries?

4. What's the best way to monitor the JK BMS while away? It's Bluetooth - not WiFi

Appreciate all your thoughts.

2. I would disable float… set top charge to 90% and call it good.

3. A fan will not do anything to cool inanimate objects… it will actually heat them further. Fans cool in two ways. They move air over a wet area causing evaporation which cools that surface… or they move cooler air into a warmer space.
Moving the same temp air around a room only heats the air with friction and motor heating.
If the room is too warm for the cells, degradation will occur.

 

[crossy]

As above, I'd disable or drop float and leave well alone.

I would also put in some shade plants to keep your solar shed at something approaching ambient, creating some airflow from outside and through the shed may be useful.

We are just north of BKK and our packs don't get much above 35C even on really blistering days. We are using bananas as shade so of course we can eat / sell the fruit too.

 

[Rednecktek]

However, now I think I want to install some IP cameras and motion activated lights while I am away so I will need to run a router, the cameras themselves and then of course the lights. Therefore I think I'll have to keep an inverter running. Here are my questions:

With a little leg work, all those should be available in 12v varieties and you can skip the inverter all together. Another option would be variable DC->DC transformers if you needed to take your 12v and kick it to 16v or whatever. Otherwise, get a Pure Sine and save your poor electronics.

 

[curiouscarbon]

hi!

1. recommend to run as much computer stuff from DC if possible. eg 12V regulator from battery to router. lots of options there. to your point, for mandatory AC stuff, 300W PSW pure sine wave will ensure the long unattended operation will be happy for the electronics

2. perhaps disable float and set a lower bulk/absorb voltage. like less than 3.425V per cell. perhaps 3.34V per cell or even less. many options ought to slightly improve lifetime of cells (13.7 V and 13.36V respectively for 4S LiFePO4)

3. blowing 40C air onto LFP cell will bring it to 40C, which is above 30C. there is some evidence growing to indicate keeping LFP cell above 30C for long time will result in some shorter life of cell operation. if cell is 45C and blow 40C air on it then yes this should help. i am experimenting with peltier thermoelectric cooling/heating of LFP cells to enable easy long operation in elevated environment temperature eg 40C. happy to share more info if thats of interest. by insulating the battery and changing temperature of metal plate cells sit on (electrically insulated from cells of course)

4. no experience with JK. but two options might be available. one is learn raspberry pi JK communication and have raspberry pi connect to bluetooth and use some program to forward that over wifi or ethernet to remote. another option maybe connect to wired serial data interface on JK BMS if available. then microcontroller like arduino could potentially read JK BMS data to computer over USB and then internet to remote

cool project and good luck!

 

[curiouscarbon]

by the way, in case interested about reading material about temperature and long term aging of LFP cells, these resources available

Why temperature of lithium cells is important

Temperature is an important parameter that influences the aging of a lithium battery. At 35°C a lithium cell ages twice as fast as it does at 15°C. So if the battery’s useful life is 15 years at 15°C, it will be 7.5 years at 35°C. I summarize...

diysolarforum.com

Calendar Aging and Lifetimes of LiFePO4 Batteries and Considerations for Repurposing

A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Master of Applied Science in Chemical Engineering. by John Catton Abstract In response to rising petroleum prices, the demand for lower...

diysolarforum.com

The Degradation Behavior of LiFePO4/C Batteries during Long-Term Calendar Aging

Abstract: With widespread applications for lithium-ion batteries in energy storage systems, the performance degradation of the battery attracts more and more attention. Understanding the battery’s long-term aging characteristics is essential for...

diysolarforum.com

General LiFePO4 Degradation vs Temperature

Concerned about your LiFePO4 batteries ♨️Overheating♨️ or ❄️Freezing❄️and losing ability to hold charge due to operating temperature? This is a research paper that carries out charging and discharging at set temperatures, and evaluating the...

diysolarforum.com

in essence,

10-25 C seems to be LFP very happy zone for long life

30 C and above there seems to be evidence of slightly faster degradation per time and per cycle

40 C extra degradation expected

 

[BigBrosMo]

As above, I'd disable or drop float and leave well alone.

I would also put in some shade plants to keep your solar shed at something approaching ambient, creating some airflow from outside and through the shed may be useful.

We are just north of BKK and our packs don't get much above 35C even on really blistering days. We are using bananas as shade so of course we can eat / sell the fruit too.

Thanks for your input. There is a tree that provides some shade although it's covered in vines that wrap themselves around the water tank and cause havoc. There's also some rubber trees that admittedly are much higher now than they were years ago. I'll run some tests in March (hottest time I am here near Ranong) to see what I am getting temp-wise.

 

[BigBrosMo]

With a little leg work, all those should be available in 12v varieties and you can skip the inverter all together. Another option would be variable DC->DC transformers if you needed to take your 12v and kick it to 16v or whatever. Otherwise, get a Pure Sine and save your poor electronics.

I guess I'll go the Pure Sine route... just checked costs and they have really come down so its marginal increase for me over the MSW version. I considered the pure DC route but there's no big lines into the house from the solar shed for DC. It's a 2.5mm/14awg wire. Voltage drop would be too great I think with that for DC but will do the calcs to confirm.

 

[BigBrosMo]

hi!

1. recommend to run as much computer stuff from DC if possible. eg 12V regulator from battery to router. lots of options there. to your point, for mandatory AC stuff, 300W PSW pure sine wave will ensure the long unattended operation will be happy for the electronics

2. perhaps disable float and set a lower bulk/absorb voltage. like less than 3.425V per cell. perhaps 3.34V per cell or even less. many options ought to slightly improve lifetime of cells (13.7 V and 13.36V respectively for 4S LiFePO4)

3. blowing 40C air onto LFP cell will bring it to 40C, which is above 30C. there is some evidence growing to indicate keeping LFP cell above 30C for long time will result in some shorter life of cell operation. if cell is 45C and blow 40C air on it then yes this should help. i am experimenting with peltier thermoelectric cooling/heating of LFP cells to enable easy long operation in elevated environment temperature eg 40C. happy to share more info if thats of interest. by insulating the battery and changing temperature of metal plate cells sit on (electrically insulated from cells of course)

4. no experience with JK. but two options might be available. one is learn raspberry pi JK communication and have raspberry pi connect to bluetooth and use some program to forward that over wifi or ethernet to remote. another option maybe connect to wired serial data interface on JK BMS if available. then microcontroller like arduino could potentially read JK BMS data to computer over USB and then internet to remote

cool project and good luck!

I like where your heads at with the peltier! Too funny I was thinking about exactly that yesterday when I made this post. I have an old cooler here that runs on 12v with peltiers in it to reduce ambient temperature by 20c. It was actually my original cooling solution before a 220v fridge was an option (before solar became affordable) but it didn't work worth a shit really. My beer was "cool" but not cold. My main concern at the time. haha

I've thought about putting my Lifepo4 battery pack in the old cooler but would be worried about condensation. I might try running an experiment with the lid off, just to see how much power it uses... any other thoughts on that? Cool indeed.

I'll look a little into the rasp pi but I am not sure I have the time left for the learning curve this season. I'd need something relatively "off the shelf" at this point.

Thanks for your input! Much appreciated.

 

[time2roll]

Consider a fan to bring overnight cooler air into the battery space. Cooler thermal mass can carry through the heat of the day better.
I agree with the smaller inverter. Although I would get only sine wave. Needs can change and the premium is not huge.
Unless it is possible for the battery to get very low, consider charging to a slightly lower voltage during your time away.
If the power does cut out, will everything reboot, synchronize, and reconnect when power is restored?

 

[Bluedog225]

Off topic but I’d love to hear more about Thailand. Which part? And why do you leave in the rainy season? I thought it would be a break from the smoke and heat.

 

[BigBrosMo]

Off topic but I’d love to hear more about Thailand. Which part? And why do you leave in the rainy season? I thought it would be a break from the smoke and heat.

Thanks for asking. I live/work in Canada and need to fund this lifestyle choice so while I have at times been able to work remotely over the years the timezone difference makes it less than ideal. I also really enjoy the Canadian summer and my friends back home. My intention when I built the house here 12 years ago was to work 6 months at home and spend 6 months here. Realistically with inflation, forex, and personal responsibilities that has evolved to 3 to 5 months here annually.

Where I am here (off the coast of Ranong, about halfway down the Thai peninsula) rainy season is generally May to October, so I work around that. No smoke here and my primary goal is to escape the Canadian winter! Rainy season is nice for some time... but it rains a lot, everything is always wet, and with everything shut down (ie resorts/restaurants close) it can get a little lonely/boring on the island at that time. I will probably retire here and be fine at that point - but for now I appreciate mixing it up.