No worries. I'm hoping that is what they eventually do. It seems like they didn't think beyond adding the heaters to help keep battery warm. Which if you had grid access is fine I guess (although likely a waste of power as you mentioned). I don't have grid access, so I think I will likely have to try and keep them from freezing at night.
Charging LFP below 32F - 0C freezing temperature - possible - with newer chemistry?
- Thread starter eXodus
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HighDesertOffgrid
Solar Addict
- Joined
- Sep 15, 2022
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Hopefully the heater circuit isnt physically downstream of the charge circuit. In that case no amount of firmware updates may fix it.
Well, well well. After doing some youtube searching, it looks like someone recently discovered that the BMS CAN heat with the charge mosfets off. It turns out that the BMS waits 30 minutes before turning on the heating fet when under temp protection is triggered. Kind of strange.
Partimewages
Solar Addict
Couldn't you just put an in line (circuit) stat that closes at 35F or 2C? It would keep the heater from running until it's cold.
You can do a lot of things. Just was trying to figure it out using the BMS as-is, as it is supposed to be able to handle it. Turns out it was just some poor documentation on seplos's part.
grizzzman
Photon Vampire
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Perhaps to avoid an on edge trigger?
Daddy Tanuki
Solar Wizard
the fact I have to quote Sunshine tells you something.
the only cells that are safe to charge below freezing are the ones where the maker says you can. so in the case of Winstons pay more, get Yttruium doping of the cathode and charge to way way below zero... other wise stop dancing and figure out a way out of the hole you dug.
sunshine_eggo
Happy Breffast!
We are getting drilled in by Will and other people knowledgeable about the subject - do not charge below freezing.
Like every other knowledge - that piece of advice has an expiration date - since technology moves on.
There are more and more manufacturers are coming out - saying - we don't do low temperature -cut off, but low temp charge limitation.
"When charging lithium iron phosphate batteries below 0°C (32°F), the charge current must be reduced to 0.1C and below -10°C (14°F) it must be reduced to 0.05C. Failure to reduce the current below freezing temperatures can cause irreversible damage to your battery. "
How do LiFePO4 batteries perform in cold temperatures? | RELiON
How do LiFePO4 batteries perform in cold temperatures?www.relionbattery.com
Can be charged at temperature down to -20°C for cold weather use (sub Zero version)
Charging Your Lithium Battery Below Zero - DC Battery Technologies
How to correctly charge your Lithium Battery is a frequently asked question. By following this simple guide, you will have all the knowledge to look after your battery efficiently!dcbattery.tech
My first chemistry question was when looking deeper into the subject - why is everyone focused on the freezing point of water? In college, I talked with chemistry experts. Found https://essays.edubirdie.com/chemistry-help for this. They said that there was no such accurate pattern. There is no H2O in common LFP chemistries. Every solution has a different freezing point - it would be quite a coincident that all batteries are freezing a 32F 0C.
My potential unpopular opinion on the subject:
All that public bashing on missing low temp CUTOFF is leading manufacturers to not develop low temperature chemistries.
There is still research going on low temp charging , but not as much as there could be, with the single minded focus of the DIY video publishing community - in ripping batteries apart and putting sensors ins freezing WATER and waiting for the current to drop to zero.
Study on the Capacity Fading Effect of Low-Rate Charging on Lithium-Ion Batteries in Low-Temperature Environment
By taking a cylindrical LiFePO4 power battery as the research object, the cycle performance test was conducted under different charging current aging paths in a preset low-temperature environment and combined with EIS results to analyze the dynamic characteristics of the battery during the aging...www.mdpi.com
When you look at various scientific studies - you can see that the effect on LFP is gradual.
View attachment 182635
It essentially means - +1C is not massively safer then -1C Zero is just random value chosen for familiarity.
Impact of Test Conditions While Screening Lithium-Ion Batteries for Capacity Degradation in Low Earth Orbit CubeSat Space Applications
A wide variety of commercial cylindrical lithium-ion batteries are available for use in nanosatellites (CubeSats) that cycle in low Earth orbit (LEO). This space application differs greatly from the conditions used to create the manufacturer datasheets that CubeSat teams rely on to screen cell...
Fluorinated Solvent Molecule Tuning Enables Fast-Charging and Low-Temperature Lithium-Ion Batteries
Yanbing Mo, Gaopan Liu, Yue Yin, Mingming Tao, Jiawei Chen, Yu Peng, Yonggang Wang, Yong Yang, Congxiao Wang, Xiaoli Dong, Yongyao Xia"
-20C is bad for Lithium - do not get me wrong - that will kill current chemistries pretty fast. But 0C is a rather arbitrary cutoff in my opinion.
Lets get the debate up and point out the flaws in my Thesis.
I think they chose 0C arbitrarily as a value familiar to many, even though +1C and -1C aren't very different. It's kind of like the qwerty keyboard layout, which was designed for mechanical typewriters to prevent keys from sticking. And although there are already more ergonomic ones, out of habit this is still used.
Still, I wouldn’t charge at low temperatures unless absolutely necessary.
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Daddy Tanuki
Solar Wizard
It takes so little power to keep batteries warm through the night that it is really a moot point I think.
I am heating three packs of cells 2 x 16s winston 400 ah and one pack of calb 3p16s 500 ah. The most expensive part is the 6mm aluminum plates for the heating pads to attach to and spread out the heat.
The heating pads draw 50 watts to heat all of the cells per hour, and keep them between 15-25 °c. Thats less than the parasitic load for many of the Chinese AIO inverter units that a lot of members use here on the forum.
So figure 50 watts from say 1600 to 0900 or 17-18 hours. a little a little under 1kW from a 70kw bank. and I can charge immediately at the full out put of my PV array which in the morning tapers up of course but I have seen upwards of a 120 amps at 53 volts before.
YMMV
![IMG_1910[1].JPG](https://diysolarforum.com/data/attachments/215/215549-e01a896c4ea819c9ba06bd3fa9336768.jpg?hash=4BqJbE6oGc "IMG_1910[1].JPG")
![IMG_1899[1].JPG](https://diysolarforum.com/data/attachments/215/215550-6d9738e2d546630d277e3e4d50632f14.jpg?hash=bZc44tVGYw "IMG_1899[1].JPG")
50W can be very significant in certain situations, like mine. Off-grid, only 1000W of used solar panels. Many winter days I'm not getting 1KW of recharging. I ended up just converting everything I could to DC so I could just switch off the inverter entirely. With Starlink + Home Assistant + Solar Assistant + 2 POE cameras all DC I can stretch my 304AH 48V battery to a little over a month. Next winter I think I'm just going to flip the breaker on the cells and try and get out there to recharge once a month.
Daddy Tanuki
Solar Wizard
with the prices of used panels as cheap as they are you could add 4 or 5 panels and totally make up for any deficit the heating pads used.
OffgridR&D
New Member
These super capacitor+ battery hybrids seem legit, I got some a couple years ago and they're up to spec so far. They're rated for 1C charge rate at -40C. I've tested them down to 15°F it hasn't been colder here.
The company likes to call them capacitors and is a bit strange in ratings; the "4000F" lithium batteries test at 4000mah on my bench. The 4.2 is typical lithium ion, company says don't discharge below 2.75v. There's a larger capacity flat cell, and the company markets complete 48v 100ah solar storage units
I hope this isn't spam, I'm a fan not a partner with the company here's a contact:
Sincerely,
Emily Yang
DONGGUAN CITY GONGHE ELECTRONICS CO.,LTD.
Mobile/Wechat/Whatsapp: +86 18926185568
Email: emily@gongheenergy.com
Offical Website: www.gongheenergy.com
The company likes to call them capacitors and is a bit strange in ratings; the "4000F" lithium batteries test at 4000mah on my bench. The 4.2 is typical lithium ion, company says don't discharge below 2.75v. There's a larger capacity flat cell, and the company markets complete 48v 100ah solar storage units
4.2V 4000F_东莞市共和电子有限公司
东莞市共和电子有限公司为企业提供4.2V 4000F,4.2V 4000F价格,4.2V 4000F参数相关信息.
www.gongheenergy.com
I hope this isn't spam, I'm a fan not a partner with the company here's a contact:
Sincerely,
Emily Yang
DONGGUAN CITY GONGHE ELECTRONICS CO.,LTD.
Mobile/Wechat/Whatsapp: +86 18926185568
Email: emily@gongheenergy.com
Offical Website: www.gongheenergy.com
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Daddy Tanuki
Solar Wizard
well fine ship a set for free to will to test and put through the paces... that or whomever he designates.
HarryN
Solar Addict
It might be easier to just use a propane heater to keep the room at 40 F.
Daddy Tanuki
Solar Wizard
That and some good insulation
Because like usual in physics, there is no hard cut-off temp. I stop at 5C for example, but as you pointed out as long as you lower the charge current you can charge below 0C as well. However, this is not easy to implement: you now need to be able to limit current based on temperature. Much easier to just have a cut-off at 0C and call it a day.
By the way, I tried charging an LFP cell at close to -20C. It doesn't even charge properly because the internal resistance is so high you don't get a decent current at 3.6V in the first place:
Charging LFP Cell at -17C – Up North and Personal
www.upnorthandpersonal.net
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